NOTE ON THE EVIDENCE FOR CLIMATIC CHANGES FROM SUB-OCEANIC CORES

BY C. D. OVEY, B.Sc., F.G.S. British Museum (Natural History)

That climatic changes are reflected in the type of sediments and the faunal contents of cores taken from the ocean floor is now firmly established. Cores of up to nearly three metres in length, taken by Dr. C. S. Piggott in 1936 on board the cable ship " Lord Kelvin )' in an approximate line across the North Atlantic from the Newfoundland Banks to the continental slope off the south- west of Ireland, revealed alternating layers of glacial marine beds and warmer oozes (Bradley et a h , 1942). It is estimated, however, that these cores would only cover the period of the last major advance of the ice age-the Wisconsin of America or the Wiirm of Europe. Similar climatic changes have been identified by corm studied by Dr. W. Schott from the equatorial Atlantic during the " Meteor ') Expedition and, according to Professor Pettersson (1949), between Madiera and Martinique, by Dr. F. B. Phleger from the east comt of America and the Mediterranean and by Dr. H. G. Stubbings from the Indian Ocean.

With the recent return of the Swedish Deep-sea Expedition, under the leadership of Profemor Hans Pettersson, much valuable information is expected which may prove to be revolutionary to our present knowledge of glacial and post-glacial climatic fluctuations, for a new corer wm used on board the "Alba- tross '), invented by Dr. B. Kullenberg. This apparatus, known m the Kullen- berg piston core-sampler, could penetrate to the unprecedented depth of some 15 metres (Wiseman, 1947).

Only recently Dr. G. E. R. Deacon at a joint discussion of the Royal Metero- logical Society and the Royal Astronomical Society indicated the reliability of sub-marine cores in showing post-glacial climatic changes. It would seem that such evidence could far more easily be interpreted than any provided on land whether geological or physiographical, or from any obtained from the fossil remaim of flora or fauna,% On land there were too many disturbing influences such as erosion, the recent accumulation of alluvium, vegetation, and even the effect of human civilization masking the truth. Under the ocean, on the other hand, sedimentation wm usually continuous, irrespective of whether the surface waters were at one time swept by predominantly tropical air masses or by polar air bearing drifting ice and icebergs to much lower latitudes than today. The further from land, the slower would be the rate of accumulation of bottom sedi- ments-an important fact, for 15 metres of core taken in the remote deep water would give evidence for a greater period of time than any taken elsewhere.

TEE EVIDENCE

In cores, evidence for climatic change is shown by several distinct types of deposits. For cold periods, where the currents at the ocean surface were cold and icebergs drifted to 30' latitude or below, beds rich in erratic debris are found. These beds pass laterally into red clay or oozes in regions free from drift ice. The time may come when petvrological and palaeontological examination of some

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of the mineral and fossil contents of marine glacial deposits will tell 11s whence came the melting icebergs which scattered their enrased moranic nieteri:rl over wide areas of the ocean floor to build up these beds. Consider the signific- ance of tracing the evolution of ocean currents by means of the drift direction of melting icebergs ! Ocean currents are a function of wind direction ; wind direction is a clue to pressure distribution which, in its turn, combined with our knowledge of the distribution of the extended ice caps during the major Pleisto- cene glaciations, would suggest where the main tracks of depressions travelled to bring the necessary snow to feed the ice caps in Scandinavia, Britain and else- where. This is a glimpse of the possibilities in tracing not merely climatic fluctuations but weather evolution since, perhaps, the beginning of the Pleisto- cene Period, a million or more years ago.

Warm periods are marked by calcareous oozes rich in the remains of the shells of minute marine protozoa known as foraminifera (see Plate IV). These minute creatures live widely distributed over the seas and oceans ; while far the grcatest number of species live either on the bottom or attached to other marine animals or plants, a few are pelagic and form part of the swarming life, known as plankton, living in the surface layers and subject to the whims of waves antl currents. These are discernible, structurally speaking, through a microscope. Certain of these species are characteristic of cold antl others of warm waters, the latter always being far more abundant. Those whose remains are found in the deposits between the glacial beds mentioned above indicate cool temperate sur- face water conditions, perhaps a little warmer than today in some instances. In the tropics, distinctive tropical assemblages of them alternate with accumula- tions of cooler types corresponding to glacial deposits further north. The im- portant fact about these temperature-indicating organisms is that their evol- ution has been so slow that many of their species have remained unchanged for the last 30 million yeam, ever since Miocene times, so that if the cores can be raised to give a continuous record of ocean sediments since those days, much valuable information will be obtained for the climatologist, geologist, geo- grapher, meteorologist and a host of other scientists.

THE “ ALBATROSS ” CORES

The first of the Swedish Deep-sea Expedition’s cores has been examined for its foraminifera1 content by Dr. F. B. Phleger (1948). This core was raised in August 1947 from the floor of the Caribbean Sea, below 2,677 fathoms of water, and was 1,640 cm. in length. Although only 75 samples were examined, each a centimetre in thickness, the results clearly indicate a l temting warm and cold periods (see Figure 1). It must be remembered that the faunal remains are a reflection primarily of ocean currents, probably within the upper 1000 metres, and not directly of climatic conditions ; nevertheless i t would be difficult to conceive how cold surface currents could flow into the Caribbean during tropical periods.

