COIltribut1on to the knowledge of the outflow of tha Am,aZQQ River

w~tars into che OC83n

J. R. Donguy

In terma of flow rate. the Amazon River iatho fir£t river in the

world. Navigable for several thousand kilometcrs. its a~ual dilcharge

han been observed linea 1903. The A;rozon delta ~la51 carefully studied.

mainly with reference to depth. and currents. Since 1950 sav8Tal cruises

have iuve.tigated the outflow and the mixing of the freshwater in the ocean.

Le Floch (1955) ha, Itudied the northea.tern part of the delts. clo•• to

Guiana. Noreira da Silva (1959) made a .urvey in the entire e.tuary during

the 1ntemaU,onal GoOphy8ical 'Year. There Wo)l a Japanese cru1ae in 1957/

I

and the relultl were published in Japanase (1958). DuTini EquaLant I

(1963) the B./v BBlltlOGA of the Brazilian Navy made a curvey in the estuary

from Para River till off Cayenne. ;In !-13rch 1965. the R/v PILLSBURY fromt

the Institute of Marine Science. University of rofilll:U. """again studied this

area. tb"i. publication give. mainly the result ,of tho lettor survay but

frequent reforencel are made to tho preceding cruises.

Hydrologic rate and meteorology

Jhe bydro~og1c rata of the Amazon Rivor ls characterized by a low-

water mark·in October-November and Q maximu~ flo~ in June (Pig. 1). The

flow of the Am!lZal River ha. rarely been mt!.3Qurad. Parde (1956) thought

"the mean ouaht to exeeed lOO.OOOm3/aec (Oltmon. Ste1nberg. AIDe&. Davis.

1963).

The awHing of July cccurs a lmolt at thli end of the rainy lea£on and

the low water mark a little before the end~of the dry loaSOD (December).

Dur1na the rainy seSion (January tUl June) the "SaiUng Directionl"

1ndicate moinlythe N-B trade~indQ and low and variable winde during the

dry ....011.

General hydrographie eharacteriltica

The hydrographie atationl studied hore were made off the coneinental

eholf and out of the influance of tha Amazon River. on the cruis. P 6502 of

thœ B/v FILLS!UR1. that i. to lay during the raiay 508100.

tbeao .tation. show the folloviaa characteriltlc0:

1) Thera li a eoincldence of the thermocline and the eal1nlty maximum--

~he1r depth li about 100 ~ter. (r1a. 2). Bowevar from the offing to the

lhore, we ob.erve the l&oline. going down firlt, but eoming up clole to

the ~ont1n.nt.l Ihelf.

2) !he sa linity œzimum oblerved bore il le88 \thon 3&.70°/00. It

eel3mlJ to 4cere••e frcm the offina to tha shore but probably it WD.' not

a~ctly 4et.rùdned becaueo of lnaufficient eamp11ng. The thermocline il

almost 00 2 par mater. At ·ltatiOD. claie ta the continental ~bclf, WB

cbserve a a.cond thermocllne at h depth of 250 metare a880~iated with s

balocline (r1S. 2). lt appcara that tha water ~8I 18 div1ded into tvo

pertl by coatact vith the continental Ihelf, one part comtaa up to the surface

about 150 matera, the other part .1nking down balow.*

3) 'rba T-S curva 1000 Ub 8 p.rfoctly norm l one for the tropicn l

Atlaatlc Ocean ('lg. 3). Wo notice the homogonoity of the surfaco layer in

teGperature and salinity. the average taœperature 10 26°5 and tho average

o One knowa thar. i. a second thermocline in the aouthern Atlantic st a

dcpth of about 250 mater. (Defant 1936). UOWQvor tha intensity of thi.

oecoud thermoclino reaches hore 1° p~r metar, according te the batbythermo-

-2-

1 •

1 •

aill1nity 35.90%0. A Itraigbt Une 18 drawn througb the pointa T-6°

0-34.5°/00, and 1'-18° 8-36.0% 0. This otrLlight lino 18 the mean relation

ob.erved in the aouthern At lanUe (Sverdrup 1942). the observations are in

good agreeme.lt wHh tlJi.s l:tr<li.c~ht line.

