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Chemical oceanography and primary productivity in upwelling regions
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Chemical Oceanography and Primary Productivity Chemische Ozeanographie und Primiirproduktion OcCanographie chimique et productiviti d’eau froide
R. C. DUGDALE,
in Upwelling Regions des Meeres in Auftriebsgebieten
primaire marine dans des rbgions de remont6e
Seattle*
Abstract: Features of the circulation, uptake, and regeneration of particularly nitrogen, phosphorus, and silica in upwelling regions are discussed in the light of recent contributions to nutrient uptake and regeneration theory. Emphasis is placed on the critical role of silica in the productivity of coastal upwelling areas and the resulting usefulness of this element as an indication of the recent history of circulation and production processes in an upwelling area. The significant contribution of herbivore regeneration to the nutrient regime of an upwelling area is described. Data from the Peru coastal upwelling system are discussed and interpreted in view of the physical and biological processes considered in the paper. Zusammenfassung: Merkmale der Zirkulation, Nahrstoffaufnhame und Regeneration, insbesondere von StickstoffPhosphor- und Silikatverbindungen in Auftriebsgebieten werden nach den Erkenntnissen aus jiingsten BeitrZgen iiber Nzhrstoffaufnahme und Regeneration diskutiert. Besondere Aufmerksamkeit wird der kritischen Rolle des Siliziums in der Produktivitit kiistennaher Auftriebsgebiete und der Brauchbarkeit dieses Elementes als Indikator in neueren Untersuchungen von Zirkulations- und Produktionsprozessen in Auftriebsgebieten gewidmet. Es wird der bemerkenswerte Anteil der Regeneration der Pflanzenfresser am Nrhrstoffhaushalt in Auftriebsgebieten beschrieben. Zahlenwerte aus dem System des peruanischen Auftriebs werden in diesem Aufsatz diskutiert und im Hinblick auf die physikalischen und biologischen Prozesse gedeutet.
1. introduction The basic relationships between the composition of sea-
shows clearly that large variations from these basic pat-
water and the growth of phytoplankton
terns of interaction can be expected. Departures from
for some time. The work of HARVEY
REDFIELD
and co-workers
(e.g.
have been clear (1963) and of
REDFIELD,
KETCHUM
average conditions are especially apparent in areas of high primary production, and consequently in coastal
ing of the basic interactions between algal growth and
upwelling regions the real-world situation is considerably different from the conventional view of chemical-biologi-
seawater composition and the references given above should be consulted as fundamental. While the concepts
cal processes in the sea. In this paper, the dynamic structure of chemical-biological interactions in coastal upwell-
and RICHARDS,
1963) has produced a broad understand-
ing is outlined. Emphasis is placed upon the inorganic
developed by these and other investigators continue to be valid in dealing with large areas of the oceans and long periods of time, the detailed understanding being developed of the processes - both of water circulation and
of uptake and regeneration are now reasonably well known for these nutrients and this knowledge may con-
the physiology of nutrient uptake and regeneration -
tribute to the analysis of other lesser known processes.
*
A basic objective of the paper is to put aside ideas that primary production in coastal upwelling regions can be described completely in terms of simple advection to the
Dr. R. C. DUGDALE, Department of Oceanography, University of Washington, Seattle, Wash., 98195, USA. Contribution No. 604 from the Department of Oceanography, University of Washington. This work was carried out as a part of the U. S. effort in the International Biological Program; was sup ported by National Science Foundation Grants 68-20182 and GB-18568.
forms of nitrogen, phosphorus, and silica, as the processes
surface of nutrient laden deep water, followed by phytoplankton uptake.and growth. I am greatly indebted to Mr. James I. ANDERSON for many stimulating discussions, especially concerning the problem of silica circulation in upwelling regions.
48
2,
2.1.
Geoforum 11172
Factors Affecting the Nutrient Content of Surface Waters
portant to remember that the shape of the nutrient pro-
Circulation
files above the pycnocline is influenced strongly by biological and physical events in an upwelling region and is
particularly phosphate, nitrate, and silicate. It is im-
areas is given by SMITH (1968). In Fig. 1 a diagram of the Benguela Current region is used to show upwelling
not merely a reflection of source water conditions. ldeally, to compare the effects of different characteristic nutrient profites on euphotic zone nutrient concentra-
features common to it and other regions of coastal up welling. While considerable variation can be expected to
tions in upwelling areas, profiles from the different major upwelling systems should be used. However, the profiles
occur in different upwelling systems, the diagram can be
shown in Fig. 2 serve to demonstrate the importance of the origin of upwelling water. It is immediately apparent
A recent review of circulation processes in upwelling
used to illustrate the possible physical modifications of deeper water prior to arrival in the euphotic zone. First, it can be seen that the origin of the upwelling water may be on or off the shelf and the source depth may vary considerably, from depths of perhaps 200-400 m up to pycnocline depths. Several mixing processes then alter the composition of the source water. The diagram indicates the presence of vertical circulation cells, one means by which mixing and recirculation of upwelled water may occur. Regions of horizontal shear in the surface waters between the large plumes and a corresponding backflow upstream also undoubtedly are characterized by strong mixing as well. The nature of the upwelling sources and mixing processes further are influenced by the position of the deep compensating current, which may move cioser to the coast and sometimes rise' onto the shelf.
in all the three major oceans that above about 200 m, relatively small changes in the depth of an upweliing source can lead to significant differences in nutrient concentrations and production in the upwelled water. Likewise, it is apparent that a cubic meter of water upwelied in the Atlantic Ocean would result in a considerably smaller crop of phytoplankton than the same amount of water upwelled from the Pacific or Indian Ocean, since the general levels of nutrients in the sub-surface water are higher in the last two. The most striking differences are seen in the silicate profiles, where the poverty of the Atlantic in this compound is readiiy seen and the wellknown tendency for silicate to reach higher concentrations in the lower depths than do nitrate and phosphate is illustrated. Silicate, although much neglected since it
The ~herni~a~ and biological significance of the geographi-
is required only for diatoms and not for the other important phytoplankton, appears to be a key nutrient in upwelling production systems (ZUTA and GUlLLEN,
cal and vertical variations in the sources of upwelling water is related directly to the concentration profiles of
1970), a point that wilt be treated further in succeeding sections. A consequence of the accumulation of silicate
2.2.
Nutrient profiles
Fig. 1 0 A representationof upwelling processes in the BenguetaCurrent region (from HART and CURRIE, 1960). The circulation illustrated is apparently typical of coastal upweiling. * Der Auftrieb im Gebiet des Benguelastromes (nach HART und CURRIE, 1960). Die dargestetfte firkulation ist typisch fiir den Auftrieb in Kiistengebieten.
Geoforum 11/72
49
i, 1 20to
N03-
-N (ug - atoms/liter)
Silicate (pg- atoms/liter)
Fig. 2 l
The vertical distribution of phosphate, nitrate, and silicate in the three major oceans (from RICHARDS,
l
Die Vertikalverteilung
von Phosphat, N&at
und Silikat in den drei grol3en Ozeanen (nach RICHARDS,
1968). 1968).
at depth is that the nitrate/silicate ratio generally de-
especially with depth, between nitrate/silicate vs & plots
creases with depth. Deviations from this norm can be
from non-coastal upwelling and from coastal upwelling
used to detect processes affecting one or the other nu-
situations.
trient. For example, in Fig. 3a-q 6, is plotted against nitrate/silicate ratios. These plots were made from data obtained in several regions of the Pacific Ocean as indicated in the figures. The rapid rise in the nitrate/silicate ratio near the sea aurface, resulting from nutrient recycling within the euphotic zone in the region of coastal upwelling in Peru, is shown clearly in Fig. 3a. This SWface effect is not seen in the Coasta Rica Dome upwelling region (Fig. 3b) and is not so apparent off northern Peru (Fig. 3~). Below the surface region of mixing and uptake by phytoplankton,
a slower decrease in ratio occurs
2.3.
Nutrient uptake
The general principles of nutrient uptake and regeneration are given in the paper by REDFIELD er al. (1963). Briefly it appears that the mean atomic ratios of uptake (based on plankton composition ratios) of carbon, nitrogen and phosphorus are 106:16:1 and that the regeneration ratios in water below the euphotic zone are about the same. Silicate regeneration appears to be slower, accounting in part for the relatively slow but continuous increase
(Fig. 3a, b, c), reflecting the continuously increasing concentration of silicate with depth beyond the point where
of silicate with depth. The uptake of silicate is not so well known but it may be taken up, relative to carbon
nitrate and phosphate have reached the maximum values seen in Fig. 2. The slow decrease with increasing depth may be interrupted when denitrification, the reduction of nitrate to nitrogen gas, sets in at very low oxygen concentrations, with the result that the nitrate/silicate ratio reverses its trend and goes through a minimum value as shown in Fig. 3a, b. The absence of a denitrification hook is illustrated in Fig. 3c, plotted from data taken from northern Peru waters. The data taken in the Costa Rica Dome region (Fig. 3b) are included to show the similarity,
and phosphorus, in approximately nitrate.
the same ratios as
The uptake processes, when studied on physiological time scales, are by no means so regular and predictable as the above ratios might imply. Although the work has only begun, working primarily with inorganic nitrogen, the pattern of nutrient uptake is becoming known. Details can be found in DUGDALE (1967), EPPLEY et al. (1969), and MaclSAAC and DUGDALE (1969). Briefly, the uptake by phytoplankton of a limiting nutrient is described
50
Geoforum 11/72
81 d I
i
aoi
I
24.m
X50
1
25.00
I
25.50 Stgma -
I
100
1
26.50
/
2700
1
2750
T
--I
Fig. 3b
81 0
1
2L,00
marine phytoplankton I
2L.50
I
2500
I
25.50 Sigma-T
I
26.00
I
26.50
t
I
27W
n.50
trate
for a number of species. Comparable experiments with limiting phosphate have not been made and experi-
Fig. 3a
by the following Michaelis-Menten
expression which also
describes transport across the membranes of bacteria and other non-photosynthetic
populations. Batch culture experi-
ments done with individual species by EPPLEY et 01. (1969) have given the K, values for ammonium and ni-
organisms (MONOD,
1942).
ments with limiting silicate have been fruitless until recently. However, Michaelis-Menten kinetics have been seen to be obeyed by Skeletonema costatum grown under silicate limitation in algal chemostats (HARRISON, DAVIS,
and DUGDALE,
unpublished).
