Tidal influence on particulate organic carbon export fluxes around a tall seamount (original) (raw)
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Deep Sea Research II, 2009
The suspended particulate organic matter (sPOM) around two isolated NE Atlantic seamounts, Seine (331460N 141210W; summit at 170m) and Sedlo (401190N 261400W;summit at 780 m), was studied over a period of 2 years during four 2–4-week oceanographic surveys. Elemental (C and N), chlorophyll a and lipid biomarker concentrations and N stable isotopic values were variable close to the surface (40–90 m), although some chlorophylla enrichment above the summits was discerned sporadically. Results from near-surface waters showed a generally ‘‘fresh’’, mainly phytoplankton signature in sPOM with some seasonality, which was more pronounced around Sedlo. sPOM concentrations and composition changed with depth, apparently controlled by seasonality and proximity to the seamounts. A few metres above the Seine summit, the suspended particulate organic carbon (sPOC) concentrations and labile polyunsaturated fatty acids (% of lipids) were higher than elsewhere at similar depths (200m) in summer 2004. In the same season at Sedlo, polyunsaturated fatty acids were also relatively more abundant (up to 43% of total lipids) around the topographic feature throughout the water column, indicating supply of more labile sPOM, perhaps by advection, downwelling or passive sinking of locally produced phytoplankton and/or in situ production. The high-quality sPOM that seems to be present around the seamounts could provide an important food source to the biological community.
Seamounts are considered to be ''hotspots'' of marine life but, their role in oceans primary productivity is still under discussion. We have studied the microbial community structure and biomass of the epipelagic zone (0-150 m) at two northeast Atlantic seamounts (Seine and Sedlo) and compared those with the surrounding ocean. Results from two cruises to Sedlo and three to Seine are presented. Main results show large temporal and spatial microbial community variability on both seamounts. Both Seine and Sedlo heterotrophic community (abundance and biomass) dominate during winter and summer months, representing 75% (Sedlo, July) to 86% (Seine, November) of the total plankton biomass. In Seine, during springtime the contribution to total plankton biomass is similar (47% autotrophic and 53% heterotrophic). Both seamounts present an autotrophic community structure dominated by small cells (nano and picophytoplankton). It is also during spring that a relatively important contribution (26%) of large cells to total autotrophic biomass is found. In some cases, a ''seamount effect'' is observed on Seine and Sedlo microbial community structure and biomass. In Seine this is only observed during spring through enhancement of large autotrophic cells at the summit and seamount stations. In Sedlo, and despite the observed low biomasses, some clear peaks of picoplankton at the summit or at stations within the seamount area are also observed during summer. Our results suggest that the dominance of heterotrophs is presumably related to the trapping effect of organic matter by seamounts. Nevertheless, the complex circulation around both seamounts with the presence of different sources of mesoscale variability (e.g. presence of meddies, intrusion of African upwelling water) may have contributed to the different patterns of distribution, abundances and also changes observed in the microbial community.
