Download Translation Series No. 421

4, •
!ARCHIVES
FISHERIES RESEARCH BOARD OF CANADA
.Transleion Seties No. 421
PRIMARY PRODUCTION IN THE ATLANTIC OCEAN
By Yu. I. Sorokin and L. B. Klfàshtorin
Original title:
From:
Pervichnarà produktsin v atlanticheskom okeane
Trudy Vsesofûznogo Gidrobiologicheskogo Obshchestva, Vol. 11,
pp. 265-284. 1961.
Preliminary translation by W. E. Ricker;
edited by J. D. H. Strickland
•
Distributed by the Fisheries Research Board of Canada,
Biological Station, Nanaimo, B. C.
April, 1963
During the expedition of the steamer Sedov when oceanographic investigations in the Mediterranean Sea and central Atlantic were carried out in accordance
with the program of the International Geophysical Year, in February-June 1958,
preparations were made to study phytoplankton and also primary production in
waters of the seas and oceans using the isotope 140. Determination:of primary
production in the tropical zone of the Atlantic Ocean had not been carried out
previously.
Primary production of organic matter is the main foundation of life in the
ocean. Determinations of its magnitude make it possible to assess the general
biological productivity of different regions of the oceans and seas. Such an
evaluation of biological activity in the Mediterranean Sea and Atlantic Ocean is
of great importance for the organization of the best possible fishing industry.
The route of the Sedov cut across almost all the principal currents of the
Atlantic Ocean. Hence the primary production which we have determined, and the
species composition of the phytoplankton, gives a picture of the productivity of
Atlantic waters as a whole, and makes it possible to compare the average
production of Atlantic waters with that of other oceans.
The first reliable determinations of primary production of waters of the
central part of the Atlantic Ocean were made by Steemann-Nielseman&Jenseniin
1952-1953 using the isotope method, during the round-the-world oceanographic
expedition of the Danish research vessel Galathea (Steemann-NielsenrancLJensen,
1957). However the route of the Galathea in the Atlantic was principally in
coastal waters near the west coast of Africa, in the Sargasso Sea, and in the
North Atlantic current, and did not include the tropical waters of the Equatorial
currents. In the open part of the Atlantic Ocean the Galathea occupied 12
stations in all, which were mostly situated on the transect Panama-England.
In 1955-1956 Currier (1957), on the research vessel Disq=_II ., made 7
determinations of primary productivity in the northeastern part of the Atlantic
Ocean off the coasts of Portugal and Morocco; these included 3 determinations in
the open ocean, the remainder being in the coastal zone.
[page 266] During the voyage of the Sedov, 93 stations were occupied for
the determination of the 24-hour magnitude of the primary production under 1
square metre of water surface, of which 7.8 stations were in the open part of the
Atlantic Ocean, 8 in the coastal zone, and 7 in the Mediterranean Sea. Concurrently, studies of the characteristics of photosynthesis were carried out both
directly in the ocean and by determining the mount and species composition of
the phytoplankton.
Methods
Primary production of the photosynthesis by phytoplankton was determined
radiocarbon method developed )Dy Steemann-Nielsen,(1952). The technique
the
by
of the determinations, and a method of setting up experiments to ascertain the
24-hour production under 1 m2 of surface had been worked out in the process of
studying the primary production of the Volga reservoirs (Sorokin, 1956, 1958).
The applicability of this method to the ocean was checked during a methodological
voyage of the Institute of Oceanology of the AN SSSR's research vessel Vitiaz
(Sorokin and Koblents-Mishke, 1958).
2
Our method makes it possible to determine the primary production of photosynthesis under 1 m 2 without placing bottles in the water at every station. For
this purpose it is sufficient to determine the actual 24-hour magnitude of
photosynthesis in a sample of water from the surface (Sfp ) and adjustment coefficients giving the relationship of the rates of photosynthesis at other depths
in the sea to the incident light--Kt 9 and to the character of the vertical
distribution of living phytoplankton--K r .
To determine Sfp 9 water samples are put Into light bottles, with ground
glass stoppers having a volume of 500-600 cm 2 9 and to them is added about 2ml
of a working solution of "labelled" carbonate, containing radioactive carbon 14C
(Na214CO3) 0 The vessels were held 24 hours on deck in a large wooden vat
painted inside a grey-blue colour. The vat was filled with water from the
surface, and the temperature of the water was maintained close to the temperature
of the water in the sea. Tests show that the photosynthesis determined In
bottles with the same water samples gave close results when held in the sea and
when on deck in the vat. For example, at station 12 bottles. held In the sea had
photosynthesis equal to 0.0754 mg/1 9 while bottles in the vat had 0.0768 mgA,
Special experiments showed that prepared [predvaritelnye] membrane filters
such as are used for filtering phytoplankton from fresh water,introdUced_errors when used to determine phytoplankton production in the sea, because these filters
would let part of the small peridinean algae go through them, and these comprise
an important part of the marine phytoplankton. In addition, the prepared
filters were not uniform and their penetrability varied considerably« In order
to use filter No« 5 freely, this being the one through which the water passed
much more poorly than through less fine predvaritelnye filters, it is necessary
to use a funnel with a very large filtering area. The size of the latter, in
turn, depends on the area of the opening of the end-window counter Etortsovyi
schetchik] used. We determined the activity of the filters Under an end-Window
counter with an opening having a diameter of 30 mm. This made it possible to
use a funnel with a filtering diameter of 26 mm for filtering the samples.
The filtering apparatus which we have employed is very suitàble for use
on board vessels that are tossing about (Fig. 1). As a iule it is easy to filter
500 to 600 ml of water through a No. 5 filter that has been boiled before it is
used, in a funnel with a filtering circle of 25 mm diameter. When there is a
considerable plankton "bloom" in the sea, the volume of water filtered decreases
to approximately [page 267] 300 m1 9 which is more than sufficient for a determination of the magnitude of photosynthesis.
