Post on 11-Feb-2022
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And where it does, nutrients upwelling from the depths create lush planktonic feeding zones for the world's fisheries.
n a summer day, when a stiff northerly wind blows along the Oregon coast, and there's a line
in the sea where the color changes from a clear cobalt blue to a murky green— that's a day fishermen know they can make a good catch. And catch they do. The silver salmon, tuna, and other fish congregate in certain greenish areas where they feed on thriving pastures of marine plants and animals—and if the
fishermen are there on the spot, the haul is good.
Fishermen worth their salt in all oceans have long known signals of wind, sea color, frontal lines, and temperatures in their special fishing areas—it's part of the lore of the sea. Yet, although they can recognize areas where the fish might be, they have been unable to predict these spots when winds and sea currents change.
Now, after several years of research, some of the factors that create good catches are becoming beautifully clear.
In many slow and ponderous ways— by action of the t ide^ the rotation of the Earth: and changes in seasons, winds, and temperatures—the waters of the world are constantly mixing, over-iurr.ir.e. and wciim^ up, biir.ging dissolved chem^ai nutrient- irorn the sea
depths to the surface, and churning oxygen-rich water from the surface down again to the deep sea.
These complex vertical and horizontal motions, vital to the living resources of the sea, may occur in the middle of the oceans, or at boundaries of different water masses, in eddies around the lees of island or land promontories projecting into a current, or over ridges and canyons beneath the open sea.
However, the most dynamic ocean turnover process is coastal upwelling, a phenomenon by which nutrients from the dark depths are periodically brought up in certain areas to the sunlit surface layers where photosynthesis can take place and where they can become available to microscopic plant life. These one-celled plants, phytoplankton, provide the base of the complex food chain of ocean life. Provided with nutrients and using energy from the Sun for photosynthesis, they multiply into large masses, offering feasting grounds for zooplankton and larger fish and creating the most productive fish-producing regions in the world.
Fishing yields in these upwelling areas and their immediate vicinity are at least a thousand times higher than in other oceanic areas. The coastal upwelling areas, comprising only one-tenth of one percent of the total area of the world's oceans, are estimated to contain more than half of the ocean's fish catch—a total fishery yield of more than 40 million metric tons a year.
Progress in understanding the theory of the upwelling phenomenon has reached a point of worldwide significance, states Richard Barber of Duke University's Marine Laboratory at Beaufort, North Carolina, and national coordinator of the Coastal Upwelling Ecosystem Analysis (CUEA) program. CUEA, part of the International Decade of Ocean Exploration, was started by the National Science Foundation to investigate the physical and biological aspects of upwelling. With more than 29 principal investigators and 13 U.S. research and educational institutions and organizations, CUEA has initiated a series of experiments and theoretical observations. Its purpose is to provide systems models for predicting on a daily basis the changing sites, courses, extent, temperatures, and various other factors of upwelling systems in particular locations. Eventually such system modeling
would be used to predict the production of the world fisheries on the basis of a few significant meteorological and ocean-ographic measurements.
Where it happens
- lthough upwelling may take place anywhere in the ocean, it occurs more regularly and most con
spicuously along the western edges of continents in the. low and mid latitudes, particularly along the western coasts of the Americas and of Africa. In these regions, the prevailing winds blow equatorward, and this, in combination with the Earth's rotation, causes the surface water to move away from the coast. The surface water is replaced by water from the depths.
There are only a few places in the world where conditions exist to form strong persistent upwelling over large regions. One is along the Peruvian coast, where the Peru Current flows northward west of Chile and Peru. Another region of marked upwelling occurs along the coasts of Baja California, California, Oregon, and Washington, where the California Current flows south. Here the upwelling peak moves up the coast with the warming weather in May, June, and July as the North Pacific atmospheric high pressure cell intensifies and north
erly winds develop along the coast. By October it is finished. A third intensive upwelling area is along Southwestern Africa, with most intense activity in the southern spring months of September and October. A fourth dominant upwelling system occurs farther north— along Northwestern Africa.
Contrary to the "west coast rule," important coastal upwelling also develops in the region of Eastern Africa where, during the annual southwest monsoon, the Somali Current flows from the Southern Hemisphere up the east coast of Africa and along the Arabian coast into the Arabian Sea.