Application of this kinetic information to the understandwhere V
= specific uptake rate of the limiting nutrient, units in time-r.
vmax = maxjmum specific uptake rate. s
= concentration of limiting substrate.
KS
= limiting substrate concentration for V = V,,x/2.
The Michaelis-Menten expression describes a rectangular hyperbola, a saturation curve as shown in Fig. 4. Such curves have been found by MaclSAAC and DUGDALE (1969) in experiments with r5 N tracer compounds to apply to ammonium and nitrate uptake by some natural
ing of phytoplankton productivity in upwelling or other regions of the sea requires more information than presently available, especially in the areas of nutrient interactions. However, from results of chemostat experiments with Skefetonemu costut~m (CONWAY, DAVIS, HARRISON, and DUGDALE, unpublished) the following tentative summary can be made for that species, and by extrapolation and from observations at sea, for other fast-growing diatoms. 1. Approximate
kinetic constants:
vmax = 0.18 KS@%)
hr-’
= 1 pgAt/l
K,(NQ)
= 1 PgAtf)
‘K s(SiO4)
= 1 I.cgAt/l
Geoforum 11/72
51
SFig. 4 Nutrient uptake as a function of nutrient concentration, according to the Michaelis-Menten expression. Terms are discussed in the text. Nahrungsaufnahme als eine Funktion der N4hrstoffkonzentration nach dem MichaeliLMenten-Ausdruck. Bweichnungen sind im Text erlgutert.
2. Interactions: a) Growth on limiting nutrient results in drastically lowered uptake and use of that nutrient; for example, silicate per cell is reduced to as little as 10 % of that
+
Q, x00
I
1
I
2150
zso
2550 Sipma-
4
I
2SJxl
I
2650
I
2700
1 2250
Fig. 3c
achieved under saturating silicate concentrations. Approximately the same reduction in nitrogen uptake and content is seen under nitrogen limitation, accompanied by a drastic decrease in chlorophyll content. b) The uptake of nitrate is influenced strongly by ambient ammonium concentrations of the order of 1 MgAt/l. Apparently the effect is to reduce V,, ~0~ as a function of increasing ammonium concentration (CONWAY, unpublished). The uptake of nitrate also is coupled
Fig. 3
strongly to incoming visible radiation (MaclSAAC and DUGDALE,
l
l
The nitrate/silicate rat-m plotted against ot for three areas in the eastern Pacific Ocean: (a) all stations from the Peru coast taken during PISCO, (b) 26 stations taken in the Costa Rica Dome area (about 10 ON, 90 “w) on Thompson cruise 26 in February 1968, and (c) stations taken near the northern Peru coast on Anton Bruuff 1s. Das Nitrat/silikat-Verhgltnis gegeniiber der Dichte ot fiir drei Regionen im iistlichen Pazifischen Orean: a) alle Stationen vor der peruanischen Kiiste wrhrend des PISCO-Unternehmens, b) 26 Stationen im Gebiet des Costa Rica-Auftriebs (etwa 10 ON, 90 “W) auf der Thompson-Fahrt 26 im Februar 1968 und c) Stationen vor der nordlichen peruanischen Kiiste auf der Anton Bruun-Fahrt 15 (Mlrz/April 1966).
1972). Both factors are incorporated
into a submodel developed to predict nitrate uptake in the Peru upwelling region (DUGDALE and MacISAAC, 1971). 3. Ratios of uptake: Two extreme nutrient conditions can be considered in terms of the above. In one case, with all nutrients in excess, uptake ratios something like the usual composition atomic ratios might be expected. In the second, where one nutrient becomes limiting with all others in excess, the uptake ratio of excess nutrients to limiting nutrient will rise drastically. Intermediate condi-
Geoforum 11/72
52
tions with one nutrient limiting growth and others at concentrations less than those allowing maximum
up-
take rates would be expected to result in intermediate ratios, although this area is not well documented. The composition of algae in batch cultures often has been
the problem of micro-nutrient availability in relation to upwelling, and further reference will be made to their
seen to change as deficiencies develop in the medium (REDFIELD
etu/., 1963) and now it is possible to
coriclusions in a following section.
observe the effects of deficiency directly on uptake. Uptake ratios observed by CONWAY,
In this discussion of primary nutrient uptake, the assumption has been made that trace metals and other microconstituents are available to the phytoplankton in the necessary amount but not at such high concentrations as to be inhibitory. BARBER et a/. (1971) have discussed
DAVIS and
2.4.
HARRISON (unpublished) in chemostat cultures of Skeietonema costatum under nitrogen and silica
Nutrient regeneration
Nutrient regeneration in an upwelling region takes place primarily through two processes, bacterial regeneration at the sediment-water interface and in the water column, and by grazing activities of herbivores. The importance of the latter thus far has not been included in discussions
limitation are given in Table 1. Clearly, the concept of a universal uptake ratio is erroneous when dealing with real populations of phytoplankton encountering varying ambient nutrient concentrations.
of nutrient processes in upwelling waters (e.g. JONES, lq71; CALVERT Table 1 0 Nutrient nutrient
In Fig. 5, the circulation of the primary nutrients, phosuptake
ratios for Skeletonemu
limitation
from CONWAY, 0 Verhaltnisse costutum
and PRICE, 1971).
DAVIS,
bei 18 %(unverijff.
Doubling time
grown under
at 18 ‘C (unpublished
data
NBhrstoffe
der N;ihrstoffe
N:Si:P (atoms)
(hrs)
fiir Skeletonemu
authors found that about half of the nitrogen primary
in AlgenChemostaten
Werte von CONWAY,
itation
DAVIS
Nitrogen Doubling time
und HARRISON).
Limitation N:Si:P
tion can be made in nature with nitrogen since both
(atoms)
species of nitrogen are used by phytoplankton, and ammonium is rapidly regenerated. For the purposes of dis-
(hrs)
11.3:1.2:1.0
26.6
2.8:2.3:1.0
19.8
11.6:1.4:1.0
21.6
3.2:2.6:1
16.9
10.7:1.4:1.0
16.5
4.1:2.9:
13.8
9.0:2.5:1.0 11.2:1.3:1.0
mean ratio
production was new production, i. e., based on nitrate uptake, and the other half was regenerated production, i.e., based upon ammonium. From Fig. 5 and DUGDALE and GOERING (1967) it can be seen that such a distinc-
36.4
mean ratio
up-
welling region. Details of the flow of nitrogen in the Peru upwelling system can be found in DUGDALE and GOERING (1970). Using the “N tracer technique these
and HARRISON).
der aufgenommenen
bei Begrenzung
Silica LI
cosfutum
in algal chemostats
phorus, nitrogen, and silica, is diagrammed for an
3.3:2.6:1
.O 1 .o
.O
cussion in this paper, the euphotic zone nitrogen supply will be considered as based entirely on nitrate, with ammonium regarded as a derivative of that compound. It is not possible to distinguish between new and regenerated phosphorus uptake as it is for nitrogen, because
Fig. 5 l The approximate phosphorus,
pathways
nitrogen,
circulation,
and biological
take and regeneration
of
and silica up-
in an up-
welling region. l Schemata
der AblZufe
Phosphor-,
Stickstoff-
Siliziumzirkulation biologische Regeneration triebsgebiet.
in der und
sowie die
Aufnahme
und
in einem Auf-
53
Geoforum 11 f72
as shown in Fig. 5, distinct ionic species do not appear to be produced in the regeneration of phosphorus. As far as is known, silica regeneration results in ionic species not recognizably different from the Si04 supplied from newly upwelled water. However, silica regeneration takes place within the water column at such a relatively slow rate that all silicate taken up in the euphotic zone may be considered as new. Although the fractions of regeneration attribu~ble to herbivores and to bacterial action witl vary from region to region, the analysis of DUGDALE and GOERING (1970) and the experiments reported by WH lTLEDGE and PACKARD (1971) show that regeneration of nitrogen and phosphorus by the anchoveta populations in the Peru upweliing system take ptace at such high rates that the anchoveta must be the ~minant regenerators there. Direct silica regeneration was found to take place through anchoveta grazing activities at 1O-20 % of the rate for nitrogen. Table 2, reprinted from WHITLEDGE and PACKARD (1971), summarizes these regeneration
lb I
76”W
l
1
LO’
20’
Fig. 6
measurements.
0 Sampling grid used on the PISCO cruise to Peru (March-April 1969). Grid squares are five nautical miles on a side; CM denotes current meter locations.
Table 2 l Excretion rates of the Perucian anchovy (Engroulis
ured during P&CO (from WHITLEDGE
ringens) meas-
and PACKARD,
1977 ).
0 Aus~he~u~sraten des peruanischen Anchovis (Engroutis ringem) wiihrend der P&CO-Expedition (von WHITLEDGE and PACKARD, 1971). Excretion Product
dLO’
Number of Measurements
fig-at/g dry wtlhr
kbg_at/g body N/hr
* Stationsraster auf der PISCO-Fahrt in die peruanischen Gew&ser (M&z/April 1969). Die SeitenlTnge des Rasterquadrates bett%gt 5 Seemellen; CM bezcichrtet die Positionen der Strommesser.
progress. The upwelling water outcropping near the shore appears to come from the upper 75 m, at least along the
Ammonia-N
7
4,47
40.6
line determined by the five stations. This water is further identified (Fig. 7c) by its low (for surface water) nitrate/
Creatine-N
7
3.37
30.6
silicate ratio (1.6-2.4)
it. The distribution of water by nitrate/silicate ratio in bands along the coast is a useful characteristic in terms of
Urea-N
3
3.29
29.9
Phosphate-P
7
2.84
25.8
Silicate-Si
7
0.64
5.82
relative to the water seawards of
all aspects of the analysis of an upwelling system. The downward trends of the isotherms and isopycnals (Fig. 7a, b) beginning at about 75 m indicate the presence of
3.
of the Nutrient Regime in the Peru Coastal Upwelling Region
Generation
the Peru Undercurrent flowing southward (WOOSTER and G ILMARTIN, 1961). Current meters set at locations marked on the grid (Fig. 6) as CM-l and CM-2 during
The conditions and processes discussed in the preceeding section and their results and interactions can be illustrated
PISCO showed flow to the southeast below 25 meters, while the surface drift as shown by parachute drogues
using data obtained from the same area on the coast of Peru
was to the northwest over most of the grid (SMITH et of.
on Anton Bruun Cruise 15 and T. G. Thompson Cruise 36
1971). The undercurrent can be recognized in Fig. 7c, d, and e, respectively, from low nitrate/silicate ratios,
(PISCO). Most of the data used are from the PlSCO expedition from a location on the south Peru coast near Cabo Nazca, 15 “S latitude. The grid shown in Fig. 6 was occupied with a iarge series of stations on this cruise. 3.1.