Thele propertiel ara cbaraetarilUc of tho rLliny senson. We observe

\.'bat happen. dur1ng the dry sesson in October. Le Ploch (1955) found the

seM* eoiocidœnce of the thermocline with the ~~linity œanimum. their depth

reaeh1na 150 metera. C10Qe to the cont in.nCa l Ilhe lf the 180Une. hava the

ea.ne btthavlor, coming up above 250 matent oinking down bolow. The T-S

curwl are very limilar dur1ng both lealonl. In the "urfaca layer wo obtain

an average temperature of 270 0 and an average salin1ty of 36.100/00 during

the month of OCtober.

Prom..thelG oblenationl ue cone lude tbs t the genera l hydrographic

ebaraet_ri.tiel are almoat conltant during the year.

lbeoretlca1 Itructure of the outflov of AmBon River

K. Tabu (1954 and 1955) hal studied the thaorctiCd l ahapo of a\

river outf low into the ocean.

We 8uppole tbat the Amazon River ia flowing perpendiculsrly to the

Ihore ioto the ocean, the ahoro il the ordinate, ito pcrpendicular line 1s

the ab.eilas and the middle of the o.tusry the origine

Ws ccns1der a water ma •• whoae higher layer haa a denslty ~ 0 and a

th1.cknel8 h and who.. lowar layer bas a denlity \;> d.

Tabao IhovI the ~quation:

'..

, .

y - 1 l l- x2 +. (y _ 1)2 1 j

l )-1- (y - 1 Ta nx

y +

r . y + 1

~. baias the pro••ure st the 2 ùe~lh. i. equal tO:~t

p =~ { f (CY . 1)'T8n-1

f bein8 the CorioU. parametor f-2ù,l,'1" Ah the latera 1 mixing factor.

21 the w1dth of the C8tuary, Mo the flow rate of the river.

Tbe mouth of the Amazon J,lver 18 opproximata1y on the &quator and thora

la no Corioli. force. Th. firlt term of thls equation il then cqua1 to zero

and the aquation P.O gives the theoretlc81 linits of, the ~ter of Amazon

I.iver into th. ocaanl

4 Ah mol

"{

2 2' 2x - y + 1

\ f'-~x=2-+-(Y-+-l-)~2'c-'\'-(Tx--:=2~+-(-y-_-1-)"2:--"

\( / \ /

"(= 0,1

J

Tb& limit of th. rivor vat.ra ia then the hyperbola whoae the equatlon ie

x2 + y2 + 12D 0

~. can build the theoretical limite of the waters of t~zon Rivor

and Fara River ('i&. 4)

!.eal .tructura of the outflo1f of the Amazon River

wœ cam atudy the horizontal etructure of the outf1ow of AmBBon River

w1th the halp of aevera 1 crullel trom October to lily. we hava two crulles

durag the Dry Sea.on ftnd the lov water unrk of Am3&OQ Rivera

OUOK II

ALMUAITI BALDANHA

October 1953

Nov8mb.r 1958

-4-

J •

Qnd three cruilai during the rainy oanaon and the lncrQaoing rata of

AGraZOl\ tt1verl

.. BBRTIOGA, BQlJA.LAlrl 1

PILLSBUlY. P 6502

tom-MARD

Uarch 1963

March 1965

May 1957

We remark firat the real structure of the outflow of Amazon River 18

very dlfferent tram the theoret1cal one. Tho ioohalinee are parallcl to

the shore Bnd to tho bathymetric linee, therafore parpend1cular to the

thaorotical 11mit (Pia. S through 6) ••

Bowaver thare are lem. d1fferencc8 vith tha Oe8eonl.

1) Ibring the dry lIesson and Lhe low water limit. a11 the outfloy 1a

golog nortberly slong the ahore. Ealt of Para River. the water haa.a very

hlgh ea l1n~ty more than 37°/00 (More ira da SUva 1959). 'Ihe 1aoha lines look

8' :l.f they are following the bnthymctric ]bC"s in i1 l1orth ...ùat~rn direction.

~, from 20°/00 to 35% 0. the 1.ohallncs arQ close togother and the

ocunic va t~r in cOQUet ha. 8 S8 Uri1ty higher than 360 /00. we cone lude /

that there 11 lov mixing a loug this bu'..Uld.l l'Y. The on ly mi:dng 11 rr.ade

probably in the north of Cabo Oranze. off Guiana (Fig. 5-6).

