Trophic pathways and carbon flux patterns in the Laptev Sea     

Michael K. Schmid  Dieter Piepenburg  Alexander A. Golikov  Karen von Juterzenka  Victor V. Petryashov  Michael Spindler 《Progress in Oceanography》2006,71(2-4):314

The Laptev Sea is a high-Arctic epicontinental sea north of Siberia (Russia) that is one of the least understood regions of the world’s ocean. It is characterized by a shallow and broad shelf plateau, high influx of river water, sediments and nutrients during summer, long-lasting sea-ice cover from October to May, and the formation of a narrow flaw-lead polynya off the fast-ice edge during winter.Here, we describe results of a German–Russian research project (1993-present), presenting the distribution patterns and dynamics of its marine flora and fauna, as well as pathways and processes of coupling between sea-ice, water-column and sea-floor biota.Three ecological zones are distinguished along a combined east–west and Lena-impact gradient, differing in the composition of pelagic and benthic communities. In general, high Chl a concentrations in the sediments indicate a tight coupling between sympagic and pelagic primary production and nutrient supply to the benthos throughout the entire Laptev Sea. However, there were pronounced regional differences between the ecological zones in magnitude of primary production and trophic dynamics. Primary production during the ice-free summer was highest in the estuarine zone most strongly influenced by the Lena River (210 mg C m⁻² day⁻¹). The western and northeastern Laptev Sea yielded 55 and 95 mg C m⁻² day⁻¹, respectively. Moreover, the zones differed in the partitioning of carbon flux between zooplankton and benthic food webs. In the Lena zone zooplankton carbon demand was about 31 mg C m⁻² day⁻¹ whereas in the western zone it was 21 mg C m⁻² day⁻¹ and in the eastern zone 4 mg C m⁻² day⁻¹. Total benthic carbon demand was 32 mg C m⁻² day⁻¹ for the Lena zone, 56 mg C m⁻² day⁻¹ in the western zone and 100 mg C m⁻² day⁻¹ in the northeastern zone.A carbon budget constructed for the Laptev Sea indicates that (1) a high proportion of primary production is channelled through the benthic trophic web, bypassing the pelagic trophic web, and (2) autochthonous primary production in the northeastern and western Laptev Sea might not be sufficient to fuel both pelagic and benthic secondary production and, hence, input of allochthonous organic carbon is required to balance the overall carbon demand.  相似文献   

The production of biogenic silica in the Weddell and Scotia Seas     

B. Quguiner  P. Trguer  D.M. Nelson 《Marine Chemistry》1991,35(1-4)

During the EPOS leg 2 cruise (European Polarstern Study, November 1988–January 1989), the production rate of biogenic silica in the euphotic zone was measured by the ³⁰Si method at stations in the Scotia and Weddell Seas.The highest integrated production rates were observed in the Scotia Sea (range: 11.2–20.6 mmol Si m⁻² day⁻¹), the marginal ice zone of the Weddell Sea exhibiting somewhat lower values (range: 6.0–20.0 mmol Si m⁻²day⁻¹).Our results demonstrate that as far as biogenic silica production is concerned the marginal ice zone of the Weddell Sea is considerably less productive than that of the Ross Sea. Our results also indicate that the water of the Antarctic Circumpolar Current (ACC) could be more productive in late spring and early summer than at the beginning of spring. Possible reasons for the differences among the three subsystems (Ross Sea, Weddell Sea and ACC) are discussed.  相似文献   

Phytoplankton productivity in the western subarctic gyre of the North Pacific in early summer 2006     

Tetsuichi Fujiki  Kazuhiko Matsumoto  Shuichi Watanabe  Takuji Hosaka  Toshiro Saino 《Journal of Oceanography》2011,67(3):295-303