Circulation and vertical distribution of nutrients
The sections (95 km long) shown in Fig. 7 (a-h) were made along line 12 of the grid out from Pt. San Juan (Stas. 14-18). The on-shore upward trends of the isotherms and isopycnais (Fig. 7a, b) reflect upwelling in
low oxygen levels, and high nitrite concentrations. These three parameters reflect the denitrification that had occurred or was occurring in the undercurrent water or adjacent sediments according to ev.idence given by GOERfNG (1968), FIADEIRO and STRlCKLAND (1968), and GOERlNG and PAMATMAT (1971). The effects of both upwelling and the Peru undercurrent are seen in the distribution of nitrate, silicate, and phosphate concentrations as well (Fig. 7f-h).
I 90
60
75
ttam mow
olrt.“c*
30
45
+
150
0
‘6
wrl,
. I1 4
Station Wumbw*
. . .
.
2L3
.
. .
IL
150
.
.
.
l
-01 .
l
I 01
i 01
i
i
.
.
I
.
200
\
0’
/
.
264
1
.
z
303
g s
.
.
L
i
D6
.
, 90
I 75 Oistmc*
from
*honoun)
O~s*wtcc
from
rhwr(km)
d)
b)
Fig. 7 0 The distribution
360
of (a) temperature,
section made during PISCO,
(b) ot, (c) nitrate/silicate
extending
ratio, (d) oxygen,
(e) nitrite,
(f) nitrate,
about 95 km out from the coast in the Peru upwelling
with solid circles. The stations were taken over a 16 hr period.
(g) silicate, and (h) phosphate
region. Locations
in a
of data points are shown
SMii 10
Nmlbur 17
(5
16
I4
.
.
.
;a$_ . .. .
.
.
.
.
.
.
.
. .
l
.
1
.
.
.
S104,pg-~tomrll1t*r
.
.
. 400
NO2 .pg-dom‘,Li*.r
105
460
I
90
75
60 45 Dtrtancr tram shore (km)
20
15 6)
0
50 2.2 .-’
.
l
IO0
150
150
.
200
ZOO
.
250
260 P04.p9-a9omr/Llln .
a
F 300 z‘I
300; ;
c:
360
360
.
.
400
400
Owance
60 45 tramshare (km)
450 30
15
1
90
,
75
460 60
46
30
15
0
Fig. 7 Die Verteilung von (a) Temperatur, (b) Dichte ot, (c) Nitrat/Silikat-Vsrhgltnis, (d) Sauerstoff, (e) Nitrit, (f) Nitrat, (g) Silikat und (h) Phosphat auf einem Schnitt wghrend des PISCO-Unternehmens, der ungefdhr 95 km von der K&e in das peruanische Auftriebsgebiet hineinreicht. Positionen mit Wertangaben sind durch schwarze Punkte gekennzeichnet. Die Stationen wurden wghrend einer Dauer von 16 Studen durchgefiihrt.
Geoforum 11/72
56
3.2.
Distribution of nutrients and temperature at the surface
A set of surface maps of temperature, chlorophyll, nitrate, silicate and nitrate/silicate ratio are shown in Fig. 8a-e. These figures were abstracted from maps produced on board the J~u~~~~n during PISCO, using an automated data system receiving thermister, fluorometer, and automatic chemical analysis data. Water was pumped from a depth of 3 m as the ship steamed over a prescribed path. Data points were recorded at one minute intervals, punched onto paper tape, and read into an IBM 7 130 computer. After computer processing, the contours were drawn under computer control on a CalComp plotter. The maps were available within hours of the completion of a survey track. The maps shown in Fig. 8 reveal the plume structure of the center of upwelling studied on the PISCO cruise. These and maps from other passesover the grid (Fig. 6) on the same cruise have been described and analyzed in detail by WALSH et al.(1971). This analysis showed the cold center in the vicinity of grid point A8 (Fig. 8a) and the plume orientation to the northwest to be persistent features. The cold temperatures exhibited at the origin of this plume (Fig. 8a) are seen to correlate spatially with the highest nutrient concentrations (Fig. 8c, d) and the lowest chlorophyll (Fig. 8b). just to the north of this outcrop of upwelled water some southward flow occurs resulting in a persistent front that can be seen in the figures as restricting the northward expansion of the plume. The primary nutrients generally decline in the direction of mean flow of the plume to the northwest due to uptake and mixing, resulting in concentric bands of concentration distribution. Differential uptake and regeneration processes, mixing, and decreased depth of upwelling source combine as well to produce the concentric bands of nitrate/silicate ratio shown in Fig. 8e.
3.3.
Uptake of nutrients along the axis of an upwelling plume
The data obtained on Anton Bruun Cruise 1.5 (RYTHER et (II., 1970; DUGDALE and GOERING, 1970) substantiate the sequence of nutrient uptake and regeneration developed earlier in this paper. In the Anton 5ruun work, a drogue was placed in cold, nutrient-rich water near the coast where upwelled water was arriving at the surface. The ship followed the drogue for five days and the change in phosphate, nitrate, silicate and ammonium concentrations was observed (Fig. 9a-d). Silicate decreased to undetectable levels in a reasonably regular way, while considerable nitrate remained at the fifth day. The phosphate concentration clearly was maintained by regeneration, and the same is true for ammonium which actually increased in the course of the experiment. The changes
Geoforum 11/72
I
ls-
ND3 I SiO,
4
4
Fig. 8 The surface (3 m) distribution during a single night survey of (a) temperature, (b) chlorophyll, (c) nitrate, (d) silicate, and (e) the nitrate/silicate ratio over a portion of the PISCO sampling grid in the Peru upwelling region.
75’
Die Oberfilchenverteilung (3 m) fiir (a) Temperatur, (b) Chlorophyll, (c) Nitrat, (d) Silikat und (e) das Nitrat/silikatYerhiltnis
wBhrendeiner einzigenNachtaufnahmefiir einen Abschnitt des PISCO-Unternehmensim peruanischenAuftriebsgebiet.
in concentration observed were the result of uptake, regeneration, and the advection of additional upwelling water from below (not necessarily so rich as the water outcropping at the origin of the plume, e. g. see Fig. 7 f-h) making the computation of ratios of change between these nutrients a virtually meaningless exercise. However, measurements of nitrate and ammonium uptake were made and provide the basis for a partial analysis of the processes taking place. The total inorganic nitrogen up take appeared to be correlated closely with the concentration of silicate (Fig. 10). The shape of the curve in Fig. 10 is linear over the time span observed; however, further reductions in total inorganic nitrogen uptake might be expected in some fairly short time following the exhaustion of silicate. SiOL.pg-
otcms/lit*r
Looking at the PISCO nutrient distribution in Fig. 8, it appears that the analysis DUGDALE and GOERING (1971) applied to the Anron Bruun data holds at least generally for the plume mapped on the Thompson. Where
58
Geofotum t l/72
Phosphate
20c
0
i
L
5
I
10
4
t5
20
SiO,,@g-atoms/Liter Fig. 10 l The relation of total inorganic nitrogen uptake to silicate concen-
tration observed during the Anton Bruun Peru drogue experiment (50 % light-penetration depth). Station numbers are shown for each observation
Nitrate
l Dar Verhaltnis der Ge~mtaufnahme
von anorganischem Nitrat zur Silikatkonzentration nach Beobachtungen wahrend des Peru-DriftExperiments von Anton Bruun (in Tiefe von 50 % Lichtintensitat). Die Stationsnummern sind fi& die einzlenen Beobachtungen angegeben.
the plume meets the western edge of the grid, silicate has been reduced by 75 % from the source concentration, nitrate by about 50 %, and phosphate (from station data) by only about 30 %. Sufficient measurements of ammonium concentration and uptake are not available, but it appears likely that the total inorganic nitrogen uptake on the PISCO cruise would show a relation to silicate concentration similar to that seen on the Anton Bruun cruise. The partition of nitrogen uptake between ammonium and nitrate was regulated by the ambient ammonium concentration during the Anton Bruun experiment, as shown in Fig. 11. The ratio of the maximal specific uptake rates for nitrate and ammonium is a linear function of the ammonium concentration. As ammonium concentration increased, down plume in this case, nitrate uptake was re-
a’
I
6
’
1 Fig. 9
’
12 18
I
6
I
I
I
t
L
6 12 18 12 18 3 2 time and day
,
6
h
I
12 18 G
I 6 5
* Changes in concentration of (a) phosphate, (b) nitrate, (c) silicate, and (d) ammonium observed in a five-day period on Anton Bruun cruise 15 (March-April 1966), as the ship followed a drogue in Peruvian waters (50 % light-penetration depth). l Anderungen in der Konzentration
von (a) Phosphat, (b) M&rat, (c) Silikat und (d) Ammoniak beobachtet fiir die Dauer von fiinf Tagen auf der Anton Bruun-Fahrt 15 (M&/April 1966) als das Schiff einen markierten Fleck in den peruanischen Gewassern verfotgte. (Gemessen in Tiefe mit 50 % Intensitat des Tagesiichtes.)
duced and replaced by ammonium uptake. This linear relationship also has been observed in the Mediterranean Sea under conditions strongly influenced by a sewage outfall (MaclSAAC and DUGDALE, 1972), and probably can be considered to be generally applicable where ammonium and nitrate occur together in the sea. Barber et u/. (1971) made experiments during PISCO showing that on some stations natural chelators apparently were missing resulting in severe reductions in measured nutrient uptake and photosynthesis. In these cases, the differences between conditioning correlated well with differences in water masses. When the upwelled water
Geoforum
11/72
59
the basis of anchoveta
schools with a density of 100 fish per m3. Based on this school size, the results suggest that
the integrated daily ammonium uptake by phytoplankton under a m2 can be supplied by regeneration in 2 hours.
34
Creatine, occur at order of observed 3.5.
1
0'
0.5
1.0
1.5
2.0
25
3.0
Nitrate/silicate
ratios in new surface waters
Since silicate appears to behave as a virtually non-regenerated nutrient in upper waters, it may be used as a reference nutrient. plotted
NH,+-N,ug-atoms/Liter
urea, and phosphate excretion were found to about the same rates as for ammonium, on the OS-O.8 pg-At/liter/hr. Silicate excretion was to be about 0.1 pg-At/liter/hr.