After filtration, the wet filters are transferred to a filter paper folded
into several layers, and to separate the radioactive carbonate from them they
are moistened with a few drops of a solution containing 2% HC1 and 3% NaCi. The
acid and filters are neutralized, after this moistening, by a 3% solution of
soda. By using this means of ramoving carbonates, the algae are treated while
they are still alive. Therefore, their contents are not washed by the acid, as
happens when working with [otmershie] cells on drained filters«
After being treated in this way the filters are counted in a definite
position in an end-window counter;
Along with the samples held in the light, similar samples were held for
24 hours in darkness. Measurement of the radioactivity of the filters obtained
when the samples held in darkness are filtered, gives the size of the correction
- 3 —
for fixation on the filters of radioactive carbon resulting from fixation of GO2
by the algae in darkness, for adsorption or contamination of he "working"
solution of marked carbonate by organic molecules containing 14C. The difference
between the activity of the filtrates fran the analogous samples held in light
and in darkness gives the magnitude of the activity of 14C assimilated by the
phytoplankton cells in the process of photosynthesis during the time of the
experiment.
The magnitude of Sf p iS. -.calbulâtèd-fromthe_fôrmulà.:
S fp
r.Sk.1.06
mg CA
where r is the radioactivity of the algae on the filter (after correction by
means of the dark bottle) after filtering the total volume of the sample under
conditions where its volume amounts to 500 ml; the coefficient 1.06 is the
correction for the "isotope effect" (delay in assimilation of 14002 in comparison with 12002 in the process of photosynthesis, which according to the data of
Sorokin (1959) amounts to about el); R is the total activity of the bicarbonates
and CO 2 in the water after adding to it the working solution Of isotope; Sk is
the total quantity of carbon in the water as CO 2 and bicarbonates, in mg CA.
In the event it is impossible to filter the total sample of water an
aliquot portion is filtered and frun this the radioactivity of the algae in the
total sample is computed.
[page 268] The magnitude of R was determined periodically several times
during the expedition. For its determination 2m1 of "working solution" of
labelled carbonate (see below) was added to 500 ml of tap water; 2 ml of the
solution used was added to a test tube with 4 ml 0.1 N KOH. Then 1 ml of 1%
solution of NH4C1 and 1 ml of 10% BaC12 was added. After heating it at a
temperature of 80°C for 10 minutes the precipitate of BaCO3 which had formed was
filtered out on membrane filter No. 2 in the same funnel as had been used for
filtering samples in the determination of r. The radioactivity of the precipi• tate of BaCO 3 on the filter with the correction for self-absorption (see
Steemann-Nielsen, 1952), multiplied by 500, gives the magnitude of R.
The total quantity of carbon as CO2 and bicarbonates is computed from
several approximate versions we have made of a formula available in a book by
A.H.W. Harvey (1948), which involve the magnitude of t°, pH and S°Ao of the
sea water, which was determined at each station by the chemists and hydrologists
of our expedition.
The working solution of radioactive carbonate was prepared by diluting a
concentrated commercial preparation to a 0.005 N solution of KOH. To the working
solution 100 mgA Na 2003 was added as a "carrier". Before using, a amall portion
of the working solution was filtered through a membrane No. 1 or No. 2 which
had been twice boiled in distilled water and reinforced in a plexiglass filtering funnel. Filtration of the working solution freed it from organic particles
(mainly bacteria) containing 14C. This filtered working solution was used for
2 or 3 days after it was filtered, and then a new portion was filtered.
Depending on the quantity of phytoplankton, the working solution was used
at the following activities: in coastal waters with a great quantity of
4
vegetation--0 0 5-0 0 8 x 106 imp// ml l ; and in waters of the open ocean, poor in
phytoplankton--1 0 3 x 10 6 imp ml.
As indicated earlier, in order to calculate the production under 1 m2 of
water surface it was necessary to determine the correction coefficients Kt and Kr
a number of depths which make possible a calculation of the rate of photoat
synthesis in the open water. The method of determining Kt and K r has been
described in earlier articles (Sorokin, 1957 9 1958).
The coefficients Kr (the relation between productivity of photosynthesis
and the vertical distribution of phytoplankton)were determined during the present
voyage at every drift station. For these determinations, water samples taken
from various depths in the open water were placed in light bottles. Into these
bottles equal volumes of the working solution of isotope were added, after which
they were kept on deck in the shade for 2-4 hours at a uniform moderate illumination. As controls dark bottles were used, containing samples from two depths-the surface and 75 m. The dark bottles with the sample from the surface layer
served as the control for samples from depths from 0 to 50 m; and the dark
bottle with the sample from 75 m served as control for the samples from 50-150m.
After the time mentioned, the water from the bottles was quickly filtered through
membrane filters. The ratio of the activity of the filters obtained after
filtration of the samples from the different depths (after correction by means
of the corresponding control) to the activity of the filter from the sample from
the surface, represents the size of K r for these depths.
In order to select depths for the determination of Kr most correctly without overlooking in the process the layers of greatest concentration of phytoplankton, during the present voyage, before selecting the samples, the hydrologists
of the scientific group of the Institute of Oceanology of the Academy of Sciences
of the USSR made a determination of the vertical distribution of water temperature using an electrothermobathysond. [page 269] In cases where there was
temperature stratification, supplementary samples were taken for the determination of K r ,:at intervals of 3-5 m, in addition to the samples at the standard
levels. Published information (Semina, 1957), and also determinations of Kr in
the Pacific Ocean (Sorokin, 1957) show that phytoplankton is canmonly concentrated
in the thermocline. While increasing the frequency of samples taken in the
thermocline zone we also made an attempt to obtain supplanentary data that would
shed light on the effect of temperature stratification on the character of the
vertical distribution of phytoplankton in the open water, and on the production
under 1 m2 of sea surface.
The standard levels for the determination of Kr were dàosen to agree with
the levels used by the Institute of Oceanology of the Academy of Sciences of the
USSR for taking samples of filterable plankton, namely 0 9 10 9 25 9 35 9 50 9 75 9
10
and 150 m.
The coefficients Kt were obtained at 24-hour stations, since their determination requires long exposure of bottles in the sea. To determine K t a 20-litre
bottle was filled with water from the surface or from two different levels
(0 and 50m) 0 The water was immediately poured into a light bottle having a
volume of about 0.55 litres; these were fixed in pairs in special holders, and
1
[Probably = disintegrations per minute per ml--J.D.H,S.]
-5 were attached to the cable by means of a clamp, This made it possible to have
material from two parallel bottles at each depth.
To the bottles fixed in the containers, 2 ml of working solution of isotope
were added in a dark room, The bottles with samples treated in this manner were
brought on deck in a tightly covered box which protected them from the light.
Then the containers -with the bottles were swiftly removed from the box one by
one and each in turn was clamped to the cable and lowered into the ocean at the
desired distance from each other. At the end of the cable a weight of 50-75 kg
waS hung in order to keep the wire angle to a minimum. For controls, bottles
were held on deck in the light for a period equal to the time required for the
setting out and recovery of the experiment, but the rest of the time they were
held in darkness.
