13. interstitial water studies, leg 25 · calcium: complexometric titration with egta (tsu-nogai et...

13. INTERSTITIAL WATER STUDIES, LEG 25

Joris M. Gieskes, Scripps Institution of Oceanography, La Jolla, California

ABSTRACT

Interstitial water analyses from sediments collected during Leg25 of the Deep Sea Drilling Project have revealed that in thesouthwest Indian Ocean, great chemical activity exists insediments in various depositional environments. Variablesedimentation rates allow us to set some interesting boundaryconditions on chemical and transport processes in theseinterstitial waters, particularly with regard to the distribution ofdissolved sulfate. In terrigenous rapidly deposited sediments, largedepletions are observed in magnesium and potassium, whereasrelatively small decreases in dissolved calcium occur. In slowlydeposited detrital sediments, also, large decreases in potassiumand magnesium coincide with very large calcium increases. Intruly pelagic sediments, a one to one replacement of magnesiumby calcium is observed in the interstitial waters, presumably dueto reactions in the basal sediment layers. Biogenous deposits havegreat influence on dissolved silica (sponge spicules andradiolarians) and on dissolved strontium (carbonate recrystal-lization). Otherwise, dissolved silica reflects the clay mineralogyand shows variations which seem particularly dependent on thepresence or absence of kaoUnite. Variable dissolved manganesevalues reflect reducing conditions and/or availability ofmanganese in the solid phases for mobilization in reducingsediments.

INTRODUCTION

During Leg 25, the Gio mar Challenger cruise in thesouthwest Indian Ocean, an intensive program of samplinginterstitial waters and their connate sediments was carriedout. To date, such programs have been a regular featureduring all legs of the Glomar Challenger, the results ofwhich have been published in the various Initial Reports.During Leg 15, a more intensive geochemical program wascarried out (see Part V, Geochemical Investigations in theCaribbean Sea, Leg 15 in Volume 20, 1973). Duringthat leg, special attention was given to Sites 147, 148, and149, with emphasis on close-spaced sampling, the study oftemperature of squeezing artifacts (cf. Mangelsdorf et al.,1969; Fanning and Pilson, 1971), as well as the study ofstable isotopes in both the liquid and solid phases.

These studies of the interstitial water chemistry ofdeep-sea sediments have often established smaller or largerdeviations from the average composition of seawater,particularly with regard to some of its major constituents.The depth distribution of all the major cations and anionsdepends upon their reactivity in the sedimentary column aswell as on the rate of supply of these ions in the case where,at a certain location in the sediment column, reactionsoccur that involve such ions. This rate of supply, usuallycontrolled by molecular diffusion processes and/or upwardadvection of interstitial water due to compaction, alsodepends on the rate of sediment accumulation. Rapidsedimentation can cause the sediment-interstitial watersystem to become closed to exchange with the overlyingseawater.

The various sites investigated during Leg 25 contain arather large variety of sedimentary sequences. Detaileddescriptions of the various sites are given in the site reports(Chapters 2 through 10, this volume) as well as in thecontributions of Leclaire, Moore, and Vallier (this volume).It is not deemed appropriate to repeat many of thesedescriptions in this report, and only the major lithologicfeatures are recorded in the various figures giving thealkalinity distributions.

Of major interest, in addition to the mineralogicalstudies of Matti et al. (this volume), are the rates ofsedimentation in these holes as well as the position and"duration" of the sedimentation hiatuses. This informationis summarized in Figure 1. No certainty exists about thenature of these sedimentation breaks, i.e., whether theyrepresent prolonged periods of no sedimentation or"negative" sedimentation, due, for instance, to the scouringaction of bottom currents (cf. Leclaire, this volume).Whatever the cause of these sedimentation breaks, it is ofimportance to investigate the effect, if any, they may havehad on the distribution of the various ions in the interstitialwaters.

In sediments with rapid accumulation rates (usuallymore than 2 cm/1000 y), one often observes an increase inthe alkalinity (mostly bicarbonate ions) with depth,generally as a result of sulfate reduction processes. At acertain depth, a maximum alkalinity value is oftenobserved, followed by a rapid decrease in this parameter(see, for instance, Gieskes, 1973). In this case, diffusionalsupply of seawater sulfate ions or loss of bicarbonate ions iseither not possible (closed system) or not fast enough to

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J. M. GIESKES

10 20 30 40 50 60 70 90 100 m i l l . y e a r s

Pl iM i o c e n e O l i g o c e n e Eocene P a l e o c e n e

L a t e | M i d d l e ] E a r l y | L a t e | E a r l y | L a t e [ M i d d l e ! E a r l y | L a t e | E a r 1 y | Maas. | Camp. | S a n t • ] C o n • j T u r . | C e n • | A l b . [ A p tC r e t a c e o u s

1 0 0 -

2 0 0 -

3 0 0 -

4 0 0 -

5 0 0 ^

6 0 0 -

7 0 0 -

Break 246 V—

Break 249 -V.fTECT

I Break 239Break 249

10 20 30 40 50 m i l l , years

— Break 241

Figure 1. Sedimentation rate diagram-Leg 25.

nullify any gradients. In slowly accumulating sediments(<l cm/1000 y), one usually does not observe such maximain alkalinity. However, in such sediments, one can stillobserve changes in the concentrations of various ions, andalmost invariably one observes, below a certain depth, agradual decrease in the alkalinity, presumably due either tothe loss of carbon dioxide (or bicarbonate) by calciumcarbonate precipitation or to silica reconstitution processes(cf., Siever, 1968a).

There is considerable debate about the possiblesignificance of changes in the chemical composition ofinterstitial waters of deep-sea sediments, both with regardto their origin and to fluxes of elements into or out of theocean, little work has been done on the connate solidphases to verify postulated diagenetic mechanisms, usuallybecause it is thought that the amounts of products of thesediagenetic changes are too small to be detected. If this wereso, then these studies would be irrelevant with regard tostudies of overall geochemical mass balances. It is possible,however, that observed chemical changes in the interstitialwaters are the result of reactions that started at or near theseawater-sediment interface and still go on after burial. Thisseems to be the case, for instance, at Site 149 (Leg 15), asdemonstrated by Gieskes (1973), Sayles et al. (1973a),and Lawrence (1973). The latter author gave convincing

evidence for this concept in his oxygen isotope studies onpore waters and solid silicates.

Leg 25 provided a variety of holes that lend themselvesexcellently to investigations of the possible influence ofsedimentation rates (or of sedimentation breaks) on thenature of observed chemical gradients. The various holesinvestigated also represent very different regimes ofsedimentation, providing an excellent opportunity to studythe nature of chemical changes, if any, in terms of possiblediagenetic processes taking place in the sediments.

The specific aspects to which the present study willdirect itself are:

1) Establishment of criteria that may serve as a guide inthe determination of possible seawater contaminationduring retrieval of the sediment in the drilling process.

2) Further elucidation of temperature-induced effectson the chemical composition of interstitial waters; sucheffects arise from the retrieval of these waters underconditions of temperature and pressure different fromthose prevailing in situ.

3) Characterization of chemical changes, if any, in theinterstitial waters that may yield information on ongoingdiagenetic processes in the sediments and also on otherprocesses affecting the interstitial water chemistry.

362

INTERSTITIAL WATER STUDIES

4) Study of the nature of chemical gradients withdepth. Such information is especially important in studiesof fluxes of materials in the overall geochemical system ofthe ocean and the sediments.

METHODS

Samples were obtained by means of so-called Manheimsqueezers (Manheim and Sayles, in press). After thesediment was allowed to warm up in capped core-barrelsections, a "punch in" pH measurement was made (seebelow). Then the sediment was carefully scraped to removethe outer 5 to 10 mm and subsequently divided into twoparts; one part was used in the room-temperature squeeze(23°C ± 2) and the other was loaded into the cold squeezer,which was then stored in a refrigerator at 5°C for 1 to 2hours. Any remaining sediment was stored for furtherlaboratory examination.

Alkalinity and pH measurements were carried outimmediately upon retrieval of the samples. The acidifiedsample was then sealed in a PVC tube for further analysis inthe home laboratory.

Most analytical methods used in this study have beenpublished in the Leg 15 Initial Reports (Gieskes, 1973).Modifications are discussed below.

Alkalinity: Potentiometric titration (Gieskes, 1973;Gieskes and Rogers, 1973). No sodium chloride was addedto the 0.1 TV HC1 solution so that titrated samples could beinvestigated for chlorinity as well as for other constituents.Whatman No. 50 filters were used for the squeezingoperations. As discussed previously (Gieskes, 1973),some residual acid is retained in these filters, which makesmeasured alkalinity and pH values slightly low. Errors dueto this procedure can be as large as 0.25 meq/1 in alkalinityand about 0.2 pH units (cf. also Fanning and Pilson, 1971;Gieskes, 1973). We now have found that Whatman No. 1filter paper has no such adverse effects (Jim Pine, personalcommunication). The present data, therefore, may besomewhat lower than the "real" values. The precision,however, remains better than 1 percent. The author,therefore, cautions against using the data of this report forcalculating the degree of saturation of the interstitial waterswith respect to calcite, but would like to stress theirusefulness for comparative purposes.

pH: The pH was measured using "punch in" electrodes,"flow through" electrodes, and, finally, a combinationelectrode in the alkalinity titration vessel (Gieskes, 1973).For reasons discussed above, "flow through" and "vessel"pH values may be 0.1 to 0.2 pH units too low. Agood measure of the effect of the filter paper will be anylarge discrepancy between these values and the "punch in"pH value, though differences can also be due to CO2 losses,etc. (cf. Gieskes, 1973).

Calcium: Complexometric titration with EGTA (Tsu-nogai et al., 1968) as modified by Gieskes (1973) wasused. Copenhagen IAPSO standard seawater was used as thestandard. Corrections for strontium were made using theexperimental Sr values.

Magnesium: The values of magnesium were obtainedfrom EDTA titrations (Ca + Sr + Mg) and subtraction of(Ca + Sr) from these titrations. Again, H-butanol was usedas an extractant, but we did find that this procedure affectsthe end point to a small degree (1% using 0.5-ml standard

seawater aliquots, 0.5% using 1-ml aliquots). This is due toa shift in the equilibrium constants of Eriochrome Black-Twith H+ and Mg++ ions as a result of the change in thedielectric constant. We found, however, that if the samplesize and the size of the standard seawater aliquot wereequal, errors became negligible. Reproducibility was betterthan 0.2 percent. Again, IAPSO standard seawater was usedfor the standardization of the EDTA solution using the newMg/Cl ratio of Carpenter and Manella (1973).

Dissolved Silica: An appropriate version of the methodof Strickland and Parsons (1968) was used.

Chloride: Chlorinity was determined on samples pre-viously titrated (onboard ship) for alkalinity using a Mohrtitration with AgN03 and K2Crθ4 as indicator. Corrections(less than 1%) were made for the added HC1. Whenevernonacidified samples were available, chlorinity valuesagreed within 1 percent.

Salinity: Total dissolved solids ("salinity") were meas-ured using a Goldberg refractometer. Sayles, et al (1970)found that this "salinity" agreed well with their measuredion sums.

Ammonia: The method of Solorzano (1969), asmodified by Presley (1971) and Gieskes (1973), wasused. We found that nonacidified samples showedconsiderably less dissolved ammonia than did those thatwere titrated for alkalinity and subsequently stored at pH

3.0. There is no guarantee that some ammonia is still notlost (presumably due to inorganic oxidation and/orbiochemical consumption, since sometimes molds werefound to grow in the samples), but the data should serve asa relative indicator of the sulfate reduction process.

Sulfate: The titration method of Cescon and Macchi(1973) was used. IAPSO standard seawater was used as astandard.

Manganese: 1 ml of sample was diluted with 4 ml ofdistilled water, and 0.1 ml of a 50,000 µg/ml Lanthanum(La) solution was added. Standards were made in La Jollapier water (range 0-10 ppm Mn in undiluted samples).Analysis was done by means of atomic absorption (AA)spectrometry, using a Perkin-Elmer Model 403 spec-trometer.

Strontium: 2 ml of the manganese solution was furtherdiluted with 8 ml of a 5000 ppm La solution. Analysis wascarried out by AA spectrometry. Standards were preparedby making solutions of 10 to 100 ppm Sr in distilled waterand diluting them in a manner similar to the dilution of thesamples.

