Nutrient-rich Deep Water Research Articles

Distribution and sources of particulate organic matter in a mesoscale eddy dipole in the Mozambique Channel (south-western Indian Ocean): Insight from C and N stable isotopes

This study investigates eddy induced transport processes that affect the sources and sinks of organic matter in the Mozambique Channel (MC). Eddies generated in the MC interact with the continental shelf and have been hypothesized to act as conveyor belts that entrain coastal production offshore. A combination of natural isotope tracers, elemental composition and physico-chemical variables allowed distinguishing two sources of organic matter within the eddy dipole. Near the surface, coastal POM was entrained at the anti-cyclonic boundary and further transferred into the eddy. Anti-cyclonic surface POM containing coastal POM was downwelled into deeper layers where decomposition greatly affected its composition. In contrast, cyclonic water promoted new production, by upwelling nutrient-rich deep waters into the euphotic zone. This production circulated through the mixed layer of the cyclone and was possibly advected into the boundary. Boundary F(max) and surface waters shared characteristics with the cyclone and anti-cyclone respectively as the result of both import of primary production of cyclonic origin occurring at F(max) and entrainment of coastal biological material at the surface. In the overall low productivity environment of the MC, it is likely that the continuous migration of mesoscale eddies along the shelf plays an important ecological role both in enhancing pelagic production and transporting coastal production offshore.

Mixing in the Barents Sea Polar Front near Hopen in spring

Observations were made of hydrography, nutrients and shear microstructure in the water column across the Barents Sea Polar Front near Hopen. Profiles were collected in early May 2008 along a 125-km section extending from the Hopen Trench, across the front between the Arctic and Atlantic origin waters, and on toward the Spitsbergenbanken. Additionally a 10-h time series station was undertaken near the front. The Polar Front was identified near the 150m isobath, coinciding with the 1°C isotherm, with strong horizontal gradients in the temperature and salinity fields, which compensated in density. A second tidally-generated front with a strong horizontal density gradient was detected on the bank, dominated by salinity gradients due to ice melt. Biological activity was elevated between the two fronts. Nutrients were depleted in the euphotic zone where the chlorophyll concentrations were significantly enhanced relative to the stations on the warm side of the Polar Front and in the tidally mixed area. Below a turbulent surface layer, the water column on the warm side of the front was quiescent. Farther on the bank the turbulent boundary layers near the surface and seabed merged and the entire water column was turbulent. Energy arguments show that tidal straining together with stirring due to wind and tides can overcome the stratification induced by melting and heating, maintaining the tidal front. A mechanism is proposed whereby high nitrate concentrations on the warm side of the front are transported along the isopycnals onto the bank where tidal mixing then effectively mixes the nutrient-rich deep water upward, sustaining the phytoplankton bloom.

Warming Oceans, Phytoplankton, and River Discharge: Implications for Cholera Outbreaks

Phytoplankton abundance is inversely related to sea surface temperature (SST). However, a positive relationship is observed between SST and phytoplankton abundance in coastal waters of Bay of Bengal. This has led to an assertion that in a warming climate, rise in SST may increase phytoplankton blooms and, therefore, cholera outbreaks. Here, we explain why a positive SST-phytoplankton relationship exists in the Bay of Bengal and the implications of such a relationship on cholera dynamics. We found clear evidence of two independent physical drivers for phytoplankton abundance. The first one is the widely accepted phytoplankton blooming produced by the upwelling of cold, nutrient-rich deep ocean waters. The second, which explains the Bay of Bengal findings, is coastal phytoplankton blooming during high river discharges with terrestrial nutrients. Causal mechanisms should be understood when associating SST with phytoplankton and subsequent cholera outbreaks in regions where freshwater discharge are a predominant mechanism for phytoplankton production.