2)' D:Oring the rain)' eeaeon and during the increaB1ng rata of Amazon

Biver. the outflow ha. the lIama ahapo along thœ shore. Tho 1GOM lines are

.1'0 vary clole. but, if tha frelhwater 18 goina mainly northarly, it appaars, .

tbere li an ealtorly tran.port slona the shore, in the loutheaot of the

We can m3ke a epace-time graphie aiang the ~ridian. soOU, welt of

the œoutb. and 47OW. e~st of, the œouth (Fig •. 9-10). Wu cee st SOOw the

-5-

.'

. \

sal1nlty 11 incrœastng froo the shon (20 00' [~) to th!! offing. The 180-

baline. are closest tOGother in Jsnuary which la the end of the dry Gelllon

and 'bppear more' oaparated from Hay ta Octoher.

At 470W tbe water hao Q very high salinity befora January. From

January to May,the iaohaline. ere more and more eeparated. A nucleus of.. -1·

high lalinity (36.~oi~? i9 pusbed off. from December to Marcb.

It appaar.·i~t·tbewhole year, the outflow of ~zon River 18 going, ", :~~. .

œalnly Rortherly clole to the .hore but it io going allo es.terly Itarting

December.

We caR ftnd ;anexplanat1on in the oceanographie and meteorolog1cal

environmeut. Durtna the whol. y.ar, the generel circulation br1ngl a Itrons.", ..

welterly lurfaè. curr.ôt (about 2 knots). Thore are allo, Bt lealt during.':.' .. ,' ,:.~ :t.>~ ~' .. "..

the raiD, lealan,.tradewindl blowing from aalt to west. The outflow current1.;" . ".) ... ;{ ,~:,:." .. ". , .

. . .. ' .~

15 not aufflciant tO'goasainlt the general circulation and all the fresh·. ,

vaur 1. puahad a long the Ihor••

Bowvar leveral facta put seme .troubla in tbi8 conclusion. The

cru1ael P 6502 of 'B/v PiUSBURY and Equalant 1 of a/V.SERTIOGA, made both

in Marcb, IhON very different re.ulta." ,

DurtnS Equalant, 1," the data of the other shipl working east of Amazon. ,",': ~. .! .'

River Ihov th. 'ô~tfi~';waa not goina out of the merid1an 460 and B/v'~ ,~1 .~<' :... ~~ '~'~l~~~' "

BiRtIOGA found~rY .10~.\'811111ty (28°/00) on the IOOridian 520 (iig. 7).o • ~ ..

',~ .. " i~ " .

Durloa P6502 tho..··outflow of Amazon River wal not goi~i nortb of 40 00N. .... '.; '. '~'. '.

, "

but we donot'kn~w what:~;ppencd esst of the meridian 460 becaus8 WC bave

no deta. A loutherlr curront ~~a ob~orved thon, close to tho .hore, in the

north of Amazon River (fig. 8).

- -6-

It 11 neçeesary to admit that the waBt<!rly current 16 not perœnent

and ClolDlBtiwas li 11 the outflow io golna e:l5Jtarly.

Ulfortunataly we have no information abol.\t the mixing of Amazon Rivor

uatera iD the ocean. Dur1ng Rqualant 1 there wae no data weat of the

mer1dian 52° and during P 6502 no obiervatlon8 cast of the merldlan 46°.

Likcwiae the other crui8e~ occurred ooly batween th~ merldisne 460 and 52°.

Divergenc. of tbs oceanic watar in contact with Amazon River

INril\1 the ralny eeasoa. we remark et oach cruitl8 (PILLSBURY. BER'lIOGA.

'l'01O-K&.iU) en area of high uUnity (:li: k;i:~L ::'·.;,.\;"'/0':') ~~uLltcù cff the

mouth of Amazon River. Tilis \later C:lU only \.·u;!~ ~::ç.m the de~)th and liluggo8te

the premence of a divœrgence.

We cao ~~ e,v~rt1cal .alinity section approximatciy perpendicular

to the ahore from Cebe Norte to the point at 5°00 N and 47°00 W during

the follovingcrui ••• ;

OIlSOK Il

~B 8ALDANnA

BDTIOGA

fILLSIUi.Y

October 1953

tlcvembar 1958

K:1rch 1963

Karcb 1965

The•• vertical .a1inity .ecticn. eppear as different phs.ai of the

• l!l1!UDe phenomana.