Potassium: 0.5 ml of the manganese solution wasdiluted with 10 ml of a 5000 ppm La solution. Analysis wascarried out with the Perkin-Elmer Model 403 spectrometerin the emission mode. Standards were made of 100 to 500ppm K in a background of 10,000 ppm Na, carryingthrough the dilutions as for the samples. CopenhagenIAPSO standard seawater was used as an additionalstandard.

Accuracies of the various measurements are affected notonly by the precision of the methods but also by the han-dling of the samples. Also, errors are inevitably introducedin the squeezing process. In Table 1, estimates are presentedof both accuracies and precisions of the various analyses.Note that the accuracy of the alkalinity and pH data also

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J. M. GIESKES

TABLE 1Accuracy and Precision of Analyses

Method

Alkalinitya

pH*

Ca

Mg

S 0 4

Cl

N H 4

SiO2

MnSr

K

Accuracy<%)

10

0.2 (pH)

2

2

2

2

10

5

10

5

5

Precision(%)

0.5

0.1 (pH)

0.2

0.2

0.5

0.5

5

25

2

2

aAccuracy affected by WhatmanNo. 50 paper.

depends on the variable filter paper effect. The estimatederror is a maximum error.

RESULTS

Results of the various analyses are presented in Tables 2through 7, as well as in Figures 2 through 45. Theadvantage of using these figures is clear as they give aninstantaneous impression of the distributional trends of thevarious parameters.

The pH data are reported at 25°C, assuming atemperature coefficient of 0.01 ρH/°C. Measurements werealways carried out in the range of 20° to 26° C (laboratorytemperature) so that corrections never exceeded 0.06 pHunits. The cold squeeze pH values (5°C), therefore, must beaugmented by 0.2 pH units to yield the value at 5°C. Thedata for pH and alkalinity are presented in more significantfigures than seem justified; I have retained this notation forease in comparing the various measurements.

In the lower parts of the holes, very small amounts ofinterstitial water sometimes were retrieved (2-3 ml). Suchsamples were subsequently diluted with distilled water.Some of the laboratory analyses suffered in accuracy bythis procedure, and these data are bracketed in theaccompanying figures.

The validity of some of the pore water data can alwaysbe questioned because of the ever-present chance ofseawater contamination. Often cores show large drillingdisturbances and sometimes so-called "drilling breccias,"i.e., small chunks of sediment loosely aggregated in the corebarrel. Also, as a result of the coring procedure, the outsideof the core is in contact with seawater. Thus, even thoughcare is taken to scrape off the contaminated outside of thecore section and to avoid squeezing disturbed drillingbreccia, the chance of contamination is always present.

During the course of this investigation, I found thatthere exists a very strong linear correlation betweendissolved magnesium and dissolved calcium in holes withslow rates of sedimentation (Sites 239, 245, and 249; cf.Figures 6, 31, and 43) and a rather uniform correlation

between these parameters in holes with rapid rates ofaccumulation (Site 242; cf. Figure 24). Very few points donot fall on these smooth curves, and those points also showanomalies in the depth distribution (cf., Figures 5, 23, 30,and 42). In addition, these anomalies are usuallyaccompanied by similar anomalies in dissolved sulfate(Figures 21 and 41). It is the author's opinion that suchanomalies can best be explained as a result of slightseawater contamination (usually less than 20%). Reactionrates, especially for reactions involving sulfate and magne-sium ions (silicate reconstitution or dolomite formation), areusually sufficiently slow to cause rather smooth curves inthe depth distribution of these parameters. Only a very fewsamples are subject to this suspicion of contamination; so,in general, the data do represent true compositional trendsin the interstitial waters.

Site 241 presents a somewhat more complex problem.Here, rather irregular changes occur in the distributions ofmagnesium and sulfate. At 150 and 180 meter depths,somewhat unexpected values of alkalinity, dissolved silica,dissolved sulfate, and dissolved magnesium occur which aresuggestive of 20 percent or less seawater contamination.Changes in the smoothness of the depth distribution ofmagnesium below 300 meters are not as easily explained,but I cannot assert that these are not due to slight amountsof seawater contamination. For that reason, I have drawn asmooth curve through the magnesium distribution inFigure 16. Also, the secondary extrema in the SO4" andNH4+ distributions in Figures 14 and 15 may not beentirely realistic.

In general, the depth distributions of the various ionsseem realistic, and not withstanding some possiblecontamination problems, the trends are well established. Aninteresting problem involves the components that appear todepend on very rapid reequilibration processes, i.e.,alkalinity, silica, and perhaps dissolved calcium. Thetemperature dependence of the alkalinity and dissolvedsilica will be discussed presently, but the large temperaturedependence of these parameters suggests that pressureeffects may not be entirely negligible. The total changes indissolved calcium are very large; yet, even though changesin alkalinity with temperature are relatively large,temperature effects on dissolved calcium are small. Loss ofCO2 during the retrieval of the cores cannot lead to largeenrichments in calcium because no large changes inalkalinity are observed and also because loss of CO2 shouldlead to decreases in dissolved calcium, not to increases. Ibelieve, therefore, that the observed calcium changes arereal.

On a future cruise, attempts will be made to samplesome interstitial waters in situ in order to test the abovesuggestion and also to provide an estimate of the relativeeffects of pressure on the distribution of the variouschemical parameters, particularly those of alkalinity,dissolved silica, and dissolved calcium.

TEMPERATURE EFFECTS

Temperature of squeezing effects has been welldocumented by the investigations of Mangelsdorf et al.(1969), Bischoff et al. (1970), Fanning and Pilson (1971),Sayles et al. (1973a), and Gieskes (1973). It appears

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that for the ions Mg++ and K+, these effects are mainlycaused by cation exchange equilibria with the clays, but foralkalinity, dissolved silica, and perhaps calcium, thesituation may be complicated by solubility equilibria.Hammond (1973) attempted to unravel the temperatureeffects on alkalinity and pH on the basis of the observationsmade during Leg 15. He suggested that, upon warming, theclay minerals can release hydrogen ions and cause asubsequent dissolution of calcium carbonate. Observeddecreases in dissolved calcium could then still be explainedby temperature effects on ion exchange equilibria with theclays (cf. Gieskes, 1973).

Temperature effects on magnesium and potassium are, ingeneral, similar to those observed in previous studies (e.g.,Sayles et al., 1973a) with the possible exception of Site249, where reverse effects are noted. Temperature effectson dissolved strontium are negligible, at least within theprecision of the data. It is important to note that none ofthe gradients in Mg++, K+, or Sr++ are obscured by thesetemperature artifacts. One observation is remarkable, andthat is the essential parallelism of the warm squeeze and thecold squeeze values (see, for instance, Figures 31 and 32).This is not necessarily proof that the observed irregularitiesin the depth distributions are real, but rather that the coresection under investigation, contaminated or not, wasreasonably homogeneous.

Thus, interstitial water data obtained only from roomtemperature squeezes will not obscure any gradients inconcentrations, and, in fact, the slopes of these gradientswill be little affected by the temperature effects. Forsurface cores, of course, the temperature problem is muchmore important because, in such cases, one desires toextrapolate the gradients to the sediment-seawater interface(Sayles et al., 1973c).

In the present study, alkalinity values are always lowerin the low temperature squeezes. The magnitude of theeffect is variable and usually ranges from 0.3 to 1.2 meq/1.Particularly pronounced effects occur in the chalk sectionof Site 249 (Figure 39). An interesting problem is posed bythe data of Site 242. At the actual prevailing bottom (orsurface of sediment) temperatures of about 1°C, thealkalinity maximum will almost disappear! Of course, it ispossible that pressure effects may act in the reversedirection. In the near future, it is hoped to employ an insitu interstitial water sampler to check on such effects inrapidly accumulating sediments. Changes in pH are almostalways such that pH values (measured at room temperature)are higher in the cold squeezes than in the warm squeezes.These pH values will be even higher (i.e., roughly by 0.2 pHunits) after appropriate correction to the squeezingtemperature of 5°C. These observations are in qualitativeagreement with those made during Leg 15 (Gieskes,1973; Hammond, 1973), but the observed effects are ofgreater magnitude. This can be explained from the longerequilibration time allowed for in the present study. Theobservations lend strong support to the tentativeconclusions of Hammond (1973) about the involvementof hydrogen ion exchange with the clays and subsequentincreases in alkalinity due to calcium carbonate dissolution.This may indeed explain the temperature effect ondissolved calcium. Whereas previous studies, including those

of Leg 15, always showed higher cold squeeze calciumvalues, this is not so in the case of the Leg 25 samples. It isprobably not too farfetched to speculate that if longertemperature adjustment had been allowed during Leg 15,trends in the temperature effects on dissolved calciummight have reversed. Again, no gradients in dissolvedcalcium are obscured, but those of alkalinity are extremelysensitive to temperature effects.

Effects of temperature on dissolved silica are very similarto those observed in previous investigations, e.g., Fan-ning and Pilson (1971) and Sayles et al. (1973a). Themagnitude of the effect depends slightly on the lithologies;it is highest in sediments with relatively high clay anddetrital mineral contents and lowest in the highlycalcareous section of Site 249. This suggests that clayminerals are chiefly responsible for these temperatureeffects. This subject deserves further investigation. Again,the temperature effect is never large enough to obscuredefinite trends in the depth distribution of dissolved silica.

CHEMICAL CHANGES IN INTERSTITIAL WATERS

In this section, observations on the chemical changesobserved in the interstitial fluids will be briefly describedfor each individual site. These changes will be related toobservations made on changes in the lithologies (see sitereports and the reports of Leclaire and Vallier, this volume)as well as to those on the mineralogies (Matti et al., thisvolume).

Site 239

This hole shows generally low rates of sedimentation,i.e., less than 2 cm/1000 y (cf. Figure 1). In such holes,usually no maxima are observed in the alkalinity, as isconfirmed for this hole by the data presented in Figure 2.Disregarding the sometimes large variations in the depthdistribution of this property in the upper part of the hole,the data suggest a gradual decrease in the alkalinitydownwards. This decrease is related to the decrease inalkalinity that often is postulated to coincide with silicatereconstitution reactions (MacKenzie and Garrels, 1965;Siever, 1968a).

Dissolved silica values follow closely the lithologies ofthis hole. Between 70 and 120 meters, sponge spicules arereported to be present in fairly large quantities (Leclaire,this volume). The presence of opaline silica maintains thehigh dissolved silica values in this depth range. The gradientin dissolved silica from 10 to 120 meters is not necessarily asimple diffusion gradient between two zones of fixeddissolved silica concentrations. Rather, the dissolved silica islikely to be maintained at some steady state concentrationwhich depends on the relative abundance of clay mineralsversus that of sponge spicules.

The depth distribution of dissolved sulfate shows aninteresting shape and suggests two principal zones wheresulfate reduction occurs at higher rates than elsewhere.These zones range between 70 and 120 meters and in thehole segment below the sedimentation hiatus (cf. Figure 4).Indeed, in the range from 100 to 140 meters, pyrite wasobserved, especially in foram tests. Much of this pyrite, ofcourse, may have formed shortly after the deposition of

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J. M. GIESKES

sediment in this segment of the hole (Berner, 1970;Sholkovitz, 1973).

Changes in dissolved calcium and magnesium are verylarge in this hole, as is shown in Figure 5. The gradients inthe depth distributions of these ions are almost linear to adepth of 150 meters, but below that there is a very distinctcurvature. From the X-ray data of Matti et al. (thisvolume), we observe that in the section below 150 metersthe mineral palygorskite (attapulgite) increases in the<2µ-size fraction, particularly in the section below thesedimentary hiatus (Figure 1). This mineral is a highmagnesium alumino silicate which often has beenpostulated to be a product of the diagenetic alteration ofmontmorillonite (von Rad and Rösch, 1972; Vallier, thisvolume). Much of the palygorskite in the deeper part of thehole may have formed shortly after the deposition of thesesediments, but it is not possible to rule out detritalcontributions of palygorskite (Goldberg and Griffin, 1970).If the palygorskite is, indeed, of diagenetic origin, then itsformation may still be a continuing process and it willprovide a sink for the magnesium. If this is so, then noespecially highly dissolved silica or magnesium concentra-tions seem to be required for this reaction. Of course, theselayers also contain a small amount of chlorite in the mineralassemblage which could also take up Mg++ ions, especiallyif this chlorite has been deposited in a degraded crystallineform (Griffin and Goldberg, 1963). Of importance is thepronounced correlation between the dissolved calcium andmagnesium data (Figure 6). Changes show a ratio ΔCa++/ΔMg++ = 1.8. If different reactions, not related toeach other, were responsible for these changes, such arelationship would not be expected unless by coincidence. Isuggest that this presents strong evidence that onediagenetic process is responsible for the observed changes incalcium and magnesium. Though I have no proof thatfurther formation of palygorskite1 in the deeper parts ofthe hole constitutes the main sink for magnesium ions, Isubmit that this is a likely candidate.

