The first investigations on the distri-

SOME CHEMlCAL ASPECTS OF THE MARINE ENVlRONMENT OFF THE AMAZON AND PAR1\. RlVERS I BRAZIL

(Received 3/20/1971)

ARGEO MAGLIOCCA

Instituto Oceanográfico da Universidade de são Paulo

SYNOPSIS

This paper describes the sa1inity, temperature, di s solved oxygen and inorganic phosphate distributions for the Brazil northern coast, with special reference to the marine envi r onment of f the Amazon and Pa

rá rivers.

The change in direction of the coast with the consequent cIJange in the axis of the Guiana Current together with the large amount of sus pended matter contributed by river waters, create peculiar conditions on the continental shelf. These conditions are a1so influenced by tre wind and rain system. Out from the continental shelf Tropical Atlantic oceanic conditions are prevalent.

In contrast to the very low fert i lity of the Guiana Current the coastal waters, direct1y influenced by the rivers, show a supersatu ration of dissolved oxygen. The nutrients absorbed by suspended matter are partly 1iberated when the rivers mix with the oceanic water. How-ever, the low light penetration restricts the oxygen production to only few meters.

INTRODUCTION

Paulo was responsible for the area between 00 _{- lOoN Latitude and 042}0 _{- 052}0_W Longi-tude (Fig. 1).

The oceanographic cruise "EQUALANT I" aboard the Brazilian Navy Destroyer CT. "Ber tioga", comprised two series of observations ma de during the periods 20-28th February 1963 (sedes A) and 15-30th March (sedes B). The two series differ in that series A consists of principally deep water stations, and series B of stations on the

continent~l shelf. The cruises were part of

an oceanographic research program under the "International Cooperative Investigations of the Tropical Atlantic" (ICITA). The Oceano-graphic Institute of the University of são

Publ. no. 309 do Inst. Oceano da USP

Bolm Inst. oceanogr. S Paulo, 20:61-84

The first investigations on the distri-bution of dissolved oxygen in the Atlantic Ocean waters, appear in Wattenberg (1938) and Seiwell (1937). However, the oceanogra-phic data on the Tropical Atlantic is scarce, especially in areas close to the northern coast of Brazil, and is even more scarce for areas around the estuaries of the Amazon and Pará rivers. Some expeditions, liMe teor" (1925-27) ,

(1957-58)

"Dana" (1921-22) ,

and "M. Lomonozov"

"Crawford" (1963) give limited information on chemical distributions whereas the work of the "Almirante Saldanha",

(1958) and "Toko-Maru" (1957) give more d~ tailed information in the vicinity of the

Amazon and Pará rivers.

The oceanographic conditions of the area concerning the continental shelf are strong-ly influenced by the presence of n large water mass from the rivers Amazon and Pará, and beyond the limit of the continental shelf influenced by a complex diversity of surface and deeper currents.

The present paper gives the result s of the EQUALANT I (Ct. "Bertioga") cruise(series B) specifically for dissolved cxygen and inorganic phosphate and in more detail for the stations influenced by the rivers Amazon and pará.The station list and

oceano-graphic data were prepared by the National Oceanographic Data Center (1964) and published by ICITA.

The Winkler method has been used for determinations of dissolved oxygen and the results refer to the absolute values of oxygen as well as to the relative saturation values i.e. as a percentage of total satu-ration for a known chlorinity and

tempera-ture, following Truesdale

&

Gameson (1957).

The determination of inorganic phosphate was obtained by the molybdate method

using a electrophotometer ELKO 11; the chlorinity was measured by the Knudsen method and the hydrogen concentration was measured by a Metrohm potentiometer.

HORIZONTAL DISTRIBUTION

SURFACE

SALINITY - Considering the isohaline 350 /00 as the outer limit of the influence of the fresh water from the Amazon and Pará rivers (Figs. 2 and 3), it is observed that the penetration of these waters over the con-tinental shelf extends northeasternly almost reaching the edge of the continental shelf. Thereafter they flow, NW,

coast (Fig. 2).

parallel to the

From the diagram the mixing process and its displacement towards the northeast may be followed. Surface isohalines show clearly that the water from the rivers is contained by the Guiana Current and follows the gener-al direction of that current (i.e. NW). The curve of the northern coast-line forces the fresh-water from the rivers Amazon and Pará to run closer to the coast as far as Orange, where it is reinforced by the

Cape out-flow from the Oyapoque river, which

determi-62

nes the conditions recorded at station 14, in front of Cayenne. To the east of the Pará river mouth it is observed that 350 /00 surface isohaline lies inshore on the conti-nental shelf.