Paleoenvironmental changes in the Pacific sector of the Southern Ocean (Antarctica) during the past 2.6 Ma

Two deep-sea cores (ANTA95-157 and ANTA98-1) were collected in the Pacific sector of the Southern Ocean across the present-day position of the Antarctic Polar Front Zone (APFZ) to document paleoenvironmental changes during the last 2.60 Ma. The stratigraphic framework was established using a combination of diatom marker species, Accelerator Mass Spectrometry (AMS) 14C datings, magnetostratigraphy, and oxygen stable isotopes. The study was based on carbon and nitrogen isotopes of diatom-bound organic matter, dry bulk density, magnetic susceptibility, carbonates and biogenic silica contents. Large continental inputs were recorded during glacial periods and major iceberg melting occurred at 2.45 Ma and during the Middle Pleistocene Revolution (MPR) time interval. Diatom production increased during the Early Pleistocene and remained significant ever since, with the exception of the MPR period and immediately before. Lower glacial diatom productivity linked to higher nitrogen utilization might have characterized the period between Marine Isotope Stages (MISs) 15–13 (0.6 and 0.5 Ma), whereas succeeding glacial stages experienced an increase of diatom productivity promoted by the inflow of nutrient-rich deep waters. The low diatom production observed during interglacial stage 11 could be explained with a southward shift (up to 4°) of the Polar Front (PF) with respect to its present position. Paleoproductivity levels have been confirmed as lower than those measured in other sectors of the Southern Ocean, with reduced differences among glacial and interglacial stages.

Preliminary report on the first appearance of nutrient-rich deep water in inner zone of the Kuril Arc

Preliminary report on the first appearance of nutrient-rich deep water in inner zone of the Kuril Arc

High Arabian Sea productivity conditions during MIS 13 – odd monsoon event or intensified overturning circulation at the end of the Mid-Pleistocene transition?

Abstract. Marine isotope stage (MIS) 13 (~500 000 years ago) has been recognized as atypical in many paleoclimate records and, in particular, it has been connected to an exceptionally strong summer monsoon throughout the Northern Hemisphere. Here, we present a multi-proxy study of a sediment core taken from the Murray Ridge at an intermediate water depth in the northern Arabian Sea that covers the last 750 000 years. Our results indicate that primary productivity conditions were anomalously high during MIS 13 in the Arabian Sea and led to extreme carbonate dissolution and glauconitization in the deep-sea sediments. These observations could be explained by increased wind driven upwelling of nutrient-rich deep waters and, hence, by the occurrence of an exceptionally strong summer monsoon event during MIS 13, as it was suggested in earlier studies. However, ice core records from Antarctica demonstrate that atmospheric methane concentrations, which are linked to the extent of tropical wetlands, were relatively low during this period. This constitutes a strong argument against an extremely enhanced global monsoon circulation during MIS 13 which, moreover, is in contrast with results of transient climate modelling experiments. As an alternative solution for the aberrant conditions in the Arabian Sea record, we propose that the high primary productivity was probably related to the onset of an intensive meridional overturning circulation in the Atlantic Ocean at the end of the Mid-Pleistocene transition. This may have led to an increased supply of nutrient-rich deep waters into the Indian Ocean euphotic zone, thereby triggering the observed productivity maximum.

Long-term variability of shelf water intrusion and its influence on hydrographic and biogeochemical properties of the Seto Inland Sea, Japan

The variability of the pathway of the Kuroshio is known to control that of the intensity of upwelling of the cold and nutrient-rich deep shelf water at the shelf-break point. This study has investigated the influences of the long-term variability of the hydrographical and biogeochemical conditions at the shelf-break point on those in the inner Seto Inland Sea. Results from observations conducted since 1972 by prefectural fisheries observatories showed a temporary decrease of temperature in the lower layer of the entrance of Kii Channel in summertime in the specific years when the Kuroshio pathway favored deep shelf water intrusion. A corresponding change in temperature was also found in the inner shelf sea, such as western Osaka Bay and Harima-Nada. The model developed in this study covers a 30-year period and well reproduces the temporal change in temperature. It also shows sufficient reproducibility in both seasonal behavior of hydrographical and biogeochemical properties and the inter-annual variability of hydrographical properties throughout the eastern Seto Inland Sea. It was found that the inter-annual variations of annual total flux through the section at the entrance to Kii Channel affect the inter-annual variation of the observed concentration of Dissolved Inorganic Nitrogen (DIN) in Harima Nada, but the effect was smaller than those of river input and other parameters.