We deployed a profiling buoy system incorporating a fast repetition rate fluorometer in the western subarctic Pacific and carried out time-series observations of phytoplankton productivity from 9 June to 15 July 2006. The chlorophyll a (Chl a) biomass integrated over the euphotic layer was as high as 45–50 mg Chl a m⁻² in the middle of June and remained in the 30–40 mg Chl a m⁻² range during the rest of observation period; day-to-day variation in Chl a biomass was relatively small. The daily net primary productivity integrated over the euphotic layer ranged from 144 to 919 mg C m⁻² day⁻¹ and varied greatly, depending more on insolation rather than Chl a biomass. In addition, we found that part of primary production was exported to a 150-m depth within 2 days, indicating that the variations in primary productivity quickly influenced the organic carbon flux from the upper ocean. Our results suggest that the short-term variability in primary productivity is one of the key factors controlling the carbon cycle in the surface ocean in the western subarctic Pacific.  相似文献   

The distributions of, and relationship between, He and nitrate in eddies     

W.J. Jenkins  D.J. McGillicuddy Jr.  D.E. Lott III 《Deep Sea Research Part II: Topical Studies in Oceanography》2008,55(10-13):1389

We present and discuss the distribution of ³He and its relationship to nutrients in two eddies (cyclone C1 and anticyclone A4) with a view towards examining eddy-related mechanisms whereby nutrients are transported from the upper 200–300 m into the euphotic zone of the Sargasso Sea. The different behavior of these tracers in the euphotic zone results in changes in their distributions and relationships that may provide important clues as to the nature of physical and biological processes involved.The cyclonic eddy (C1) is characterized by substantial ³He excesses within the euphotic zone. The distribution of this excess ³He is strongly suggestive of both past and recent ongoing deep-water injection into the euphotic zone. Crude mass balance calculations suggest that an average of approximately 1.4±0.7 mol m⁻² of nitrate has been introduced into the euphotic zone of eddy C1, consistent with the integrated apparent oxygen utilization anomaly in the aphotic zone below. The ³He–NO₃ relationship within the eddy deviates substantially from the linear thermocline trend, suggestive of incomplete drawdown of nutrients and/or substantial mixing between euphotic and aphotic zone waters.Anticyclone (A4) displays a simpler ³He–NO₃ relationship, but is relatively impoverished in euphotic zone excess ³He. We suggest that because of the relatively strong upwelling and lateral divergence of water the residence time of upwelled ³He is relatively short within the euphotic zone of this eddy. An estimate of the recently upwelled nutrient inventory, based on the excess ³He observed in A4's lower euphotic zone, is stoichiometrically consistent with the oxygen maximum observed in the euphotic zone.  相似文献   

A nitrate and silicate budget in the equatorial Pacific Ocean: a coupled physical–biological model study     

M. -S. Jiang  F. Chai  R. C. Dugdale  F. P. Wilkerson  T. -H. Peng  R. T. Barber   《Deep Sea Research Part II: Topical Studies in Oceanography》2003,50(22-26):2971

A coupled physical–biological model was developed to simulate the low-silicate, high-nitrate, and low-chlorophyll (LSHNLC) conditions in the equatorial Pacific Ocean and used to compute a detailed budget in the Wyrtki box (5°N–5°S, 180–90°W) for the major sources and cycling of nitrogen and silicon in the equatorial Pacific. With the incorporation of biogenic silicon dissolution, NH₄ regeneration from organic nitrogen and nitrification of ammonia in the model, we show that silicon recycling in the upper ocean is less efficient than nitrogen. As the major source of nutrients to the equatorial Pacific, the Equatorial Undercurrent provides slightly less Si(OH)₄ than NO₃ to the upwelling zone, which is defined as 2.5°N–2.5°S. As a result, the equatorial upwelling supplies less Si(OH)₄ than NO₃ into the euphotic zone in the Wyrtki box, having a Si/N supply ratio of about 0.85 (2.5 vs. 2.96 mmolm⁻² day⁻¹). More Si(OH)₄ than NO₃ is taken up with a Si/N ratio of 1.17 (2.72 vs. 2.33 mmolm⁻² day⁻¹) within the euphotic zone. The difference between upwelling supply and biological uptake is balanced by nutrient regeneration and horizontal advection. Excluding regeneration, the net silicate and nitrate uptakes are nearly equal (1.76 vs. 1.84 mmolm⁻² day⁻¹). However, biogenic silica export production is slightly higher than organic nitrogen (1.74 vs. 1.59 mmolm⁻² day⁻¹) following a 1.1 Si/N ratio. In the central equatorial Pacific, low silicate concentrations limit diatom growth; therefore non-diatom new production accounts for most of the new production. Higher silicate supply in the east maintains elevated diatom growth rates and new production associated with diatoms dominate upwelling zone. In contrast, the new production associated with small phytoplankton is nearly constant or decreases eastward along the equator. The total new production has a higher rate in the east than in the west, following the pattern of surface silicate. This suggests that silicate regulates the diatom production, total new production, and thereby carbon cycle in this area. The modeled mean primary production is 48.4 mmolCm⁻² day⁻¹, representing the lower end of direct field measurements, while new production is 15.0 mmolCm⁻² day⁻¹, which compares well with previous estimates.  相似文献   