1) Dur1ng the PILLSBUiY cruioe. P 6502. tha œsxlmùm .a1inity, .1nking

clown north of 7°00 wa. coming up frOl11 SoOO N to the continental ,heU. It

W8, the beltaninS of the rainy .esson and the Qurface .a1inlty occurred

between 35.So/00 and 36.0%0 (rlg. 11).

2) Dur1ng Equalant 1, ln l1arch a,lao, the maximum sal1nity. coming

up from 40 30 ' N tQ the cootincnta l cl::.: ~ l, 1',; ':-1 1 aLü,au;:) dcpth (30meters)

and \Jal golna down in li northern direction "'Ul'V~ l:i~.! .,l"ia-.:.i..e...ll nucleus of

maximum .811n1ty~ It ~aa olso Che beginning of the r~iny season but tha

~roceeB appear~ more forward tban during P 6502. We muet remark that there

19 ln.tab111ty: the T 3t 30 11lCt:~re ig otroneer th:10 the 'J_ ut 50 metcrs (F1g.~ ~

12) •

3) During the ORSOli cruilile. in Octobcr 1953, the maximurTl 50 liaity

reached the aurfacs betwean 4°00 N and 5°00 N. It W8S the dl~ sealon but

the flow rata of the Amazon River ~ia cxccptlonnlly high during thie year

<'lg. 13).

4) During the ALHIRAt{IE SALDANHA crulae. in November. the .urface

!slinity us. higher than 36.0°/00 from 2°00 N ta SOOO N. It waa the end of.

the dry .ela.on snd the low water mark of Amazon River. Uowever the nux1mum

aa11n1ty wa. coming up fro~ 50 00'N to 4°00'N st 8 dGpth of 100 metera but

Einhing dOWll in il nort.h. ... nl direction close to th,~ ~~urbce (FiG. 14).

Dut'ing the crui.se 1'05')2 ','I~ ç,br;:~r,,"~ ::.::c Lù"ee first phdsee st different

phces:% the first pha.~ oaat of AWlzon Ri.vcr~ the second pM80 vest of

'~'a.'1Z0n R1ver and the th1rd C;llj l10rth of :'1:;;IZ011 River.

We can conclude that lG the procc8a of a divergence. ù\deed it lG

not an upwell1ng. SQ there la no Coriolis forca and the wind la perpendlcular

ta the .horG. The cause of th1a divergence iB probably the affect of tbo

welterly current as~1n.t the continental ehelf uhich ot1rs up the deep water

and. Dear th. surface. the effect of Aoazon watar whlch rever.as the process •

•C011C lul10n

Yb. purpo.e of this 8tudy wns to giva tha aopect of the outflow of

AmlzOQ Rlver during the year. Thh a.pect 1a very impcrfect: we Dowalmoet

-8-

notblng about the outflow from ~by ta October. During most of the cruises

the ares clole to the mouth W8S carefully studied but ~e hlve no inforn~tion

about tne are~ ~here the waters arc mixing. It ahould be interest1ng to

mske a cruiae during the 8welling of Amazon River with tha main purpose to

find the mixing area and to study 1t.

-9-

'\

-1 (J) -

BIELIOGRAPHIE .

COCHRANE J. D. - Equatorial unciercurrent and related currentsoff Rra 5 i l in Mélrch ;md Apri l 1963. Sc ience

142 (3593) : 6G9-671.

DEFANT A. , 1936 - Die Troposph5re des Atlantis~hen Ozeans. WiseEng. Deusch. Atl. Exp. ~eteor. 1926~ l Teil.

DONGUY JJo R0' H/\RDIV ILLE J. et lE GUEN J. Co, 1965 - Le parcoursmaritime des eaux du Congo. Cahiers Océanogra­~hiques, ~VII, nO 2, ~p. 8~-97.