Experiments for the determination of K t lasted 12 hours or 24 hours. The
bottles were held in the ocean usually at the following depthsg 0, 5, 10, 15,
25, 35, 45, 60, 90, 120, 150 m. At the 24-hour stations, along with the
determination of Kt, two scientists of the Institute of Oceanology, V. Grinberg
and V. Snopkov, determined the underwater illumination by means of a hydrophotometer, Inasmuch as the coefficients Kt are rather uniform over great regions
of the ocean which have uniform properties of their water messes (Sorokin, 1957),
the magnitude of the Kt 's obtained at the 24-hour stations were used for the
computation of production under 1 m2 of ocean surface at neighbouring drift
stations. Interpolation between the coefficients Kt and Kr (see Table 1 of the
appendix) obtained at corresponding levelsl makes it possible to compute the
relative rate of photosynthesis at different depths (K s ) and to find graphically
the coefficient Kf (the ratio of the area ABC and ABCD, Fig. 2), by means of
which the daily production under 1 m 2 of ocean surface (Sf) can be computed by
the formula (Sorokin, 1957):
Sf=S
g/m2
where Xis the depth in meters to which the measurements of Kt andK r were made.
[page 271 11 Collections of filterable plankton for quantitative determination were made acbording to the ueual methods at standard depths (see above).
The volume of the samples used was 1 litre. The species composition of the
plankton was studied both from net collections and also frOm filters ueing
membrane filter No. 5 and prepared filters, after running the greatest possible
volume of water through them.
To compute the biomass of zooplankton the catch of a juday net was used,
having the diameter of the opening 37 cm, and made of silk No. 38. From the
collecting jar of the net the sample was poured into a special vessel, where the
zooplankton settled out into its narrow portion. Using a vacuum pump, water
from the vessel was drawn off through a tube whose opening was covered with silk
mesh, after which the volume of the settled zooplankton was measured.
The daily magnitude of the primary production of photosynthesis of phytoplankton under 1 m 2 of ocean surface was determined during the voyage of the
1
In the event the depths chosen for the determination of Kt and Kr did not
coincide, the magnitude of 1{.:é9 for the levels at which the Kr was determined,
were found graphically«
6
Sedov at all the 24-hour and drift stations. At 24-bour stations No. 2 and 39
it.was determined 3 times. In addition, at intervals between the drift stations,
hile the vessel was under way, water samples were collected from the surface
for the determination of primary production in 1 litre (Sfp , see above). By
using the magnitude of Sfp obtained in this way and the correction coefficients,
Kt and K r , obtained at neighbouring drift or 24-hour stations, it was possible
to compute the production under 1 m 2 for these intermediate stations. In all 93
determinations of the production under 1 m 2 were made during the course of the
voyage (see Fig. 2, 3 and appendix).
Results
of
Investigations of Primary Production
The eastern and middle parts of the Mediterranean Sea at the beginning of
the voyage were characterized by unusually small primary productions (0.02-0.03
g/m 2 )0 The phytoplankton at this time was still at its winter numerical minimums
its numbers did not exceed 60,000 cells/M 3 0
The principal species of phytoplankters were the diatoms Thallasipsira
gravida, Bacteriastrum âmalinum and the peridinians Peridinium ovum', Oxytoxum
smagmus,, p_yrocuLLs 02.212a.u.tuuu. Water of this part of the Mediterranean
is very poor in biogenic elements. The quantity of salts of nitrogen and
phosphorous is here much less than in the open part of the Atlantic Ocean
(Thomsen, 1931), and this apparently is the cause of the poor development of
phytoplankton. The sparsity of life, particularly of phytoplankton, in the
eastern part of the Mediterranean has been noted by other authors also (Jespersen,
1937).
In the western part of the Mediterranean Sea (stations III, IV, V and Va)
where the temperature is lower (14°, as compared with 15.5° in the eastern part)
a sharp increase in primary production was observed--up to 1 g/m 2 along the
coasts of Algeria. Small peridinians appeared in large numbers in the plankton.
The first two stations (1 and 2) in the Atlantic Ocean were not far from
the coast of Portugal. The primary production here was also rather high,
particularly at station J. (1.39 g/M 2 )0 The abundance of phytoplankton reached
1.45 million cells/M3 0 Its species composition had also changed. Diatoms
predominated over peridinians in the flora. Of the former, Rhizosolenia elate,
Ghaetoceros coarctatus, Rh0 hebetata weré present in important numbers, and of
the peridinians--Pyropystis fusiformis, Ceratium carriense, C. contortum,
Pyrocystis
[page 272] Some distance from shore, at stations 2a,.3 and 3a in the waters
of the Ganary Current, primary production decreased to 0 01 g/m2 . SteemannNielsen and Jensen (1957) also observed a very small production in this region.
Near the Canary Islands and Madeira (stations 4, 5) the productivity of the water
increased to 0.4-0.7 g/M 2 , this apparently being associated with the existence
of eddies of the Canary Current around the system of islands, which carry up to
the surface layers deep waters, rich in biogenic substances. At stations 6, 7
and 8 primary production remained at the level characteristic of tropical waters
of the equatorial currents (0.2-0.3 g/M2 )0
The further route of the Sedov came close to the zone of discharge to the
surface layers of cold deep waters in the region of the west coast of Africa
7
and Cape Verde. The approach of deep waters to the surface off the west coast
of Africa is caused by the influence of the northeast trade winds, which drive
warm surface waters which are replaced by deep waters. The thermocline here was
very strongly developed, and was situated at a depth of 20-30 m 9 that is in the
photosynthetic zone (Fig. 4). The deep waters, entering the zone of photosynthesis, enrich the surface layers of the water with salts of nitrogen and
phosphorous, which in turn produce an intense development of phytoplankton in
these regions. The photosynthetic production at stations 11 and 12 9 situated
150 and 50 miles from Cape Verde rose to 1.4-3.4 g/m 2 . The greatest production
(3.8 g/m2) observed by Steemann-Nielsen and Jensen at the time of the voyage of
the Galathea around the world was also recorded in the region of the west coast
of Africa (Walvis Bay), [page 273] which these authors considered to be one of
the most productive places in the World Ocean'.