Particle fluxes associated with mesoscale eddies in the Sargasso Sea     

K.O. Buesseler  C. Lamborg  P. Cai  R. Escoube  R. Johnson  S. Pike  P. Masque  D. McGillicuddy  E. Verdeny 《Deep Sea Research Part II: Topical Studies in Oceanography》2008,55(10-13):1426

We examined the impact of a cyclonic eddy and mode-water eddy on particle flux in the Sargasso Sea. The primary method used to quantify flux was based on measurements of the natural radionuclide, ²³⁴Th, and these flux estimates were compared to results from sediment traps in both eddies, and a ²¹⁰Po/²¹⁰Pb flux method in the mode-water eddy. Particulate organic carbon (POC) fluxes at 150 m ranged 1–4 mmol C m⁻² d⁻¹ and were comparable between methods, especially considering differences in integration times scales of each approach. Our main conclusion is that relative to summer mean conditions at the Bermuda Atlantic Time-series Study (BATS) site, eddy-driven changes in biogeochemistry did not enhance local POC fluxes during this later, more mature stage of the eddy life cycle (>6 months old). The absence of an enhancement in POC flux puts a constraint on the timing of higher POC flux events, which are thought to have caused the local O₂ minima below each eddy, and must have taken place >2 months prior to our arrival. The mode-water eddy did enhance preferentially diatom biomass in its center, where we estimated a factor of three times higher biogenic Si flux than the BATS summer average. An unexpected finding in the highly depth-resolved ²³⁴Th data sets is narrow layers of particle export and remineralization within the eddy. In particular, a strong excess ²³⁴Th signal is seen below the deep chlorophyll maxima, which we attribute to remineralization of ²³⁴Th-bearing particles. At this depth below the euphotic zone, de novo particle production in the euphotic zone has stopped, yet particle remineralization continues via consumption of labile sinking material by bacteria and/or zooplankton. These data suggest that further study of processes in ocean layers is warranted not only within, but below the euphotic zone.  相似文献   

Influence of basin-scale and mesoscale physical processes on biological productivity in the Bay of Bengal during the summer monsoon     

K.R. Muraleedharan  P. Jasmine  C.T. Achuthankutty  C. Revichandran  P.K. Dinesh Kumar  P. Anand  G. Rejomon 《Progress in Oceanography》2007,72(4):364-383