Mesoscale physical–biological–biogeochemical linkages in the open ocean: An introduction to the results of the E-Flux and EDDIES programs

Mesoscale currents, fronts, and eddies are ubiquitous and energetic features of ocean circulation. These phenomena, sometimes referred to as the “internal weather of the sea,” accommodate a diverse set of physical, chemical, and biological interactions that influence marine biogeochemistry on a wide range of timescales. These biogeochemical processes include the “biological pump”, i.e. the transfer or flux of biologically produced organic matter and associated elements from the surface ocean to depth (Ducklow et al., 2001; Volk and Hoffert, 1985). Within ~ 80% of the world’s oceans, the productivity and species composition of the autotrophic organisms that contribute to the biological pump are typically limited by major nutrients (e.g. nitrogen, phosphorus, and silica), or trace metals (e.g. iron). Primary production in such oligotrophic regions therefore depends mostly on intense recycling of nutrients within the surface sunlit waters, with only a small fraction supported by that entering from the atmosphere, or from the physical transport of nutrients from nutrient-rich deep waters below. Evidence that mesoscale and submesoscale phenomena play a role in the latter process dates back more than two decades (Angel and Fasham, 1983; Franks et al., 1986; Ring Group, 1981; Tranter et al., 1980; Venrick, 1990; Woods, 1988).

The influence of a mature cyclonic eddy on particle export in the lee of Hawaii

Abstract Mesoscale eddies may enhance primary production (PP) in the open ocean by bringing nutrient-rich deep waters into the euphotic zone, potentially leading to increased transport of particles to depth. This hypothesis remains controversial, however, due to a paucity of direct particle export measurements. In this study, we investigated particle dynamics using 234Th–238U disequilibria within a mesoscale cold-core eddy, Cyclone Opal, which formed in the lee of the Hawaiian Islands. 234Th samples were collected along two transects across Cyclone Opal as well as during a time-series within the eddy core during a decaying diatom bloom. Particulate carbon (PC), particulate nitrogen (PN) and biogenic silica (bSiO2) fluxes at 150 m varied spatially and temporally within the eddy and strongly depended on the 234Th model formulation used (e.g., steady state versus non-steady state, inclusion of upwelling, etc.). Particle fluxes estimated from a steady state model assuming an upwelling rate of 2 m day−1 yielded the best fit to sediment-trap data. These 234Th-derived particle fluxes ranged from 332±14 to 1719±53 μmol C m−2 day−1, 27±3 to 114±12 μmol N m−2 day−1, and 33±20 to 309±73 μmol Si m−2 day−1. Although PP rates within Cyclone Opal were elevated by a factor of 2–3, PC and PN fluxes were the same, within error, inside and outside of Cyclone Opal. The ratio of PC export to PP remained surprisingly low at

Nitrogen dynamics within a wind-driven eddy

Abstract Wind-driven cyclonic eddies are hypothesized to relieve nutrient stress and enhance primary production by the upward displacement of nutrient-rich deep waters into the euphotic zone. In this study, we measured nitrate (NO 3 − ), particulate carbon (PC), particulate nitrogen (PN), their stable isotope compositions ( δ 15 N-NO 3 − , δ 13 C-PC and δ 15 N-PN, respectively), and dissolved organic nitrogen (DON) within Cyclone Opal , a mature wind-driven eddy generated in the lee of the Hawaiian Islands. Sampling occurred in March 2005 as part of the multi-disciplinary E-Flux study, approximately 4–6 weeks after eddy formation. Integrated NO 3 − concentrations above 110 m were 4.8 times greater inside the eddy (85.8±6.4 mmol N m −2 ) compared to the surrounding water column (17.8±7.8 mmol N m −2 ). Using N-isotope derived estimates of NO 3 − assimilation, we estimated that 213±59 mmol m −2 of NO 3 − was initially injected into the upper 110 m Cyclone Opal formation, implying that NO 3 − was assimilated at a rate of 3.75±0.5 mmol N m −2 d −1 . This injected NO 3 − supported 68±19% and 66±9% of the phytoplankton N demand and export production, respectively. N isotope data suggest that 32±6% of the initial NO 3 − remained unassimilated. Self-shading, inefficiency in the transfer of N from dissolved to particulate export, or depletion of a specific nutrient other than N may have led to a lack of complete NO 3 − assimilation. Using a salt budget approach, we estimate that dissolved organic nitrogen (DON) concentrations increased from eddy formation (3.8±0.4 mmol N m −2 ) to the time of sampling (4.0±0.09 mmol N m −2 ), implying that DON accumulated at rate of 0.83±1.3 mmol N m −2 d −1 , and accounted for 22±15% of the injected NO 3 − . Interestingly, no significant increase in suspended PN and PC, or export production was observed inside Cyclone Opal relative to the surrounding water column. A simple N budget shows that if 22±15% of the injected NO 3 − was shunted into the DON pool, and 32±6% is unassimilated, then 46±16% of the injected NO 3 − remains undocumented. Alternative loss processes within the eddy include lateral exchange of injected NO 3 − along isopycnal surfaces, remineralization of PN at depth, as well as microzooplankton grazing. A 9-day time series within Cyclone Opal revealed a temporal depletion in δ 15 N-PN, implying a rapid change in the N source. A change in NO 3 − assimilation, or a shift from NO 3 − fueled growth to assimilation of a 15 N-deplete N source, may be responsible for such observations.