The development of phytoplankton in the region of Cape Verde reached the intensity of a 'b loom". The number of cells per m3 amounted to 13.35 millions.
The transparency decreased to 10 m and the water had a yellow-green colour. This
region was the most southern one that had a numerical preponderance of diatoms
over peridinians. Among the diatoms ahmzuolenia alata, Rh delicatula, Nitzschia
sp., Thallasiotrix delicatula, Stephanodiscus Ealmnriana, Thallasiosira subtilis
occurred in greatest numbers.
Peridinians were represented mainly by the following species: Ceratium
carriense, C. furca, Peridinium deoressum, Pvrocystis aseudonoctiluca. Of rare
occurrence were Bacteriastrum sp., Rhyzosolenia stolterfothii, Itvloc lindrus
danicus, jj
is caudata.
In the region of the Cape Verde Islands primary production of the water
was also rather high (0.4-0.5 g/m 2 ). On arrival in the tropical water zone of
the equatorial countercurrent and the southern trade-wind current, the primary
production decreased to 0.1-0.3 g/m 2 . Some increase inside this zone was
observed in the region of the convergence of the equatorial countercurrent
(stations 17, 18) and when traversing the rapid part of the southern trade-wind
current, which can carry phytoplankton from the region of the Benguela Current
(stations 216, 218 and 22).
The bulk of the phytoplankton in the region of tropical waters of the
equatorial current and countercurrent consists of the peridinians Ceratiumcarriense, C. massiliense, C. fusus, C. furca, EmenylLu 2m21212919ILLAn, and
rarely C. teres, Ornithocercus quadratus. The abundance of algae in these waters
was about 11,000 cells/m3 .
In the zone of tropical waters with sparse oceanic plankton we encountered
a region with a large number of the bluegreen alga Oscillatoria thiebautii, which
form colonies of a diameter up to 1-2 mm. According to the data of Hentschel
and Wattenberg (1930) and Hentschell (1933) this alga is encountered in large
numbers in waters of the Antillean Current. From there it falls into the gyral
of the Sargasso Sea and is apparently carried into the Atlantic. As individual
filaments O. thiebautii was encountered along almost our whole routez in the
Canary Current, the Sargasso Sea, and all of the tropical zone«
Uasurements of primary production in the region of intermingling of the
warm Kurosio Current and the cold Oyasio Current off the coast of Japan, made in
1957 9 gave a larger figure--up to 6 g/m 2 (Sorokin and Koblents-Mishke, 1958).
- 8On passing over into the zone of high temperature in part of the northern
trade-wind current (stations 25-30) primary production decreased to inconsiderable
levels (0.01-0.06 g/m 2 ) with the mallest quantity at station 28--0.008 g/m 2 0
In the surface layer of water at the latter station the 24-hour primary production
scarcely amounted to 0.1 mg C/M 2 0 Such small intensity of photosynthesis in this
region Is evidently associated with the phenomenon of "aging" of the surface
waters of the equatorial current (Sverdrup et al., 1946). These waters traverse
a very long distance, over a long period of time, and scarcely mix with cold
deep waters at all. Thus they are greatly impoverished in salts of nitrogen,
phosphorous and silicon, which are consumed by algae and are carried down to
deep strata when they sink after dying (see Fig. 4) 0
Approaching the American continent, the surface layers of waters begin to
sink deeper, occupying an ever greater thickness of the water column. The thermocline is pushed down into a depth of 100-150 m, and [page 274] at •the border of
the Sargasso Sea it finally disappears completely from the photosynthetic zone
(see Fig. 4). Under these conditions there is no possibility of even a weak
accession of biogenic substances, such as convective mixing will provide in
these tropical waters if the thermocline is in the illuminated productive zone.
Because the Sargasso Sea is a closed gyral, consisting of the same surface
waters with a tendency to sink gradually (Sverdrup et al., 1946) 9 biogenic
elements almost completely disappear from a tremendous thickness of water. The
quantity of phosphorous at the southern limit of the Sargasso Sea in the 0-100 m
interval was almost nil (Fig. 4). A phosphorous concentration of 0.5 mg•atoms
per m3 in the Sargasso Sea itself can be found only at a depth of several
hundred metres (Thomsen, 1937).
Figure 5 shows the vertical distribution of phosphorous in the Sargasso
Sea and in waters of the North Atlantic current. We see that in the photosynthetic zone of the Sargasso Sea phosphorous is completely absent, while in
the North Atlantic current it is present at the very surface and the quantity
rapidly increases with depth.
The absence of biogenic substances in the thick surface layer of water,
which is associated with special hydrological conditions and which is the cause
of the unusual poverty of life in the waters of the Sargasso Sea, has been
remarked earlier by phytoplankton investigators (Lohmann, 1920; Jespersen, 1937).
In spite of the considerable transparency of the water and the great thickness
of the [photosynthetically] active layer (up to 130 m 9 see Fig. 6) 9 photosynthetic production here on the average equals 0.01-0.06 g/ 2 (stations 30-36).
In 1 m3 of surface water it does not exceed a few tenths of a milligram
[desiâtykh dolei milligramma]. At stations 28a-30, situated at the boundary of
the Sargasso Sea, a considerable development of the bluegreen alga Oscillatoria
thiebautii was observed. In general, however, the abundance of phytoplankton
in the surface water layers of the Sargasso Sea was extremely low--from 200 to
3000 cellse, which is quite in line with the very wall production. The
development in the Sargasso Sea of floating Sargasso weed and colonies of bluegreen algae may be associated with the presence in these surface waters of
symbiotic bacteria, which assimilate molecular nitrogen and thus supply the
plants with their requirements of this biogenic element.
Steemann-Nielsen and Jensen (1957) determined the primary productivity
of the Sargasso Sea at several stations, at the same time of year as we did,
and obtained figures of the same order (0.04-0.05 g/ 3 )0 These were the
smallest primary productions that they observed during the whole course of the
Galathea's voyage around the world.
At the northern limit of the Sargasso Sea a graduai increase in quantity
of phytoplankton was observed, which resulted from the appearance of the
peridinians Ceratium carriense, C. karsteni, C. contortum, C. farce, C.
pen-Lamnum, Peridinium steinii. On leaving the Sargasso Sea, beginning with
stations 36-39 9 primary production increased 5-10 times, attaining 0.1-0 04 g/m 2 0
[page 275] The diatoms Thallasiosira subtilia, Th. rotula, Rhizosolenia hebetata,
Rhalata, Rh0 castracanei began to appear in the plankton.