Progress in Oceanography, 2008
Particulate organic carbon (POC) is vertically transported to the oceanic interior by aggregates and their ballasts, mainly CaCO 3 and biogenic opal, with a smaller role for lithogenic aerosols through the mesopelagic zone. Diel migrating zooplankton communities effect vertical transport and remineralization of POC in the upper layers of the ocean. Below 1.5 km, the presence of zooplankton is reduced and thus the aggregates travel mainly by gravitational transport. We normalized the fluxes of POC, CaCO 3 , and biogenic opal from data published on samples collected at 134 globally distributed, bottom-tethered, time-series sediment trap (TS-trap) stations to annual mole fluxes at the mesopelagic/bathypelagic boundary (m/b) at 2 km and defined them as F m/b C org , F m/b C inorg , and F m/b Si bio . Using this global data set, we investigated (1) the geographic contrasts of POC export at m/b and (2) the supply rate of P CO 2 to the world mesopelagic water column. F m/b C org varies from 25 (Pacific Warm Pool) to 605 (divergent Arabian Sea) mmolC m À2 yr À1 ; F m/b C inorg varies from >8 (high latitude Polar Oceans) or 15 (Pacific Warm Pool) to 459 (divergent Arabian Sea) mmolC m À2 yr À1 ; and F m/b Si bio , the most spatially/temporally variable flux, ranges from 6 (North Atlantic Drift) to 1118 (Pacific Subarctic Gyre) mmolSi m À2 yr À1 . The oceanic region exhibiting the highest POC flux over a significantly large region is the area of the North Pacific Boreal Gyres where the average F m/b C org = 213, F m/b C inorg = 126, and F m/b Si bio = 578 mmol m À2 yr À1 . F m/b C org and F m/b C inorg are particularly high in large upwelling margins, including the divergent Arabian Sea and off Cape Verde. One of the data sets showing the lowest flux over a significant region/basin is F m/b C org = 39, F m/b C inorg = 69, and F m/b Si bio = 22 mmol m À2 yr À1 in the North Pacific subtropical/tropical gyres; Pan-Atlantic average fluxes are similar except F m/b Si bio fluxes are even lower. Where C org /C inorg and Si bio /C inorg are <1 defines the ''Carbonate Ocean", and where these ratios are P1 defines the ''Silica Ocean". The Carbonate Ocean occupies about 80% of the present world pelagic ocean between the two major oceanographic fronts, the North Pacific Polar Front and the Antarctic Polar Front, and the Silica Ocean is found on the polar sides of these fronts. The total global annual fluxes of F m/b C org , F m/b Based on our global F m/b C inorg and recently estimated global primary production of PIC, 36-86 teramolC yr À1 of PIC is assumed to be dissolved within the upper 2 km of the water column.
Enhanced but highly variable bioturbation around seamounts in the northwest Pacific
Deep Sea Research Part I: Oceanographic Research Papers, 2019
Seamounts are a unique ecosystem in marine environment, but the relevant understanding is limited. In this study, sedimentation and bioturbation around the Pako Guyot of Magellan, and the Lamont, Scripps, Arnold, and Pot Guyots of Marcus-Wake seamounts in the northwest Pacific were evaluated using 230 Th ex and 210 Pb ex as tracers. Our results showed that the linear sedimentation rate and the mass accumulation rate ranged from 0.12 to 2.50 mm/ka and from 0.06 to 1.14 kg/m 2 /ka with averages of 1.27 � 0.80 mm/ka and 0.49 � 0.30 kg/m 2 /ka respectively. The accumulation flux of organic carbon in surface sediments was estimated to be 0.10-4.52 g C/ m 2 /ka. The bioturbation coefficients ranged from 1.01 to 27.1 cm 2 /a with an average of 10.8 � 9.2 cm 2 /a, which is higher than those in abyssal sediments or predicted by traditional empirical equations. The enhanced bioturbation supports the view that seamounts are hotspots for pelagic and benthic organisms. The bioturbation intensity showed a great variability with the maximum around 40 km away from the edge of seamount summit. The bioturbation coefficient correlated positively with sedimentation rate and accumulation flux of organic carbon in surface sediments, indicating that the supply of organic matter is a main driving force for enhanced bioturbation around the seamounts. The increase in sedimentary organic matter promotes the activities of benthic organisms. More research is needed to gain a deep understanding of bioturbation in seamounts in the context of future climate change.
