Upwelling Of Nutrients Research Articles

NUMERICAL EXPERIMENTS OF SEASONAL VARIATION OF WATER QUALITY IN OSAKA BAY

In examining the seasonal variation of water qualities and ecological characteristics, it is of great importance to establish eco-system numerical modelling accompanied with 3-D baroclinic flow model. The model describes the biological and chemical processes in the estuarine lower trophic eco-system in terms of chlorophyll-a, inorganic nitrogen, inorganic phosphorus, organic nitrogen, organic phosphorus, COD, DO. The model performance in simulating seasonal variation of water qualities in Osaka Bay can be conformed through the field data. In particular, the increase in phyto-plankton in the bay head is dependent of upwelling of nutrients in lower layer transported by the estuarine circulation.

Nutrient mineralization patterns in shelf waters of the Western Iberian upwelling

A set of hydrographic data collected during several cruises to the NW Iberian upwelling system has been used to assess the patterns of nutrient mineralization over the shelf. Mineralized nutrient ratios (N/P and N/Si) in the lower water column are clearly below the ratios characteristic of freshly upwelled oceanic waters. Nitrogen mineralization, in comparison to phosphorus mineralization, is incomplete, in agreement with phosphate's faster regeneration rate and the low residence time of water, which precludes complete mineralization. Silicate shows the highest enrichment as a consequence of the selective concentration of particulate biogenic silica in the near bottom waters. Diffusion of nutrients mineralized in the sediments seems to represent an important contribution. The lowest mineralization of the surveyed area is found to the north of Cape Finisterre, especially with regard to silicate. To the South, the Rias Baixas (four large embayments) return as reducing particulate organic matter (POM) a small fraction of the upwelled nutrients imported from the shelf. However, the out-flowing freshwater contributes to stratification of coastal waters, which favours POM production, accumulation and sedimentation. In addition, high levels of new dissolved organic matter (DOM) in the outflow can also enhance primary production in shelf surface waters. Finally, highest mineralization was found to the south of the River Miño, where there are no embayments and the shelf is wider. Mineralization tends to: (1) increase the potential primary production of this ecosystem by up to 50%, (nitrogen limitation) or up to 80% (silicon limitation); (2) favour the development of phytoplankton assemblages dominated by diatoms (Si enrichment double that of N and P); and (3) buffer the large spatial and temporal differences introduced by the advected nutrients. © 1997 Elsevier Science Ltd

Mechanism of the biological response to winter cooling in the northeastern Arabian Sea

THE Arabian Sea is one of the most biologically productive ocean regions1, mainly due to the upwelling of nutrients during the summer (southwest) monsoon. But the northern Arabian Sea continues to sustain fairly high biological production after the upwelling season and during much of the winter (northeast) monsoon2–4. The processes that enable this high winter productivity have hitherto been poorly understood, being variously attributed to surface cooling effects2,3 or wind-driven changes in ocean circulation4. Here we present physical, chemical and biological data that indicate that sea surface cooling drives convection processes that lead to the injection of nutrients up into the surface waters of the northeastern Arabian Sea during winter, and that this mechanism of nutrient supply is a dominant control on winter productivity. Observed seasonal changes in bacterial and microzooplankton populations may provide an explanation for the Arabian Sea 'paradox'5–8 that mesozooplank-ton biomass remains more or less invariable throughout the year.

The upwelling of nutrients in the central Skagerrak

Measurements of inorganic nutrients during four expeditions to the Skagerrak, within the SKAGEX programme in 1990 and 1991, form the basis for estimation of the magnitude of potential new primary production caused by upwelling of nutrients in the central part of Skagerrak. Calculations have been made using available transport and upwelling data given in the literature together with the concentrations of nitrogenous nutrients (nitrite, nitrate and ammonia), phosphate and silicate in the lower part of the pycnocline in the upwelling area. The potential new production of organic matter due to upwelling is estimated at 6.15 × 10 6 t C year −1 based on a vegetative period of 8 months. This corresponds to 190 gC m −2 year −1 if distributed over the entire Skagerrak area. A possible contribution to diatom production from the upwelling of silicate is estimated to be 2.09 × 10 6 t C year −1, which corresponds to 64 gC m −2 year −1.