The data for dissolved potassium (Figure 7) show aconsiderable decrease in concentration with depth. Theshape of the depth profile is very different from those ofMg++ and Ca++. Of course, the curvature in Figure 7 is notwell defined, and the dashed straight line equally wellrepresents the data. If this is the case, then the mainreaction site for K+ would be in the deeper sediment layers(perhaps involving reconstitution reactions with chlorite).

Of interest is the distribution of dissolved sodium (notshown here). If dissolved sodium is calculated from ananion-cation balance, using the data of Table 2, we observedepletions in Na+ of about 2 percent at 90 meters,5.5 percent at 220 meters, and 10.4 percent at 302 meters.These depletions are significant and much larger than couldbe explained from temperature-of-squeezing artifacts(about 1%, Sayles et al., 1973a). Such decreases have beenobserved previously in holes containing detrital sediments,e.g., Hole 137 of Leg 14 (Waterman et al., 1972). Again,diagenetic changes in clays are the most likely causes forthese sodium depletions. Another possibility is that changes

in dissolved sodium are purely due to ionic migrationcaused by conditions of electroneutrality in the interstitialwater column (Ben-Yaakov, 1972). However, the mechanicsof such a process are difficult to visualize.

Dissolved strontium is high in the calcareous section ofthis hole, i.e., from 70 to 120 meters, and, in fact, shows amaximum at about 100 meters. Manheim and Sayles (1971)suggest that this is mainly due to the recrystallization ofcalcareous microfossils (forams and/or coccoliths). Thepresent data support that conclusion, but the situation iscomplicated by the presence of fairly large amounts oftunicate spicules (Leclaire, this volume) which arearagonitic in their crystal structure (Matti et al., thisvolume). Leclaire assumes that these tunicate spicules werebrought in by turbidity currents from the nearbycontinental slope of Madagascar. Conversion of aragonite tocalcite would undoubtedly also release strontium to theinterstitial fluids. The presence of small amounts ofmicrocrystalline carbonates can also be considered asevidence for this recrystallization process.

The distribution of dissolved manganese in this hole wasstudied to only about 220 meters. This was because of alack of samples from the two lower levels. Thus, thedistribution presented in Figure 9 is incomplete. This ismost unfortunate because the lower part of the holeshowed the presence of small manganese nodules (Core 15,272-281 m). From the distribution of dissolved sulfate,however, it appears that reducing conditions prevail in thelower part of the hole. Lynn and Bonatti (1965), Li, et al.(1969) and Bischoff and Sayles (1972) suggest that underreducing conditions the concentration of dissolved manga-nese is maintained by carbonate equilibria. Indeed, acomparison of Figure 9 (manganese) and Figure 2 (alka-linity) does suggest a vague correlation between Mn+ + andHCθ3~, but, of course, this correlation could be refined iftrue pH data were available. Also, in Hole 149 of Leg 15,the correlation between the alkalinity (Gieskes, 1973)and manganese (Sayles et al., 1973a) is striking. Althoughmanganese nodules are present in Core 15, this is notnecessarily proof of present oxidizing conditions. Upondeposition of these brown clays, the conditions wereundoubtedly oxidizing, and only after deep burial did theybecome reducing. It is possible that these nodules dissolvevery slowly.

In summary, changes in the chemical composition of theinterstitial waters of Site 239 are very large. Most of thehole is "reducing" (cf. the distribution of sulfate, ammonia,and manganese). Decreases in Mg++, K+, and Na+ withdepth are significant and are probably related to diageneticchanges in the clay minerals. Such "reverse" weatheringprocesses are also responsible for the slight decrease inalkalinity with depth, and the dissolved calcium increasesmay be due to the dissolution of calcium carbonate duringthe clay mineral diagenesis.2 To prove such a mechanism isa difficult but necessary task in this type of study.

Possibly from further alteration of volcanic ashes or theirproducts.

One serious problem here is that in such a proposed coupledsilicate reconstitution and carbonate dissolution process, eitheralkalinity or molecular CO2 will be produced. Such changes should beconsiderable, yet observed changes in alkalinity and pH are only small.Loss of CO2 during core recovery is possible, but losses should belarge. This makes the above conclusions somewhat tentative.

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A final remark should be made regarding the samplefrom Core 16 (Table 2). A rather low chlorinity is observedin these samples, confirmed by low salinities (measured onboard). The reasons for this phenomenon are not wellunderstood, particularly because the other anions andcations do not show any anomalous values.

Site 241

Site 241, with a water depth of 4054 meters, is situatedat the lower end of the continental rise in the Somali Basin.This site is characterized by very high rates ofsedimentation (Figure 1). The sediments show bothbiogenous and terrestrial contributions (Leclaire, thisvolume).

Contents in organic carbon are very high in the upperzone of this hole. This, in conjunction with the high ratesof sedimentation, is responsible for the large depletion insulfate (Figure 14), the increase in alkalinity (Figure 10),and the increase in ammonia (Figure 15). These parametersare all intimately linked in the process of bacterial sulfatereduction (Berner et al., 1970; Gieskes, 1973; Hartmannet al., 1973; Sholkovitz, 1973). In general, the decrease indissolved sulfate appears to be a function of the rate ofsulfate reduction and the rate of sedimentation, and only inholes that are completely closed to diffusional communica-tion with the overlying seawaters is complete reduction ofsulfate observed (e.g., in Site 147, Leg 15; Sayles et al.,1973a). The depth distribution of alkalinity shows a classicalcurve, that is, a maximum followed by a gradual decreasewith depth. Whereas in holes such as Site 148 of Leg 15(Gieskes, 1973; Lawrence, 1973), such distributions canbe explained from changes in alkalinity due to silicatereconstitution reactions and carbonate equilibria, thesituation at Site 241 is more complicated. The distributionsof dissolved sulfate and ammonia both show extrema(Figures 14 and 15). As discussed in a previous section,concentrations of between 200 and 600 meters may, to asmall degree, be subject to slight seawater contamination(<20%), but this does not obscure the observed trends.From Figure 1, it follows that sedimentation rates below220 meters are much lower than in the upper part of thecore. Interstitial water-dissolved sulfate values during theMiocene, therefore, were probably much higher because ofan enhanced diffusional replenishment from the overlyingseawater. The fast sedimentation rates during the Plioceneand Quaternary, coupled with highly organic sediments,then led to greater isolation from the ocean.

The distribution of chlorinity is interesting and shows adecrease of 3 °/oo Cl from the surface to the bottom of thehole at 1200 meters. Such changes have been observedpreviously in Deep Sea Drilling Project holes (Sayles et al.,1972; Presley et al., 1973). This observation can beexplained either by the influence of freshwater intrusions atgreat depth, which must occur at least more than 5000meters below sea level (the distance from shore is a fewhundred miles), or by some unexplained diagenetic process.This latter process would involve either the uptake ofchloride or the production of water. Sayles et al. (1972)prefer the explanation that some unknown diageneticprocess is responsible for the uptake of chloride, and theycite the gradual increase in the Na/Cl ratio as evidence.

Calculations by charge balance from Table 3 indicate thatsodium values at 258 meters differ by 0 percent from thosecalculated from the chlorinity (using the oceanic ratio of0.5556; Culkin, 1965). At 532 meters, this difference is1 percent, at 840 meters it is +3 percent, at 980 meters it is+6 percent, and at 1070 meters it is +8 percent. The data atgreater depth are subject to fairly large errors, due to thesmall volume of pore water available (samples underwentgreater dilutions before analysis). Thus, only smallvariations in the sodium/chloride ratio occur. This, in myopinion, does not contradict the freshwater intrusionhypothesis. Perhaps isotopic studies on these interstitialwaters will shed some light on this problem.

Salinity values (Figure 12) decrease gradually withdepth. In the deeper parts, these data correlate well withthe chlorinity data, but between 4 and 400 meters, theshape of the depth distribution curve is influenced by therapid changes in dissolved sulfate, magnesium, and calcium.Whenever refractometer values are below 31 °/oo "salinity,"depletions in chlorinity can be suspected.

Dissolved silica (Figure 13) in the upper 300 metersreflects the presence of opaline silica in the form of diatomsand radiolarians (cf. Leclaire, this volume). Below 300meters, a rapid decrease in dissolved silica occurs, andvalues of 100 to 200 micromoles/l may reflect the mixedclay mineral content of the sediment (Matti et al., thisvolume).

Dissolved calcium (Figure 16) follows a pattern familiarin sediments in which sulfate reduction is relatively large;that is, it shows an initial decrease followed by an increase.Values never exceed 17.5 mmoles/1. Dissolved magnesiumdecreases continuously downhole, which, again, may be dueto clay mineral diagenesis of both the type suggested byDrever (1971) and Sayles et al. (1973a, b), i.e., exchange ofFe++ for Mg++ with nontronite (the Fe++ subsequentlyforms pyrite, FeS2), and the type suggested for Site 239,i.e., the continuous formation of palygorskite. Thepalygorskite content of this hole (<2µ fraction; Matti et al.,this volume) is rather uniform and is perhaps of detritalorigin. Recrystallization of this mineral, however, couldprovide a sink for magnesium ions. Also, sporadicoccurrences of dolomite are reported by Matti et al. (thisvolume), but, again, some of these occurrences may be ofdetrital origin. Below 850 meters however, dolomite occursin association with sand and claystone (Moore, this volume)and is probably of diagenetic origin. This, then, wouldconstitute an additional sink for magnesium ions.Interestingly, below 800 meters the ratio Ca++/Mg++ isroughly equal to one. Whether or not this might be relatedto an equilibrium situation with respect to dolomitedeserves further investigation.

Potassium values decrease gradually down the hole(Figure 17). This must be related to clay mineral uptakeprocesses. Again, chlorite (present below 550 m) may be amajor sink for these cations.

Dissolved strontium (Figure 18) shows a maximum at 250meters, almost at the base of the rapidly deposited biogenoussection. The rather gradual increase in dissolved Sr++from4to 250 meters may be due to either a gradual increase in therecrystallization of calcium carbonate or a combination ofthis process with diffusional transport processes.

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Dissolved manganese values are almost always below thedetection limit of 0.1 ppm. In rapidly accumulatingreducing sediments, this is a common phenomenon (Presleyet al., 1967). These investigators did find total manganesecontents of the bulk sediments in rapidly accumulatingterrigenous sediments to be much lower than in pelagicsediments. At the same time, such sediments usually showmuch sulfate reduction and high alkalinity values. Thus, itappears that dissolved manganese concentrations inreducing sediments depend not only on the alkalinity,which, essentially, reflects the carbonate equilibria, but alsoon the form of manganese and its concentration in the solidphases.

To summarize, Site 241 is characterized by rapidsedimentation rates, and this is reflected in the extremathat occur in the depth distributions of alkalinity, sulfate,and ammonia. Reversals in the depth profiles of the lattertwo constituents are partly related to lower sedimentationrates below 250 meters. Upward advection of freshwaterfrom the lower strata also affects these distributions.Dissolved calcium, magnesium, and potassium reflectchanges typically observed in terrigenous hemipelagicsediments and are due to both clay mineral and carbonatereactions.

Site 242

Rates of sedimentation in this hole are very similar tothose of Site 241, with a marked decrease in the Miocene.Leclaire (this volume) describes the sediments as hemipe-lagic, i.e., a nanno ooze mixed with a high amount of clayand some heavy mineral input. According to Leclaire, thepelagic part is generally dominant. Organic carbon contentsare much lower than in the upper, biogenous part of Site241. Radiolarians and diatoms also are very rare and arefound only in the Quaternary. Below 610 meters,anomalous values were measured for the thermalconductivity and the acoustic impedance (Marshall, thisvolume), but no clear mineralogic change that wouldexplain this phenomenon has been observed.