Physical forcing plays a major role in determining biological processes in the ocean across the full spectrum of spatial and temporal scales. Variability of biological production in the Bay of Bengal (BoB) based on basin-scale and mesoscale physical processes is presented using hydrographic data collected during the peak summer monsoon in July–August, 2003. Three different and spatially varying physical processes were identified in the upper 300 m: (I) anticyclonic warm gyre offshore in the southern Bay; (II) a cyclonic eddy in the northern Bay; and (III) an upwelling region adjacent to the southern coast. In the warm gyre (>28.8 °C), the low salinity (33.5) surface waters contained low concentrations of nutrients. These warm surface waters extended below the euphotic zone, which resulted in an oligotrophic environment with low surface chlorophyll a (0.12 mg m⁻³), low surface primary production (2.55 mg C m⁻³ day⁻¹) and low zooplankton biovolume (0.14 ml m⁻³). In the cyclonic eddy, the elevated isopycnals raised the nutricline upto the surface (NO₃–N > 8.2 μM, PO₄–P > 0.8 μM, SiO₄–Si > 3.5 μM). Despite the system being highly eutrophic, response in the biological activity was low. In the upwelling zone, although the nutrient concentrations were lower compared to the cyclonic eddy, the surface phytoplankton biomass and production were high (Chl a – 0.25 mg m⁻³, PP – 9.23 mg C m⁻³ day⁻¹), and mesozooplankton biovolume (1.12 ml m⁻³) was rich. Normally in oligotrophic, open ocean ecosystems, primary production is based on ‘regenerated’ nutrients, but during episodic events like eddies the ‘production’ switches over to ‘new production’. The switching over from ‘regenerated production’ to ‘new production’ in the open ocean (cyclonic eddy) and establishment of a new phytoplankton community will take longer than in the coastal system (upwelling). Despite the functioning of a cyclonic eddy and upwelling being divergent (transporting of nutrients from deeper waters to surface), the utilization of nutrients leading to enhanced biological production and its transfer to upper trophic levels in the upwelling region imply that the energy transfer from primary production to secondary production (mesozooplankton) is more efficient than in the cyclonic eddy of the open ocean. The results suggest that basin-scale and mesoscale processes influence the abundance and spatial heterogeneity of plankton populations across a wide spatial scale in the BoB. The multifaceted effects of these physical processes on primary productivity thus play a prominent role in structuring of zooplankton communities and could consecutively affect the recruitment of pelagic fisheries.  相似文献   

Spectral absorption coefficient of photosynthetically active pigments in the equatorial Pacific Ocean (165°11–150°W)     

C. Dupouy  J. Neveux  J.M. Andre 《Deep Sea Research Part II: Topical Studies in Oceanography》1997,44(9-10)

Spectral absorption coefficients of total particulate material and detritus were measured throughout the euphotic zone along the equator between 165°E and 150°W and during time-series for each of these two longitudes in October 1994 (JGOFS-FLUPAC cruise). The sum of pigments obtained by spectrofluorometry (tChla=DV−chla+Chla) was used for normalization (and was also compared to fluorometric and HPLC measurements as an intercalibration study). In order to assess the specific absorption coefficient of photosynthetically active pigments (aps) from the pigment-specific absorption coefficient for phytoplankton (a_ph^*), we made a multiple regression analysis of measured phytoplankton absorption spectra onto publishedin vivo spectra of pure pigments. This made it possible to calculate the concentrations of photoprotective carotenoids (tPPC) when HPLC measurements were not available and thus to subtract their contribution to absorption from the total phytoplanktonic absorption coefficient (a_ph). Methodological uncertainties in both coefficients used for calculating absorption coefficients and in pigment measurements are discussed. Pigments and absorption measurements made during the cruise enabled us to describe two typical trophic regimes in the equatorial Pacific ocean: oligotrophic waters of the ”warm pool“ west of 170°W and high-nutrient, low-chlorophyll waters (HNLC) of the upwelling east of 170°W. The vertical decreasing gradient of a_ph^* from the surface to the deep chlorophyll maximum (DCM) was due to a high tPPC/tChla ratio at the surface and was higher in the oligotrophic (0.14-0.065 m² mg (tChla)⁻¹ biomass dominated byProchlorococcus, rich in zeaxanthin) than in the mesotrophic area (0.07-0.06 m2 mg (tChl a)-' biomass dominated by picoeucaryotes). Below the DCM,a_ph^* reached a similar minimum value in both oligotrophic and mesotrophic areas.a^*_ps varied less than a^*_ph from the surface layer to the DCM in both oligotrophic and mesotrophic areas. The difference in a^*_ph and a^*_ps from west to east of the transect could be interpreted as a shift in the phytoplankton composition, with a dominance of procaryotes in the west and a dominance of eucaryotes in the upwelling area. Higher aps in well-lit typical oligotrophic waters indicated that phytoplankton communities dominated byProclorococcus might be more efficient for capturing light usable for photosynthesis than those present in the HNLC situation.  相似文献   

Biological components of Ross Sea short-term particle fluxes in the austral summer of 1995–1996     