At stations situated in waters of the North Atlantic current (stations
42-49) 9 primary production stayed steady at a level of 0.25-0.6 gjill 2 0 Appràximately the same quantities (0.25-0.47 g/m 2 ) were observed in this region by
Steemann-Nielsen and Jensen (1957). In the phytoplankton, in addition to the
species mentioned above, there appeared also the small peridinians Peridinium
ovatum, P. deuessum, Ceratitm declinatum, Goniaulax pely_tdu and G. rostratum.
At stations 48-49a, in the English Channel, primary production mounted
to 0.88-1.8 g/M 2 . Here we observed the spring "explosion" of phytoplankton.
The great bulk consisted of Phaeocystis pempLetli,--the usual massive species in
the "blooms" of the North Sea. In addition, the following occurred in large
numbers: Rhizosolenia setiqera, Rh. elate, Chaetoceros socialis, Lauderia
nsImuLu,
borealis, Ceratium trioos, Coscinodiscus estergmbelms,
Peridinium ovatum. The water in the English Channel had a brown colour and a
distinctive odour from the dense accumulation of plankton. The transparency
decreased •o 8 m«
After entering the North Sea, production lims greater--3.5 g/n 2--opposite
the mouth of the Thames River (station 496). In the North Sea itself it again
decreased to the same level as had been observed in the North Atlantic current
in the open part of the Atlantic.
Table 2 of the Appendix shows that the greatest difference between photosynthesis in the surface waters and the primary production under 1 m 2 (and
hence the largest value of Kf) was observed in a majority of cases at stations
situated in transparent tropical waters of the northern and southern equatorial
currents, in which a thermocline was sharply developed. Here the photosynthesis
in 1 m3 of surface waters w.as 100-800 times less than in the water column under
1 m 2 of surface, and the coefficient Kf was 0.75-5.7<, But at stations situated
in the Mediterranean Sea, and in waters of the Canary and North Atlantic currents,
this difference as a rule was not larger than 30-75 times, and the coefficient
Kf most of the time did not exceed 0.5.
The pattern just outlined reflects the fact that in the tropical zone of
equatorial currents phytoplankton accumulates in the thermocline, [page 276]
which in these waters is in the illuminated zone. Therefore the greatest effect
of photosynthesis occurs not in the zone of most favorable illumination (10-20 m)
but at a depth of 40-60% in the region of the rapid change in density, where
living phytoplankton is concentrated. But in the very surface waters that are
impoverished in phytoplankton, primary production was significantly reduced
(Fig. 7).
The accumulation of . phytoplankton above the stratified layer in tropical
waters of the equatorial currents is very clearly developed. For example at
-
10 -
some stations (13 9 14) its concentration in the stratified layer was greater
• han in the surface layer by 30-50 times (Fig. 7)0 The cause of this distribution of phytoplankton, it seems to us 9 Is not only the retention of cells whàch
are falling under the influence of the force of gravity, but also apparently
that phytoplankton reproduces at the boundary of the stratified layer much more
intensively than in the surface layer. Figure 4 shows that 9 in the surface
water layer in the equatorial currents 9 phosphates appear precisely at the
boundary of the zone of temperature and density stratification 9 which they reach
as a result of convective mixing of warm surface waters with cold waters at the
boundary of their direct contact.
At all the 24-hour stations 9 also at drift station No. 19; we determined
the relationship between photosynthesis in the water mass to the underwater
illumination (the coefficient Kt ). At station 12 these determinations were
performed 3 times and at station 34 twice. This is the first time that so
careful a study has been made of the thickness of the photosynthetic layer in
the tropical region of the ocean. Figure 6 shows that at coastal station 12 9
with an abundance of phytoplankton and poor transparency (11 m) 9 photosynthesis
quickly fell off with depth and at 15 m amounted to 50.% of its greatest
intensity'. At the ocean stations 9 on the other hand 9 where the water was blue
and transparent 9 the effect of photosynthesi s. was greatest at levels between 30
and 40 m (stations 6 9 23 9 34)0.
From the above it follows that the coefficient Kt obtained for oceanic
waters of the sub=tropical zone (stations 6 9 39) and in the tropical nearequatorial zone (stations 23 9 15 9 19) resemble each other greatly in having
similar transparency and water colour. Photosynthesis in the very surface layer
is suppressed by the excessive illumination 9 which considerably exceeds the
optiMum for photosynthesis. The zone of most effective photosynthesis occurs
in these waters at a depth of 20-30 m. Deeper down photosynthesis begins to
decrease because of inadequate illumination 9 and at a depth of i00120 in it
completely disappears. At station 19 9 situated [page 277] close to the equator
in a region of calm and continuous heavy cloud cover 9 the rate of photosynthesis
decreases more rapidly with depth than at other stations in tropical waters.
The greatest thickness of the photosynthetic zone was observed on May 9
in the Sargasso Sea at station 34. On this sunny day the transparency of the
water was 35 m [presumably by Secchi disk--IN.E.Rj. The greatest intensity of
photosynthesis was at a depth of 45 m; at 100m it was 20% of the figure just
mentioned 9 and 40% of the rate at the surface. Determination of Kt for this
station on a cloudy day, May 9 9 showed that the zone of most rapid photosynthesis
was at a depth of 30m, while at 110m photosynthesis was practically lacking.
These results confirm those which we obtained during an expedition on the ,
the Vitiaz 9 that the relation of the vertical distribution of rate of photosynthesis to underwater illumination (the coefficient Kt ) does not exhibit
significant fluctuations in large regions of the ocean which have similar transparencies. Therefore the coefficient Kt , as measured at one of the 24-hour
stations 9 can be used for the computation of photosynthetic production throughout
the water mass of large regions of the ocean having similar hydrological characteristics. The adjustment coefficients, Kt, obtained during the voyage of the
Sedov can be used by other expeditions in studying primary production in the
Atlantic and other oceans.
•
1r
[The text says "of its greatest illumination"--naibolshei osveshchen-
nosti.]
-
11
Concurrently with the determination of the Kt coefficients at many
stations, V. M. Grinberg made observations on the magnitude of the underwater
illumination using a hydrophotometer. Figure 8 shows that down to a certain
depth there is an inverse relation between photosynthesis and underwater illumination, that is, there is a suppression effect of photosynthesis in the upper
water layers. At the level where illumination is 30-50% of that at the surface
and is more favourable for algae, the rate of photosynthesis is greatest. At
levels deeper than the "bend" of the curve the rate of photosynthesis begins to
decrease parallel to the underwater illumination.