The extent of sulfate depletion in this hole is much lessthan at Site 241 (Figure 21). Similarly, less extensivechanges occur in the alkalinity and ammonia values(Figures 20 and 22). These changes, of course, are againrelated to the process of bacterial sulfate reduction. Despitethe fact that the rates of sedimentation of Sites 241 and242 are very similar in the upper parts of the holes, theextent of sulfate depletion is much less. I believe this to beprimarily a result of the much smaller quantities ofbiologically refractive organic matter in the Hole 242sediments. Again, a minimum of sulfate is observed atabout 250 meters, coinciding with a maximum of ammonia.Below 250 meters, sulfate shows a linear increase withdepth. (Note that the sulfate values below 600 meters aresubject to large errors, due to the small sample sizesavailable for sulfate analyses). From Figure 1, one observesa large change in the rate of sedimentation below about 300meters depth. For reasons similar to those discussed underSite 241, there is good reason to believe that at the time ofdeposition of the sediments during the Miocene thedecrease in interstitial sulfate was much less. I suggest thatthe linear gradient below 250 meters is essentially adiffusion gradient. Thus, the site of maximum sulfate

depletion at 250 meters serves as a sink for sulfate fromboth the upper strata and the lower ones. This should putsome interesting limitations on sedimentary sulfatereduction models.

Dissolved silica (Figure 20) is rather uniform with depthand may reflect the clay mineralogy of this hole (Matti etal., this volume). No important change is observed belowthe acoustic reflector (Marshall, this volume) at 610 meters.

Dissolved calcium (Figure 23) reveals a distribution thatis expected in holes that show rapid sedimentation andsulfate reduction. The observed decrease with depth in thealkalinity is probably related to diagenetic processesinvolving silicate minerals and magnesium and potassiumions. The profile of dissolved magnesium (Figure 23)suggests two major areas where the diagenetic reactions areproceeding at more rapid rates. First, in the zone ofmaximum sulfate depletion and secondly, in the zonebelow the acoustic reflector, i.e., below 610 meters, Mattiet al. (this volume) report the presence of chlorite below600 meters, as well as a slight increase in the amounts ofpalygorskite. The latter constituent is present throughoutthe hole and is probably largely detrital in origin. Thoughno clear evidence is available from X-ray data of diageneticchanges which might be related to the reported anomaliesin the physical properties below 610 meters (Marshall, thisvolume), the dissolved magnesium distribution suggests thepresence of some diagenetic process that constitutes amajor sink for magnesium ions (recrystallization of chloriteand/or palygorskite?). Closer investigations of the solidshave been planned.

Dissolved potassium (Figure 25) shows a rapid decreasewith depth to about 300 meters, after which only a smallchange occurs. The shape of this curve suggests that themain uptake of K+ occurs in the upper portions of thesediments and relates to the uptake of K+ by detrital clayminerals. Changes in sodium, calculated from a charge bal-ance, are less than 4 percent throughout the hole and areconsidered to be within the analytical error.

Dissolved strontium (Figure 26) increases gradually withdepth, and this reflects the continuous recrystallation ofthe nanno ooze to nanno chalk. There is no relationshipbetween Ca++ and Sr++ data. This is mainly due to the factthat calcite recrystallization occurs independently of thecarbonate equilibria regulated by the silicate reconstitutionreactions.

Dissolved manganese (Table 4) shows erratic variationsfor reasons similar to those suggested for Site 241.

In summary, Site 242 is characterized by rapidsedimentation of a hemipelagic clay and nanno oozesediment. The lesser sedimentation rates in the Miocene(below 300 m) are reflected in reversals in the profiles ofsulfate and ammonia. Dissolved silica suggests a ratheruniform type of clay mineral deposition. Changes indissolved magnesium in the sediment layers below theacoustic reflector indicate the presence of a diageneticreaction involving magnesium ions that may be responsiblefor the observed changes in the heat conductance andacoustic impedance.

Site 245

Hole 245 was probably the only hole drilled during Leg25 that has principally truly pelagic characteristics

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(Leclaire, this volume). The sedimentological aspects of thishole are discussed in more detail by Leclaire, Vallier, andWarner and Gieskes (this volume). Also of importance is themineralogical description of Matti et al. (this volume). InFigure 46, the mineralogical data on this hole (<2µfraction) are presented. Included in this figure are somedata on the carbonate-free fraction of these sediments,analyzed in a qualitative manner, without regard to the sizeof the fraction. Some typical observations can be made.Below the brown clay portion of this hole (upper 100 m),kaolinite disappears from the clay mineral assemblage and,also, mica becomes a less important constituent. Below 100meters, palygorskite becomes an important constituent,constituting more than 60 percent of the <2µ-size fraction.Often this palygorskite is associated with the zeoliteclinoptillolite. This suggests that at least a fraction of thepalygorskite may be of authigenic origin. Below 360meters, palygorskite becomes a less important constituent.At greater depths, montmorillonite becomes the dominantclay mineral and is mainly derived from volcanic ash bydevitrification. Based on these mineralogical data, the holecan be divided into three zones: 0-100 meters-brown claycharacterized by a mica-kaolinite-montmorillonite assem-blage; 100-260 meters-carbonate ooze and chalk, withcherts and a predominant montmorillonite-palygorskiteclay mineral assemblage; basal nanno ooze and chalk,characterized by volcanic ash layers and a predominantlymontmorillonitic clay fraction. In addition, these basalsediments are characterized by a high iron and manganesecontent (Warner and Gieskes, this volume).

The alkalinity profile shows rather constant values toabout 200 meters, after which a gradual decrease occurs(Figure 27). The sedimentation rates in the upper 50 meterswere slow (<0.5 cm/lOOOy), and, therefore, this observa-tion is in general accord with observations made duringprevious legs.

Dissolved silica shows a very interesting distribution(Figure 28). In the brown clay section of the hole, thevalues appear to be maintained by the mixed mica-kaolinite-montmorillonite clay assemblage. Below thisdepth, the dissolved silica goes to values of about 600µmoles/1, a value that seems to be maintained by themontmorillonite-palygorskite clay minerals. Similar valueswere obtained by Sholkovitz (1973) in the interstitialwaters of the Santa Barbara Basin sediments, which arepredominantly montmorillonitic in their clay fraction.3 Noopaline biogenous material was observed in Hole 245. Suchhighly dissolved silica concentrations may have beenfavorable for the formation of zeolites and perhaps alsopalygorskite shortly after deposition.

Dissolved sulfate shows a decrease to the lowestsampling depth in the hole (Figure 29). Below 100 meters,the gradient is essentially linear. This means that sulfatereduction still occurs in the deeper parts of the hole. It

Couture (personal communication) noticed similar relationshipsfrom an analysis of published Deep Sea Drilling Initial Reports.

could be argued, of course, that with the highersedimentation rates during the Eocene, the sulfatedepletion was much higher, but, at the very lowsedimentation rates during the last 40 m.y., it is most likelythat if no further reduction took place below 100 metersdepth, diffusional processes would have eradicated anygradients.

Data for calcium and magnesium (Figures 30 and 31)suggest essentially linear gradients with depth, as well as anexact 1:1 correspondence between the concentrationchanges. Deviations from the linear gradients are usuallyless than 5 percent and, thus, are likely to be experimental.The 1:1 ratio in the changes in dissolved calcium andmagnesium has often been interpreted as an indicator ofdolomite or high magnesium calcite formation. I do notsubscribe to this contention but would rather prefer amechanism in which magnesium is used up in a silicatereconstitution reaction. The basal layers of Hole 245 showhigh montmorillonite content, as well as many volcanic ashlayers. If these layers should be the main sink formagnesium, then a silicate reconstitution reaction involvingthe uptake of Mg++ ions and the simultaneous release ofcalcium ions at a more or less constant alkalinity wouldexplain the observed interstitial water changes in Ca++ andMg++ concentrations. This would imply that the gradientsin calcium and magnesium are primarily diffusionalgradients. I interpret the decrease in alkalinity below 200meters as due to the suggested silicate reconstitutionprocess. I should emphasize that it will be difficult to provethis mechanism. Further experimental work has beenplanned.

Changes in potassium concentrations are very small inthis hole (Figure 32), so that, apparently, there is nosignificant sink for these K+ ions in the deeper parts of thehole. Changes in sodium concentrations, calculated fromthe data of Table 5, reveal an exact correspondence (ifexpressed in meq/1) with the dissolved sulfate concentra-tions. It is well possible that dissolved sodium depletionsare not caused by diagenetic reactions but, rather, are theresult of migration as a result of overall charge balancerequirements (cf. Ben-Yaakov, 1972).

Concentrations in dissolved strontium (Figure 33)increase linearly with depth. This linear increase corre-sponds with the linear increase in calcium, but this does notnecessarily imply a causal relationship (cf. data for Site239). Rather, the linear profile may indicate a steady statemaintained by a diffusional transport gradient and anincreased amount of recrystallization of calcium carbonatewith depth (cf. Manheim and Sayles, in press). Typically,the nanno ooze turns into a nanno chalk with depth.

The distribution of dissolved manganese (Figure 34) ispuzzling. In the upper 100 meters, in almost all recoveredcores, the presence of Fe/Mn oxides, either in the form ofmicro-modules or opaque streaks, has been noticed(Chapter 7, this volume). Such occurrences are alsoreported in Cores 245-3 (121-130 m) and 245-4(159-168 m). Below that, the presence of iron andmanganese oxides becomes apparent only in the basalsediments. The dissolved sulfate profile shows curvaturedown to about 100 meters after which it becomes linear

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(cf. also, Sayles and Manheim, 1971). Such a profilesuggests that sulfate reduction takes place throughout thefirst 100 meters, but, of course, part of the curvature canbe caused by the upward advection of pore waters in thesemore porous layers. This is contradicted by the lineargradients in Ca++ and Mg++. The reducing conditionscaused by such sulfate reduction processes and thesubsequent formation of pyrite (not observed in smearslides) would provide the proper medium for electrontransport necessary to bring about the reduction ofmanganic oxides to manganous ions. If sulfate reductionwere to occur at a maximum at about 100 meters, then thiswould cause maximum formation of Mn+ + The distributionof dissolved manganese above and below 100 meters wouldthen be due mainly to diffusional transport gradients. Morequantitative work on these cores is planned, in order toverify this suggestion.

In summary, Hole 245 is the most typical pelagic holedrilled during Leg 25. Rates of sedimentation during theQuaternary through the Oligocene were relatively slow(<0.5 cm/1000 y), but below that, high sedimentation ratescorrespond to fast deposition of nanno-fossil oozes. Sulfatereduction occurs in this hole, with highest rates probably atdepths around 100 meters and below 350 meters. Reducingconditions at 100 meters are reflected in maximal dissolvedmanganese values. Magnesium decreases linearly with depth,with a corresponding increase in dissolved calcium(ΔMg++/ΔCa++= 1.0). This is possibly related to authi-genic reactions occurring in the basal sediments, which arecharacterized by volcanic ash layers and high montmoril-lonite clay fractions. The most likely process is theformation of authigenic silicates in these layers, involvinguptake of Mg++ ions and simultaneous release of Ca+ + ions.We hope to verify some of these contentions by moredetailed chemical work, as well as isotopic O 1 8 / O 1 6 studieson interstitial waters, carbonates, and silicates (cf.Lawrence, 1973).

Site 248

This site is characterized by the presence of silts andsands, especially in the upper 300 meters (Chapter 9, thisvolume). This makes the squeezing operation, in manycases, rather futile because of obvious, visible seawatercontamination. For these reasons, very few samples wereobtained, and even those samples are somewhat suspect, asfollows clearly from Sample 248-12-5 (cf. Table 6 andFigures 35 to 38). The lower part of the hole isgeochemically interesting, as is shown by the data ofMarchig and Vallier (this volume), and, therefore, it isunfortunate that it does not possess high quality interstitialwater data.

Qualitatively, the data are representative of observationsmade in rapidly depositing detrital sediments. Thealkalinity appears to have a "maximum" (undefined; cf.Figure 35), and the sulfate a "minimum" (Figure 36). Thehigher sulfates in the deeper part of the hole are probably,again, related to the corresponding lower rates ofsedimentation (cf. Sites 241 and 242). Changes in calcium,magnesium, and potassium are also as expected in rapidlydepositing detrital sediments. Again, I emphasize that the

data are too scarce to make any conclusions about wheremaximum changes may occur.

There seems little point in a further discussion of thenature of these changes. Of some interest, however, is therather small (if at all significant) increase in dissolvedstrontium (Table 6). Calcium carbonate contents are verylow in this hole (cf. Marchig and Vallier, this volume), andthis confirms the idea that observed changes in dissolvedstrontium principally reflect carbonate recrystallizationprocesses, be it aragonite (cf. Site 239), or calcite (Manheimand Sayles, in press). Increases in dissolved calcium can bedue to calcium release during silicate reconstitutionreactions involving magnesium ions.