However. in the vicinity of the Pará river it swings away from the coast approach-ing the outerlimit of the continental shelf. The southern limit of the 350 /00 isohaline seems to be near lOS. as determined by Mura-no (1963).

A wedge of highly saline surface water (36,40 /00) is seen entering from the east, isolating a mass of less saline water (35,70 /00) off shore. A similar distribution has been recorded by the "Toko-Maru" (Mura-no. 1963) at the same period of the year. During an extremely dry period the "Almiran-te Saldanha" (Silva, 1958-59) recorded a different salinity distribution with high surface salinity values throughout the area. TEMPERATURE - The region under conside-ration may be broadly subdivided by the 270_C surface isotherm (Fig. 3a) into two distinct parts; a northern one, with temperature low-er than 27°C and a southlow-ern part with templow-er- temper-ature above 270_C.

It is worth noticing in the temperature distribution (Fig. 3a) that the water from the rivers Amazon and Pará presents temper-ature values (270 _{- 27.5}0_{C) lower than those} of the water mass common to the northeastern coast of Brazil (>27.50_C).

OXYGEN - The dissolved oxygen (Fig. 3b) ranges from 5.23 ml/l to 3.44 ml/l, the high-est surface values are recorded as isolines near the coast. with a maximum value of 5.23 ml/l. at OloN and 0480_{W, in waters with} 150 /00 salinity and 27.4°C temperature. It may be observed that the values of dissolved oxygen decrease as the water from the rivers mixes out into the oceano

Although significant distributions of dissolved oxygen are recorded at the mouths of the Amazon and Pará rivers with values ranging from 4.7 to 5.2 ml/l, greater in-sight is obtained from distributions of the relative values of dissolved oxygen. Figure 3d shows three very significant character ~ is tics: 1) a narrow belt bordering the coast of over saturated water (110%) associated with the coastal drift of river to the west; 2) a 100% isoline, paraI leI to the coast beginning at the Amazon river mouth which seems to stem from a high productivity

S ociated 'wi th outflow of ri ver wa ter ; 3) a water with low relative content (90%-100%) from the northeastern coas t of Brazil,which extends over a greater part of the

region under consideration.

north

The surface distr i bution of sali n ity , temperature and dissolved oxygen show the same general features.

PHOSPHATE - The inorganic phosphate distribution (Fig. 3c) shows an average value of 0.40~gat _{P0 4-P/l with a maximum} value of 0.69~gat P0 4-P/l at 40N-45 0W.

High concentration of inorganic phosphate (0.60~gat _{P0 4-P/l)are also} record-ed near Salinôpolis at the river mouth with associated low dissolved oxygen

con-centrations (92%).

In summary it is worth mentioning that stations 23 and 24(series B), near Sa-linôpolis, have distinctly oceanic charac -teristics in alI aspects, compared to the corresponding stations 1, 2, 3 (series A), taken one month earlier.

10 m LAYER

SALINITY - The 35 0 /00 isohaline at 10 m (Fig. 4) is found in very near the coast; the lesser valued isohaline are thus res-tricted to within the river mouths with correspondingly higher salinities than those at the surface.

A fact worth-noticing is the presence of a low salinity water mass (28.9 0 /00) at station 4 in a region where salinity values range between 34 0 /00 and 35 0 /00. This is most probably due to a depression of the halocline in the centre of a vortex created in the wake of a shallow bank (15 m)situated in the river mouth.

TEMPERATURE - A distribution similar to that of the surface may be found for the temperature (Fig. 4a). At stations south of the Equator, temperature values are slight-ly higher than those at the surface, with a 28.l3 0C, near Salinôpolis (c.f. maximum surface temperature 27.790_C).

As before the 27°C isotherm may be regarded as dividing the region into two temperature regimes. However, with the exception of station 4

stations show temperatures greater 27.5 0C.

coastal than

OXYGEN - Maximum value of dissolved oxygen is 4.3 ml (c.f. 5.2 ml/l for the

Bolm Int. oceanogr. S Paulo, 20:61-84

surface) ,except at station 4 (Fig. 4b) The values of relative oxygen are every-where l ess than 100% even near the river mouth (Fig. 4d), and near Salinôpolis drops as low as 34%. From it is clear that high productivity is restricted the first 10 m.