For example,
the nitrate/silicate
in Fig. 12 against silicate concentration
ratio is at depths
Fig. 11 l The dependence on ambient ammonium concentrations of the
relative contributions of nitrate and ammonium uptake to total inorganic nitrogen uptake, as observed during the drogue experiment on the Anton Bruun cruise to Peru. Station numbers are shown for each observation. x Stab3 . Sta.66
0 Die AbhJngigkeit der relativen Beteiligung von Nitrat- und Ammoniakaufnahme an der Gesamtaufnahme von Nitrat von der Ammoniakkonzentration der Umgebung nach Beobachtungen wghrend des Drift-Experiments auf der Anton Bruun-Fahrt vor Peru.
2.5
was from the north, i.e., Subequatorial Water, maximum uptake rates were observed; when replaced with offshore, Subtropical Water, low uptake and photosynthetic rates were observed. Further, the model for nitrate uptake
0’
(DUGDALE and MaclSAAC, 1971) failed to predict the measured uptake rates at such stations. Within the Peru upwelling area, STRICKLAND et al. (1969) observed bluewater, unproductive patches and brown-water, productive areas that may correspond
to upwelled
ideas of BARBER
3.4.
Regeneration
WHITLEDGE
eta/.
(1971)
25 110
1.0 -
150
l20
according to the
4
1.5 - -10 l0
\
175
rates (1971), from experiments
have measured the excretion
rates of
anchovies and zooplankton in the Peru upwelling area (Table 2). A comparison of zooplankton excretion of ammonium with the uptake of ammonium by phytoplankton shows the inorganic nitrogen contribution from this regeneration amount of significant. tions were
lwYs
(1971).
and PACKARD
made on shipboard,
3 2:x5> 4
o
patches of un-
chelated and chelated water, respectively,
030
In .
source to be negligible. On the other hand, the ammonium excreted by the anchoveta is very Concurrent measurements of fish concentranot made, but WHITLEDGE and PACKARD have computed the excretion rates in nature on
SiO,,ug-atoms/Liter Fig. 12 The relation of the nitrate/silicate ratio to silicate concentration in the water column at two stations from the PISCO cruise to Peru. The depth (m) from which each point was calculated is given in the figure. Die Beziehung des Nitrat/silikat-Verh;iltnisses zur Silikatkonzentration in der Wassersgule auf zwei Stationen wShrend der PISCOFahrt vor Peru. Die Tiefen (m), die fur jeden MeSpunkt berechnet waren, sind in der Abbildung genannt.
60
Geoforum
11172
from 175 m to the surface for PISCO stations 63 and 68. The points from station 63 are sufficiently reguiar to
of ail three nutrients by bacterial action both in the water column and at the sediment surface is poorly
allow drawing a curve that clearly demonstrates the tendency for silicate to be depleted at a greater rate than nitrate. The points for station 68 (about 125 km offshore) fait almost perfectly on the cunte drawn for station 63 data,
known. Special emphasis now should be placed upon all aspects of silica regeneration in view of the primary
with the exception of the O-30 m depths which show reduced ratios. The results from these two stations suggest that depletion of silicate relative to nitrate is a real feature of the euphotic
zone and that mixing between
this water
role of that nutrient
in upwel~ing production
The potential function of the nekton as horizontal “retrievers“ of nutrients drifting offshore in particulate form may be an extremely production
important
factor in the high
rates observed. However,
that the fish play a significant
it must be shown
role of some kind in the
and deeper silicate-rich water produces seawater with the characteristics shown in Fig. 12. Water from similar depths
crease the phosphorus
at different
water and thence in the phytoplankton.
locations
appear to have different
ratios, but
nonetheless fall somewhere on the same line. STRICKLAND (1970) suggested that the nitrate/silicate ratio may be a useful toof in water mass identification and certainiy this is the case in upwetfing areas. The same reiations between nitrate and silicate have been found in plots of data from additional
stations taken during.PISCO
stations taken on Thompson Dome, a known
26 working
region of non-coastal
in the Costa Rica
upweiling
silica cycle or their contribution
(BROEN-
may be simply to in-
and nitrogen
concentration
in the
In this case, the
nekton role would be to affect the quality of the phytoplankton directly, rather than the quantity or rate of production. Finalty,
the question of water ~onditjoning
more attention,
and from
processes.
deserves much
since the normal photosynthesis
and nu-
trient kinetics are grossly disturbed in its absence. The activities of the phytop~~kton~ zoopiankcon and nekton
KOW, 1965).
should be considered in conjunction with the circulation and conditioning of water. For example, in Peru the
4.
source of upwelling water for most of the coast is from the north, making it possible that the life activities of the resident population to the north contribute to the
Summafy
In an assessment of the priorities in future studies of the chemical oceanography of upwelling ecosystems in relation to primary production there are many indications that silicate should receive increased attention,
This con-
clusion results from evidence (1) that diatoms are by far the dominant group of phytopjankton in the Peru upwelling region (BLASCO,
19711, and (2) that silicate is
recycled at a low rate compared to nitrogen and phor phorus, resulting in the conclusion presented in this paper that the rate of primary
production
essentially
is
fixed by the rate of addition of silicate to the euphotic zone through upweiling water. Evidence for silicate control of inorganic nitrogen production, was obtained DALE and GOERlNG lem were obtained
water quality
of upwelling
sectors to the south.
tn the end, the reader should remember
that the data and
ideas presented in this paper are largely from a single small area of one upwe~ling system and may therefore have limited applicability to other systems. However, the author feels that only by looking at upwelling processes in detail will it be possible to devetop an understanding of broader scale phenomena. At present the Peru data appear to be the only set of information suitable for this kind of analysis.
uptake, one measure of primary in the Peru region by DUG-
(7970).
Data bearing on this prob-
during a recent cruise (spring, 1971)
of the N/Of~ion Charcot, CINECA II (unpublished} to the northwest African coastal upwelling area. Preliminary analysis of the unedited data combined with a watermass analysis of the same region made by OREN (1971) suggests that control of primary production along this coast also may be dependent
on the silicate regime.
The important role of herbivores in regeneration of phosphorus and nitrogen and to a lesser extent, silica, in upwelling ecosystems has been discussed. Partition of nitrogen uptake into nitrate and ammonium fractions through the use of “N provides a powerful tool for analyzing the degree of herbivore activity and for understanding the nitrogen cycle in such regions, Regeneration
References BARBER,
R. T,; R. C. DUGDALE, 1. j. MaclSAAC, and R. L. SMITH (1971): Variations in phytoplankton growth associated with
the source and conditioning of upwelling water; lnuestigocidn pesq., 35,171-193. BLASCO, D. (1971): Composition y distribucibn def fitoplancton en la region del afloramiento de las costas peruanas; lnvestigacion pesq., 35, 61-l 12. BROENKOW, W. W. {1965): The distribution of nutrients in the Costa Rica Dome in the eastern tropical Pacific Ocean; Limnot. Oceonogr., lO,40--52. CALVERT, S. E., and N. B. PRICE (1971): Upwellin~ and nutrient regeneration in the Bengueia Current, October, 1968; Deep Sea Res., 18,505~523.
Geoforum
11/72
GUSHING, D. H. (1969): Fish. Tech. Pap. 84.
61
Upweiling and Fish Production. F/IO
DUGDALE, R. C. (1967): Nutrient limitation in the sea: dynamics, identification, and significance; Limnol. Oceanogr., 12, 685-695.
MaclSAAC, j. J., and R. C. DUGDALE (1972): Interactions of light and inorganic nitrogen in controlling nitrogen uptake in the sea. Deep Sea Res., 19,209-232. MONOD, J. (1942): Recherches SW la croissance des cultures bactkriennes. Paris 2 10 pp.
DUGDALE, R. C., and j. J. GOERING (1967): Uptake of new and regenerated forms of nitrogen in primary productivity; Limnol. Oceanogr., 12, 196-206.
OREN, 0. H. (1971): T/S relationship in the Canary Current area. Resuits of the UNDP~SF)~FAO Regional fisheries Survey in West Africa, Report No. 7, l-l 7.
DUGDALE, R. C., and 1. J. GOERING (1970): Nutrient limitation and the path of nitrogen in Peru Current production, p. 5.3-5.8 Anton Bruun Rep. No. 4, Texas A & M Press.
REDFIELD, A. C., B. H. KETCHUM,and F. A. RICHARDS (1963): The influence of organisms on the composition of sea-water, p. 26-77. In: M. N. HILL (ed.) The Sea, Vol. 2, interscience, New York.
DlJGDALE, R. C., and J. j. MaclSAAC (1971): A computation modei for the uptake of nitrate in the Peru upwelling region; Investigackk pesq., 35, 299-308. EPPLEY, R. W., J. N. ROGERS, and J. 1. MCCARTHY (1969): Half-saturation constants for uptake of nitrate and ammonium by marine phytoplankton; Limnol. Oceonogr., 14,912-920.
RICHARDS, F. A. (1968): Chemical and biological factors in the marine environment, p. 259-303. In: J. F. BRAHTZ (ed.) Ocean Engineering, Wiley & Sons, New York. RYTHER, J. H., D. W. MENZEL, E. M. HULBURT,C. J. LORENZEN, and N. CORWIN (1970): The production and utilization of organic matter in the Peru coastal current. Anton Bruun Rep. No. 4, Texas A & M Press.
FIADEIRO, M., and J. D. H. STRICKLAND (1968): Nitrate reduction and the occurence of a deep nitrite maximum in the ocean off the west coast of South America; J. mar. Res., 26, 187-201.
SMITH, R. L. 6, 11-46.
GOERING, 1. J. (1968): Denitrification in the oxygen minimum layer of the eastern tropical Pacific Ocean; Deep Sea Res., 15, 157-164.
SMITH, R. L., D. B. ENFIELD,T. 5. HOPKINS, and R. D. PILLSBURY (1971): The circulation in an upwelling ecosystem: the PISCO cruise; Investigacilw pesq., 35,9-24.
GOERING, f. J., and M. PAMATMAT (1971): Denitrification sediments of the sea off Peru; Investigackk Pesq., 35,233242.