Marcia M. Gowing  David L. Garrison  Holly B. Kunze  Christopher J. Winchell   《Deep Sea Research Part I: Oceanographic Research Papers》2001,48(12)

The Ross Sea, a region of high seasonal production in the Southern Ocean, is characterized by blooms of the haptophyte Phaeocystis antarctica and of diatoms. The different morphology, structural composition and consumption of these two phytoplankton by grazing zooplankton may result in different carbon cycling dynamics and carbon flux from the euphotic zone. We sampled short-term (2 days) particle flux at 5 sites from 177.6°W to 165°E along a transect at 76.5°S with traps placed below the euphotic zone at 200 m during December 1995–January 1996. We estimated carbon flux of as many eucaryotic organisms and fecal pellets as possible using microscopy for counts and measurements and applying volume:carbon conversions from the literature. Eucaryotic organisms contributed about 20–40% of the total organic carbon flux in both the central Ross Sea polynya and in the western polynya, and groups of organisms differed in contribution to the carbon flux at the different sites. Algal carbon flux ranged from 4.5 to 21.1 mg C m⁻² day⁻¹ and consisted primarily of P. antarctica (cell plus mucus) and diatom carbon at all sites. Different diatom species dominated the diatom flux at different sites. Carbon fluxes of small pennate diatoms may have been enhanced by scavenging, by sinking senescent P. antarctica colonies. Heterotrophic carbon flux ranged from 9.2 to 37.6 mg C m⁻² day⁻¹ and was dominated by athecate heterotrophic dinoflagellate carbon in general and by carbon flux of a particular large athecate dinoflagellate at two sites. Fecal pellet carbon flux ranged from 4.6 to 54.5 mg C m⁻² day⁻¹ and was dominated by carbon from ovoid/angular pellets at most sites. Analysis of fecal pellet contents suggested that large protozoans identified by light microscopy contributed to ovoid/angular fecal pellet fluxes. Carbon flux as a percentage of daily primary production was lowest at sites where P. antarctica predominated in the water column and was highest at sites where fecal pellet flux was highest. This indicates the importance of grazers in carbon export.  相似文献   

A novel niche for Prochlorococcus sp. in low-light suboxic environments in the Arabian Sea and the Eastern Tropical North Pacific     

《Deep Sea Research Part I: Oceanographic Research Papers》2000,47(7):1183-1205

Prochlorococcus marinus is present in all tropical and subtropical oceans, where it is often found throughout the euphotic zone, contributing significantly to phytoplankton biomass and primary production and growing at rates comparable to those of other picoplankters. Clearly, Prochlorococcus and eucaryotic picoplankton share significant niche dimensions in the open ocean. Here we report the discovery of populations of Prochlorococcus in layers below the oxyclines of the oxygen minimum zones of the Arabian Sea and the Eastern Tropical North Pacific off Mexico. The unusual aspects of these populations are that these were at times virtual monoalgal cultures found at a depth of 80 to 140 m, often below the euphotic zone, where irradiance ranged from less than 0.1 to 2% of the surface irradiance (I₀). The pigment complement of these deep populations was characterized in detail. The previously unidentified Chl-c-like pigment of Prochlorococcus is Mg-3,8-divinylpheoporphyrin a₅ monomethylester. The carotenoid complement of populations in these deep layers was similar to that of cultured Prochlorococcus strains, except for high concentrations of a 7′,8′-dihydro-derivative of zeaxanthin, quite likely parasiloxanthin. Even though cellular concentrations of pigments were very high in these populations, suggesting acclimation to low irradiance, ambient light experienced by these populations in the Arabian Sea, <0.1% I₀, may not have been sufficient to support normal photoautotrophic growth. Off Mexico these deep Prochlorococcus populations were located at 0.2 and 2% I₀ isolumes, an irradiance likely sufficient for slow growth. Environmental conditions in these layers, except for concentrations of oxygen, are similar to those found at and below the subsurface chlorophyll maxima of the subtropical central gyres. As only Prochlorococcus thrives in these layers but Prochlorococcus and eucaryotic picoplankton coexist in and below subsurface chlorophyll maxima, we conclude that the low oxygen concentrations at the deep Prochlorococcus maxima are the determining factor, but we are not able to identify any specific physiological functions that are affected by low oxygen concentrations in eucaryotes but not Prochlorococcus.  相似文献   