Nitrogen-Pulsed Systems on the Coast of Northwest Spain

Simulation models of two ecosystems—an estuary used for aquaculture and an offshore pelagic community, were used to examine the effects of upwelled pulses of nutrients versus constant inputs at the same annual rate. The estuary, the Ria de Arosa in northwest Spain (Galicia), showed little difference, in either productivity or cyclie behavior, between simulations of pulsed inputs versus constant input. This was partly because of its function as a shortterm sediment and nutrient trap and, more importantly, because of the presence in the estuarine pelagic zone of a large biomass of efficient filter-feeding mussels, unresponsive to advective transport. Most (81%) of the inwelled nutrient was transformed into biomass and harvested as seafood. This was unchanged by replacing the periodic infusions of nutrient with a constant daily rate of input. However, in the pelagic model, nutrient pulsing produced a rich dynamical behavior of the trophic components, which retained 61% of the upwelled nutrients at the end of 60 d. Replacing upwelling and relaxation with a constant current and constant low input of nutrients largely obliterated the dynamical behavior and resulted in a nutritionally impoverished system that lost from 73% to 102% of the upwelled nutrient within 60 d. Mech anistic models are put forward as useful tools for both guiding research on pulsed behavior and predicting its effects.

Mesoscale pigment fields in the Gulf Stream: Observations in a meander crest and trough

In September‐October 1988 and April 1989 a series of hydrographic transects were completed across the Gulf Stream front in a meander crest and meander trough, respectively. One of the main experimental objectives was to relate the spatial distribution of chlorophyll to the physical fields of Gulf Stream meanders. Chlorophyll distributions are derived from conductivity‐temperature‐depth (CTD)/fluorescence profiles calibrated with discrete pigment samples collected from bottles at several depths at various stations. Objective analysis (OA) maps and vertical sections, in stream coordinates, of chlorophyll on density surfaces show the chlorophyll distribution was strongly related to the structure of the Gulf Stream front. In particular, chlorophyll concentrations greater than 0.4 mg m−3 were at, or inshore of, the Gulf Stream north wall. Characteristic length scales of chlorophyll distribution determined from the horizontal and temporal correlation function are the same order (50–100 km) as length scales of the physical variables. The maximum chlorophyll concentrations in the vertical were from the surface to 50‐m depth on the western flank of the meander crest and deepened to 75‐ to 100‐m depth on the eastern flank. This coincides with the deepening of the 24.4–25.7 σθ surfaces from the western to the eastern flank of the meander crest. Although in the spring cruise the maximum chlorophyll concentrations were also found at depths between the surface and 100 m, there were no clear distinctions in pigment distributions between the western and eastern transects of a relatively weak trough. Maximum chlorophyll concentrations, 1.0–1.5 mg m−3, from the 1989 spring bloom in slope waters were about double those observed in the 1988 fall data. The primary physical mechanisms influencing the mesoscale pigment distribution in Gulf Stream meanders observed in this study are (1) outcropping of nutrient‐bearing strata in the spring, (2) meander‐induced upwelling of nutrients along sloping isopycnals, and (3) Gulf Stream‐ring interactions.

Nutrient distributions during an annual cycle across a warmcore eddy from the E. Mediterranean Sea

A detailed description of the physical, chemical and biological structure of the Cyprus eddy is given from cruises carried out in February, May, September and November 1989. The chemical data support the suggestion ( Brenner et al., Dynamics of Atmospheres and Oceans, 15, 457–477, 1991) that this eddy forms essentially in situ by the injection of 250–300 m of Levantine Intermediate Water into the upper layers of the water column. The nitrate vs temperature profile is characteristic of this longitude and not of one transported rapidly from farther west. The silicate vs depth profile at the boundary can be superimposed on that from the core if its is displaced downward by 250 m. The depth of the nitrate maximum in the core also is displaced downward by 250–300 m relative to the boundary. There was no evidence of a different origin of the core water based on nutrient profiles on Sigma-T surfaces. These data suggest that the Cyprus eddy is similar in many respects to a mid-ocean eddy, not a ring. There was enhanced productivity in the core of the eddy in winter. This bloom occurred simultaneously with deep (> 350 m) mixing of the water column, and possibly in part as the result of algal growth at unusually low light levels. There was no evidence of enhanced productivity at the boundary of the eddy, suggesting that the upwelling of nutrients was weak and that the enhanced productivity observed in the boundary of rings is more related to the strong temperature front or entrainment of shelf waters. It is cautioned that several important physical and biological features of this eddy would not have been seen using satellite imagery.