STRICKLAND, J. D. H. (1970): Part IV: Research on the marine planktonic food web at the Institute of Marine Resources; a review of the past six years of work. IMR Report No. 70-5, Univ. of Calif., unpublished manuscript, 135 pp.
in
HART, T. J., and R. J. CURRIE (1960): The Benguela Current; ‘Discovery’ Rep., 31, 123-298. HARVEY, H. W. (1963): The Chemistry and Fertility Waters. Cambridge, 240 pp.
ofSea
JONES, P. G. W. (1971): The southern Benguela Current region in February, 1966: Part I. Chemical observations with particular reference to upwelling; Deep Sea Res., l&193-208. JORDAN, R. (1971): Distribution of anchoveta (Engraulis ringens J.) in relation to the environment; lnvestigacicjn pesq., 35, 113-l 26. MaclSAAC, J. J., and R. C. DUGDALE (1969): The kinetics of nitrate and ammonia uptake by natural populations of marine phytoplankton; Deep Sea Res., 16,45-57.
(1968): Upwelling; Oceaffogr. Mar. Biof. Ann. Rev.,
STRICKLAND, J. D. H., R. W. EPPLEY, and Blanca R. de MENDIOLA (1969): Phytoplankton populations, nutrients and photosynthesis in Peruvian coastal water; Bol.Inst. Mar Peru, 2, l-45. WALSH, J. ]., J. C. KELLEY, R. C. DUGDALE, and B. W. FROST (1971): Gross features of the Peruvian upwelling system with special reference to possible die1 variation; /nvest@aci& pesq., 35,25-42. WHITLEDGE, T. E., and T. T. PACKARD (1971): Nutrient excretion by anchovies and zooplankton in Pacific upwelling regions; invest~gaci~n pesq., 35,243-250. WOOSTER, W. S., and M. GILMARTIN (1961): The Peru-Chite Undercurrent;/. mar. Res., 19,97-122. ZUTA, S., and 0. GUILLEN (1970): Oceanografia de la aguas costeras det Peru; Bol. Inst. Mar Peru, 2, 157-324.
47
Chemical Oceanography and Primary Productivity Chemische Ozeanographie und Primiirproduktion OcCanographie chimique et productiviti d’eau froide
R. C. DUGDALE,
in Upwelling Regions des Meeres in Auftriebsgebieten
primaire marine dans des rbgions de remont6e
Seattle*
Abstract: Features of the circulation, uptake, and regeneration of particularly nitrogen, phosphorus, and silica in upwelling regions are discussed in the light of recent contributions to nutrient uptake and regeneration theory. Emphasis is placed on the critical role of silica in the productivity of coastal upwelling areas and the resulting usefulness of this element as an indication of the recent history of circulation and production processes in an upwelling area. The significant contribution of herbivore regeneration to the nutrient regime of an upwelling area is described. Data from the Peru coastal upwelling system are discussed and interpreted in view of the physical and biological processes considered in the paper. Zusammenfassung: Merkmale der Zirkulation, Nahrstoffaufnhame und Regeneration, insbesondere von StickstoffPhosphor- und Silikatverbindungen in Auftriebsgebieten werden nach den Erkenntnissen aus jiingsten BeitrZgen iiber Nzhrstoffaufnahme und Regeneration diskutiert. Besondere Aufmerksamkeit wird der kritischen Rolle des Siliziums in der Produktivitit kiistennaher Auftriebsgebiete und der Brauchbarkeit dieses Elementes als Indikator in neueren Untersuchungen von Zirkulations- und Produktionsprozessen in Auftriebsgebieten gewidmet. Es wird der bemerkenswerte Anteil der Regeneration der Pflanzenfresser am Nrhrstoffhaushalt in Auftriebsgebieten beschrieben. Zahlenwerte aus dem System des peruanischen Auftriebs werden in diesem Aufsatz diskutiert und im Hinblick auf die physikalischen und biologischen Prozesse gedeutet.
1. introduction The basic relationships between the composition of sea-
shows clearly that large variations from these basic pat-
water and the growth of phytoplankton
terns of interaction can be expected. Departures from
for some time. The work of HARVEY
REDFIELD
and co-workers
(e.g.
have been clear (1963) and of
REDFIELD,
KETCHUM
average conditions are especially apparent in areas of high primary production, and consequently in coastal
ing of the basic interactions between algal growth and
upwelling regions the real-world situation is considerably different from the conventional view of chemical-biologi-
seawater composition and the references given above should be consulted as fundamental. While the concepts
cal processes in the sea. In this paper, the dynamic structure of chemical-biological interactions in coastal upwell-
and RICHARDS,
1963) has produced a broad understand-
ing is outlined. Emphasis is placed upon the inorganic
developed by these and other investigators continue to be valid in dealing with large areas of the oceans and long periods of time, the detailed understanding being developed of the processes - both of water circulation and
of uptake and regeneration are now reasonably well known for these nutrients and this knowledge may con-
the physiology of nutrient uptake and regeneration -
tribute to the analysis of other lesser known processes.
*
A basic objective of the paper is to put aside ideas that primary production in coastal upwelling regions can be described completely in terms of simple advection to the
Dr. R. C. DUGDALE, Department of Oceanography, University of Washington, Seattle, Wash., 98195, USA. Contribution No. 604 from the Department of Oceanography, University of Washington. This work was carried out as a part of the U. S. effort in the International Biological Program; was sup ported by National Science Foundation Grants 68-20182 and GB-18568.
forms of nitrogen, phosphorus, and silica, as the processes
surface of nutrient laden deep water, followed by phytoplankton uptake.and growth. I am greatly indebted to Mr. James I. ANDERSON for many stimulating discussions, especially concerning the problem of silica circulation in upwelling regions.
48
2,
2.1.
Geoforum 11172
Factors Affecting the Nutrient Content of Surface Waters
portant to remember that the shape of the nutrient pro-
Circulation
files above the pycnocline is influenced strongly by biological and physical events in an upwelling region and is
particularly phosphate, nitrate, and silicate. It is im-
areas is given by SMITH (1968). In Fig. 1 a diagram of the Benguela Current region is used to show upwelling
not merely a reflection of source water conditions. ldeally, to compare the effects of different characteristic nutrient profites on euphotic zone nutrient concentra-
features common to it and other regions of coastal up welling. While considerable variation can be expected to
tions in upwelling areas, profiles from the different major upwelling systems should be used. However, the profiles
occur in different upwelling systems, the diagram can be
shown in Fig. 2 serve to demonstrate the importance of the origin of upwelling water. It is immediately apparent
A recent review of circulation processes in upwelling
used to illustrate the possible physical modifications of deeper water prior to arrival in the euphotic zone. First, it can be seen that the origin of the upwelling water may be on or off the shelf and the source depth may vary considerably, from depths of perhaps 200-400 m up to pycnocline depths. Several mixing processes then alter the composition of the source water. The diagram indicates the presence of vertical circulation cells, one means by which mixing and recirculation of upwelled water may occur. Regions of horizontal shear in the surface waters between the large plumes and a corresponding backflow upstream also undoubtedly are characterized by strong mixing as well. The nature of the upwelling sources and mixing processes further are influenced by the position of the deep compensating current, which may move cioser to the coast and sometimes rise' onto the shelf.
in all the three major oceans that above about 200 m, relatively small changes in the depth of an upweliing source can lead to significant differences in nutrient concentrations and production in the upwelled water. Likewise, it is apparent that a cubic meter of water upwelied in the Atlantic Ocean would result in a considerably smaller crop of phytoplankton than the same amount of water upwelled from the Pacific or Indian Ocean, since the general levels of nutrients in the sub-surface water are higher in the last two. The most striking differences are seen in the silicate profiles, where the poverty of the Atlantic in this compound is readiiy seen and the wellknown tendency for silicate to reach higher concentrations in the lower depths than do nitrate and phosphate is illustrated. Silicate, although much neglected since it
The ~herni~a~ and biological significance of the geographi-
is required only for diatoms and not for the other important phytoplankton, appears to be a key nutrient in upwelling production systems (ZUTA and GUlLLEN,
cal and vertical variations in the sources of upwelling water is related directly to the concentration profiles of
1970), a point that wilt be treated further in succeeding sections. A consequence of the accumulation of silicate
2.2.
Nutrient profiles
Fig. 1 0 A representationof upwelling processes in the BenguetaCurrent region (from HART and CURRIE, 1960). The circulation illustrated is apparently typical of coastal upweiling. * Der Auftrieb im Gebiet des Benguelastromes (nach HART und CURRIE, 1960). Die dargestetfte firkulation ist typisch fiir den Auftrieb in Kiistengebieten.
Geoforum 11/72
49
i, 1 20to
N03-
-N (ug - atoms/liter)
Silicate (pg- atoms/liter)
Fig. 2 l
The vertical distribution of phosphate, nitrate, and silicate in the three major oceans (from RICHARDS,
l
Die Vertikalverteilung
von Phosphat, N&at
und Silikat in den drei grol3en Ozeanen (nach RICHARDS,
1968). 1968).
at depth is that the nitrate/silicate ratio generally de-
especially with depth, between nitrate/silicate vs & plots
creases with depth. Deviations from this norm can be
from non-coastal upwelling and from coastal upwelling
used to detect processes affecting one or the other nu-
situations.
trient. For example, in Fig. 3a-q 6, is plotted against nitrate/silicate ratios. These plots were made from data obtained in several regions of the Pacific Ocean as indicated in the figures. The rapid rise in the nitrate/silicate ratio near the sea aurface, resulting from nutrient recycling within the euphotic zone in the region of coastal upwelling in Peru, is shown clearly in Fig. 3a. This SWface effect is not seen in the Coasta Rica Dome upwelling region (Fig. 3b) and is not so apparent off northern Peru (Fig. 3~). Below the surface region of mixing and uptake by phytoplankton,
a slower decrease in ratio occurs
2.3.