PHOSPHATE - The inorganic phosphate d istri buti on (Fig. 4c) shows some interest-ing points. Station 24,near Salinôpolis,pre-sents a maximum of O.87~gat _{P0 4-P/l,} an exceptional value for coastal waters which is in accordance with the lowest value of dissolved oxygen (l.55 ml/l), and with the high temperature (28.13 0C). If nitrite values are considered they show a completely uniform distribution at all depths with the unique exception of station 24, which pre-sents a maximum value (1.20~gat _{N0 2-N/l) .The} probable explanation for this anomalous values lies in the fact that a stationary eddy forms to the east of t h e P a r á ri ve r mouth due to the changes in the outflow. The centre of the eddy stagnates, killing off the biomass produced the month before under favorable conditions. Decomposition consumes the oxygen and causes the liberation of phosphorus and nitrogen compounds to the water.

20 m LAYER

SALINITY - The 35 0 / 00 isoha1ine (Fig. 5)is restricted to the three stations near the Pará river mouth, and oceanic water predominates in the remaining part of the region. At station 14, near Cayenne, water presenting characteristics of the 50 m layer appears from 20 m down.

TEMPERATURE A sma11 region of warm water (28.6°C) is found near the coast, at Salinôpolis (Fig. 5a). From the north an intrusion of colder waters temperature below 27 0 C, is recorded. At station 14, a1so the minimum temperature for the 1ayer was en-countered, 26.0l oC. The isotherm 27°C f0110ws the same pattern of the sha1lower 1ayers except for station 14.

OXYGEN - Near Salinôpolis, a minimum of dissolved oxygen was recorded (1. 79 ml/l) , while at Cayenne (Fig. 5b), sti11 near the

coast, the maximum values for dissolved oxygen (4.6 ml/l) were recorded,associated with water from the deeper layers. The rela-tive va1ues (Fig. 5d) of oxygen show the penetration of two tongues lower than 90%

from SE and N.

PHOSPHATE Inorgan i c phosp hat e d i st ri -bution (Fig. 5c) maintains the same chara c-teristics as those of the shallower lay ers .

30 m LAYER

SALINITY - Salinit y values i n this layer (Fig. 6) are almost alI about 36 0 /0 0; a restricted zone of low salinity is record-ed, (be low 35 0 /00), around the Parâ river mouth. Using the value 35 0 /00 the limit of the infl uence of fresh water, the last trace of its presence is recorded in this layer.

TEMPERATURE - The warm water mass comi ng from the SE (Fig. 6a) with a maximum temperature of 28.0l oC at OON and 47 0W is sti 11 present.

The 27 0C isotherm still divides the area into two parts. The anomalous station near Cayenne show a temperature of 25.9 0 C, the minimum for that layer.

OXYGEN - Two facts may be pointed out in the distribution of dissolved oxygen (Figs. 6b and 6d): 1) the presence of waters with high dissolved oxygen values near Caye~ ne; 2) waters with low dissolved oxygen values, coming from the northeast.

PHOSPHATE - Inorganic phosphate main-tains the same characteristics, however an exceptional value 0.85ugat P0 4-P/I is noted for station 5 (Fig. 6c).

50 m LAYER

SALINITY - The fresh water from the rivers is no longer present (Fig. 7).

TEMPERATURE - Temperatures(Fig. 7 a) above 27 0C are still recorded as the result of the presence of water from the northeast coast. In the station near Cayenne the presence of deeper water upwelling is more marked due to the 23.9 0C isotherm (c. f. 2 70_{C) •}

OXYGEN - The d is tribution of dissolved oxygen (Fig. 7b and 7d) in that layer is not significant. In general, alI values are around 4.00 ml/l, except for stations near the 50 m isobath.

PHOSPHATE - For the inorganic phosphate (Fig. 7c) the isolines near the 50 m isobath and following it, are of special interest since a relatively high concentration of inorganic phosphate to be expected due to the proximity to the bottom. However, for the greater part values _{under 0.5ugat- P0}

4-64

P/I were found.

VERTICAL DISTRIBUTION

Fo ur s ec t ions perpendicular to and one parall el to the coast were chosen for verti-cal distribution (Fig. 1).