Increasing seasonal upwelling in the subtropical South Atlantic over the past 700,000 yrs: Evidence from deep-living planktonic foraminifera

The distribution and character of deep-living planktonic foraminifera (such as Globorotalia truncatulinoides and G. hirsuta) are particularly sensitive to the structure of the upper ocean because of the wide range of water depths over which their life cycles extend. Like other planktonic foraminifera, the deep-living species begin growing in shallow surface waters, but unlike the other species they continue growing while sinking into much deeper water. Their reproduction is synchronized with the seasonal deep-mixing and upwelling of nutrient-rich waters that precedes spring bloom. Where deep-mixing is curtailed the abundances of the deeper-dwelling species ( G. hirsuta), the deeper-dwelling varieties (e.g., left-coiling G. truncatulinoides), and the larger (presumably faster-sinking) shells are reduced (leading to an apparent acceleration in shell development). These changes are observed today in transects from the seasonally deep-mixed subtropical gyres to the seasonally-stable surface waters equatorward of the subtropical convergences. Past changes in the abundance and character of these deep-living planktonic foraminifera have been measured in a Late Pleistocene record from the subtropical western South Atlantic Ocean. Over the past 700 kyrs, abundances of these species have increased, G. truncatulinoides has changed from the predominantly shallower-dwelling right-coiling to the deeper-dwelling left-coiling variety, and the accelerated shell development characteristic of shallow mixing has shifted toward the rates normally associated with deep mixing. All this indicates that the structure of the upper ocean in the subtropical South Atlantic before 700 kyrs ago was more like that nearer the equator today where mixing is limited to the upper 100–200 m. Since that time the scale of mixing has gradually increased to more than 400 m. This implies a gradual increase through the Late Pleistocene in the seasonal upwelling of nutrients in the subtropical South Atlantic and, consequently, in the intensity of the seasonal maximum in organic productivity.

Evidence for lower productivity in the Antarctic Ocean during the last glaciation

BOTH increased biological productivity and more efficient uptake of upwelled nutrients in high-latitude oceans have been proposed1–5 as mechanisms responsible for the glacial reduction in atmospheric concentrations of carbon dioxide deduced from ice-core measurements6–8. These glacial models invoke more efficient "biological pumping9 of carbon into the deep sea by increasing the uptake of 'excess' biolimiting nutrients in the Antarctic surface ocean9 or by reorganizing chemical circulation patterns within the ocean10,11. Here we challenge this conventional view with new evidence from tracers of palaeoproductivity preserved in Antarctic sediments. Records of the accumulation rates of diatom shells, the ratio of germanium to silicon in diatomaceous opal and the carbon isotope ratio in foraminiferal carbonate all suggest lower glacial productivity and less efficient uptake of nutrients. Although alternative interpretations are possible, our results support previous studies that indicate lower glacial productivity in the Southern Ocean12,13 and raise new questions about the role of ocean productivity in models of the causes (or remedies) for changes in atmospheric concentrations of carbon dioxide.

Glacial‐interglacial CO2 change: The Iron Hypothesis

Several explanations for the 200 to 280 ppm glacial/interglacial change in atmospheric CO2 concentrations deal with variations in southern ocean phytoplankton productivity and the related use or nonuse of major plant nutrients. An hypothesis is presented herein in which arguments are made that new productivity in today's southern ocean (7.4 × 1013g yr−1) is limited by iron deficiency, and hence the phytoplankton are unable to take advantage of the excess surface nitrate/phosphate that, if used, could result in total southern ocean new production of 2−3 × 1015 g C yr−1. As a consequence of Fe‐limited new productivity, Holocene interglacial CO2 levels (preindustrial) are as high as they were during the last interglacial (≈ 280 ppm). In contrast, atmospheric dust Fe supplies were 50 times higher during the last glacial maximum (LGM). Because of this Fe enrichment, phytoplankton growth may have been greatly enhanced, larger amounts of upwelled nutrients may have been used, and the resulting stimulation of new productivity may have contributed to the LGM drawdown of atmospheric CO2 to levels of less than 200 ppm. Background information and arguments in support of this hypothesis are presented.

The effect of fish density and species combination on growth and utilization of natural food in ponds

. Interactions between bottom-feeding fish (common carp, Cyprinus carpio L., and hybrid tilapia) and a filter feeder (silver carp, Hypophthalmichthys molitrix (Valenciennes)) in polyculture were studied in fertilized ponds with no supplementary feeding. The silver carp were stocked at two densities: 1300 and 2600/ha. Growth rate and yield of each of the species were also compared with those in polyculture of bottom feeders alone, and in a monoculture of silver carp alone, at the same densities. The consumption of natural feed as melabolizable energy (ME) was calculated by the energy balance (requirement for maintenance and growth divided by the utilization efficiency). Increasing the density of silver carp reduced proportionally their own growth rate, due to the limited amount of food. Above a density of about 1000/ha, silver carp inhibit the growth rate of common carp and tilapia. This inhibition was small at 1300 silver carp/ha, but considerable at 2600/ha. However, the presence of bottom feeders increased the growth rate of silver carp at both densities. Calculated natural food consumption showed that growth interactions between species were brought about through the availability of food. The synergistic effect of the bottom-feeding fish on the silver carp is assumed to be due to the upwelling of bottom nutrients to the upper layers of water by the burrowing of the fish in the mud. Combined yield of all species in the polyculture was highest at the density of 1300 silver carp/ha (2116 kg/ha in 156 days). At 2600 silver carp/ha the inhibition of growth rate of silver carp itself, reduced total yield as compared with the lower density.