Nutrient and organic matter patterns across the Mackenzie River, estuary and shelf during the seasonal recession of sea-ice

Suspended material, nutrients and organic matter in Mackenzie River water were tracked along a 300 km transect from Inuvik (Northwest Territories, Canada), across the estuarine salinity gradient in Kugmallit Bay, to offshore marine stations on the adjacent Mackenzie Shelf. All particulates measured (SPM, POC, PN, PP) declined by 87–95% across the salinity gradient and levels were generally below conservative mixing. Organic carbon content of suspended material decreased from 3.1% in the river to 1.7% in shelf surface waters while particulate C:N concurrently decreased from 17.1 to 8.6. Nitrate and silicate concentrations declined by more than 90% across the salinity gradient, with nitrate concentrations often below the conservative mixing line. Phosphate concentrations increased from 0.03 μmol/L in the river to 0.27 μmol/L over shelf waters, thereby changing the inorganic nutrient regime downstream from P to N limitation. Dissolved organic carbon decreased conservatively offshore while dissolved organic N and P persisted at high levels in the Mackenzie plume relative to river water, increasing 2.7 and 25.3 times respectively. A deep chlorophyll- a maximum was observed at two offshore stations and showed increases in most nutrients, particulates and organic matter relative to the rest of the water column. During river passage through the Mackenzie estuary, particulate matter, dissolved organic carbon and inorganic nutrients showed sedimentation, dilution and biological uptake patterns common to other arctic and non-arctic estuaries. Alternatively, inorganic content of particles increased offshore and dissolved organic N and P increased substantially over the shelf, reaching concentrations among the highest reported for the Arctic Ocean. These observations are consistent with the presence of a remnant ice-constrained (‘stamukhi’) lake from the freshet period and a slow flushing river plume constrained by sea-ice in close proximity to shore. Nutrient limitation in surface shelf waters during the ARDEX cruise contributed to the striking deep chlorophyll- a maximum at 21 m where phytoplankton communities congregated at the margin of nutrient-rich deep ocean waters.

Manganese content records seasonal upwelling in Lake Tanganyika mussels

Abstract. Biogenic productivity of Lake Tanganyika is highly dependent on seasonal upwellings of cold, oxygen-depleted, nutrient-rich deep waters. We investigated the shell of freshwater bivalve Pleiodon spekii as a geochemical archive of these periodic hydrological changes tuned by the monsoon regime. The results of a three-year-long limnological and geochemical survey of the coastal waters performed on the dissolved and particulate fractions were compared to LA-ICP-MS profiles of Mn in five aragonitic shells from the same lake location. Three shells present very similar Mn/Ca profiles dominated by a peak that matched the concomitant increase of Mn and chlorophyll a in surface waters during the 2002 upwelling, while a shell collected during 2003 dry season detect both 2002 and 2003 upwelling events. Larger shells showing an extremely reduced growth display more than 8 Mn/Ca peaks suggesting at least an 8-year-record of seasonal changes in water composition. We postulate that Mn/Ca in shells record the conjunction of an increase of biological activity with supplied of dissolved Mn and nutriments in coastal waters, resulting in an enhanced assimilation of biogenic Mn-rich particles. By combining the most recent generation of laser ablation system and the powerful High Resolution ICP-MS, the spatial resolution could be improved down to 5 to 10 µm crater size and end up in a better constrain of the relative variations of the annual Mn peaks. Such an approach on P. spekii from Lake Tanganyika has definitively a great potential to provide recent and past records on primary productivity associated with the monsoon climate system.