In section I, (Fig. 8) the 35%0 iso-haline reaches the station 22, about 100 nm off the coast, extending from the surface to the bottom, delineating in a very marked fashion the seaward penetration of fresh water. The 30 0 /00 isohaline extends almost

50 nm off shore,but never exceeds 10 m depth. From the surface to 50 meters depth, temperature (Fig. 9) over 26.8 0C are record-ed increasing to over 27.5 0C towards the coast. Special reference should be made to the coastal station (no. 24) with a high dis-solved oxygen content (Fig. 10) in surfac'e waters of low salinity 210/00 and high temperature 27.7 0C. Below 5 m until the bottom salinity and temperature increase

(31 0 /00 and , 21!°C) and a high inorgani c phosphate (Fig. ll) is recorded.

Section 11 (Fig. 12), fronting the Ama -zon and Parâ rivers, shows the 35%0 iso -haline reaching about 150 nm off shore, and attaining a maximum depth of 20 m. A core of warm water (Fig. 13) is readily identified as extending to 30 m. Below this core we find a high value

(O.80ugat P0 4-P/l)

of inorganic phosphate (Fig.15). It is concluded that this maximum is caused by liberation of phosphate from the sediment, yet at the same time, the utilization of this phosphate by phytoplankton is impeded by the very small quantities of light penetrating the water column below 20 m. Nevertheless a distinct rise in the oxygen content of the usually oxygen-poor Guiana Current is noted (Fig.14).

In section 111, the 35 0 /00 isoline, (Fig . 16) approaches the coast and is not recorded be10w 15 m. The 150 m 1ayer shows salinities above 36 0 /00 throughout. Temper-atures above 27°C (Fig. 17) indicate the presence of the Guiana Current at stations near the coast (12 and 13). Station 13,near-est to the coast, shows a high dissolved oxygen content, (Fig. 18) for alI depths, indicating an average value of relative oxygen above saturation. For the same station,the inorganic phosphates are in a relatively high concentration which origi-nates from the sediments in the river-ocean

mixing zone (Fig. 19).

In section IV, the 35 0 /00 isoline is confined to the surface layer (Fig.20) reach-ing about 80 nm off the coast. There is evidence that the Guiana Current begins to swing away from the coast I; allowing sub-surface waters to dominate in the stations nearer the coast (Fig. 21). The

profile (Fig. 22) of the coastal

oxygen stations show 2 maximums dissolved oxygen associated with two different water masses: a surface one, restricted to a 5 m layer, in low sa-linity waters and the other at 40 m in oce-anic water. Inorgoce-anic phosphates were reduc-ed in the surface layer due to

sumption (Fig. 23).

intense

con-In section V, parallel to the coast, the outflow of the fresh water from the Pará and Amazon rivers (Fig. 24) is more intense at the mouth of the latter (station 3), and therefore salinity

than 12%0. This

values are not higher is due not only to the fresh water volume, but also to the direction of the Guiana Current in relation to the coastline. The whole section reveals the presence of a wedge shaped mass of fresh water, with a sharp interface of penetration in to the Guiana Current at the river mouth. The wedge gradually looses its intensity in a long tail of mixing.

The distribution observed can be ex-plained by the superposition of 3 wedges which relate to the outflow of three main

rivers the Pará, Amazon and Oyapoque.

Dissolved oxygen concentration (Fig,26) is directly influenced by the waters from the Amazon and Pará rivers. From 5 ml/l at the surface, .and in only 10 m, the profile, shows a sharp drop of 3.8 ml/l (station 2), or from a relative concentration of 1037. to 85%, due to mixing with oxygen-poor surface waters of the northea s t coast.

At stations 13 and 14, the isotherms show a strong presence of cooler waters; the isotherm 26°C, never found at depths

50 m, are recorded at 20 m, at station above

14, (Fig. 25). Upwe11ing waters, relatively rich in inorganic phosphate content,give relative oxygen values above s at urati on for a11

the superficial layer (Fig. 27).