Upwelling also occurs in mid-ocean spots around the Equator and in the Antarctic. In the eastern equatorial region of the Pacific Ocean, for instance, the Cromwell Undercurrent creates an uprising in an area extending eastward along the Equator from the 180-degree meridian to the Galapagos Islands.
When the polar wind blows
: " he primary driving mechanism of
t a "typical" coastal upwelling system is the wind system blowing
from an atmospheric high pressure toward the Equator and producing stress at the surface of the sea. Because of the effect of the Earth's rotation and fric-
26 MOSAIC Winter 1974
tonal forces, however, the net transport f the windblown surface water, called ,kman Transport or Drift, is directed eaward, 90° to the right of the wind in he Northern Hemisphere (to the left in he Southern).
As the surface water is pushed off-hore, cold water rises from several hun-ired meters deep, up and over the con-inental shelf, to take its place. This ipwelling may appear at the surface in 'arious patterns of tongues, plumes, and latches. Such tongues or plumes indi-ate intense upwelling locally and may .ssume many changing shapes, ranging n length and depth from a few meters o several kilometers. However, they eldom exceed ten to 30 kilometers in vidth, and ten to 20 meters in trackless. The tip of the tongue of intense ipwelling usually can be found within en to 20 kilometers off the coast. :rontal boundaries between the warm old surface water) and cold (more lewly upwelled) water masses are often iharp and distinct. Some occur over long listances, others over a space so small hat a single ship may straddle the >oundary.
An inherent feature of upwelling seems to be the presence of a narrow etlike surface current that flows along he shore in the same direction as the prevailing winds on the seaward side of :he upwelling front. At the same time is the surface current is flowing, a subsurface countercurrent is often observed -lowing away from the Equator. This is :onsidered a very important factor in :he dynamics of upwelling and its asso-:iated ecosystem. Just how much these :urrents contribute to upwelling under /arious conditions and what effect they produce is not yet clear, points out phys-cal oceanographer Robert Smith of Oregon State University, which was the renter of extensive upwelling experi-nents during the summers of 1972 and 1973.
Each regional upwelling ecosystem is a separate, complex, and dynamic phenomenon that depends upon the physical conditions of its setting. Each is subject not only to variations within the system itself—such as the configuration of the :oast and continental shelf, the strength and directions of ocean currents, and the local wind conditions—but also to influences external to it, such as the seasons and the world wind patterns.
What makes it happen. Strong winds blowing along the shore toward the Equator, combined with the Earth's rotation and frictional forces, drive the warm surface water away from the shore. It is replaced by cold, nutrient-rich water from the lower depths; phytoplankton flourish, and fish congregate to feed on the plankton.
Unpredictable prodigy
-,' lthough the upwelling regions seem well defined, the process itself
" has, as yet, no constant or dependable schedule of when it might arrive or how long it will last. The length of time an upwelling season may prevail depends primarily upon how long the dominating winds blow along the coast. This in turn depends on the strength and positions of the atmospheric highs that occur as spring and summer arrive. During the season when conditions are generally right for upwelling, the process may vary from strong persistent upwelling to none at all to strong again over a period of weeks.
These modulations may occur several times during a season of upwelling conditions. They occur when the prevailing
winds stop blowing in the direction favorable to upwelling—equatorward along west coasts—and come from other directions, hence stopping the offshore transportation of the warm surface water. This in turn shuts off the upwelling circulation of water from lower depths. The cold water remains below and the warm water above in horizontal layers. These wind changes of a few days' duration have large effects on water temperature over areas as wide as ten kilometers from the shore and as deep as 20 meters.
Once the source of nutrients is stopped or blocked, the growth of phytoplankton halts, as does the concentration of fish. The whole process collapses and the fish disperse to find their own food where they can, and fishing for the day, the week, perhaps longer, can become a haphazard affair for the fishermen.
MOSAIC Winter 1974 27
W i t h the re turn of the prevai l ing
nor ther ly winds (or southerlies in the
Southern Hemisphere) , upwell ing re
sumes , and p lank ton growth and con
centrat ion of mar ine life reoccurs.