Distribution of bioactive trace metals (Fe, Co, Ni, Cu, Zn and Cd) in the Sulu Sea and its adjacent seas

Abstract Here we present the first vertical distribution of dissolved (D) and acid-dissolvable (AD) bioactive trace metals (Fe, Co, Ni, Cu, Zn and Cd) in the Sulu Sea and the South China Sea, together with those observed previously by the same method in the western North Pacific. At a depth of 50–75 m, concentration minima of some trace metals were observed in the Sulu Sea (D-Zn, Cu and Fe) and the South China Sea (D-Zn), which coincided with the Chl a maximum, indicating scavenging of these metals including biological uptake. Above 150 m in the South China Sea, elevated concentrations of D-Co and Cu were observed, which could result from fluvial/coastal waters and/or shelf-sedimentary sources. In the surface mixed layer in the Sulu Sea, D-Fe concentrations were high (2 nM), presumably due to the flowing of waters across the Philippine Archipelago. Except for Fe, concentrations of D and AD species at each corresponding depth were not significantly different. Concentrations of AD-Fe (6.8–17 nM), below 500 m in the Sulu Sea were much higher than those of D-Fe (0.2–1.7 nM), indicating that particulate Fe is abundant in the basin, probably coming from nearby sedimentary sources. The vertical distributions of D-Ni, Cu, Zn and Cd in the South China Sea were nutrient-like and deviated slightly from those in the western North Pacific. This is caused by a rapid flushing of waters from the Philippine Sea coupled with vertical mixing within the South China Sea. The distribution of these metals in the Sulu Sea was more uniform below 500 m. The average concentrations of D-Ni, Cu, Zn and Cd in the deep water of the Sulu Sea were 6.1, 1.5, 3.3 and 0.5 nM, significantly lower than those of the western North Pacific (9.6, 2.8, 10.1 and 1.0 nM, respectively). We also found lower D-Cd/PO4, Ni/PO4 and Zn/Si(OH)4 ratios in the Sulu Sea than those of the Pacific. The depletion of these concentrations and the D-Cd/PO4 and Ni/PO4 ratios in the Sulu Sea is probably because the deep water of the basin is rapidly exchanged with shallow waters but isolated from nutrient-rich deep waters derived from the North Pacific, due to the surrounding topographic barriers including the islands and the shallow sills ( While subsurface waters were flowing along density surfaces (sigma-T values of ∼26) from the South China Sea to the Sulu Sea, the concentrations of macronutrients, D-Ni, Cu, Zn and Cd increased due to the regeneration from biogenic particles. The increases in the concentrations of bioactive elements relative to that of PO4 were N : P : Si : Ni : Cu : Zn : Cd=15 : 1 : 40 : 2.4×10−3 : 0.6×10−3 : 2.7×10−3 : 0.03×10−3 in a molar unit.

Apparent biological fractionation between Cd and PO 4 in the surface waters of the equatorial Pacific Ocean

Apparent biological fractionation between cadmium (Cd) and phosphate (PO 4) in seawater from 10 to 200 m in the western and central equatorial Pacific was examined in January 2003 at nine stations. In this study period, a surface salinity front existed at approximately 175°W, dividing oceanographic conditions into two types: the Western Pacific Warm Pool (WPWP) (westward) and the eastern upwelling zone (eastward), and, at a depth of approximately 100–150 m, a thermocline developed, separating the surface water from the nutrient-rich deep water. Based on the temperature distribution, three types of water masses were defined: within the WPWP (> 29.2 °C), outside the WPWP above the top of the thermocline (the top of the thermocline is the water depth at which the temperature is 1 °C lower than the surface temperature), and below the top of the thermocline, generally corresponding to PO 4 concentrations of less than 0.25 μM, from 0.25 μM to 0.50 μM, and over 0.50 μM, respectively. The fractionation coefficient values were determined to be 0.36, 1.09, and 1.68 for the three layers defined, respectively, on the assumption that the uptake and regeneration processes of Cd and PO 4 by the biological activity obeyed first-order reaction kinetics. Similarly, Hagino et al. (2000) [Hagino, K., Okada, H., Matsuoka, H. (2000). Spatial dynamics of coccolithophore assemblages in the Equatorial Western-Central Pacific Ocean. Marine Micropaleontology 39, 53–72] have previously found that planktonic coccolithophorid assemblages in these waters also differ between these water masses, presumably discriminating among the three layers when selecting their habitat. By analogy, I speculate that the fractionation coefficient between the two constituents Cd and PO 4 varies according to differential uptake/regeneration of the species assembly in these populations of primary producers (and grazers), where sheer biomass and environmental conditions likely also play a role.