During the voyage of the Vitiaz it was feund that in the Sea of Japan and
northwestern part of the Pacific Ocean there was an almost complete absence
[page 278] of suppression of photosynthesis in the surface layer. Here a direct
relationship was observed between underwater illumination and rate of photosynthesis in the water mass, starting at the very surface (Sorokin and
Kozlianinov, 1957). Where there is suppression by light, the relationship
between the two can be analyzed only beginning at the level of greatest rate of
photosynthesis and on downward. In Figure 9 the coefficient Kt and the coefficient of underwater illumination obtained by Grinberg are plotted. Here the
coefficients Kt are computed as the relative rate of photosynthesis at different
levels divided by the greatest rate of photosynthesis. The coefficients of
underwater illumination are also expressed in terms of the value at the level of
maximum photosynthesis. The figure shows that changes in rate of photosynthesis
at levels below those where it is suppressed by light is directly related to
changes in underwater illumination.
Thus the direct relationship between underwater illumination and rate of
photosynthesis which was discovered in northern waters, where there is no
suppression of photosynthesis by light, exists also in tropical waters below the
level of greatest rate of photosynthesis.
Steemann-Neilsen and Jensen (1957) observed a close relationship between
the primary production which they determined in various regions of the ocean and
the total biomass of zooplankton that had been observed by other authors,
approximately in the same regions. This relationship was particularly close in
warm olrgotrophic waters where seasonal fluctuations in the quantity of zoo- and
phytoplankton are small.
During the voyage of the Sedov a determination of the biomass of zooplankton
in the layer 0-200 m was made at a series of stations in waters of the equatorial
currents and at all stations on the traverse from the Sargasso Sea to the English
Channel, along with determinations of primary productivity.
Figure 10 shows that there is in fact a close relationship between primary
productivity and the biomass of zooplankton, which is most clearly developed in
tropical waters of low photosynthetic production (stations 23-39). At stations
with large primary [page 279] productions this relationship is also developed
fairly well, although the variations in production and zooplankton biomass in
this case are greater.
- 12 Conclusions [page 279]
Results of the determination of the daily size of the production of organic
matter by photosynthesis of the phytoplankton under 1 in 2 9 obtained during the
voyage of the research vessel Sedov, make it possible to reçognize the following
zones in the Atlantic Ocean separated on the basis of their productivity..
1. Zone of coastal water with primary productivity of 0.8-3.7 g G/in 2
(staion1
9 12 9 12a, 47 9 49, 496). In this zone the mass development of phytoplankton amounts to a strong "bloom". The transparency of the water is not
greater than 6-8 m, The water is greenish and has a characteristic plankton
odour. The cause of the intensive development of phytoplankton in this zone is
the abundance of biogenic elements. The latter can reach the coastal water from
river discharge from the land and dust frOm the continent (stations 1 9 49 9 49a,
496) or, as a result,transport of deep waters to the surface by the action of the
trade winds which act on the upper warm layer of water (stations 11 9 12). The
quantity of phosphates in the illuminated surface layer of the water of the
thickness of 0-50m comprises, in waters of this zone, 0.2-0.6 mg-atoms P per m3 .
Frequently in the surface layer, as a result of a great quantity of phytoplankton,
phosphates disappear completely and the phosphorous is found in the cells of the
the quantity of phosphates increases rapidly with depth, and the alge.Howvr
phytoplankton then develops much more intensively in the 2040 in layer than near
the surface. In the phytoplankton of this zone diatoms are of outstanding
importance in composition and abundance.
2. The open ocean zone of water with a primary productivity of 0.25-0.52
/ 2
[page 280] Here we may average water of the North Atlantic and Canary
currents (stations 42-46 and 2-7) and also the tropical waters of the rapid
portiOn of the south Equatorial current (stations 216, 210, 22) and the Equatorial
counter current (station 18). The development of phytoplankton is maintained here
by the fact that a certain quantity of biogenic elements from the deep layers get
into the zone of photosynthesis. In waters of moderate depth with unstable water
masses and almost complete absence of thermostratification in the uppermost layer,
biogenic elements get into the zone of photosynthesis as a result of mixing by
convection. The quantity of phosphates in the 0-120 m layer amounts to 0.1-0.2
mg-atoms P/M3. In tropical waters with average productivity, about the same
quantity of phosphates in the illuminated zone is m.aintained by turbulent mixing
of the surface waters with the deep waters by the action of eddy currents in the
surface waters in the zone of convergence o£ the Equatorial current and counter
current. The quantity of phosphates in this region at the very surface varies
from 0 to 0.1 mg-atoms P/W.
In the phytoplankton of this zone, diatoms and also the bluegreen alga
Oscillatoria thiebautii are of outstanding importance in composition and in
. numbers.
3. The
/ 2. These zone of tropical waters with a primary productivity of 0.1-0.2
igGym
waters are carried by the north Equatorial current (stations 14-17)
to the south Equatorial current (stations 23-36). The warm surface waters of
these currents move along a long path, not mixing with deep cold waters, and
they are very poor in biogenic elements. The quantity of phosphates in the 0-50m
layer is close to 0. However, deep waters are found here at a distance of 60-80 m
from the surface, and from them biogenic elements in small quantities penetrate
into the overlying layers as a result of turbulent mixing of the moving surface
waters with the deep waters at their boundary of contact.
- 13 4. The zone of transparent blue oceanic water with insignificant primary
productivity: less than 0.06g cAn 2. In this zone we may place the waters of
the north Equatorial current with the high temperature and the region of the
Sargasso Sea vortex. In this zone the water layer from the surface to a depth
of about 400 m is filled with mold" tropical waters of the Equatorial currents,
in which biogenic elements are almost completely absent and replenishment of
their stocks of these by mixing with deep waters is almost excluded.
In the phytoplankton of this zone peridineans are of greatest importance.
Literature
Semnagi, G. I. 1957. [On the question of patterns of vertical distribution
of plankton.] Trudy Vsesoiuz. gidrobiol. ob-va, Vol. 8.
Sorokin, Yu. I. 1956. [The use of C l4 for determining primary production.]
Trudy Vsesoiuz. gidrobiol. ob-va, Vol. 7.
Sorokin, Yu. I. 1957. Results of and prospects for using isotope carbon for
the investigation of the carbon cycle in water basins. Congr. Internat.