WATER MASSES SYSTEMS AND CURRENTS

Beyond the continental shelf, far from the influence of fresh water from Amazon and

Bolm I ns t. oce an ogr . S Pa ul o, 20:61- 8 4

Pará rivers, characteristic salinity maximums over 36.5 0 /00 were recorded between 75-125 m depth, just within the thermocline (Newmann

&

Pierson, 1966). Minimum sa l inity values

around 34 . 5 0 /00, are recorded at 400-900 m depth (5.2-5.5 0 C). Thereafter, salinity values increase up to a maximum of 35%0 at a depth varying between 1,000 and 1,500 m, (3.5 - 4.0 0 C) whereafter they decrease again. The TS relationship for the region free from the influence of the rivers, as well as, the vertical distribution of

temper-ature and salinities at each station, are not presented herein since they agree with those of Sverdrup et aL. (1942) .

Silva (1958-1959) in his paper emphasizes that he found in the north the same South Atlantic ocean structure mentioned in Sver-drup's "The Oceans". Silva characterizes the minimum salinity layer (34.5 0 /00) from the minimum salinity value found

eastern coast of Brazil; the

in the south-intermediate waters of the north Atlantic is recorded in a layer of 1,000 to 1,500 m and also with the maximum salinity value higher than in the east coast and, as the author emphasizes, probably with a reinforcement of waters from the Mediterranean.

Murano (1963) discusses the distribution of the water system peculiar to the whole region under observation, and mentions his paper the following 4 systems:

in

a - the south Equatorial Current (Guiana Current), displac~ng NW, beyond the conti-nental shelf, with a surface salinity of about 35.5 0 /00 - 36%0;

b - a Coastal Current, also disp lacing NW, on continental shelf, with salinity below 20.0 % 0, originating in the Amazon

river;

c - waters from Amazon and Pará rivers running initially eastwardly, with salinity lower than 20.0 0 /00 and;

d - a Northern Coastal Water, with low salinity (1520 0 /00), as mentioned by Mura

-no ~ seems to be part of the waters from

Ama-zon and Pará rivers. The details are unknown. Some of these points are raised by Luede-mann (1967) in her paper on the release

drifting bottles, during the cruises A of and B. Her results clearly show the behaviour of the bottles in the same area (stations l-A and 24-B). The bottles releas e d in March drifted southeasterly. This dependence on the lo c al season, shows that the waters from Pará

river flow eastward and confirms the for-mation of a stationary eddy at Salinõpolis at

these times of the year.

At other periods, however, l ittle may be ascertained in relation to detail s, sirtce the region under influence of the Amazon and Pari rivers is probably very much related to the wind variations, to the supply of fresh water and to the northern coastline whi c h is characterized by strong concavity at ri ve rs mouth.

the

NUTRIENTS AND OXYGEN

According to Gessner (1962), the Amazon river waters are extremely poor in soluble phosphate. However, Gessner carried out a series of experiments and verified that sediment in permanent contact with the riv'ers waters supplies phosphate to the water. Thus, the phosphate consumed by photosynthe-tic activities is constantly replaced by sediments.

According t 'o Moore (cit. in Armstrong,

1965, p. 333) the amount of phosphorus ab-sorbed by the sediment in an estuary is about 10 5 times the concentration recorded for the subjacent water. Carritt

&

Goodgal

(cit. in Armstrong, 1965, p. 333) showed

that the sediment phosphatus uptake is re-versible and that the description is favor-ed by an increase in pH. The Amazon river carries a large amount of sediment in sus-pension which supply phosphorus when it reaches the estuary. The phosphatus dis-charged in the Amazon estuary is, however, promptly consumed at the first 5 m, where the turbidity is reduced permitting light penetration. A photometric depth trans -mission was taken in cruise B at the follow-ing stations: 3, 7, lI, 15, 18, 22

ra & Tundisi, 1967).

It is worth mentioning the

(Teixei-relative values of primary productiviy found by Te~­ xeira

&

Tundisi (op. cit.) for the surface.

Taking a 100% value corresponding to 0.86 gC/m 2 /day for station 3, which is under direct influence of fresh water, the other 5 oceanic stations studied would show re-lative values under 30%. The stations near the coast, 3 and 22, showed the highest primary production , a fact specially im-portant at station 3 in front of the Amazon river mouth. The light penetration at staticn 3 did not reach deeper than 10 m (

evct'inction), while th~ 66

total

extinction), while the dissolved axygen did not reach saturation, a fact also found at station 22. Gessner (op. cit.) states that decisive changes in the dissolved

concentration are recorded at the

oxygen river mouth caused by reduction of water speed , bringing about sedimentation. The precipi-tation o f sediments would allow greater ligh~ penetration and thereby stimulating phyto-plankton development.