Global Biogeochemical Cycles, 1991
Previously published data on vertical fluxes of particulate carbon (PC), nitrogen (PN), organisms (MICRO), and extracted adenosine triphosphate (ATP) into screened sediment traps (335/xm) from the VERTEX 5 and ADIOS I programs are reexamined as they relate to biogeochemical cycling and oceanic productivity. The four stations discussed represent an oligotrophic to mesotrophic gradient in total primary production (PT), ranging from 245 to 1141 mg C m -2 d -1 and a gradient in PC flux from the euphotic zone, ranging from 12 to 164 mg C m -2 d -• for particles <335/xm in diameter. Vertical fluxes of PC, PN, MICRO, and ATP decreased as negative power functions of depth with significantly higher depth-dependent losses for ATP fluxes. The flux of intact biota (free, particleassociated, and some active "swimmers," measured microscopically and by extracted ATP) decreased rapidly in the upper 200 m, contributing as much as 52.4% at the most productive station and as little as 1.6% to the flux of PC at oligotrophic stations, remaining relatively constant or increasing slightly (to 3.4 -9.6% PC flux) between 200 and 2000 m. Multiple regression analyses, expressing fluxes as • Now at Paper number 91GB01543. 0886-6236/91/91GB-01543510.00
1989
Previously published data on vertical fluxes of particulate carbon (PC), nitrogen (PN), organisms (MICRO), and extracted adenosine triphosphate (ATP) into screened sediment traps (335/xm) from the VERTEX 5 and ADIOS I programs are reexamined as they relate to biogeochemical cycling and oceanic productivity. The four stations discussed represent an oligotrophic to mesotrophic gradient in total primary production (PT), ranging from 245 to 1141 mg C m -2 d -1 and a gradient in PC flux from the euphotic zone, ranging from 12 to 164 mg C m -2 d -• for particles <335/xm in diameter. Vertical fluxes of PC, PN, MICRO, and ATP decreased as negative power functions of depth with significantly higher depth-dependent losses for ATP fluxes. The flux of intact biota (free, particleassociated, and some active "swimmers," measured microscopically and by extracted ATP) decreased rapidly in the upper 200 m, contributing as much as 52.4% at the most productive station and as little as 1.6% to the flux of PC at oligotrophic stations, remaining relatively constant or increasing slightly (to 3.4 -9.6% PC flux) between 200 and 2000 m. Multiple regression analyses, expressing fluxes as • Now at Paper number 91GB01543. 0886-6236/91/91GB-01543510.00
Biominerals and the vertical flux of particulate organic carbon from the surface ocean
Geophysical Research Letters, 2010
1] Particulate inorganic carbon (PIC; calcium carbonate) is thought to be a significant source of light scattering in the sea. It also provides ballast for particulate matter, driving the ocean's biological carbon pump. During three trans-Atlantic cruises, we measured particle optical properties plus concentrations of the three major components of sinking aggregates [particulate organic carbon (POC), PIC and biogenic silica (BSi)]. PIC contributed 15-23% of particle backscattering in oligotrophic subtropical gyres and temperate waters. Light scattering properties allowed quantification of the surface PIC:POC ratio. The ratio of the two ballast minerals (PIC:BSi) was significantly, inversely, correlated to POC concentration, allowing robust modeling of the density of sinking aggregates. Results showed greater PIC:POC ratios and sinking rates in oligotrophic regions due to greater relative abundance of PIC. Citation: Balch, W. M.,
Food-web mediated export of biogenic carbon in oceans:hydrodynamic control
Marine Ecology Progress Series, 1996
This paper describes an approach to determine, using a small number of food-web or hydrodynamic variables, the partitioning of phytoplankton production among 3 carbon fluxes, i.e. remineralization within the euphotic zone, food-web transfer, and sinking to depth of organic particles. In order to do so, the flows of biogenic carbon in the marine pelagic environment are reduced to 5 broad path\z~ays, which are ordered along a continuum of decreasing export relative to primary production. At one end of the continuum, ungrazed phytoplankton is exported to depth and, at the other, biogenic carbon is remineralized within the bacteria-microzooplankton loop. In the present paper, export of biogenic carbon from the euphotic zone includes food-web transfer of primary production and downward flux of particulate organic carbon (POC) into deep waters. A simple model and data from the literature lead to the conclusions that: (1) the export characteristics of pelagic ecosystems are largely determined by the size structure of primary production and the matching (or, conversely, segregation) between primary production and grazing and (2) total export from the euphotic zone is a function of the delivery of mechanical energy to the upper water column whereas the partitioning of total export between foodweb transfer and sinking of POC is controlled by temporal variations in depth of the surface mixed layer Food-web transfer is significant for marine resources and sinking of POC may contribute to the regulation of climate change (sequestration at depth of biogenic carbon).