Nutrient uptake
The general principles of nutrient uptake and regeneration are given in the paper by REDFIELD er al. (1963). Briefly it appears that the mean atomic ratios of uptake (based on plankton composition ratios) of carbon, nitrogen and phosphorus are 106:16:1 and that the regeneration ratios in water below the euphotic zone are about the same. Silicate regeneration appears to be slower, accounting in part for the relatively slow but continuous increase
(Fig. 3a, b, c), reflecting the continuously increasing concentration of silicate with depth beyond the point where
of silicate with depth. The uptake of silicate is not so well known but it may be taken up, relative to carbon
nitrate and phosphate have reached the maximum values seen in Fig. 2. The slow decrease with increasing depth may be interrupted when denitrification, the reduction of nitrate to nitrogen gas, sets in at very low oxygen concentrations, with the result that the nitrate/silicate ratio reverses its trend and goes through a minimum value as shown in Fig. 3a, b. The absence of a denitrification hook is illustrated in Fig. 3c, plotted from data taken from northern Peru waters. The data taken in the Costa Rica Dome region (Fig. 3b) are included to show the similarity,
and phosphorus, in approximately nitrate.
the same ratios as
The uptake processes, when studied on physiological time scales, are by no means so regular and predictable as the above ratios might imply. Although the work has only begun, working primarily with inorganic nitrogen, the pattern of nutrient uptake is becoming known. Details can be found in DUGDALE (1967), EPPLEY et al. (1969), and MaclSAAC and DUGDALE (1969). Briefly, the uptake by phytoplankton of a limiting nutrient is described
50
Geoforum 11/72
81 d I
i
aoi
I
24.m
X50
1
25.00
I
25.50 Stgma -
I
100
1
26.50
/
2700
1
2750
T
--I
Fig. 3b
81 0
1
2L,00
marine phytoplankton I
2L.50
I
2500
I
25.50 Sigma-T
I
26.00
I
26.50
t
I
27W
n.50
trate
for a number of species. Comparable experiments with limiting phosphate have not been made and experi-
Fig. 3a
by the following Michaelis-Menten
expression which also
describes transport across the membranes of bacteria and other non-photosynthetic
populations. Batch culture experi-
ments done with individual species by EPPLEY et 01. (1969) have given the K, values for ammonium and ni-
organisms (MONOD,
1942).
ments with limiting silicate have been fruitless until recently. However, Michaelis-Menten kinetics have been seen to be obeyed by Skeletonema costatum grown under silicate limitation in algal chemostats (HARRISON, DAVIS,
and DUGDALE,
unpublished).
Application of this kinetic information to the understandwhere V
= specific uptake rate of the limiting nutrient, units in time-r.
vmax = maxjmum specific uptake rate. s
= concentration of limiting substrate.
KS
= limiting substrate concentration for V = V,,x/2.
The Michaelis-Menten expression describes a rectangular hyperbola, a saturation curve as shown in Fig. 4. Such curves have been found by MaclSAAC and DUGDALE (1969) in experiments with r5 N tracer compounds to apply to ammonium and nitrate uptake by some natural
ing of phytoplankton productivity in upwelling or other regions of the sea requires more information than presently available, especially in the areas of nutrient interactions. However, from results of chemostat experiments with Skefetonemu costut~m (CONWAY, DAVIS, HARRISON, and DUGDALE, unpublished) the following tentative summary can be made for that species, and by extrapolation and from observations at sea, for other fast-growing diatoms. 1. Approximate
kinetic constants:
vmax = 0.18 KS@%)
hr-’
= 1 pgAt/l
K,(NQ)
= 1 PgAtf)
‘K s(SiO4)
= 1 I.cgAt/l
Geoforum 11/72
51
SFig. 4 Nutrient uptake as a function of nutrient concentration, according to the Michaelis-Menten expression. Terms are discussed in the text. Nahrungsaufnahme als eine Funktion der N4hrstoffkonzentration nach dem MichaeliLMenten-Ausdruck. Bweichnungen sind im Text erlgutert.
2. Interactions: a) Growth on limiting nutrient results in drastically lowered uptake and use of that nutrient; for example, silicate per cell is reduced to as little as 10 % of that
+
Q, x00
I
1
I
2150
zso
2550 Sipma-
4
I
2SJxl
I
2650
I
2700
1 2250
Fig. 3c
achieved under saturating silicate concentrations. Approximately the same reduction in nitrogen uptake and content is seen under nitrogen limitation, accompanied by a drastic decrease in chlorophyll content. b) The uptake of nitrate is influenced strongly by ambient ammonium concentrations of the order of 1 MgAt/l. Apparently the effect is to reduce V,, ~0~ as a function of increasing ammonium concentration (CONWAY, unpublished). The uptake of nitrate also is coupled
Fig. 3
strongly to incoming visible radiation (MaclSAAC and DUGDALE,
l
l
The nitrate/silicate rat-m plotted against ot for three areas in the eastern Pacific Ocean: (a) all stations from the Peru coast taken during PISCO, (b) 26 stations taken in the Costa Rica Dome area (about 10 ON, 90 “w) on Thompson cruise 26 in February 1968, and (c) stations taken near the northern Peru coast on Anton Bruuff 1s. Das Nitrat/silikat-Verhgltnis gegeniiber der Dichte ot fiir drei Regionen im iistlichen Pazifischen Orean: a) alle Stationen vor der peruanischen Kiiste wrhrend des PISCO-Unternehmens, b) 26 Stationen im Gebiet des Costa Rica-Auftriebs (etwa 10 ON, 90 “W) auf der Thompson-Fahrt 26 im Februar 1968 und c) Stationen vor der nordlichen peruanischen Kiiste auf der Anton Bruun-Fahrt 15 (Mlrz/April 1966).
1972). Both factors are incorporated
into a submodel developed to predict nitrate uptake in the Peru upwelling region (DUGDALE and MacISAAC, 1971). 3. Ratios of uptake: Two extreme nutrient conditions can be considered in terms of the above. In one case, with all nutrients in excess, uptake ratios something like the usual composition atomic ratios might be expected. In the second, where one nutrient becomes limiting with all others in excess, the uptake ratio of excess nutrients to limiting nutrient will rise drastically. Intermediate condi-
Geoforum 11/72
52
tions with one nutrient limiting growth and others at concentrations less than those allowing maximum
up-
take rates would be expected to result in intermediate ratios, although this area is not well documented. The composition of algae in batch cultures often has been
the problem of micro-nutrient availability in relation to upwelling, and further reference will be made to their
seen to change as deficiencies develop in the medium (REDFIELD
etu/., 1963) and now it is possible to
coriclusions in a following section.
observe the effects of deficiency directly on uptake. Uptake ratios observed by CONWAY,
In this discussion of primary nutrient uptake, the assumption has been made that trace metals and other microconstituents are available to the phytoplankton in the necessary amount but not at such high concentrations as to be inhibitory. BARBER et a/. (1971) have discussed
DAVIS and
2.4.
HARRISON (unpublished) in chemostat cultures of Skeietonema costatum under nitrogen and silica
Nutrient regeneration
Nutrient regeneration in an upwelling region takes place primarily through two processes, bacterial regeneration at the sediment-water interface and in the water column, and by grazing activities of herbivores. The importance of the latter thus far has not been included in discussions
limitation are given in Table 1. Clearly, the concept of a universal uptake ratio is erroneous when dealing with real populations of phytoplankton encountering varying ambient nutrient concentrations.
of nutrient processes in upwelling waters (e.g. JONES, lq71; CALVERT Table 1 0 Nutrient nutrient
In Fig. 5, the circulation of the primary nutrients, phosuptake
ratios for Skeletonemu
limitation
from CONWAY, 0 Verhaltnisse costutum
and PRICE, 1971).
DAVIS,
bei 18 %(unverijff.
Doubling time
grown under
at 18 ‘C (unpublished
data
NBhrstoffe
der N;ihrstoffe
N:Si:P (atoms)
(hrs)
fiir Skeletonemu
authors found that about half of the nitrogen primary
in AlgenChemostaten
Werte von CONWAY,
itation
DAVIS
Nitrogen Doubling time
und HARRISON).
Limitation N:Si:P
tion can be made in nature with nitrogen since both
(atoms)
species of nitrogen are used by phytoplankton, and ammonium is rapidly regenerated. For the purposes of dis-
(hrs)
11.3:1.2:1.0
26.6
2.8:2.3:1.0
19.8
11.6:1.4:1.0
21.6
3.2:2.6:1
16.9
10.7:1.4:1.0
16.5
4.1:2.9:
13.8
9.0:2.5:1.0 11.2:1.3:1.0
mean ratio
production was new production, i. e., based on nitrate uptake, and the other half was regenerated production, i.e., based upon ammonium. From Fig. 5 and DUGDALE and GOERING (1967) it can be seen that such a distinc-
36.4
mean ratio
up-
welling region. Details of the flow of nitrogen in the Peru upwelling system can be found in DUGDALE and GOERING (1970). Using the “N tracer technique these
and HARRISON).
der aufgenommenen
bei Begrenzung
Silica LI
cosfutum
in algal chemostats
phorus, nitrogen, and silica, is diagrammed for an
3.3:2.6:1
.O 1 .o
.O
cussion in this paper, the euphotic zone nitrogen supply will be considered as based entirely on nitrate, with ammonium regarded as a derivative of that compound. It is not possible to distinguish between new and regenerated phosphorus uptake as it is for nitrogen, because
Fig. 5 l The approximate phosphorus,
pathways
nitrogen,
circulation,
and biological
take and regeneration
of
and silica up-
in an up-
welling region. l Schemata
der AblZufe
Phosphor-,
Stickstoff-
Siliziumzirkulation biologische Regeneration triebsgebiet.
in der und
sowie die
Aufnahme
und
in einem Auf-
53
Geoforum 11 f72
as shown in Fig. 5, distinct ionic species do not appear to be produced in the regeneration of phosphorus. As far as is known, silica regeneration results in ionic species not recognizably different from the Si04 supplied from newly upwelled water. However, silica regeneration takes place within the water column at such a relatively slow rate that all silicate taken up in the euphotic zone may be considered as new. Although the fractions of regeneration attribu~ble to herbivores and to bacterial action witl vary from region to region, the analysis of DUGDALE and GOERING (1970) and the experiments reported by WH lTLEDGE and PACKARD (1971) show that regeneration of nitrogen and phosphorus by the anchoveta populations in the Peru upweliing system take ptace at such high rates that the anchoveta must be the ~minant regenerators there. Direct silica regeneration was found to take place through anchoveta grazing activities at 1O-20 % of the rate for nitrogen. Table 2, reprinted from WHITLEDGE and PACKARD (1971), summarizes these regeneration
lb I
76”W
l
1
LO’
20’
Fig. 6
measurements.
0 Sampling grid used on the PISCO cruise to Peru (March-April 1969). Grid squares are five nautical miles on a side; CM denotes current meter locations.
Table 2 l Excretion rates of the Perucian anchovy (Engroulis
ured during P&CO (from WHITLEDGE
ringens) meas-
and PACKARD,
1977 ).