Tidal jets, nutrient upwelling and their influence on the productivity of the alga Halimeda in the Ribbon Reefs, Great Barrier Reef

A field experiment was carried out to study water circulation and benthic biological productivity near a passage through the Ribbon Reefs in the northern Great Barrier Reef of Australia. The currents through the passage were phase-locked with the tide. During rising tides, strong currents through the passage generated localized upwelling on the upper continental slope, enriching the depleted surface waters in nutrients, particularly nitrate and phosphate. Simultaneously, on the shelf side of the passage, a tidal jet-vortex pair system developed, which separated from the Ribbon Reefs so that the coral reefs themselves received little of the upwelled water. This was propagated as a bottom-trapped layer towards the meadows of the calcareous alga Halimeda situated several kilometres inshore of the reefs. Halimeda can accumulate nutrients, particularly nitrate, from the relatively low concentrations available from the upwelling events. The quantity of nitrogen upwelled was more than sufficient to supply the total nitrogen requirements of the Halimeda vegetation. A tidal jet also formed, offshore from the reef passage, during falling tides and the coral-covered offshore side of the Ribbon Reefs may be sustained by the subsequent vertical turbulent entrainment into the jet of deep, nutrient-rich water immediately offshore from the reef passages. These processes require a continuous barrier reef with only narrow passages several kilometers apart. Numerical models successfully reproduce the observations of jet-driven upwelling and of the dynamics of the tidal jet-vortex pair system. The model predictions are very sensitive to the details of the bathymetry of reef passages. As such data are presently unavailable, it is not yet possible to use these models to calculate the jet-driven nutrient upwelling for the whole Great Barrier Reef.

Northeast Pacific iron distributions in relation to phytoplankton productivity

Dissolved and particulate Fe concentrations, measured at three deep ocean stations on a 1600 km inshore-offshore VERTEX transect, were compared with those found at four shallow California continental margin stations. The three VERTEX profiles shared similar features: very low dissolved Fe levels (<0.1 nmol kg−1) in surface waters, increasing amounts with depth, and maxima (∼1.0–1.3 nmol kg−1) in association with the oxygen minimum. In contrast, concentrations as high as 9 nmol kg−1 of dissolved Fe were found at the shallow margin stations, in association with elevated levels of Mn (17 nmol kg−1) and Co (200 pmol kg−1).Inshore and offshore Fe distributions were evaluated in relation to the phytoplankton's requirement for this essential element. Local shelf diagenetic Fe input appears to be adequate for phytoplankton growth even in environments where increased demand results from the upwelling of major nutrients. However, the Fe laterally mixed out into the ocean's interior within the oxygen minimum and supplied to the surface via vertical mixing processes provides only a few percent of open ocean phytoplankton demand; the other 95% must be provided by atmospheric input.We also consider environments in which Fe supplies may be limiting phytoplankton growth; i.e. surface waters of the Subarctic and Antarctic, where major nutrients are never depleted. We postulate that atmospheric Fe input rates are not high enough to meet the elevated phytoplankton demand resulting from offshore major nutrient upwelling. As a result, major nutrient depletion occurs only along continental margins and ice edges, where Fe supplies should be adequate.Atmospheric dust concentrations were one to two orders of magnitude higher in glacial times than those in the present and last interglacial periods. The lower glacial atmospheric CO2 levels, which resulted from the increased biological utilization of major nutrients at high latitudes, may have been stimulated by the enhanced availability of atmospheric Fe.