Dissolved manganese values are high throughout thehole, indicating reduced conditions. Presumably, thedissolved manganese concentrations are maintained bycarbonate equilibria, causing minimum Mn+ + concentra-tions at high alkalinities (Sample 248-4-5, 125 m). Matti etal. (this volume), in fact, report the presence ofrhodocrosite at 363.4 meters. Much of this mineral mayhave formed shortly after deposition or may be due tohydrothermal effects; further investigation of the geochem-istry of these deeper strata would be very interesting, as isalso evident from the data of Marchig and Vallier (thisvolume).

Site 249

The sedimentation history of Hole 249 is verycomplicated (see Chapter 10, this volume). Quaternary andPliocene deposits are very thin, whereas the Miocenesection is rather thick. This is followed by a largesedimentary hiatus, from middle Miocene to LateCretaceous (Figure 1). The upper part of the Cretaceoussection consists mainly of clay-rich nanno chalk(170-285 m) followed by another hiatus. The lower part ofthe hole consists of olive-black claystone and volcanicsiltstone (cf. Marchig and Vallier, this volume). This lowerpart of the hole is characterized by high contents of organicmatter and generally low calcium carbonate contents. Themineralogy of this unit is characterized by high contents ofpyrite, cristobalite, and tridymite, as well as clinoptilolite.The clay mineralogy is dominated by montmorillonite,presumably derived from the devitrification of volcanic ash.The mineral palygorskite is present only in sediments above305 meters and may well be of detrital origin.

The alkalinity data (Figure 39) show a large scatter aswell as a large temperature-of-squeezing effect. Yet agradual decrease in the alkalinity is apparent, suggesting thegradual removal of bicarbonate from the interstitial waterswith depth. The fairly constant pH values suggest also thatthe total CO2 content decreases in a similar way (cf.Gieskes, 1973; Takahashi et al., 1973).

Dissolved silica values (Figure 40) are rather constant ineach lithological unit, and, interestingly, the temperature-of-squeezing effect increases with the amount of clay in thesediment assemblage. This, of course, as has been discussedbefore, strongly suggests that clay minerals have a largeeffect on dissolved silica, be it due to ion exchangephenomena (doubtful, because at a pH of 7.5, only a smallpercent of the dissolved silica is ionized) or to solubilityeffects. In the lower lithological unit, values are much

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higher, and, again, this may be related to the very differentlithology.

The dissolved sulfate profile is most intriguing. From thesurface of the hole to about 260 meters, the sulfate showsan essentially linear gradient (Figure 41) with only verysmall and random variations. I interpret this as purely adiffusion gradient without any significant consumption ofsulfate by sulfate reduction processes in the upper 270meters of the hole. Any pyrite present in the sediment (cf.Marchig and Valuer, this volume) must have formed shortlyafter deposition of these sediments. In the lowersedimentary layers, it appears that larger decreases occur inthe dissolved sulfate, and, in my opinion, this indicates thatin these highly organic sediments, bacterial sulfatereduction processes are still important.

Gradients of calcium and magnesium are linear in theupper 170 meters. Below that, slight curvature occurs in thechalk unit, but large changes occur in the deepersedimentary layers. Again, there is a strong linearcorrelation between these changes (Figure 43), withΔCa++/ΔMg++= 1.6. As at Site 239, where the ratio was1.8, this correlation suggests a coupled process involved inthese changes. Uptake of magnesium, probably in thereactive parts of this deep volcanogenic sediment, andsimultaneous release of calcium, is apparently still anongoing process. The linear gradients in the upperlithological unit may, therefore, again represent essentiallydiffusional gradients.

Dissolved potassium data (Figure 44) are erratic. Thereappears to occur a small depletion with depth, but theprofile, in general, cannot serve as an indicator of probablesites of significant removal.

Of interest again, is the distribution of dissolvedstrontium (Figure 45). The depth profile suggests that inthe upper portion of the hole, i.e., the nanno ooze section,extensive and increasing recrystallization of calciumcarbonate takes place. The maximum at 150 meters is dueto the simultaneous removal of strontium to the lower andhigher strata by diffusion. In fact, some of the releasedstrontium may be taken up in the lower units by selectiveabsorption by clay minerals (cf. Marchig and Valuer, thisvolume).

In summary, Site 249 is characterized by a sedimentarysequence with highly variable sedimentation rates andsedimentation hiatuses. Except for dissolved strontium, itappears that for most other constituents (sulfate,magnesium, and calcium) the lower volcanogenic sectionacts as a sink or source, whereas the distribution of theseconstituents in the upper 250 meters is mainly determinedby a linear diffusional gradient, extrapolating to seawatervalues at the sediment-seawater interface.

SUMMARY AND CONCLUSIONS

The results of the interstitial water studies carried out onsamples collected during Leg 25 are in general agreementwith observations made during previous Deep Sea Drillingcruises. Much of this previous work has been summarizedrecently by Manheim and Sayles (in press).

During Leg 25, various types of sediments were drilled;these range from mostly detrital sediments on a continentalslope (Site 241) to almost truly deep-sea pelagic deposits

(Hole 245). In the following, results for these variouscategories are briefly summarized.

1) The first category is terrigenous hemipelagicsediments, i.e., sediments with both large detrital and largebiogenic contributions, characterized by fast sedimentationrates, which are represented by Sites 241, 242, and 248. AtSite 241, the biogenous contributions are large in the upper300 meters and consist of nanno-fossil oozes with largecontributions of siliceous organisms (diatoms and radio-larians). The biogenous contributions at Site 242 are foundthroughout the hole and consist mainly of foram-bearingnanno oozes and chalks. Biogenous contributions at Site248 are very small and are mainly restricted to the upperpart of the hole.

Each of these holes is characterized by fairly largedepletions in SO4", small depletions in Ca+ + in the upperpart (followed by more or less large increases), largedepletions in Mg++ and K+, and increases (again in theupper parts) in alkalinity (HCO3') and NH 4

+ . All threeholes show a minimum in the depth distribution ofdissolved SO 4", which is related to lower sedimentation inthe deeper parts of the holes.

2) The second category is hemipelagic sediments withgenerally slow sedimentation rates, characterized by largedetrital silt and clay inputs originating from turbidites. Site239 is typical here, and even the biogenous part ischaracterized by some shallow-water components, such asaragonitic tunicate spicules. A hole of rather similar natureis Site 137 in the Atlantic Ocean (Waterman et al., 1972),although, there, the biogenous components show adifferent depth distribution.

Relatively small depletions occur in SO 4", which is notunexpected in sediments with accumulation rates of lowerthan 2 cm/1000 years. No maximum occurs in thealkalinity, but large depletions occur in Mg++ and K+,accompanied by very large increases in Ca+ +. Strong linearcorrelations between Ca+ + and Mg++ suggest that thechanges in these concentrations are coupled, probablyrelated to processes involving silicate reconstitution. Suchprocesses, if coupled, would result in only minor changes inthe alkalinity.

3) The third category is pelagic deep-sea sediments thatare deposited both above and below the calcium carbonatecompensation depth (Hole 245). In such holes, usuallycharacterized by low sedimentation rates, often no changesare noted in any of the major constituents of interstitialwater, i.e., the overlying seawater composition ismaintained. In some holes, however, large gradients in Ca+ +

and Mg++, usually in a 1:1 relationship (i.e., ΔCa++/ΔMg+ += 1), are observed, not necessarily reflecting largeror smaller sedimentation rates. In fact, Holes 70, 71, and 72in the equatorial Pacific (Manheim and Sayles, 1971) showthe largest gradients in Ca+ + and Mg++ in the hole with theslowest rate of accumulation. Only Sr+ + values did show agood correlation between the gradient and the sedimenta-tion rate (Manheim and Sayles, 1971). In Hole 245, itappears that the main reaction site for Mg++ and Ca+ + is inthe basal sediments, which are characterized by volcanic ashinputs (cf. Vallier, this volume; Warner and Gieskes, thisvolume). I suspect that the gradients in Holes 70, 71, and72 can be due to similar basal beds of "reactive" sediments,

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or they may be due to differences in volcanic contributions tothese holes. None of these holes were drilled to basement, sothese observations are, necessarily, speculative. Only smallchanges are observed in SO4" and alkalinity, and changes inK+ are negligible, i.e., within the error limits.

Site 249 could be classified under this category, but onlywith hesitation because of the rather irregular sedimenta-tion history of the hole.

It is important to note that in many of the holesreported on here the biogenous calcareous and opalinecontributions are localized in parts of the hole. Forinstance, sponge spicules in Site 239 are mainly found from70-120 meters, in association with calcitic (nannoplankton) and aragonitic (tunicate spicules) skeletons.Radiolarians are abundant at Site 241 from 0-300 meters,in association with nanno-fossil oozes. Nanno-fossil oozesand chalks characterize the entire Site 242, whereas in Hole245 they are present from 100 meters to the basaltic sill.Biogenous material is virtually absent at Site 248, and atSite 249, a Miocene nanno-fossil ooze 160 meters thickoverlies a Cretaceous chalk section 110 meters thick, belowwhich a rapid decrease occurs in biogenous components.

The presence of these biogenous components has largeeffects, on dissolved silica values (Sites 239 and 241). Also,the distribution of dissolved Sr+ + clearly correlates with thepresence of carbonate oozes and chalks, whether suchbiogenous material is aragonitic or calcitic in origin. TheSr+ + profiles relate to calcium carbonate recrystallizationprocesses (cf. Manheim and Sayles, in press) in the sedimentcolumn. Only in holes which show contributions ofcalcareous organisms throughout, or at least in the deeperparts, are linear gradients in Sr+ + found (Site 242 and Hole245). In all the other holes, nonlinear profiles with extremain the calcium carbonate sections of the holes support thisrecrystallization concept.

Dissolved silica values seem to reflect the lithologies ofthe sediments. Though the well-known temperature-of-squeezing effect will cause an uncertainty of ±100 µmoles/1SiO2, the present study suggests that for sedimentassemblages with nonexistent or very small biogenous silicacontributions, the dissolved silica reflects the claymineralogy. In holes where the clay assemblages, especiallythe <2µ fraction, contain mica, kaolinite, montmorillonite,and palygorskite, a value of 200 µmoles/1 SiO2 ±100 iscommon; when kaolinite is absent (cf. Hole 245), but mica,palygorskite, and montmorillonite are present, values of650 µmoles/1 SiO2 ±100 are observed. Couture (personalcommunication) found similar relationships from ananalysis of previously published Deep Sea Drilling data.MacKenzie et al. (1967) and Siever (1968b) carried outequilibration studies between pure alumino silicates (e.g.,kaolinite and montmorillonite) and seawater at various pHvalues. Especially, Siever's (1968b) experiments indicatethat inter alia pH is a controlling factor. I conclude,therefore, that the dissolved silica values are regulated bythe clay mineral assemblage, as well as by the particularchemistries (i.e., contents in Mg++, Ca+ +, K+, and HCO3")of the interstitial water sediment system. More experi-mental work of the type performed by Siever (1968b), butin clay mixtures of low water content, should verify someof these tentative conclusions.

Whenever opaline silica is present in appreciableamounts, the dissolved silica seems to be regulated by thissedimentary component (cf. Sites 239 and 241).

Dissolved SO 4 " and N H 4

+ are direct reflections ofsulfate reduction processes. Apparently, such processes stilltake place in deeply buried sediments, and, presumably,such processes are still essentially bacterially controlled. Inholes that show rapid sedimentation rates, sulfatedepletions are usually accompanied by maxima in thealkalinity values. At rates slower than 2 cm/1000 y, thealkalinity maximum disappears. The depth and theintensity of the alkalinity maximum seems to be a functionof the rate of sedimentation as well as the amount oforganic matter present in the sediment. Larger amounts oforganic matter also probably imply larger fractions that areeasily metabolized by bacteria. This would explain theobservations at Sites 241 and 242, where sedimentationrates are very similar but where different amounts oforganic matter are incorporated in the sediments. Themaximum in the alkalinity is usually thought to be thedirect result of sulfate reduction processes. This phenom-enon has been discussed in some detail by Gieskes (1973)and by Lawrence (1973). The latter author assumed thatthe maximum corresponded to the depth in the sedimentwhere the precipitation of CaC03 proceeds at a maximumrate. Indeed, this maximum in alkalinity corresponds to aminimum in Ca+ +. Below this, the relative importance ofsulfate reduction processes and the coinciding productionof HCθ3~ diminishes, whereas silicate reconstitution reac-tions become more important, resulting in decreasingvalues of Mg++ and HCO3~ and increasing Ca+ + values.