Conf. on Radioisotopes. Paris.
Sorokin, Yu. I. 1958. [Primary production of organid m.atter in the water mass
of Rybin Reservoir.] Trudy biol. stantsii %orok" AN SSSR, Vol. 3.
Sorokin, Yu. I., and O. I. Koblents-Mishke. 1958. [Primary production in the
Sea of Japan and a part of the Pacific Ocean. . .] Doklady AN SSSR,
Vol. 122, Nos 6.
Sorokin, Yu. I., and M. V. Kozlianinov. 1957. [Determination of the relation
[page 281] between photosynthesis of phytoplankton and illumination of the
water mass in the Sea of Japan and the Pacific Ocean.] Doklady AN SSSR,
Vol. 116, No. 5.
Sorokin, Yu. I., and O. I. Koblents-Mishke. 1958. [Primary production in the
Sea of Japan and that portion of the Pacific Ocean situated near Japan, in
the spring of 1957.] Doklady AN SSSR, Vol. 122, No. 6.
Harvey, H. S.
lit-ry.
1948.
[Biochemistry and physics of the sea.]
Izd-vo inostr.
Gurrier, R. I • 1957. Some observations on organic production in the northeast
Atlantic . Rapp. et precès-verbaux réunions, Vol. 144.
Hentschel, E.
Bd. 11.
1933. Allgemeine Biologie des Südatlantischen Ozeans.
Meteor,
Hentschel, E., and H. Wattenberg. 1930. Plankton und Phosphat in der
Oberflachenschicht des Südatlantisdhen Ozeans. Ann. Hydrogr. u. Mat.
Meteorol., Bd, 58.
Jespersen. 1937. Quantitative investigation on the distribution of macroplankton
in different oceanic regions. 1Dana"—Rep., N 7.
- 14 Lohman, H. 1920. Die Bev81kerung des Ozeans mit Plankton nach den Ergebnissen
der Zentrifugenfange warend der Austreise der "Deutschland", 1911,
zugleich ein Beitrag sur Biologie des Atlantischen Ozeans. Arch. Biontol.
Steemann-Nielsen, E. 1952. The use of radio-active carbon (C 14 ) for measuring
organic production in the sea. J. Conseil., Vol. 18.
Steemann-Nielsen, E., and A. Jensen. 1957.
"Galathea"-Rep., Vol« 1.
Primary oceanic production.
Sverdrup, H. U., M. W. Johnson and K. H. Fleming.. 1946. .The oceans, their
physics, chemistry and general biology. N. Y.
Thomsen, H. 1931. Nitrate and phosphate contents of Mediterranean water.
Danish Oceanogr. Exped. 1908-1910, Vol. 3, No. 6.
Thomsen, H. 1937. Hydrographical observations made during the "Dana" expedition.
"Dana"-Rep., No. 12.
Appendix
Table 1. [page 281] An example of the computation of 24-hour production of photosynthesis at station 6
under 1 m 2 of sea surface, from the primary data.
(Sk = 27.0 mg CA, r
K
Depth
K
r
Radio-activity
of algae on
the filters
(imp/A
K
t
r
Radio-activity
of algae on
the filters
(impte)
24O imp/i,:R =-3.36'x 10 6 imp/1):- .
Relative
rate of
photosynthesis
K
s
x K )
K
r
tt
Final
correction
coefficient
(K )
f
0
176
1.00
100
1.00
1.00
10
128
0.73
120
1.2
0.86
20
280
1.59
172
1.72
2.73
30
192
1:09
124
1.24
1.35
ri
50
160
0.91
62
0.62
0.56
0••
75
116
0.66
42
0.42
0.004
100
8
0.04
12
0.12
150
0
0
0
0
0.545
t
• 0,
00•
= relation of rate of photosynthesis to underwater illumination.
24-hour
production
under 1 m2
of surface
0.00204
0.167
• ••
• •
•
• • •
•o
•
•
ar o o
00
0 • 0
K r = relation of photosynthesis to vertical distribution of phytoplankton.
K
•
24-hour
production
in the sample
from the surfacé
mg/À9
9 0 •
• •0
- 16 -
Table 2 0 [pages 282-284] Results of determinations of the magnitude of primary
production of photosynthesis in the Mediterranean Sea and the Atlantic
Ocean.
24-hour
24-hour
Magnitude
production in
of the
production
the water
under 1 m 2 of
Situation of the Station Station coefficient,
sample
from
water surface
computed for
No.
(sea, oceanic current)
the surface
g C/in2
0-150 m
mgC/
Mediterranean Sea
Ia
II
III
IV
V
Va
North Atlantic current
1
2
Canary current
North Equatorial current
2a
3
3a
4
4a
46
5
6
7
7a
8
9
10
10a
106
11
lla
12
12a
126
13
13a
14
14a
15
15a
16
16a
Equatorial countercurreni
- .17
18
0.177
0.229
0.207
0.32
0.129
00•
0.241
0.312
000
Q.14
0.47
•dib•
O
OO
0.543
0.545
0.362
0.426
0.615
0.213
11,
00
O
00
O
00
0.435
00•
0.23
0.203
0.78
5.7
O
1.24
0- 11•
0.511
0.292
0.207
0.312
0.0013
0.00076
0.00059
0.0027
0.0206
0.0296
0.0297
0.034
0.023
0.0203
0.08
1.02
0.436
0.44
0.038
0.0135
1.39
0.67
0.0027
0.0050
0.0057
0.0105
0.0087
0.0061
0.0053
0.00204
0.0048
0.00165
0.11
0.11
0.124
0.76
0.62
0.431
0.0432
0.167
0.261
0.206
060027
0.0106
0.00434
0.0098
0.028
0.296
0.022
0 00495
0.0486
0.73
0.0292
0.00058
0.0022
0.00227
0.00255
0.00184
0.00211
0.00167
0.0036
0.173
0.98
0,158
0.358
1.022
1.085
1.43
1.76
1.68
2.81
3.41
0.495
0.415
0.424
0.185
0.133
0.092
0.073
0.114
0.0063
0.0078
0.197
0.37
continued.
- 17 -
Table 2 (cont'd)
Situation of the Station
(sea, oceanic current)
Station
No.