The values of consumed oxygen or its apparent utilization were evaluated by means of the actual oxygen content and the values of the oxygen solubility in the sample in equilibrium with the atmosphere at 760 nm of Hg, regarding salinity and temperature (Ri-chards & Corwin, 1956), for the stations l-A, 24-B; 2-A and 23-B, we find the aver-age values of : 0.71 ml/l, 2.27 ml/l, 0.68 ml/l and 0.78 ml/l. A great increase of

consumed oxygen may be seen in the corre-lationed stations l-A and 24-B. At stations 2-A and 23-B a s'mall increase was recorded. In general, the same conditions were record-ed throughout the column at stations 2-A and 23-B, for 32 days. The difference observed does not indicate an intense change in oxygen contento For stations l-A and 24-B, with 32 day interval, the water column showed an average increase of 1.56 ml/l for apparent oxygen utilization. However, the surface of station l-A was saturated with oxygen (105%). The surface values compared of stations l-A and 24-B show an increase of 0.49 ml/I.

Therefore, the great change found in the apparent utilization of oxygen,

only to the station nearest to the and particularly within the top 5 m.

refers co as t ,

Since the salinity and temperature conditions re-mained the same for both stations (l-A and 24-B) it may be assumed that the variation recorded at the surface is not physical altering the partial pressure of the oxygen in liquid phase.

On the other hand, nitrogen combined in its inorganic forms(nitrite,nitrate,ammonia) seems to be supplied by the water of the Ama zon and Pari rivers, since the water mass carried by the South Equatorial Current is practically exhausted in inorganic nitrogen. During the Equalant I, some determinations of nitrite were made (Ct. "Bertioga", "M. Lomonosov", "Zvezda" and "Olonets"). Other-wise no determinations were made for others

forms of nitrogen . The area covered by " M. Lomonosov" , "Zvezds" and "Olonets" expe-ditions (NODC, 1964) was 004°W - 0200_{W and} l20_{S - 09}0_{S, and the nitrite data indicate}

extremely low values not only i n t he e ub-su rf ace but also in the de eper l ay er s,besi des a regular structure of dissolved oxygen contento Thus the inorganic nitrogen should be supplied by the water rivers.

SUMMARY

1 - The penetrat i on of the fresh waters fro m Amazon and Pará rivers over the conti-nental shelf extends northeasternly almost rea c hing the edge of the continental she1f. Ther eaf ter, they are contained by the Guiana Current and follow the NW direction of that Current.

2 - The temperature of waters «350 /00) is 270_C

the less saline 27.s oC lower than the water mass from the northeastern coast of Brazil ( >27.s oC).

3 - The highest dissolved oxygen values (5.23 ml/l) are found near the coast in waters with 150 /00 salinity and 27 . 4°C

temperature, and in the first 5 m.The values o f dissolved oxygen decrease as the water f ro m the rivers mixes into the oceano

4 - The river water carries a larger am ount of sediment in a position to supply phosphorus when it reaches

phosphate discharged in

the estuary. The the estuary is promptly consumed within the top 5 m. This is due to a reduction of turbidity promoted by sediment settling permiting deeper light penetration.

ACKNOWLEDGEMENTS

The author wishes to acknowledge Mr. Norman J. Rock for his criticaI

kind revision .

reading and

RESUMO

1 - A penetração da agua doce dos rios Amazonas e Pará, extende-se na direção NE atingindo a borda da plataforma continen-tal, onde são retidas pela corrente da Guiana tomando a direção dessa corrente ,is to e, NW.

2 - A temperatura das água s menos sali-nas «350 /00) está entre 270_{C - 27,soC, inf~} rior à temperatura da massa d'água origin~ ria da costa nordeste do Brasil (>27,50_C).

Bolm Inst. oceanogr. S Paulo, 20:61-84

3 - Os altos valôres de oxigênio dissol-vido (5,23 ml/l) são encontrados próximos

à

costa em águas com 150 /00 de salinidade e 27,40_{C de tempe r atUTa, nos primeiros 5 m.} Os valôres de oxigênio dissolvido decrescem na medida em que as águas dos rios se mistu-r am com as aguas oceânicas.

4 - A agua dos transportam grandes

rios Amazonas e Pará quantidades de matéria em suspensao pronta a fornecer fósforo ao atingir o estuário. Pela sedimentação e con sequente redução de turbidês, o fosfato 1ibe rado é prontamente consumido.