Some upwell ing systems take place
year after year in specific areas. O the r s
m a y cont inue for several years wi thout
in ter rupt ion and then fail ca tas t rophic-
al ly—such as the failures of upwell ing in
1965, 1971 , and 1972 off the coast of
Peru. In previous years, the Peruvian
upwell ing has created the world 's most
product ive fishery area. In 1970, 22 per
cent of the total world fish ca tch—most ly
anchovies—was harvested. W i t h the ab
sence of upwell ing—el Nino or " T h e
Chi ld ," as it is called—in 1971-72, the
anchovy catch dropped from 12.3 million
tons in 1970 to 4.5 million tons in 1972
— a t ragedy for Peru which for decades
had depended on the more t han ten mil
lion tons of anchovy catch, from which
near ly 70 percent of the world 's fishmeal
was produced. Scientists say the fish
stocks are slowly recovering wi th the
resumpt ion of upwel l ing in 1973, bu t
they have not yet mult iplied to their
former numbers . This d is rupt ion has
raised several quest ions as to whe the r
the diminished number s of anchovies are
caused by overfishing dur ing el Nino, or
perhaps by a na tura l decrease in the
biological cycle of the fish. O t h e r tragic1
failures blamed on similar circumstances
were the disappearance of the California1
sardine and Hokka ido herr ing .
The sunlit zone
i thout doubt , coastal upwell ing
systems produce rich biological
g rowth and activity. This high
productivi ty of organic mat te r is limited
to the sea surface layers where sunlight
is sufficient for pho tosyn thes i s . Solar
radiat ion penetra tes t h r o u g h this upper
sea layer, the euphotic zone, to depths
of about 11 to 28 meters , depending on
the concentrat ion of the mar ine popula
tions or on turbidity. Into this zone are
b rought up the deep sea's n i t rogen, phos
phorus , and silicon; in ion form or as
compounds of ni t ra tes , ni t r i tes , phos
phates , and silicates. I ron and traces of
other minerals are also present .
At first, the cold, newly upwelled wa
ter is low in plant and animal popula
t ion; it takes a while for p r imary bio
logical activity to start , explains Richard
Dugdale , a biological oceanographer
from the Universi ty of W a s h i n g t o n . As
one-celled p lankton mult iply , they grad
ually consume and reduce the amoun t of
nut r ients . At the same t ime, oxygen con- '
tent increases. Along the surface waters ,
oxygen is near sa tura t ion , and toward
the seaward edge of the spreading plume'
it has been measured as h igh as 130 per
cent of saturat ion.
As an indication of the extent to which
upwell ing increases product ion of pri
mary marine life, p h y t o p l a n k t o n cell
counts in the Peruvian upwel l ing eco
system, in a good year, have been meas
ured as high as 138,000 per liter. This
compares to a normal ocean densi ty of
1,000 to 10,000 per liter.
Feeding directly on the p lant and ani
mal p lank ton are the herb ivorous zoo-
p lank ton and fin fishes, such as tuna ,
salmon, anchovies, mullet , and herr ing,
which are caught by f ishermen or eaten
by other carnivorous preda tors including
birds , boni to , squid, and sea lions. In
the Peruvian region, it is est imated that
the annual numbers of fish captured by
fishermen are probably matched by those
consumed by mar ine p reda tors .
As the upwell ing tongue of cold water
spreads over the sea surface and is
28 MOSAIC Winter 1974
oved seaward by the wind, it carries e products of this biological activity—• e excreta, dead and decaying plants, limals, and other organic compounds—-hich gradually sink toward the bottom • the sea. As this material drifts down-ard, it is acted upon by bacteria near e surface which reduce it again to in-•ganic nutrients that may be taken up / phytoplankton, dissolved into the sea, • come to brief rest on the sea floor ;fore being upwelled again—a complete :osystem recycling. Moreover, though the processes are
3t yet well understood, there seems to i nutrient recycling within various lay's arid currents of the sea in an up-elling region—through local mixing and mvection currents, or subsurface shore-ard transport, or through injection at ie source of upwelling. The proportion : regenerated nutrients in a fully devel-?ed upwelling ecosystem is quite high, 'ne estimate is that a dense school of srbivorous fishes grazing on a phyto-.ankton crop, through its excreta alone, roduces the daily nitrogen requirements " the phytoplankton in just two hours.