Decline of the marine ecosystem caused by a reduction in the Atlantic overturning circulation

Reorganizations of the Atlantic meridional overturning circulation were associated with large and abrupt climatic changes in the North Atlantic region during the last glacial period. Projections with climate models suggest that similar reorganizations may also occur in response to anthropogenic global warming. Here I use ensemble simulations with a coupled climate-ecosystem model of intermediate complexity to investigate the possible consequences of such disturbances to the marine ecosystem. In the simulations, a disruption of the Atlantic meridional overturning circulation leads to a collapse of the North Atlantic plankton stocks to less than half of their initial biomass, owing to rapid shoaling of winter mixed layers and their associated separation from the deep ocean nutrient reservoir. Globally integrated export production declines by more than 20 per cent owing to reduced upwelling of nutrient-rich deep water and gradual depletion of upper ocean nutrient concentrations. These model results are consistent with the available high-resolution palaeorecord, and suggest that global ocean productivity is sensitive to changes in the Atlantic meridional overturning circulation.

Upwelling-driven nearshore hypoxia signals ecosystem and oceanographic changes in the northeast Pacific.

Seasonal development of dissolved-oxygen deficits (hypoxia) represents an acute system-level perturbation to ecological dynamics and fishery sustainability in coastal ecosystems around the globe. Whereas anthropogenic nutrient loading has increased the frequency and severity of hypoxia in estuaries and semi-enclosed seas, the occurrence of hypoxia in open-coast upwelling systems reflects ocean conditions that control the delivery of oxygen-poor and nutrient-rich deep water onto continental shelves. Upwelling systems support a large proportion of the world's fisheries, therefore understanding the links between changes in ocean climate, upwelling-driven hypoxia and ecological perturbations is critical. Here we report on the unprecedented development of severe inner-shelf (<70 m) hypoxia and resultant mass die-offs of fish and invertebrates within the California Current System. In 2002, cross-shelf transects revealed the development of abnormally low dissolved-oxygen levels as a response to anomalously strong flow of subarctic water into the California Current System. Our findings highlight the sensitivity of inner-shelf ecosystems to variation in ocean conditions, and the potential impacts of climate change on marine communities.

Effect of wind induced water movements on nutrients, chlorophyll-a, and primary production in Lake Tanganyika

We determined the spatial and temporal distribution of major plant nutrients, dissolved oxygen, chlorophyll-a and primary production, at three deep-water locations in Lake Tanganyika to infer patterns of water displacements and to interpret the impact of wind-generated changes in nutrients on the timing and magnitude of phytoplankton production.In the southern end of the lake, the onset of cooler, windier conditions during May–September caused stratification weakening, tilting of isotherms and upwelling of dissolved inorganic nitrogen and soluble reactive phosphorus from nutrient-rich deeper waters. These factors coincided with an increase in chlorophyll-a concentrations but not with clear evidence of increased primary production. An internal seiche at that time seemed associated with similar but less pronounced events at the other stations after cessation of the winds.We suggest that internal seiching can spread kinetic energy throughout the lake, triggering upward nutrient fluxes through mixing elsewhere. The response to water displacements in terms of nutrient supply to the epilimnion seems to be governed by differences in the strength of vertical temperature, and by nutrient and dissolved oxygen gradients. At the most northern station, these gradients were strongest and closest to each other and throughout the year primary production rates, phosphorus and chlorophyll-a concentrations in the euphotic zone appeared generally higher than at the other stations, probably also because of increased nutrient input from the Rusizi River.We emphasise that the intra- and interannual differences between the strength of lake stratification and wind regime are of major importance in determining the extent of upwelling events upwind as well as internal seiching strength and duration. That consequently affects the extent of internal nutrient loading throughout the lake and ultimately plays an important role in the lake trophic status.