GADE H. G. - On sorne oceanoqraphie observations in the south­eastern Caribbean Sea and the adjacent AtlanticOcean with special reference to the influenceof the Orinoco River. Bol. deI Instituto Ocean~

grafico, Vol. 1, nO 2. Universidade de Oriente,pp. 287-342. c.Ae 6971oo/(

lE FlOCH Jo, 1955 - Esquisse de la structure hydrologique del'Atlantique Equatorial au large de la Guyane

et de l'ern~ouchure de l'Amazone. Bull. C.O.E.C oVII, nO 10, pp. 450 -'467

MûREIRA da SILVA P. C., 1959 - Reconhecumento oceanografico do

estuario do Amazonas. Anais Hidrografico TomoXVII. Directoria de Hidrogrêfia e Navigacas.

Rio de Janeiro, pp. !51 - 164 0

OlTMAN R. E., STEHNREHG Ho, M,lES F. C., DA'IIS L. l. - Amazon

River Investigations Reconnaissance Measurementsof July 1963. U. S. Geological Survey'sCircular nO 486.

PARDE M., 1956 - Quelques aperçus relatifs à l'hydrologie brési­

lienne. La Houille Planche, p. 51.

SVERDHUP, JOHNSON and FlHaNG, 191~2 - The Oceans. Prentice HalL

TAKANO l(b·"J-._1954 - On the salini ty and the ve.loci ty distribution. - .....,

off the ~outh of a river. Jo Oceanogr. Soc.

Japan 10/3, 92 - 8.

TAKANO K., 1955 - A complimentary note of the diffusion of theseaward river flow off the mouth. J. Oceanogr.

Soco Japan 11/4, 147 - ')0

u. S. National Oce~nographic Dat~ Ccnt~r 1964 DQta Report G - 3:L.)UALANT 1. Washinqton O. C.

Sailing Directions for South Americ~. U.S. Hydrographie Office.

Publ. nO 23, Vol. 1.

A report of fishing grounds investigdtions in Central and

Southern America by R/V T0KO WJ\RU (Octo 1956­July 1957) Office of Fisheries Japan 1958

(en japonais).

/

AMAZON RIVERMEAN ANNUAL RATE AT MANAUS

CIRCULAR No. 486 U.S. GEOLOGICALSURVEYFIG. 1

JUN JUl AUG SEP Dei NOV DEe

J'

51° 50· 49° 48° 41° 46° 45° 44°1°'r---';;~--"";;";"__"""";,,;~ ~ "",",,,- ---,Taken tram 8razilion chart no. 10

DEPTHS IN METER5

3219

\IOI~

"" "'--\~o/i "', 106 1839Som ·..I00m\

4149

4100

'-.....

4œO

3456

2915

. .'

1609

ATLANTIC

2290 0 CE AN

69

33

216

1874

. . . . .. . ..

o

60

"~\Kl2

....r.,

5° 73

•

,/

/,1

1•1,

1JrJ

1•1

1/

/,/

,/./

;'

•200

100

300

400m ---- station océanique

" cot ière

12

5°1 11

50

150

100

200-35.0 ______

. -35.0

250

or

Mars 1965J.E. PILLSBURY

300 Croisière P-6502- m

, .

. '."

JON1

Octobre 1953ORSOM TI

5°1

11

,..,.-....--.~35;,;.:;;.5 ·35.5

50

200

150

250

300m

100

..,

..

50°

Novembre 1958A.SALDANHA

OCEAN

ATLANTIOUE

, .

7°51° 50° 49° 48° 47° 46° 45° 44°

..

6°

36.0

l,

OCEAN

A TL ANTIOUE

"\\

Octobre 1953ORSOM II

f\

51° 50° A9° 48° 47° 46° A5° A4°7°

\36,0

,

OCEAN

ATLANTIQUE

Mars ·1963

8.ERTIOGA

Croisière ÉOUALANT l

/\

Novembre1958A.SALDANHA

• J >

100

150

200

250

300m

".'x

30

1309

40

1321

50 N1

360

.35, a

,.: #

50

100

150

200

250

2°. 03 104 05 06 07

-::--_-.35.5

5° N1

300m

--.35:Q----·35. 0

Mars 1963

BERTIOGACroisière EOUALANT 1

... ~ .~

•

N

Donguy Jean-René. (1965).

Contribution to the knowledge of the outflow

of the Amazon River waters into the ocean.

s.l. : s.n., 22 p. multigr.