xpeditions for upwelling
cientists have been aware of upwelling for a long time, particularly along the coast of Peru,
'here the occurrence of el Nino has been ?corded by fishermen for more than 30 years. Scientific attempts to define nd describe the upwelling system itself, owever, did not occur until the early 900's. In the late 1920's and 1930's, idividual oceanographers began making tajor contributions to the studies. In 968 an Upwelling Biome Program was icluded as ; part of the International iological Program, and studies were lade along the Peruvian coast and in the lediterranean. With CUEA established i 1971, four expeditions took place in ie succeeding two years to investigate ie biological and physical effects of pwelling: MESCAL I and II off Baja alifornia in the springs and summers f 1972 and 1973; and CUE I and II off \e Oregon coast in the same years.
The latest major experiment, CUE II, perating from July through August 973, took place on a site some 80 kilo-leters long along the Oregon coast 'om Newport to Cape Lookout, and ^tending some 60 kilometers into the acific Ocean. CUE II, co-directed by
James O'Brien of Florida State University and Dale Pillsbury of Oregon State University, was set slightly north of the 1972 CUE I site, at a place where the topography of the continental shelf is simpler and smoother. Here scientists hoped to avoid the complicated sea circulations created by ridges and bumps of the sea bottom and to simplify the simulations of models.
Three research vessels—the "workhorse" Cayuse which can make a 180° turn "on a quarter" to place or pick up buoys and objects from the sea; and the more elegantly equipped Oceano-grapher and Yaquina—made repeated journeys back and forth over the area to measure temperatures, salinities, densities, and changes in currents. On another vessel, the Thomas G, Thompson, scientists made detailed studies on chemical nutrients, plankton, and fish, and compiled maps charting temperature zones, flow of currents, and areas of nutrients and biological activity. An instrumented aircraft from the National
Center for Atmospheric Research operated over the area during August, measuring sea surface temperatures, air humidity and temperatures, and wind systems.
Since 1965, arrays of buoys moored on Oregon's continental shelf have been used to record currents and temperatures. During CUE II more buoys were installed in arrays extending from land out to sea some 60 or more kilometers— across the continental shelf and over the edge of the continental slope. These buoys—spaced several kilometers apart, depending on the configuration of the sea floor or the currents—recorded temperatures and currents from the surface to the sea floor. They helped scientists "follow" various ebbs and flows of currents as the winds changed and the season progressed. Buoys from NOAA's Pacific Marine Environmental Laboratory were moored at single points along the array to measure the wind, solar radiation, and currents near the surface. Buoys from Oregon State University
MOSAIC Winter 1974 29
Taking the sea's temperature, Equipment is placed at strategic points off the Oregon coast during CUE-ll.
measured current velocities and direc
tions at different depths.
Scientists found the 1972 data lacking
in adequate information on wind direc
tions and changes. Since wind is rec
ognized as the major driving force in
upwelling systems, emphasis was made
in 1973 on increasing wind data from
anemometers on land and sea stations.
In addition to new data-gathering
techniques and equipment, a wholly new
shipborne computerized data storage,
processing, and display system was used
in 1973, packed totally in a van about
half a room large, and placed on board
the Thomas G. Thompson. This system
acquired data on the spot, processed it, and provided scientists with a nearly
"real time" look at the area they were
studying to help them update their plans during the cruise.
A step closer to prediction
ome parts of the upwell ing process
have been successfully simulated
on two-dimensional , two-layer ,
t ime-dependent numerical models over
coastal regions of simple topography
under steady wind condit ions. James
O'Brien and John J. Walsh , Univers i ty
of Wash ing ton , are working on models
tha t encompass basic features—the slope
and configuration of the coastal shelf,
the direction and speed of wind, b io
logical variables, the flow of currents
and countercurrents , and the size and
movemen t of the upwell ing.
But since upwell ing is a th ree-d imen
sional affair, actually four w h e n one con
siders the time factor, O'Brien and his
co-workers are developing a three-
dimensional , t ime-variable circulation
model to handle the m a n y variables oc
curr ing during upwell ing. " W i t h this
mode l , " O'Brien says, " w e hope to pre
dict factors such as wid th of the upwel l
ing tongue , the times and areas for
upwel l ing to appear, and the flow of
currents .
"Numer ica l models of t ime-dependent
oceanographic phenomena have a par
ticularly promising fu ture ," he says.