Seasonality in East Africa's coastal waters

A review of existing literature and data on seasonal patterns in East Africa's coastal waters indicates distinct seasonality in physical, chemical and biological oceanographic parameters. Seasonal patterns are dictated by the behavior of the Inter-Tropical Convergence Zone (ITCZ) which creates 2 distinct seasons the northeast and southeast monsoons. SE monsoon (March to October) meteorological parameters are characterized by high cloud cover, rainfall, river discharge, terrestrial runoff and wind energy while solar insolation and temperatures are low; SE monsoon oceanographic parameters are characterized by cool water, a deep thermocline, high water-column mixing and wave energy, fast currents, low s a h ~ t y and high phosphorus. These parameters are reversed during the NE monsoon. Nitrogen availability and planktonic primary productivity are high along the Somali coast and estuarine and river discharge areas during the southeast monsoons due to nutrient upwelling and terrestrial runoff. In near-shore waters off Tanzania, nitrogen fixation is the major source of nitrogen and is highest during NE monsoons when the water column is stable. Coral reef benthic algal biomass and diversity is greatest during the SE monsoons. Fish catch and reproduction are highest during NE monsoons in Kenya and Tanzania. Transition periods between monsoons may also be important times in determining productivity and reproduction.

Variations of upwelling and associated nutrient nitrogen dynamics off the north‐west coast of South Island, New Zealand

Abstract The surface distribution and metabolic uptake of nitrate and ammonium were investigated as they related to the movements of water in the upwelling zone off the north‐west coast of South Island, New Zealand. Analyses were also made of chlorophyll a and paniculate nitrogen as indicators of phytoplankton biomass. The movement of water and resulting dispersion from the upwelling focus were shown to differ greatly from day to day; this could confound simple correlations between nutrient nitrate and phytoplankton. A suitable model to investigate metabolic processes due to influx of fertile upwelled water which could avoid this problem can be based upon assays of NO3 and NH4 uptake by the plankton. These assays, done with 15NH4 and I5NO3, could provide an operational index for identifying the zone of nett production due to nutrient upwelling.

Phytoplankton growth response to wind induced regional upwelling occurring around the Izu Islands off Japan

From frequent field observations performed in coastal waters around the Izu Islands, Japan, a clear regional upwelling associated with the wind was detected baside Niijima Island. Nutrient supply by the upwelling into the euphotic zone was confirmed, and the subsequent phytoplankton growth supported by the upwelled nutrients was evaluated. The upwelling and the nutrient supply occurred within a day over an area ofca. 400 km2, and phytoplankton growth response occurred only a few days after the upwelling. Such regional upwelling is considered to be one of the major mechanisms supporting the high productivity of coastal waters.

Ecological Significance of Upwelling Events in Lake Ontario

Upwelling events in Lake Ontario were studied to determine (1) their significance as mechanisms to provide nutrients from the hypolimnion to the epilimnion and (2) their impact on resident plankton communities of the nearshore zone. It was concluded that such events did not result in sufficient mixing to recharge nutrient stocks of these areas. Upwellings were characterized as being temporal displacements of nearshore water masses which returned at the end of each event. Plankton communities of the nearshore area were displaced with the water mass and therefore received little or no benefit from the upwelled nutrient rich hypolimnetic waters. Evidence is provided to suggest that diatom species such as Asterionella formosa Hass and Fragilaria crotonensis Kitton were able to grow in the upwelled hypolimnetic water, and upwellings might be a mechanism to inoculate these species into the epilimnion of deep lakes prior to the autumn overturn. Upwelling events also caused rapid shifts in the species composition of zooplankton communities. Such shifts were particularly pronounced within 1 km of the shoreline.

Oceanographic Controls on Organic Matter in Miocene Monterey Formation, Offshore California: ABSTRACT

Analyses of the type and amount of organic matter in Tertiary through Quaternary sediments drilled during DSDP Leg 63, off the coast of California, can be used to provide insights into the controls of deposition of the Monterey Shale. The regional oceanography, rather than basin silling, controls the accumulation of organic matter in these sediments. The laminated, siliceous, and organic-rich Monterey Shales were deposited under anoxic conditions within a well-developed oxygen minimum zone like that in today's Gulf of California. The oxygen minimum zone became strongly developed in response to increased upwelling and productivity caused by global cooling following development of an Antarctic ice sheet 13 to 14 m.y. ago. A drop in sea level 10 to 11 m.y. ago lowered the ba e of the anoxic oxygen minimum zone to water 2,500 to 3,000 m deep permitting substantial accumulation of organic matter in the late Miocene and early Pliocene of the California borderland at DSDP Site 467. The base of the minimum stayed near this level until the Quaternary, then rose to 1,500 to 2,000 m, where it remains today. Phosphorite, indicative of a high rate of supply of nutrients, formed at the same time as the Monterey Shale, during the period of intensive upwelling from 13 to 14 m.y. into the Pliocene. A lessening of upwelling and supply of nutrients, and development of the oxygen minimum zone from the early Pliocene into the Quaternary, is implied by these data. The changes are associated with a warming trend and a rise in sea level. End_of_Article - Last_Page 999------------