Dr. Phleger (1948) has suggested a tentative’interpretation of his results on broad lines as is indicated in the righthand column of the diagram. He uses the nomenclature of four of the major American continentd ice advances of the

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Pleistocene-Nebraskan, Kansan, TlliIloiiL11 ant1 IViscotisin,--tlie fifth, t lio Iowan, not specifically designahd here but usually rccognived in U.S.A., iiiiglit be hcluded as the lower stages of the Wisconsin.

DC?m in WARM , - COLD ARC^ CMI. 1-

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Fig. 1. Approximate relative changes in surface water temperaturos, b e d on the percentage variations of rold and warm water foraminifera from eore 34 (15.4 metres in length), " AlbatrosR " Ststion 10 (1947), Caribbean Sea. The top few centimetres, representing about the post-glacial period, were in such 8 fluid condition that they were lost when the core was extrac+ted from the coring

apparatus. (Baeed on Phieger, 1948)

DATING OB OORES The complexity of timing ocean corn has been greatly simplified recently

by the Urry (1942) radioactive technique b d on the ratios of the conoentra- tiona in the sediments of the non-equilibrium series uranium, ionium and radium,

WEATHER .JVLY 1!14!) To face p . 230

THE ‘‘ ALBATROSS ” The ship used by the Swedish Deep Sea Expedition 1947-48 for ooeenographical research. The Kullenberg piston core-sampler ueed on this expedition h a provided a total length of over M English mile of bottom cores. Fmm these c o w past climatic ohengee can be de- fected over 8 period of 8t leeat 8 million ye813 and perhaps in phee comiderebly longer

PLATE III

JUL’T’ 1949

An example of the conrentrated organic remains extracted from the surface of ocean’ ooze in tropiral waters. The different species of shells of such marine protozoa (Foramini- fera) reflect the temperature of the surface layers of the water in which they live, and arc wet1 in the study of oceaii cores as indicators of past climatic change. Magnified I5 times

The inset shows a ronrentrate from a sample of deepwater ooze taken by the “Terra Sova ” from the Ross Sea. The minute foraminifera1 shells shown here in this cold water sample are in striking rontrast to the assemblage from tropical waters. Magnified 8 times

Pltotogruplrs by ]

PLATE IV [ M. G. Sawyere

assuming that the concentration of radioactive elements from the sea water or other sources has remained constant throughout the period of deposition. Thia method is likely to be more accurate in the deeper parts of the ocean where sedimentation is steady and not contaminated either by radioactive minerah brought in by river sediments or by local volcanic activity. In shallower water, too, the rate of sedimentation in a single core is likely to be extremely variable. Phleger suggests that tho possible rate of accumulation in the Caribbean core waa in the order of one centimetre in 1000 years, making the whole period of accumulation over 16 million years.

INFERENCES

Many believe that major cold periods of the past were contemporaneous over the world ; some evidence for this has already been accumulated from core studies. Many minor cold fluctuations may have been more localized but this can only be proved by correlations of cores and tying up such evidence with geological information on land. Several things seem certain, however, from our present knowledge. Firstly, the tropics were colder than today ; normally icebergs in the cold periods flowed at least as far south as the Azores ! Secondly, the polar front was displaced Bouthwamb, a theory which supports the geological view that pluvial periods of the Pleistocene in the Mediterranean were concurrent with maximum ice advances over Europe, signifying the pas- sage of depressions into the Mediterranean area as a prevailing meteorological phenomenon. Thirdly, the fact that glacial marine deposits have been found further south than the Azores and laterally from America to Ireland indicates drifting icebergs over the whole of the northern half of the North Atlantic. The source of the material in these deposits, as alreadg mentioned, might be approximately traceable to their platm of origin poeoibly in Greedand, North Eastern Amerioa, the British Islee or ehwhere.

To understand the origin of ica agee and leaeer cold periods it is insufficient to trme the evidence from continental aepoaite and to attempt a basis for pres- sure distribution entirely on it. If tihe omma OBL~ be made to divulge their secrets, the student of paat climatic changes stands a far better chance to explain the phenomena on land but he will have to beoome acquainted with much lit- erature which it is anticipated will eventually be forthcoming in the special studies of the many branches of science whioh are likely to be involved in the interpretation of the Swedish Expedition's aoree. It is a pity, however, that we are unlikely to discover fossil upper winds to help in paRt climatic analpis !

REFER E N C M8

BILADLEY, w. H., etalia, 1942 PETTERSSON, H., 1949 .... PHLICQER, F. B., 1948 .... URRY, W. D., 1942 .... .... MSEMILN, J. D. H., 1947 ....

U.S. Qml. 8 m y , Prof. Paper 196, p.8.

G&b. Vet. Vitt.-Samh. H d . , ser. B.5, N0 .14 . A w . Journ. Sci., Vol. 240, pp. 426-436. Nature, Vol. 160, p. 410.

T ~ w , Shkholm., V O ~ . I , pp. 1-5.

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