0 Aus~he~u~sraten des peruanischen Anchovis (Engroutis ringem) wiihrend der P&CO-Expedition (von WHITLEDGE and PACKARD, 1971). Excretion Product
dLO’
Number of Measurements
fig-at/g dry wtlhr
kbg_at/g body N/hr
* Stationsraster auf der PISCO-Fahrt in die peruanischen Gew&ser (M&z/April 1969). Die SeitenlTnge des Rasterquadrates bett%gt 5 Seemellen; CM bezcichrtet die Positionen der Strommesser.
progress. The upwelling water outcropping near the shore appears to come from the upper 75 m, at least along the
Ammonia-N
7
4,47
40.6
line determined by the five stations. This water is further identified (Fig. 7c) by its low (for surface water) nitrate/
Creatine-N
7
3.37
30.6
silicate ratio (1.6-2.4)
it. The distribution of water by nitrate/silicate ratio in bands along the coast is a useful characteristic in terms of
Urea-N
3
3.29
29.9
Phosphate-P
7
2.84
25.8
Silicate-Si
7
0.64
5.82
relative to the water seawards of
all aspects of the analysis of an upwelling system. The downward trends of the isotherms and isopycnals (Fig. 7a, b) beginning at about 75 m indicate the presence of
3.
of the Nutrient Regime in the Peru Coastal Upwelling Region
Generation
the Peru Undercurrent flowing southward (WOOSTER and G ILMARTIN, 1961). Current meters set at locations marked on the grid (Fig. 6) as CM-l and CM-2 during
The conditions and processes discussed in the preceeding section and their results and interactions can be illustrated
PISCO showed flow to the southeast below 25 meters, while the surface drift as shown by parachute drogues
using data obtained from the same area on the coast of Peru
was to the northwest over most of the grid (SMITH et of.
on Anton Bruun Cruise 15 and T. G. Thompson Cruise 36
1971). The undercurrent can be recognized in Fig. 7c, d, and e, respectively, from low nitrate/silicate ratios,
(PISCO). Most of the data used are from the PlSCO expedition from a location on the south Peru coast near Cabo Nazca, 15 “S latitude. The grid shown in Fig. 6 was occupied with a iarge series of stations on this cruise. 3.1.
Circulation and vertical distribution of nutrients
The sections (95 km long) shown in Fig. 7 (a-h) were made along line 12 of the grid out from Pt. San Juan (Stas. 14-18). The on-shore upward trends of the isotherms and isopycnais (Fig. 7a, b) reflect upwelling in
low oxygen levels, and high nitrite concentrations. These three parameters reflect the denitrification that had occurred or was occurring in the undercurrent water or adjacent sediments according to ev.idence given by GOERfNG (1968), FIADEIRO and STRlCKLAND (1968), and GOERlNG and PAMATMAT (1971). The effects of both upwelling and the Peru undercurrent are seen in the distribution of nitrate, silicate, and phosphate concentrations as well (Fig. 7f-h).
I 90
60
75
ttam mow
olrt.“c*
30
45
+
150
0
‘6
wrl,
. I1 4
Station Wumbw*
. . .
.
2L3
.
. .
IL
150
.
.
.
l
-01 .
l
I 01
i 01
i
i
.
.
I
.
200
\
0’
/
.
264
1
.
z
303
g s
.
.
L
i
D6
.
, 90
I 75 Oistmc*
from
*honoun)
O~s*wtcc
from
rhwr(km)
d)
b)
Fig. 7 0 The distribution
360
of (a) temperature,
section made during PISCO,
(b) ot, (c) nitrate/silicate
extending
ratio, (d) oxygen,
(e) nitrite,
(f) nitrate,
about 95 km out from the coast in the Peru upwelling
with solid circles. The stations were taken over a 16 hr period.
(g) silicate, and (h) phosphate
region. Locations
in a
of data points are shown
SMii 10
Nmlbur 17
(5
16
I4
.
.
.
;a$_ . .. .
.
.
.
.
.
.
.
. .
l
.
1
.
.
.
S104,pg-~tomrll1t*r
.
.
. 400
NO2 .pg-dom‘,Li*.r
105
460
I
90
75
60 45 Dtrtancr tram shore (km)
20
15 6)
0
50 2.2 .-’
.
l
IO0
150
150
.
200
ZOO
.
250
260 P04.p9-a9omr/Llln .
a
F 300 z‘I
300; ;
c:
360
360
.
.
400
400
Owance
60 45 tramshare (km)
450 30
15
1
90
,
75
460 60
46
30
15
0
Fig. 7 Die Verteilung von (a) Temperatur, (b) Dichte ot, (c) Nitrat/Silikat-Vsrhgltnis, (d) Sauerstoff, (e) Nitrit, (f) Nitrat, (g) Silikat und (h) Phosphat auf einem Schnitt wghrend des PISCO-Unternehmens, der ungefdhr 95 km von der K&e in das peruanische Auftriebsgebiet hineinreicht. Positionen mit Wertangaben sind durch schwarze Punkte gekennzeichnet. Die Stationen wurden wghrend einer Dauer von 16 Studen durchgefiihrt.
Geoforum 11/72
56
3.2.
Distribution of nutrients and temperature at the surface
A set of surface maps of temperature, chlorophyll, nitrate, silicate and nitrate/silicate ratio are shown in Fig. 8a-e. These figures were abstracted from maps produced on board the J~u~~~~n during PISCO, using an automated data system receiving thermister, fluorometer, and automatic chemical analysis data. Water was pumped from a depth of 3 m as the ship steamed over a prescribed path. Data points were recorded at one minute intervals, punched onto paper tape, and read into an IBM 7 130 computer. After computer processing, the contours were drawn under computer control on a CalComp plotter. The maps were available within hours of the completion of a survey track. The maps shown in Fig. 8 reveal the plume structure of the center of upwelling studied on the PISCO cruise. These and maps from other passesover the grid (Fig. 6) on the same cruise have been described and analyzed in detail by WALSH et al.(1971). This analysis showed the cold center in the vicinity of grid point A8 (Fig. 8a) and the plume orientation to the northwest to be persistent features. The cold temperatures exhibited at the origin of this plume (Fig. 8a) are seen to correlate spatially with the highest nutrient concentrations (Fig. 8c, d) and the lowest chlorophyll (Fig. 8b). just to the north of this outcrop of upwelled water some southward flow occurs resulting in a persistent front that can be seen in the figures as restricting the northward expansion of the plume. The primary nutrients generally decline in the direction of mean flow of the plume to the northwest due to uptake and mixing, resulting in concentric bands of concentration distribution. Differential uptake and regeneration processes, mixing, and decreased depth of upwelling source combine as well to produce the concentric bands of nitrate/silicate ratio shown in Fig. 8e.
3.3.
Uptake of nutrients along the axis of an upwelling plume
The data obtained on Anton Bruun Cruise 1.5 (RYTHER et (II., 1970; DUGDALE and GOERING, 1970) substantiate the sequence of nutrient uptake and regeneration developed earlier in this paper. In the Anton 5ruun work, a drogue was placed in cold, nutrient-rich water near the coast where upwelled water was arriving at the surface. The ship followed the drogue for five days and the change in phosphate, nitrate, silicate and ammonium concentrations was observed (Fig. 9a-d). Silicate decreased to undetectable levels in a reasonably regular way, while considerable nitrate remained at the fifth day. The phosphate concentration clearly was maintained by regeneration, and the same is true for ammonium which actually increased in the course of the experiment. The changes
Geoforum 11/72
I
ls-
ND3 I SiO,
4
4
Fig. 8 The surface (3 m) distribution during a single night survey of (a) temperature, (b) chlorophyll, (c) nitrate, (d) silicate, and (e) the nitrate/silicate ratio over a portion of the PISCO sampling grid in the Peru upwelling region.
75’
Die Oberfilchenverteilung (3 m) fiir (a) Temperatur, (b) Chlorophyll, (c) Nitrat, (d) Silikat und (e) das Nitrat/silikatYerhiltnis
wBhrendeiner einzigenNachtaufnahmefiir einen Abschnitt des PISCO-Unternehmensim peruanischenAuftriebsgebiet.
in concentration observed were the result of uptake, regeneration, and the advection of additional upwelling water from below (not necessarily so rich as the water outcropping at the origin of the plume, e. g. see Fig. 7 f-h) making the computation of ratios of change between these nutrients a virtually meaningless exercise. However, measurements of nitrate and ammonium uptake were made and provide the basis for a partial analysis of the processes taking place. The total inorganic nitrogen up take appeared to be correlated closely with the concentration of silicate (Fig. 10). The shape of the curve in Fig. 10 is linear over the time span observed; however, further reductions in total inorganic nitrogen uptake might be expected in some fairly short time following the exhaustion of silicate. SiOL.pg-
otcms/lit*r
Looking at the PISCO nutrient distribution in Fig. 8, it appears that the analysis DUGDALE and GOERING (1971) applied to the Anron Bruun data holds at least generally for the plume mapped on the Thompson. Where
58
Geofotum t l/72
Phosphate
20c
0
i
L
5
I
10
4
t5
20
SiO,,@g-atoms/Liter Fig. 10 l The relation of total inorganic nitrogen uptake to silicate concen-
tration observed during the Anton Bruun Peru drogue experiment (50 % light-penetration depth). Station numbers are shown for each observation
Nitrate
l Dar Verhaltnis der Ge~mtaufnahme
von anorganischem Nitrat zur Silikatkonzentration nach Beobachtungen wahrend des Peru-DriftExperiments von Anton Bruun (in Tiefe von 50 % Lichtintensitat). Die Stationsnummern sind fi& die einzlenen Beobachtungen angegeben.
the plume meets the western edge of the grid, silicate has been reduced by 75 % from the source concentration, nitrate by about 50 %, and phosphate (from station data) by only about 30 %. Sufficient measurements of ammonium concentration and uptake are not available, but it appears likely that the total inorganic nitrogen uptake on the PISCO cruise would show a relation to silicate concentration similar to that seen on the Anton Bruun cruise. The partition of nitrogen uptake between ammonium and nitrate was regulated by the ambient ammonium concentration during the Anton Bruun experiment, as shown in Fig. 11. The ratio of the maximal specific uptake rates for nitrate and ammonium is a linear function of the ammonium concentration. As ammonium concentration increased, down plume in this case, nitrate uptake was re-
a’
I
6
’
1 Fig. 9
’
12 18
I
6
I
I
I
t
L
6 12 18 12 18 3 2 time and day
,
6
h
I
12 18 G
I 6 5
* Changes in concentration of (a) phosphate, (b) nitrate, (c) silicate, and (d) ammonium observed in a five-day period on Anton Bruun cruise 15 (March-April 1966), as the ship followed a drogue in Peruvian waters (50 % light-penetration depth). l Anderungen in der Konzentration
von (a) Phosphat, (b) M&rat, (c) Silikat und (d) Ammoniak beobachtet fiir die Dauer von fiinf Tagen auf der Anton Bruun-Fahrt 15 (M&/April 1966) als das Schiff einen markierten Fleck in den peruanischen Gewassern verfotgte. (Gemessen in Tiefe mit 50 % Intensitat des Tagesiichtes.)
duced and replaced by ammonium uptake. This linear relationship also has been observed in the Mediterranean Sea under conditions strongly influenced by a sewage outfall (MaclSAAC and DUGDALE, 1972), and probably can be considered to be generally applicable where ammonium and nitrate occur together in the sea. Barber et u/. (1971) made experiments during PISCO showing that on some stations natural chelators apparently were missing resulting in severe reductions in measured nutrient uptake and photosynthesis. In these cases, the differences between conditioning correlated well with differences in water masses. When the upwelled water
Geoforum
11/72
59
the basis of anchoveta
schools with a density of 100 fish per m3. Based on this school size, the results suggest that
the integrated daily ammonium uptake by phytoplankton under a m2 can be supplied by regeneration in 2 hours.