" W i t h models from exper iments CUE I
and II already feeding forecasts on a
general scale, we hope numerical studies
will be applied to other upwel l ing re
gions th roughout the wor ld . "
The accumulation of data and test ing
of ha rdware and techniques du r ing CUE
II and other CUEA exper iments have
been building up to a large in terna t ional
project, J O I N T I, scheduled for February
t h rough M a y 1974 off the no r thwes t e rn
coast of Africa.
" J O I N T I is the first major exper iment
wi th all components of the CUEA pro
gram functioning toge ther , " says Barber.
The internat ional research project will be
conducted in the area of Cape Blanc in
cooperat ion with scientists from France,
G e r m a n y (East and W e s t ) , U.S.S.R.,
Tracks of winds, Arrows on this vector chart show how the wind blew daily aiory, the Oregon coast during July and Auguj-i "f 1972. Prevailing winds blew from the nc.!-> most of the time, but reversed around July 2, 6, 31, and August 15. During theo< reversals, upwelling slowed, shore watei temperatures rose, and fishing was generally poor until north winds picked up again.
Spain, the United Kingdom, and Mauritania—all participants in an even larger international program called Cooperative
Investigations of the Northern Part of
the Eastern Central Atlantic.
"The primary research objective of
JOINT I is exactly the same as the cen-
30 MOSAIC Winter 1974
al scientific objective of the CUEA pro-•am," he says: "to develop a total sys-m model of the complex process of swelling." The complete understanding of the
swelling phenomenon depends on the entification and correlation of changes . global atmospheric and ocean current rculations and in local mesoscale epilations—essentially on the dynamics lat drive, or fail to drive, upwelling. More data on physical processes and
lechanisms are still needed. For in-:ance, what are the effects on upwelling 'om irregularities of the sea bottom )pography? What energy transfers oc-xv from the wind to the ocean surface i different wind velocities and under iffering conditions of surface sea rough-ess? What are the qualitative appor-onments of sources of upwelled water nder different conditions of tempera-ires and currents? These are some of \e questions that scientists plan to ex-lore during the JOINT I expedition.
rotecting the ocean's resources
he major practical benefit of an upwelling prediction system for locations throughout the world is that
shermen will be able to obtain an bove-average harvest with less time 'asted searching for fishing locations. . potential hazard, of course, is that nee the actual time and place of up-'elling can be predicted, fishermen will verfish the resources of the sea.
"Scientists are aware of the possibil-ies that, with scientific and technolog-:al knowledge such as we are finding, shermen may take more from the sea aan can be naturally replaced," says arber. Any kind of control over fishing ghts and international legal codes is Dmplex and hard to enforce, especially >r the smaller coastal nations. Cer-linly, lack of regulation has contributed } the ruin of several fishing industries—-le California sardines, for instance, or ae menhaden on the East Coast.
Overfishing as well as other factors ach as ocean pollution is a serious threat ) be considered and controlled in order D maintain life and productivity of the ea. "Yet we have to be careful in inter-reting what we think affects the marine opulation," points out Barber. "Other actors have to be considered—for in-tance, the natural biological cycles of
International rendezvous. In the summer of 1974 scientists from more than half a dozen nations will fake part in JOINT I to study upwelling dynamics off the West African coast.
fish population. At times a species of fish may become abundant; at other times in their biological cycle there may be a natural decrease in their numbers."
By gaining a deeper understanding of the physical and biological dynamics of upwelling, scientists, fishermen, and national legislators will have more potential control over the supply of fish stock. "In other words," Barber says, "scientists can forecast the possibility of upwelling and hence productivity of fish in certain local areas. The fishing industry and national resources offices can then be alerted as to whether they should reduce their fishing quota or shorten the fishing season to let the fish
stock be replenished. Or in a good year they can increase their fishing harvest without damaging the stock."
Already, In some countries, fishing controls have been Instituted. In Peru, for instance, fishing regulations are extremely strict. For the small, newly developing coastal countries it is important that their marine resources be under legal protection.
"For the world as a whole," says Barber, "there is a high payoff in the new scientific and technological knowledge of upwelling and fish harvest. Large and small nations need cooperation in order to preserve, protect, and manage these resources of the sea." •
MOSAIC Winter 1974 31