Of interest in the present study is the clear minimumthat occurs in dissolved SO 4 " at Sites 241, 242, and 248.Generally, during periods of slower sedimentation,dissolved sulfate depletions can be expected to have beenless, so that, upon the onset of faster sedimentation, SO4"depletion would become larger, thus leading to theobserved minima. The rate of the sulfate reduction processis sufficiently fast for such a minimum to develop.Diffusional supply of SO 4 " from above and below wouldbe too slow to eradicate the minimum. Depletions in Mg++

and K+ take place throughout the core at such rates thatextrema are not observed, even though at Site 241, theslightly higher Mg++ values at 325 meters than those at 258meters may be caused in a similar manner. However, asdiscussed in the section on the validity of the data, wecannot assert whether this does, indeed, occur, or whetherthe differences are due to small seawater contaminations.At Site 242, no anomalous reversals in the Mg++ gradientare observed.

Although the present studies are not conclusive aboutthe nature of the reactions that are responsible for thechanges in the composition of interstitial waters observed, Ifeel that some tentative conclusions can be drawn. These,of course, still warrant further verification. In thefollowing, a brief summary is given of the possible reactionsrelated to the observed changes.

Dissolved Silica: This component seems to reflect themixed clay mineral assemblages or, whenever fairly largeamounts of opaline biogenous silica are present, thesolubility of this latter solid component.

372


Alkalinity. Increases are usually due to the productionof HCO3" ions in the bacterial sulfate reduction processes.Decreases are related both to the precipitation ofcarbonates and the "consumption" of alkalinity in silicatereconstitution reactions.

Sulfate and Ammonia: These changes are related tobacterial sulfate reduction processes.

Calcium: Changes are mostly related to calciumcarbonate precipitation processes (during sulfate reduction)or due to release of calcium during silicate reconstitution.The latter process, however, is not entirely certain and hasnot been tested rigorously.

Magnesium: Changes are due to formation of authigenicsilicates (palygorskite?); formation of intermediate mont-morillonites during the alteration of volcanic ash (Hole245); uptake in recrystallized detrital clay minerals, e.g.,chlorite.

Strontium: Changes are due to recrystallization ofcarbonates, aragonitic (tunicate spicules) or calcitic(nannoplankton).

Potassium: Changes are due to reconstitution of clayminerals and uptake in detrital poorly crystallized clays,e.g., chlorite. Potassium depletions are usually observedonly in rapidly depositing detrital sediments.

Manganese: Dissolved manganese values higher than 0.5ppm usually imply reducing conditions and are due to thereduction of manganese dioxide phases. In rapidlyaccumulating detrital sediments, dissolved manganese valuesare low, in spite of reducing conditions. This is probablydue to the great dilution in manganese in the solid phases.

ACKNOWLEDGMENTS

Special thanks go to Don Marsee for his great help insecuring many good and reliable samples and to SusanBrady, an undergraduate volunteer, who did some of thecareful calcium and magnesium analyses.

This work was generously supported by NSF GrantGA-33229.

REFERENCES

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Berner, R. A., 1970. Sedimentary pyrite formation: Am. J.Sci., v. 268, p. 1-23.

Berner, R. A., Scott, M. R., and Thomlinson, C, 1970.Carbonate alkalinity in the pore waters of anoxic marinesediments: Limnol. Oceanogr. v. 15, p. 544-549.

Bischoff, J. L., Greer, R. E., and Luistro, A. O., 1970.Composition of interstitial waters of marine sediments:temperature of squeezing effect: Science, v. 167, p.1245-1246.

Bischoff, J. L. and Sayles, F. L., 1972. Pore fluid andmineralological studies of recent marine sediments:Bauer Depression region of East Pacific Rise: J.Sediment Petrol, v. 42, p. 711-724.

Carpenter, J. H. and Manella, M. E., 1973. Magnesium tochlorinity ratios in seawater. Limnol. Oceanogr. v. 78, p.3621-3626.

Cescon, B. S. and Macchi, G. R., 1973. A microvolu-metric determination of sulfate in pore waters. InHeezen, B. C, MacGregor, I. G., et al., Initial Reportsof the Deep Sea Drilling Project, Volume XX: Washing-ton (U. S. Government Printing Office), 811-812.

Culkin, F., 1965. The major constituents of seawater. InRiley, J. P. and Skirrow, G. (Eds.), Chemical Oceanog-graphy: New York Academic Press, v. 2, p. 121-162.

Drever, J. L., 1971. Magnesium-iron replacement in clayminerals in anoxic marine sediments: Science, v. 172, p.1334-1336.

Fanning, K. A. and Pilson, M. E. Q., 1971. Interstitial silicaand pH in marine sediments: some effects of samplingprocedures: Science, v. 173, p. 1228-1231.

Gieskes, J. M., 1973. Interstitial water studies, Leg 15.Alkalinity, pH, Mg, Ca, Si, PO4, and NH4. In Heezen,B. C, MacGregor, I. G., et al., Initial Reports of theDeep Sea Drilling Project, Volume XX: Washington(U. S. Government Printing Office), 813-829.

Gieskes, J. M. and Rogers, W. C, 1973. Alkalinitydetermination in interstitial waters of marine sediments:J. Sediment Petrol., v. 43, p. 212-211.

Goldberg. E. D. and Griffin, J. J., 1970. The sediments ofthe northern Indian Ocean: Deep Sea Res., v. 17, p.513-537.

Griffin, J. J. and Goldberg, E. D., 1963. Clay-mineraldistribution in the Pacific Ocean. In Hill, M. N. (Ed.),The Sea: New York (Interscience) v. 3, p. 728-741.

Hammond, D. E., 1973. Interstitial water studies, Leg 15.A comparison of the major element and carbonatechemistry data from Sites 147, 148, and 149. In Heezen,B. C, MacGregor, I. G., et al., Initial Reports of theDeep Sea Drilling Project, Volume XX: Washington(U. S. Government Printing Office), 831-850.

Hartmann, M., Muller, P., Suess, E., and van der Weijden,CH. , 1973. Oxidation of organic matter in recentmarine sediments: "Meteor" Forsch-Ergeb. Reihe C No.12 p. 74-86.

Lawrence, J. R., 1973. Interstitial water studies, Leg 15.Stable oxygen and carbon isotope variations in water,carbonates, and silicates from the Venezuela Basin (Site149) and the Aves Rise (Site 148). In Heezen, B.C.,MacGregor, I. G., et al., Initial Reports of the Deep SeaDrilling Project, Volume XX: Washington (U. S.Government Printing Office), 891-899.

Li, Y. H., Bischoff, J. L., and Mathieu, G., 1969. Themigration of manganese in the Arctic Basin sediment:Earth Planet. Sci. Lett., v. 7, p. 265-270.

Lynn, D. C. and Bonatti, E., 1965. Mobility of manganesein diagenesis of deep sea sediments: Marine Geol., v. 3,p. 457-474.

MacKenzie, F. T. and Garrels, R. M., 1965. Silicates:reactivity with sea water: Science, v. 150, p. 57-58.

MacKenzie, F. T., Garrels, R. M., Bricker, O. P., andBickley, F., 1967. Silica in sea water: control by silicaminerals: Science, v. 155, p. 1404-1405.

Mangelsdorf, P. C, Wilson, T. R. S., and Daniell, E., 1969.Potassium enrichments in interstitial waters of recentmarine sediments: Science, v. 165, p. 171-173.

Manheim, F. T. and Sayles, F. L., 1971. Interstitial waterstudies on small core samples, Deep Sea Drilling Project,Leg 8. In Tracey, J. I., Sutton, G. H., et al., InitialReports of the Deep Sea Drilling Project, Volume VIII:Washington (U. S. Government Printing Office), p.857-869.

Manheim, F. T. and Sayles, F. L., in press. Composition andorigin of interstitial waters of marine sediments, basedon deep sea drilling cores. In Goldberg, E. D. (Ed.), TheSea: New York (Interscience), v. 5.

Presley, B. J., 1971. Techniques for analyzing interstitialwater samples. Part 1: determination of selected minorand major inorganic constituents. In Winterer, E. L.,

373

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Presley, B. J., Brooks. R. R., and Kaplan, LR., 1967.Manganese and related elements in the interstitial watersof marine sediments: Science, v. 158, p. 906-910.

Presley, B. J., Culp, J., Petrowski, C, and Kaplan, I. R.,1973. Interstitial water studies, Leg 15. Major ions, Br,Mn, NH 3 , Li, B, Si, and δ C l 3 . In Heezen, B.C.,MacGregor, I. G., et al., Initial Reports of the Deep SeaDrilling Project, Volume XX: Washington (U. S.Government Printing Office), 805-809.

Sayles, F. L., Manheim, F. T., and Chan, K. M., 1970.Interstitial water studies on small core samples, Leg 4. InBader, R. G., Gerard, R. D., et al., Initial Reports of theDeep Sea Drilling Project, Volume IV: Washington (U. S.Government Printing Office), p. 401-414.

Sayles, F. L. and Manheim, F. T., 1971. Interstitial wateranalyses on small core samples, Deep Sea DrillingProject, Leg 7. In Winterer, E. L., Riedel, W. R., et al.,Initial Reports of the Deep Sea Drilling Project, VolumeXVII, Washington (U. S. Government Printing Office), p.871-881.

Sayles, F. L., Manheim, F. T., and Waterman, L. S., 1972.Interstitial water studies on small core samples, Leg 11.In Hollister, C. D., Ewing, J. I., et al, Initial Reports ofthe Deep Sea Drilling Project, Volume XI: Washington(U. S. Government Printing Office), p. 997-1008.

Sayles, F. L., Manheim, F. T., and Waterman, L. S.,1973a. Interstitial water studies on small core samples,Leg 15. In Heezen, B. C, MacGregor, I. G., et al., InitialReports of the Deep Sea Drilling Project, Volume XX:Washington (U.S. Government Printing Office), 783-804.

Sayles, F. L., Waterman, L. S., and Manheim, F. T., 1973b.Interstitial water studies on small core samples, Leg 19.In Creager, J. S., Scholl, D. W., et al., Initial Reports ofthe Deep Sea Drilling Project, Volume XIX: Washington(U. S. Government Printing Office), p. 871-874.

Sayles, F. L., Wilson, T. R. S., Hume, D. H., andMangelsdorf, P. C, Jr., 1973c. In situ sampler for marinesedimentary pore waters: evidence for potassiumdepletion and calcium enrichment: Science, v. 181, p.154-156.

Scholkovitz, E. R., 1973. Interstitial water chemistry of theSanta Barbara Basin sediments: Geochim. Cosmochim.Acta, v. 37, p. 2043-2073.

Siever, R., 1968a. Sedimentological consequences of asteady-state ocean-atmosphere: Sedimentology, v. 11, p.5-29.

Siever, R., 1968b. Establishment of equilibrium betweenclays and sea water: Earth Planet. Sci. Lett., v. 5, p.106-110.

Solorzano, L., 1969. Determination of ammonia in naturalwaters by the phenol-hypochlorite method: Limnol.Oceanogr., v. 14, p. 799-801.

Strickland, J. D. H. and Parsons, T. R., 1968. A manual forsea water analysis: Bull. Fish. Bd. Canada, v. 167, 311PP.

Takahashi, T., Prince, L. A., and Felice, L. J., 1973.Interstitial water studies, Leg 15. Dissolved carbondioxide concentrations. In Heezen, B. C, MacGregor,I. G., et al., Initial Reports of the Deep Sea DrillingProject, Volume XX: Washington (U. S. GovernmentPrinting Office), 865-876.

Tsunogai, S., Nishimura, M., and Nakaya, S., 1968.Complexometric titration of calcium in the presence oflarge amounts of magnesium: Talanta, v. 15, p. 385-390.

von Rad, U. and Rösch, H., 1972. Mineralogy and origin ofclay minerals, silica, and authigenic silicates in Leg 14sediments. In Hayes, D. E., Pimm, A. C, et al., InitialReports of the Deep Sea Drilling Project, Volume XIV:Washington (U. S. Government Printing Office), p.727-747.