34
Creatine, occur at order of observed 3.5.
1
0'
0.5
1.0
1.5
2.0
25
3.0
Nitrate/silicate
ratios in new surface waters
Since silicate appears to behave as a virtually non-regenerated nutrient in upper waters, it may be used as a reference nutrient. plotted
NH,+-N,ug-atoms/Liter
urea, and phosphate excretion were found to about the same rates as for ammonium, on the OS-O.8 pg-At/liter/hr. Silicate excretion was to be about 0.1 pg-At/liter/hr.
For example,
the nitrate/silicate
in Fig. 12 against silicate concentration
ratio is at depths
Fig. 11 l The dependence on ambient ammonium concentrations of the
relative contributions of nitrate and ammonium uptake to total inorganic nitrogen uptake, as observed during the drogue experiment on the Anton Bruun cruise to Peru. Station numbers are shown for each observation. x Stab3 . Sta.66
0 Die AbhJngigkeit der relativen Beteiligung von Nitrat- und Ammoniakaufnahme an der Gesamtaufnahme von Nitrat von der Ammoniakkonzentration der Umgebung nach Beobachtungen wghrend des Drift-Experiments auf der Anton Bruun-Fahrt vor Peru.
2.5
was from the north, i.e., Subequatorial Water, maximum uptake rates were observed; when replaced with offshore, Subtropical Water, low uptake and photosynthetic rates were observed. Further, the model for nitrate uptake
0’
(DUGDALE and MaclSAAC, 1971) failed to predict the measured uptake rates at such stations. Within the Peru upwelling area, STRICKLAND et al. (1969) observed bluewater, unproductive patches and brown-water, productive areas that may correspond
to upwelled
ideas of BARBER
3.4.
Regeneration
WHITLEDGE
eta/.
(1971)
25 110
1.0 -
150
l20
according to the
4
1.5 - -10 l0
\
175
rates (1971), from experiments
have measured the excretion
rates of
anchovies and zooplankton in the Peru upwelling area (Table 2). A comparison of zooplankton excretion of ammonium with the uptake of ammonium by phytoplankton shows the inorganic nitrogen contribution from this regeneration amount of significant. tions were
lwYs
(1971).
and PACKARD
made on shipboard,
3 2:x5> 4
o
patches of un-
chelated and chelated water, respectively,
030
In .
source to be negligible. On the other hand, the ammonium excreted by the anchoveta is very Concurrent measurements of fish concentranot made, but WHITLEDGE and PACKARD have computed the excretion rates in nature on
SiO,,ug-atoms/Liter Fig. 12 The relation of the nitrate/silicate ratio to silicate concentration in the water column at two stations from the PISCO cruise to Peru. The depth (m) from which each point was calculated is given in the figure. Die Beziehung des Nitrat/silikat-Verh;iltnisses zur Silikatkonzentration in der Wassersgule auf zwei Stationen wShrend der PISCOFahrt vor Peru. Die Tiefen (m), die fur jeden MeSpunkt berechnet waren, sind in der Abbildung genannt.
60
Geoforum
11172
from 175 m to the surface for PISCO stations 63 and 68. The points from station 63 are sufficiently reguiar to
of ail three nutrients by bacterial action both in the water column and at the sediment surface is poorly
allow drawing a curve that clearly demonstrates the tendency for silicate to be depleted at a greater rate than nitrate. The points for station 68 (about 125 km offshore) fait almost perfectly on the cunte drawn for station 63 data,
known. Special emphasis now should be placed upon all aspects of silica regeneration in view of the primary
with the exception of the O-30 m depths which show reduced ratios. The results from these two stations suggest that depletion of silicate relative to nitrate is a real feature of the euphotic
zone and that mixing between
this water
role of that nutrient
in upwel~ing production
The potential function of the nekton as horizontal “retrievers“ of nutrients drifting offshore in particulate form may be an extremely production
important
factor in the high
rates observed. However,
that the fish play a significant
it must be shown
role of some kind in the
and deeper silicate-rich water produces seawater with the characteristics shown in Fig. 12. Water from similar depths
crease the phosphorus
at different
water and thence in the phytoplankton.
locations
appear to have different
ratios, but
nonetheless fall somewhere on the same line. STRICKLAND (1970) suggested that the nitrate/silicate ratio may be a useful toof in water mass identification and certainiy this is the case in upwetfing areas. The same reiations between nitrate and silicate have been found in plots of data from additional
stations taken during.PISCO
stations taken on Thompson Dome, a known
26 working
region of non-coastal
in the Costa Rica
upweiling
silica cycle or their contribution
(BROEN-
may be simply to in-
and nitrogen
concentration
in the
In this case, the
nekton role would be to affect the quality of the phytoplankton directly, rather than the quantity or rate of production. Finalty,
the question of water ~onditjoning
more attention,
and from
processes.
deserves much
since the normal photosynthesis
and nu-
trient kinetics are grossly disturbed in its absence. The activities of the phytop~~kton~ zoopiankcon and nekton
KOW, 1965).
should be considered in conjunction with the circulation and conditioning of water. For example, in Peru the
4.
source of upwelling water for most of the coast is from the north, making it possible that the life activities of the resident population to the north contribute to the
Summafy
In an assessment of the priorities in future studies of the chemical oceanography of upwelling ecosystems in relation to primary production there are many indications that silicate should receive increased attention,
This con-
clusion results from evidence (1) that diatoms are by far the dominant group of phytopjankton in the Peru upwelling region (BLASCO,
19711, and (2) that silicate is
recycled at a low rate compared to nitrogen and phor phorus, resulting in the conclusion presented in this paper that the rate of primary
production
essentially
is
fixed by the rate of addition of silicate to the euphotic zone through upweiling water. Evidence for silicate control of inorganic nitrogen production, was obtained DALE and GOERlNG lem were obtained
water quality
of upwelling
sectors to the south.
tn the end, the reader should remember
that the data and
ideas presented in this paper are largely from a single small area of one upwe~ling system and may therefore have limited applicability to other systems. However, the author feels that only by looking at upwelling processes in detail will it be possible to devetop an understanding of broader scale phenomena. At present the Peru data appear to be the only set of information suitable for this kind of analysis.
uptake, one measure of primary in the Peru region by DUG-
(7970).
Data bearing on this prob-
during a recent cruise (spring, 1971)
of the N/Of~ion Charcot, CINECA II (unpublished} to the northwest African coastal upwelling area. Preliminary analysis of the unedited data combined with a watermass analysis of the same region made by OREN (1971) suggests that control of primary production along this coast also may be dependent
on the silicate regime.
The important role of herbivores in regeneration of phosphorus and nitrogen and to a lesser extent, silica, in upwelling ecosystems has been discussed. Partition of nitrogen uptake into nitrate and ammonium fractions through the use of “N provides a powerful tool for analyzing the degree of herbivore activity and for understanding the nitrogen cycle in such regions, Regeneration
References BARBER,
R. T,; R. C. DUGDALE, 1. j. MaclSAAC, and R. L. SMITH (1971): Variations in phytoplankton growth associated with
the source and conditioning of upwelling water; lnuestigocidn pesq., 35,171-193. BLASCO, D. (1971): Composition y distribucibn def fitoplancton en la region del afloramiento de las costas peruanas; lnvestigacion pesq., 35, 61-l 12. BROENKOW, W. W. {1965): The distribution of nutrients in the Costa Rica Dome in the eastern tropical Pacific Ocean; Limnot. Oceonogr., lO,40--52. CALVERT, S. E., and N. B. PRICE (1971): Upwellin~ and nutrient regeneration in the Bengueia Current, October, 1968; Deep Sea Res., 18,505~523.
Geoforum
11/72
GUSHING, D. H. (1969): Fish. Tech. Pap. 84.
61
Upweiling and Fish Production. F/IO
DUGDALE, R. C. (1967): Nutrient limitation in the sea: dynamics, identification, and significance; Limnol. Oceanogr., 12, 685-695.
MaclSAAC, j. J., and R. C. DUGDALE (1972): Interactions of light and inorganic nitrogen in controlling nitrogen uptake in the sea. Deep Sea Res., 19,209-232. MONOD, J. (1942): Recherches SW la croissance des cultures bactkriennes. Paris 2 10 pp.
DUGDALE, R. C., and j. J. GOERING (1967): Uptake of new and regenerated forms of nitrogen in primary productivity; Limnol. Oceanogr., 12, 196-206.
OREN, 0. H. (1971): T/S relationship in the Canary Current area. Resuits of the UNDP~SF)~FAO Regional fisheries Survey in West Africa, Report No. 7, l-l 7.
DUGDALE, R. C., and 1. J. GOERING (1970): Nutrient limitation and the path of nitrogen in Peru Current production, p. 5.3-5.8 Anton Bruun Rep. No. 4, Texas A & M Press.
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DlJGDALE, R. C., and J. j. MaclSAAC (1971): A computation modei for the uptake of nitrate in the Peru upwelling region; Investigackk pesq., 35, 299-308. EPPLEY, R. W., J. N. ROGERS, and J. 1. MCCARTHY (1969): Half-saturation constants for uptake of nitrate and ammonium by marine phytoplankton; Limnol. Oceonogr., 14,912-920.
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