5 - Além da plataforma continental e fo-ra da influência dos rios as condições prev~ lecentes são as mesmas para o Atlântico Equ~ toria1.

REFERENCES

ARMSTRONG, F. A. J. 1965.

GESSNER, F. 1962.

Phosphorus. In: RILEY, J.P. & SKIRROW, G., ed. Chemical oce-anography. London,Acad. Press, vo1. 1, p. 323-364.

Observações sôb re o regime do fosfato no rio Amazonas. Bolm Mus. para. "Emilio Goeldi, n9 1, p. 74-83.

LUEDEMANN, E. F.

1967. Preliminary results of dri ft-bottle releases and recoveries in the western Tropical At-lantic. Bolm Ins t. oceanogr., vo1. 16, p. 13-22.

NATIONAL OCEANOGRAPHIC DATA CENTER. 1964.

MURANO, M. 1963.

Data report, EQUALANT I.

Washington, Department of Com -merce, Coast and Geodetic Sur-vey,2 vol. (Publ. G-3, NODC general series).

Survey report of the Brazilian fishing grounds. Japan, Minis-try of Agriculture and ForesMinis-try. Fishing Agency, p. 351-364. (In Japanese) .

NEWMANN, G. & PIERSON, W. J.

1966. PrincipIes of physical ocean-ography . New Jersey, Prentice Ha11, xii + 545 p.

RICHARDS, F. A. & CORWIN, N.

1956. Some oceanographic applications of recent determinations of the

solubility of oxygen in sea water. Col!. Repr. Woods Role oceanogr. Instn, Contr. n9 852. SEIWELL, R. R.

1937. The minimum oxygen concen t r ation in the western basin of the North Atlantic. Papo phy.Oce-anogr. Met., voI. 5, n9 3, 24p. SILVA, P. de C. M. da

1958-59. Reconhecimento oceanográfico do estuário do Amazonas. Anais hi-drogr., voI. 17, p. 53-82. SVERDRUP, H.V., JORNSON, W. & FLEMING, R. R.

68

1942. The oceans: their physics, chemistry and general biology. New Jersey,Prentice-Rall,1087p.

TEIXEIRA, C. & TUNDISI, J.

1967. Primary production and phyt~ plankton in equatorial waters. BulI. mar. Se., vol. 17, n9 4, p. 884-89I.

TRUESDALE, G. A.

&

GAMESON, A. L. H.

1957. The solubility of oxygen in saline water. J. Cons, perm. int. Explor. Mer, vol. 22,n9 2, p. 163-166.

WATTENBERG, R.

1938. Die Verteilung des Sauerstoffs und des Phosphats im Atlantis-chen Ozean. Wiss. Ergebn. dt. atlant. Exped. "Meteor", 1925 -27, voI. 9.

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OCEAN

2

MAR NHÃO

FIG. 1 - Stations occupied during EQUALANT I, February-Karch, 1963. Cruise A (open c i rc1es) and cruise B (dots) . Roman numbers indicate vertical sections discussed i n texto

Bolm Inst. oc eanogr . S P a ul o, 20:6 1 -8 4

CEARÁ

to'

•

Fi g. 2

•

5' •

•

•

FIG. 2 - Surface Amazon and Pará rivers fresh water percentual values.

..

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•

Fig. 30

FIG. 3M - Surface temperatures (oC)

•

Fig. 3c

FIG. 3c - Surface inorganic phosphate

(].Jgat _{P0 4 -P /1).}

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.

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FIG. 3 - Surface salinities (%0),

.,-

.

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FIG. 3b - Surface dissolved oxygen (ml/l)

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•

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m dissolved

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FIG.

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50 m saliníties FIG. 7a

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50 m dissolved oxygen FIG. 7c 50 m inorganic phosphate FIG. 7d 50 m relative oxygen

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(%0).

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(].Jgat P04-P/I).

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FIG. 24 - Section V . Salinities (u /00).

..

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FIG . 25 - Section V. Tempe r atures (oC).

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FIG. 26 - Section V. Dissolved oxygen (ml/l) .

15 I.

• - - - _ _ ..J_ •

___ - - - - _ --..

::=:==---=-=-=-_.-

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FIG. 27 - Section V. _{Inorganic phosphate ( v gat P0 4-p/l)} and relative oxygen (%).