Waterman, L. S., Sayles, F. L., and Manheim, F. T., 1972.Interstitial water studies on small core samples, Leg 15.In Hayes, D. E., Pimm, A. C, et al., Initial Reports ofthe Deep Sea Drilling Project, Volume XIV: Washington(U. S. Government Printing Office), p. 753-762.

374


TABLE 2Site 239 (21° 17.67 S, 51°40.73 E; 4971 m)

Sample Subbottom(Core, Depth

Section) (m) pHa pHb pHc AlkdCl€ SO, Caf Mgf Kf Srf SiO NH,

143-24-35-35-36-584849-412-312-313-316-316-318-2

wwwwcwwcwwcwwcw

42070808090135135145209209220285285302

7.597.57

7.387.59

7.407.44

7.557.727.367.39

7.387.397.827.397.257.497.51

7.607.637.317.357.657.317.417.717.347.267.267.317.35

7.22

2.391.862.061.481.232.652.271.612.031.621.401.21

<0.50.170.62

19.619.819.7519.819.820.019.919.819.719.7

19.619.019.020.3

27.927.325.126.426.125.225.025.325.824.425.024.2(21.4)

22.2

10.411.015.714.915.019.023.023.222.130.331.835.553.857.962.0

53.653.650.950.151.049.145.045.946.041.845.139.933.228.425.5

11.410.58.8

8.87.57.56.97.45.15.34.43.7

3.7

0.210.390.550.550.550.590.560.560.490.430.430.400.33

0.33

0.30.00.50.60.30.02.21.52.29.38.38.3

33521848550642464580055046026016119819862294

96416020820315113718318383186145

35.235.235.235.2

35.235.2

35.235.235.535.234.134.136.3

Note: w = 23°C ± 2; c = 5°C ± 1. Parenthesis around figures indicates doubts as to accuracy.aPunch in values."Flow through values.cVessel values.dInMeq/l.e In%o1 In m mole/1.Sin ppm."In µmole/1.

375

J. M. GIESKES

TABLE 3Site 241 (02°22.24'S, 44°40.77'E;4054 m)

Sample

(Core,Section)

1-4 w

2-2 w

2-2 c

3-4 w

4-3 w

5-3 w

5-3 c

6-5 w

7-3 w

8-3 w

8-3 c

10-3 w

11-3 w

13-3 w

13-3 c

15-3 w

19-1 w

21-4 w

23-3 w

23-3 c

25-4 w

27-3 w

28-2 w

29-2 w

SubbottomDepth(m)

5

12

12

50

60

68

68

110

145

182

182

220

258

325

325

400

532

582

686

686

840

980

1070

1168

pH*

7.10

7.05

7.05

6.95

6.82

7.00

6.89

6.78

pΦ

7.22

7.10

7.03

6.98

6.99

7.10

6.94

7.17

7.08

7.28

6.88

6.95

7.25

7.96

pHc

7.32

7.19

7.12

7.10

7.07

7.24

7.05

7.27

7.18

7.58

7.02

7.06

7.31

7.20

(7.15)

Alkd

6.22

10.03

9.90

14.80

15.45

16.10

14.70

17.75

12.95

15.00

13.75

10.50

4.00

<1.3

3.20

2.32

3.25

<1.2

0.48

2.60

1.93

1.75

3.10

αe

19.7

19.7

19.6

19.6

19.6

19.6

19.5

19.5

19.5

19.3

19.4

19.1

19.4

19.2

19.8

18.8

18.5

18.8

18.6

17.5

17.5

15.8

16.8

16.6

so4f

26.0

21.3

20.3

12.4

10.8

11.98.8

9.0

5.9

10.0

7.2

5.8

(4.2)

4.9

7.4

11.5

11.7

17.0

14.0

12.0

8.2

6.0

10.5

9.5

Caf

9.0

7.6

7.4

6.6

6.1

5.8

5.1

6.3

7.0

7.2

5.8

8.5

10.2

9.9

9.5

15.2

17.6

18.0

16.8

16.6

14.2

15.0

14.7

Mgf

54.1

53.0

52.7

49.9

46.1

45.1

46.6

41.9

44.6

41.2

43.2

38.9

36.8

38.6

38.7

35.9

32.9

26.5

24.1

20.8

12.8

14.2

17.3

Kf

12.4

13.4

11.6

12.5

12.5

11.1

10.9

10.0

10.5

8.6

7.8

6.2

5.1

3.3

3.8

2.5

2.9

1.8

2.5

Srf

0.10

0.14

0.15

0.21

0.23

0.24

0.27

0.30

0.33

0.37

0.38

0.32

0.30

0.27

0.24

0.24

0.25

0.18

0.24

Mng

0.9

0.2

0.0

0.0

0.0

0.0

0.0

0.0

0.0

0.2

0.0

0,0

0.4

0.3

0.0

0.0

0.0

0.0

0.0

0.0

0.0

0.0

SiO2

h

860

932

820

980

960

940

900

1060

520

740

650

790

906

180

55

326

242

182

172

52

100

79

79

108

N H4h

262

428

374

700

740

700

830

825

770

790

650

525

540

470

340

294

450

360

280

410

420

380

Se

35.2

34.9

35.2

34.1

34.1

33.6

33.0

33.0

32.2

32.4

32.7

32.2

31.9

31.4

31.1

30.2

28.6

29.7

26.5

27.8

28.6

Note: w=23°C± 2;c = 5°C± 1.aPunch in values.^Flow through values.cVessel values.dInMeq/l.e In°/ 0 0

fin m mole/1.Sin ppm.nInµmole/l.

376


TABLE 4Site 242 (15°50.65'S, 41°49.23'E; 2275 m)

Sample(Core,Section)

1-3 w

1-3 c2-3 w3-3 w4-5 w4-5 c5-3 w6-2 w6-2 c7-5 w8-4 w9-3 w

10-5 w12-2 w13-5 w15-2 w

SubbottomDepth(m)

4

455

132152152235310310407483560607622635652

pHa

7.26

7.327.467.41

7.48

pHb

7.29

7.807.30

7.287.637.347.327.867.49

PHC

7.36

7.767.317.297.357.727.407.377.987.43

(7.03)(7.65)

Alkd

3.59

2.905.505.405.534.003.852.79

« 22.50

<1.7<0.8

0.850.550.65

<0.35

19.4

19.519.619.619.619.719.619.819.719.619.719.9

(20.0)(19.6)

so4f

28.1

27.820.013.612.712.910.812.112.612.816.815.014.0

15.412.3

Caf

9.8

9.07.36.76.46.17.47.87.2

11.716.016.620.121.221.822.9

Mgf

52.3

53.648.744.343.444.239.939.239.636.236.731.926.220.923.220.1

Kf

11.512.110.310.37.86.87.35.45.35.8

3.4

4.3

4.3

Srf

0.11

0.110.210.320.320.330.470.470.46

(0.59)(0.76)0.750.790.940.810.80

Mnë

1.0

0.90.80.00.10.10.10.00.0

0.60.50.00.00.7

SiO2h

238

157178183156

8717012546

142188

8587

114106187

NH4h

84

100275425390420515455515440

370285

350270

S e

35.2

35.535.233.833.6

33.333.3

33.834.134.434.134.134.634.1

Note: w= 23°C ±2;c = 5°C ± 1.

aPunch in values."Flow through values.cVessel values.dInMeq/l.e In%oflnm mole/1.Sin ppm.hlnµmole/1.

377

J.M.GIESKES

TABLE 5Site 245 (31°32.02'S, 52° 18.11'E; 4857 m)

Sample

(.Core,Section)

245-1-4 w

245-1-4 c245-2-CC w245-2-CC c245-3-5 w245-3-5 c245-4-4 w245-4-4 c245-5-4 w245-5-4 c245-6-2 w245-8-1 w245-9-2 w245-11-4 w245A-1-5 w245A-1-5 c245A-2-4 w245A-2-4 c245A-4-5 w245A-4-5 c245A-6-2 w245A-6-2 c245A-7-5 w

Subbottom

jJeptn(m)

10

107070

125125165165212212246284313333

303058587676

104104145

Pm

7.33

7.40

7.30

7.44

7.33

7.33

pHb

7.34

7.357.277.147.13

7.227.24

7.397.387.30

7.337.417.277.357.15

7.30

7.267.267.137.207.337.237.187.21

7.107.157.187.077.31

(7.44)7.29

7.22

7.03

7.16

Alkd

2.65

2.442.952.563.032.792.482.332.71

<2.02.442.11

<l. l1.243.062.702.712.382.552.382.822.532.88

Cie

19.5

19.619.519.519.519.719.719.819.6

19.619.8

19.519.419.7

19.619.619.519.719.6

SO 4

f

29.0

29.027.326.7

(23.9?)25.224.824.824.224.923.822.121.922.128.027.527.126.826.927.326.026.725.2

Caf

10.9

11.013.113.717.618.019.019.121.621.622.424.327.128.112.312.413.314.013.514.316.216.718.4

Mgf

(52.0)

54.652.354.747.649.047.448.045.445.043.842.838.537.552.254.352.053.152.154.251.053.248.1

Kf

10.011.811.110.7

8.610.5

9.010.7

8.69.7

9.28.87.28.8

10.18.9

10.49.6

10.08.99.07.6

10.5

Srf

0.11

0.090.140.130.190.190.190.230.24

0.250.300.320.350.120.120.130.160.140.140.170.180.19

Mn8

0.0

0.11.62.13.93.92.82.71.3

0.70.50.41.20.70.72.82.63.73.55.64.93.5

Siθ2h

226

177205148390368565533611472620656622642179131209163190142330256530

NH4h

5290

1558978

115113156114180250220165

74123123106

72134

102

S e

35.5

35.235.235.235.235.235.235.335.2

35.235.534.934.135.235.535.835.535.535.2

35.2

Note: w= 23°C± 2;c=5°C± 1.

aPunch in values.^Flow through values.cVessel values.dInMeq/l.eIn°/0o

flnm mole/1.Sin ppm.nIn.µmole/l.

TABLE 6Site 248 (29°31.78'S, 37°28.48'E; 4994 m)

Sample(Core,

Section)

2-2 w2-2 c4-5 w4-5 c

10-1 w10-1 c11-1 w11-1 c12-5 w14-3 w

SubbottomDepth(m)

55

125125325325365365395412

pHa pHb

7.35 7.447.84

7.68 7.768.377.66

pHc

7.397.807.768.357.458.207.25

(7.63)7.36

Alkd

4.533.886.505.882.061.841.961.621.781.36

Cie

19.419.419.619.519.319.619.719.719.719.6

so4f

27.427.417.517.722.023.221.021.325.020.8

Caf

11.010.89.59.4

21.022.625.626.437.235.6

Mgf

52.654.650.251.744.946.140.440.136.435.9

11.410.38.37.75.34.97.36.36.55.7

Srf

0.100.110.14

0.180.170.160.160.160.19

Mnë

9.86.60.90.26.54.46.53.93.54.7

SiC•2h

53536216971

19894

655388735433

N H 4h

10687

322374159203228270117

18

Se

35.235.234.134.134.434.434.4

35.234.1

Note: w = 23°C ± 2; c = 5°C ± 1.aPunch in values.^Flow through values.cVessel values.d InMeq / l .eIn % ofin m mole/1.gin ppm.nIn µmole/1.