Enhancing fish stocks with wave-powered artificial upwelling

Ocean fisheries are declining worldwide due to overexploitation. Productivity could be enhanced and the problem alleviated by pumping nutrient-rich deep ocean water (DOW) to the surface to feed phytoplankton, the bottom end of a marine food chain, mimicking natural upwelling which sustains the most productive ocean fishing grounds in the world. Various pump types and power sources have been proposed for this purpose. The present article proposes a simple wave-powered pump to demonstrate the concept cost-effectively at prototype scale. Possible solutions to the problems of dilution and plunging of dense, nutrient-rich DOW are discussed. Two further possible benefits of this proposal are discussed: by extracting wave energy, relatively calm fishing grounds may be created close to markets, and by pumping up very large quantities of cold DOW, the surface temperature could be lowered enough to reduce coral bleaching on parts of the Great Barrier Reef.

Vertical Nutrient Distributions in the Western North Pacific Ocean: Simple Model for Estimating Nutrient Upwelling, Export Flux and Consumption Rates

A one-dimensional, steady-state model has been developed to understand the factors controlling vertical distributions of nutrients such as nitrate and phosphate in the western North Pacific water columns. The model includes simple physics and some biogeochemical processes. Nutrients are supplied by upwelling of nutrient-rich deep waters with a constant upwelling velocity and nutrient regeneration due to decomposition of sinking particulate matter; the latter is expressed by an exponential-type export flux. Nutrients are consumed in the water column due to uptake by marine organisms, represented by a first-order substrate kinetics. The consumption rate constant is given as an exponential function of depth. The model has been applied to a data set of WOCE (World Ocean Circulation Experiment) P9 one-time measurements observed in the western North Pacific. The calculated curves fit well to observed vertical nutrient profiles from 100 m depth to over 2,500 m depth at 35 stations from 19°N to 33°30′ N along 137°E with correlation factors of greater than 0.998. A modified model, including a correction term representing a depth-dependent upwelling velocity, can reproduce observed vertical nutrient profiles at 32 stations from 5°N to 18°30′ N along 137°E with correlation factors greater than 0.993. The results support the hypothesis that most of the vertical nutrient profiles in the western North Pacific are controlled by particle export flux, consumption rate, remineralization rate and upwelling velocity.

Water mass characteristics in the Cenomanian US Western Interior seaway as indicated by stable isotopes of calcareous organisms

Stable oxygen isotopes taken from taxon-specific planktic foraminifera are potential sources of water mass density proxy data and paleoclimate information. Material suitable for stable isotope analysis is uncommon in the middle to late Cenomanian strata of the Western Interior of the USA. However, well preserved material from 17 correlative horizons at five localities across SE Montana and NE Wyoming has provided an opportunity to obtain reliable δ 18O data from foraminiferal samples, fine-fraction carbonate (e.g. calcareous nannofossils) and inoceramid prisms. With the exception of inoceramids, which for a benthic organism have stable isotopic compositions resembling surface-dwelling calcareous organisms, these data indicate that the water column was vertically stratified and water masses were anomalously depleted in 18O. Within samples, planktic and benthic foraminifera display strong vertical gradients in δ 18O and δ 13C of several per mil. The vertical gradient of δ 18O ranges from more negative nearer the sea surface to less negative at the sea floor, with a gradient of about 4‰. This implies less saline/warmer waters near the surface with increasingly more saline/colder waters with depth. This isotopic distribution indicates a stably stratified water column at least seasonally. In addition, a persistent vertical carbon isotope gradient of 2–3‰ suggests a strong nutrient gradient that if mixed would result in high surface water fertility. Preservation of high amounts of organic carbon in the sediments corroborates this inference. Although the water column was stratified overall, the nutrients necessary to promote high productivity were clearly renewed at least seasonally. Nutrient renewal could have been achieved by (1) winter cooling of the upper layer allowing deeper seasonal mixing with nutrient-rich deep waters, (2) seasonal shallowing of the pycnocline into the photic zone, (3) entrainment and decomposition of organic matter at the previously proposed frontal convergence, (4) upwelling of nutrient-rich deep waters along the previously proposed oceanic front, or (5) mixing of ‘shelf’ waters with more oceanic waters across an oceanic front.