Magnitude
of the
coefficient,
computed for
24-hour
prpduction in
thé Water,-
sample from
thesurface
0-150 m
South equatorial current
North equatorial current
Sargasso Sea
North Atlantic current
18a
19
19a
20
20a
21
21a
216
218
22
23
24
24a
25
26
26a
600
0.8
000
1.52
...
0.481
400
OUD
...
0.347
0.91
0.751
000
0.77
0.77
...
27
28
28a
29
29a
0.188
0.55
...
0.815
30
30a
31
31a
32
33
34
34a
35
36
0.426
36a
37
37a
38
39
39a
40
41
42
43
43a
...
0.73
000
000
1.4
...
0.61
0.64
0.63
...
0.346
0.67
eoe
0.83
0.37
0.43
0.63
0.56
0.395
0.57
...
24-hour
pi.oduttioni
under 1 m 2 of
water surface
g C/M 2
0.00117
0.00092
0.0008
0.00083
0.00143
0.000475
0.00035
0.0044
0.0059
0.000605
0.00102
0.0012
0.0013
0.00056
0.000505
0.0011
0.141
0.051
0.16
0.189
0.028
0.032
0.024
0.311
0.401
0.347
0.141
0.136
0.156
0.064
0.057
0.0315
0.0013
0.000097
0.00071
0.00131
0,00097
0.0294
0.008
0.086
0.172
0.0585
0.0066
0.0008
0.00018
0.000109
0.00092
0.000134
0.00069
0.00056
0.00019
0.00134
0.040
0.051
0.038
0.0099
0.085
0.0138
0.065
0.029
0.010
0.102
0.0045
0.00124
0.00264
0.00136
0.00162
0.00292
0.0057
0.00125
0.0036
0.00535
0.007
0.45
0.136
0.326
0.17
0.09
0.19
0,54
0.114
0.216
0.455
0.33
continued
- 18 -
Table 2 (cont'd)
Situation of the Station
(sea, oceanic current)
Station
No.
Magnitude
of the
coefficient,
computed for
0-150 m
English Channel
North Sea
44
44a
45
45a
46
47
0.29
48
49
49a
496'
0.26
0.18
49B
0.376
0.335
0.135
0:
0
•
•••
24-hour
24-hour
production in
' the water.
sample 'from
production
under 1 m 2 of
water surface
g CAl2
#.1eAurfabe
mgC/5r
0.0057
0.0046
0.0054
0.013
0.0153
0.435
0.25
0027
0.308
0.57
0.765
0.88
0.129
0.017
0.067
0.131
0.51
0.32
1.8
3.5
0.0134
0.36
ezzabeipeeNce ezect
Fig. 1.
2671 Diagram of the setup for
filtering.
[The sample being filtered is on the
left; the tube at right goes to an
air pump.]
[page
100
Fig. 2.
200
2701 Graphical representation
of the adjustment coefficient K r ,
Kt and Ks Mp,M7,14to] as measured
at station 6%
[page
Fig. 3.
[page 2701 Map of the route of the Sedov and the trend
of the Primary productions measured along the route.
0 05 10 5 P me - amcw
0 05 la 15 2b 4 t
"
0
'
.
'
'
'
20 -,
.
ts" 60
80
;
b
MW
.
%
•
120
100
Cm .210
Cm 262
Cm 268
rpennala
10.11iuge 81damo- -repeulenbieft
flpu6pealciebie8oe Cellepeoe
vacmb letwea 8k- Cupeaccoda ewe
puctebnoe
(y *urea)
Oirdamopienbffoe
damopueibmmeyelluR
1778velfue
inechwe
Fig. 4.
p
age 272) Vertical distribution of phosphates
ontinuous line) and changes in the density of the
water (i ei) in various regions of the Atlantic (from
Hentschel and Wattenberg, 1930). [Top scale-phosphorous in mg-atoms; scale below it—density.]
0,5
1,0
„
0
0
•
/-;
liziarnee
\
200 -
ka
It
■
\I
\ff
1
1
so-
[page 274] Vertical distribution of
phosphorous in the Sargasso Sea (Dane
station No. 3542--curve I) and in the
North Atlantic current (Dana station
No. 4158--curve II) (Thomsen, 1937).
Fig. 5.
j
.
.70
tun 1110,e
i00% 100% 0%
11
tz
.
(J10
/00%
ton ton
/00%/88%
..
.
1.10
0
341
9
60
(9e .
90
120
1.50
Fig. 6.
I
t
III
LY
Relation between rate of photosynthesis
and the penetration of light (Kt) in different
regions of the Atlantic Ocean.
Uhe Arabic numbers in each panel are Sedov station
rumbers.]
!!
[page 275
]
zo
t
foe
Ceeptioe JhBarnopu, Pegepo- fimearemuve
anbuoe memeoue
ckoe movernie
Fig. 7.
Fig. 8.
[page 2761 Vertical distribution of
active phytoplankton, K r .
Continuous line --(Kr ); broken line-changes in water density (A ei.).
Left panel--waters of the north
equatorial current; rlght panel—
North Atlantic current.
[page 2771 Relation between photosynthesis
and light penetration (Kt) at station 6.
The continuous line is Kt, and the broken
line is the coefficient of underwater
illumination (/).
100X
ego
10070
/00%
10
27
20
1
30
.
•
‘‘z1
50
•
60
/
I
90
'00
(
•
1I
.
•//
70
80
/w/
/
te qg
f
f
1
/
I
1
I
/
i
I 0m81
eing
n77.12 (. e
•
C177. 12(11V
Fig. 9.ble_22110 Relation between photosynthesis
and light penetration (Kt), starting from
the level of greatest rate of photosynthesis.
Solid line—et; broken line --coefficient of
underwater illumination (1).
lb H 2
150 1,5
F
125
1 25
-a100 10
4.
75 0,7 •
a 50 05 a
a
to
a.
25 . 0,25
✓
• a.
rr
•..
Id
B.
h
u
17/
58
12 18 20 23 25 27 29 30 31 32 33 39 35 35 37 38 39 1/0 Ill 113 /Ill 115 le
Cape:woo& mope
Time/came Bed/
flegepo - enwevmelecee
Ifffeapcleoe
Inevelltie
npokliamopllanômaimavb,
megewel
Fig. 10.
Results of concurrent determinations of primary
productivity and zooplankton biomass in the Atlantic Ocean.
1--primary production under 1 m 2 of water surface, in grams
of C per m2 per 24 hours; 2--biomass (in g) of zooplankton
under 1 m 2 of water surface in the layer 0-200m.
[page 2791