378


TABLE 7Site 249 (29°56.99'S, 36°04.62'E; 2088 m)

Sample(Core,Section)

1-5 w

1-5 c

2-2 w

2-2 c

4-5 w

4-5 c

6-5 w

6-5 c8-5 w8-5 c

10-5 w10-5 c12-5 w12-5 c14-5 w14-5 c15-5 w15-5 c16-1 w16-1 c17-5 w17-5 c19-3 w19-3 c21-5 w21-5 c23-3 w23-3 c25-2 w26-1 w28-1 w30-2 w

SubbottomDepth(m)

7

7

15

15

33

33

50

5070709090

109109136136157157168168185185225225263263290290310320337375

pHa

7.44

7.44

7.50(18° C)

7.52

pHb

7.52

7.47

7.47

7.47

7.39

7.58

7.32

7.587.367.597.407.587.397.677.297.83

p H c

7.50

7.53

7.46

7.51

7.41

7.69

7.397.707.407.677.387.697.377.827.277.617.437.577.367.627.34

(7.42)7.377.307.437.967.477.197.33

Alkd

2.68

2.52

2.73

2.39

2.74

2.07

2.64

(1.85)2.551.842.201.632.551.831.98

<l.O1.75

<<l.O1.160.642.121.501.70

<0.31.100.21.901.521.360.680.760.78

Cie

(18.9)

19.3

19.2

19.4

19.6

19.2

19.5

19.619.619.319.6

19.419.219.619.719.219.719.619.3

19.419.5

19.419.4520.019.520.120.119.1

so4f

27.8

27.8

27.6

26.9

27.1

26.9

26.825.6

26.2

25.525.024.925.024.225.825.0

24.6

23.2

22.423.024.223.0.21:518.315.416.3

Caf

10.1

10.2

10.5

10.6

11.5

11.1

11.8

11.312.211.612.912.113.512.914.413.715.114.014.713.916.618.218.8

21.021.125.624.430.232.037.042.5

Mgf

52.5

54.6

52.6

54.4

52.1

52.4

51.8

52.151.251.651.750.950.850.249.950.248.250.349.447.547.446.847.1

45.445.247.045.639.839.535.531.7

Kf

10.2

11.0

11.0

10.7

9.9

11.1

10.410.710.310.49.89.69.89.3

10.19.5

9.59.78.08.1

7.57.7

7.2

7.5

(8.9)

Srf

0.10

0.17

0.17

0.26

0.24

0.32

0.300.350.350.410.380.420.420.420.410.41

0.450.390.410.340.35

0.320.32

0.27

0.23

0.25

Mnë

0.0

0.0

0.0

0.3

0.0

0.0

0.0

0.00.00.10.00.00.00.00.00.20.0

0.00.00.00.00.1

0.20.2

0.5

0.1

0.5

SiO2h

218

128

123

107

86

105

87102759873

105749952

14057

10262

18098

205

18771

625410333426426436

NH4h

3

Se

35.2

35.2

35.2

35.2

35.5

35.2

35.435.235.235.234.135.235.235.235.2

35.234.935.235.235.235.235.235.2

35.535.534.436.3

Note: w= 23°C± 2 ; c = 5 ° C ± 1.

aPunch-in Values. These values not corrected to 25° C.t>Flow through values.cVessel values.d InMeq / l .eIn°/ooflnm mole/1.Sin ppm.hlnµmole/1.

379

J. M. GIESKES

• = 23°CX = 5°C

777777BASALT

SO,, m mo les /1

• = 23°CX = 5°C

Figure 2. Site 239-alkalinity. Figure 4. Site 239-sulfate.

300 400 500 600 700 80010 20

o 2 0

100

H IN

M

ETE

RS

DE

PT

300

400

\

\\ Ca++

\

\

777777BASALT

30 40301 '

• x

50401

/

^ _

^ ^f

60

m moles/1

/

/

70501

•

Mg++

X •

CA++Mg++

/

23°C5°:

Figure 3. Site 239-silica.Figure 5. Site 239-calcium and magnesium.

380

20

30

40

50

60


Ca

Mg= 1

• = 23°CX = 5°C

10 20 30

Figure 6. Site 239-calcium vs. magnesium.

40 50

Ca

60 70

381

J. M. GIESKES

• = 23°CX = 5°C

i r

777777BASALT

• - 23°CX 5°C

Figure 9. Site 239-manganese.

Figure 7. Site 239-potassium.

c0

100

DE

PT

H

IN

ME

TE

RS

o

300

400

-

-

BASALT

-

0.20 0.401 1

1

A

/

0.601 1

Sr m moles/1

J

0

• = 23°X = 5°

.80

1

Cc

Figure 8. Site 239—strontium.

- NANNO OOZE

SILTY CLAY& CLAYEY SILT

IE •2 600

eq. / l

10 12 14 16

Figure 10. Site 241-alkalinity.

SILTY CLAY8. CLAYEY SILT

CLAYSTONE

CLAYSTONE

CLAYSTONE+ SILT

382


500

gI£ 600

s

Figure 11. Site 241-chlorinity.

100

200

300

400

500

600

700

800

900

000

100

200

5

-

-

-

-

28 301 1

"SALINITY" ' / . .

/

X /

/

j•x 7X

321 '

y

X

/

34

1 • ' •

\ ^

• = 23°CX = 5°C

u

100

200

300

400

500

•IH

tk!

z 600

700

800

900

1000

1100

1200

-

-

X

-

X

-

-

<

-

2001

\

J

1/

/

p

>

/

\\

400

1SlO2

µ moles/1

/

600' 1

• - ^ ~ ~

X

— — —

800

•

•—

1000 1200

1 ' 1

-̂

• = 23°CX = 5°C

Figure 13. Site 241-silica.

1

100

y.oo

300

400

500

S 600

700

800

900

1000

1100

1200

-

-

-

-

-

-

10

X

\

\

C×) C )/

C ) I

1(•) '

1

C )

C )

20

_—•k •—30" '

>Oµ m moles/1

• = 23°CX = 5°C

Figure 12. Site 241-"salinity. Figure 14. Site 241-sulfate.

383

J. M. GIESKES

• = 23°CX • 5°C

Figure 15. Site 241-ammonia.

o

100

200

300

400

500

600

700

800

900

1000

1100

1200

) 5• • • i | •

-

-

× 7

/

(x) / (•)

• hi

i

w

10 15

1 ' X' > ' 1/ Λ K+ m moles/1

X /

yyf

S

• ' 23°CX = 5°C


o10

100

2oα

JOO

400

500

600

700

8!10

900

1000

100

200

-

_

-

-

-

-

-

-

-

-

/

\•

//

Mj20

' x - -l/

•\•1

•\ + +• Ca

)

x

•\\

2030

//

/, / /\ / /

\ /

A/

J ///

t1

// 1 T 7 dolomite

/ / // ' /

/ I\

/\\•

40

1 'oles/1

/

Φ , Mg

X/ x//•*—dolomite

•

50

1' y

•

X

C a "M g + +

^x - '

• 23°C= 5°C

• = 23°CX 5°C

Figure 16. Site 241-calcium and magnesium.Figure 18. Site 241 - Stron tium.

384


GRAYFORAM RICHNANNO OOZE

GRAY CLAY

FORAM BEARING- NANNO OOZE

" GRAY CLAY

FORAM BEARINGNANNO CHALK

- BROWN CLAY

NANNO CHALK

ACOUSTICREFLECTOR

1 1 Xl̂ _ L_^_^^ 1 1 1

^"^^ ~^-^ meq/1

N\( 1

. \

#/• = 23°C

- X = 5°C

Figure 19. Site 242-alkalinity\

0

100

ZOO

300

400

500

600

'00

J

-

-

X

-

-

100

1

f

2001 X 1

\

\\•

\

\

\\\\\

~ •

~~pt—i—300

1 •

SiO2 u moles/1

• " 23°CX = 5°C

Figure 21. Site 242-sulfate.

0

100

200

300

400

500

600

700

) 100

~- -K.

_

-

-

-

-

2001

3001

1—110%

4001

\

/

/

5001

NH,,+

\

\

1

6001

µ moles/1

• •

X =

7001

23°C5°C

Figure 20. Site 242-silica. Figure 22. Site 242-ammonia.

385

J. M. GIESKES

50 Mg+

30 Ca +

V

Figure 23. Site 242-calcium and magnesium.

• = 23°CX = 5°C

386


20

25

30

35

40

45

50

55

• = 23°CX - 5°C

10 20 30 40

Ca

Figure 24. Site 242-calcium vs. magnesium.

387

J. M. GIESKES

u

100

200

300

400

500

600

700

1

-

-

-

/• /

/

/

/

/

/

/

/

/

- . /

/

1

1

•

/

/

1 1 1

K+

m m o l e s / 1

/

/

X

1 1 X

^ ^

• = 23°CX = 5°C

5 200 -

BROUNCLAY

VARIEGATEDCLAY

NANNO OOZE

. NANNO PALEOOZE ORANGE

PINKISHGRAY

CHERTS

NANNOCHALK A S H E S

DARK Mn RICHNANNO OOZE

BASALT

m e q . / l

I l l 1

X

X

w\ \

,x ^/ \

x a

•

• = 23°C

Figure 25. Site 242-potassium. Figure 27. Hole 245-alkalinity.

0.000

100

200

300

400

JOO

600

700

-

-

-

-

-

-

-

-

-

0.20

\

\

1

\

A

0.401 '

\ \x \

0.601

π

V

\

0.80+ + ' 1

Srmoles/1

\ "

\• " 23°CX 5°C

•

0 100 200 300 400 500 600 700 800 900

77777777- BASALT

/ \

• " 23°CX = 5°C

Figure 26. Site 242-strontium. Figure 28. Hole 245-silica.

388


60 Mg+

40 Ca+

a

2 200

• = 23-CX = 5°C

2 200

moles/1

• = 23°CX = 5°C

Figure 29. Hole 245-sulfate. Figure 30. Hole 245-calcium and magnesium.

389

J. M. GIESKES

10

Ca

MgH= 1.0

Mg

• = 23°CX = 5°C

Figure 31. Hole 245—calcium vs. magnesium.

390


W-- — . . .

Figure 32. Hole 245-potassium.

K+ m moles/1

• • 23°CX = 5°C

5 200 -

1

IX

4

' i-I

BASALT

1 1 1

• -X X #

^

X

1 1

Mn ppm

—

—1 1 1

• = 23°C

X = 5°C

Figure 34. Hole 245-manganese.

0.10 0.20π ' 1 r•

Sr m moles/1

xv

w\M

\ x\Λw

\

• = 23°CX 5°C

0

100

o o

300

400

SANDY SILT

SILT/CLAY RICH

NANNO OOZE

CLAYEY SILT

SILTY CLAY

SILTY SAND

COARSE SAND

CLAYEY SANDY

SILT

LAMINATED

SILT BEARING

CLAY

SILT RICH

CLAY

-

BROWN CLAY

///////////////

BASALT

1 1 = >

meq./I

/

/

X

X

- xi —

/

/

• -_i^ 1 r-

• > 23°C

X • 5°C

Figure 33. Hole 245-strontium. Figure 35. Site 248-alkaUnity.

391

J. M. GIESKES

9*

\

®

BASALT

Figure 36. Site 248-sulfate.

• » 23°CX • 5°C

25 30 35 40 45 50 555 10 15 20 25 30 35

60 Mg+ +

40C + +

\

Tx ~

®

777777///////////BASALT

Figure 37. &Ye 248-calcium and magnesium.

2 200

K m moles/1

X

77777777777777//BASALT

• • 23°CX = 5°C


g 200

GRAYFORAM RICHNANNO OOZE

-

- CLAYS

FORAM BEARINGNANNO CHALKS

_ GRAYVOLCANIC ASH

SILTSTONES

CLAYEYSILTSTONES

SILTYCLAYSTONES

BASALT

I 1raeq./l

i .<

*•

1 X '

s ix

~~~y

• = 23°CX = 5°C

Figure 39. &Ye 249-alkalinity.

392


100 200 300 400 500 600 7001

X1 1X/1

X1 /x1 \X

X- \ \

X .

\\\/

_

-

BASALT

_I 1 1 1S i O •molβs/1

\\

\•

• — - .

_ — —

•\

i i

RADS

SPONGESPICULES

• = 23°CX • 5°C

• = 23°CX = 5°C

Figure 40. Site 249-silica. Figure 42. Site 249-calcium and magnesium.

2 200 -

1 1 1

_

-

-

-

•

/BASALT

1

J1

• X/

/ ×/• //

1 #'x

•X

j•/•1

x/• X/

{•J•

1 s o 1

m moles/1

• = 23°CX = 5°C

Figure 41. Site 249-sulfate. Figure 43. Site 249-calcium vs. magnesium.

393

J. M. GIESKES

2 200

1 i i I

X

SJ

Λ\ /• /-A'-

\

®


i 1 r

• - 23°CX = 5°C

0.301 1 "i 1 r

Sr+ + HI moles/1

Figure 45. Site 249-strontium.

• = 23°CX = 5°C

10 20 30 40 50 60 70 90 100

100

200

300 -

percent {%) clay mineral

400 -

Mont.; Pa ly . ; Mica

Mont.; P a l y . ; C l i n .l i t t l e Mica

Mont.; Paly.; Clin.; Mica

• Montmoril lonite

+ Kaolinite

A Mica

® Palygorskite

A Ash Layer

Figure 46. Hole 245-clay mineralogy of <2µ-size fraction.

A*

394

13. interstitial water studies, leg 25 · calcium: complexometric titration with egta (tsu-nogai et...

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