Diurnal changes in the bio-optical properties of the phytoplankton in the Alborán Sea (Mediterranean Sea)     

Jesús M. Mercado  Teodoro Ramírez  Dolores Corts  Marta Sebastin  Andreas Reul  Begoa Bautista 《Estuarine, Coastal and Shelf Science》2006,69(3-4):459

The changes in the phytoplankton absorption properties during a diurnal cycle were investigated at one station located in the north-western area of the Alborán Sea. The experiment was performed in spring when the water column was strongly stratified. This hydrological situation permitted the establishment of a deep chlorophyll a (chl a) fluorescence maximum (DFM) which was located on average close to the lower limit of the mixed layer and the nutricline. The relative abundance of pico-phytoplankton (estimated as its contribution to the total chl a) was higher in the surface, however, micro-phytoplankton dominated the community at the DFM level. Chl a specific absorption coefficient (a*(λ)) also varied with optical depth, with a* (the spectrally average specific absorption coefficient) decreasing by 30% at the DFM depth with respect to the surface. A significant negative correlation between the contribution of the micro-phytoplankton to the total chl a and a* was obtained indicating that a* reduction was due to changes in the packaging effect. Below the euphotic layer, a* increased three-fold with respect to the DFM, which agrees with the expected accumulation of accessory pigments relative to chl a as an acclimation response to the low available irradiance. The most conspicuous change during the diurnal cycle was produced in the euphotic layer where the chl a concentration decreased significantly in the afternoon (from a mean concentration of 1.1 μg L⁻¹ to 0.7 μg L⁻¹) and increased at dusk when it averaged 1.4 μg L⁻¹. In addition, a* and the blue-to-red absorption band ratio increased in the afternoon. These results suggest that a*(λ) diurnal variability was due to increase in photo-protective and accessory pigments relative to chl a. The variation ranges of a*(λ) at 675 and 440 nm (the absorption peaks in the red and blue spectral bands, respectively) in the euphotic layer were 0.01–0.04 and 0.02–0.10 m² mg⁻¹ chl a, respectively. Approximately 30% out of this variability can be attributed to the diurnal cycle. This factor should therefore be taken into account in refining primary production models based on phytoplankton light absorption.  相似文献   

Short-term variability of fCO₂ in seawater and air–sea CO₂ fluxes in a coastal upwelling system (Ría de Vigo, NW Spain)     

J. Gago  M. Gilcoto  F. F. Prez  A. F. Ríos 《Marine Chemistry》2003,80(4):247-264

Coastal upwelling systems are regions with highly variable physical processes and very high rates of primary production and very little is known about the effect of these factors on the short-term variations of CO₂ fugacity in seawater (fCO₂^w). This paper presents the effect of short-term variability (<1 week) of upwelling–downwelling events on CO₂ fugacity in seawater (fCO₂^w), oxygen, temperature and salinity fields in the Ría de Vigo (a coastal upwelling ecosystem). The magnitude of fCO₂^w values is physically and biologically modulated and ranges from 285 μatm in July to 615 μatm in October. There is a sharp gradient in fCO₂^w between the inner and the outer zone of the Ría during almost all the sampling dates, with a landward increase in fCO₂^w.CO₂ fluxes calculated from local wind speed and air–sea fCO₂ differences indicate that the inner zone is a sink for atmospheric CO₂ in December only (−0.30 mmol m⁻² day⁻¹). The middle zone absorbs CO₂ in December and July (−0.05 and −0.27 mmol·m⁻² day⁻¹, respectively). The oceanic zone only emits CO₂ in October (0.36 mmol·m⁻² day⁻¹) and absorbs at the highest rate in December (−1.53 mmol·m⁻² day⁻¹).  相似文献   

Deep ocean fluxes and their link to surface ocean processes and the biological pump     

T. Rixen  M.V.S. Guptha  V. Ittekkot 《Progress in Oceanography》2005,65(2-4):240

Intense studies of upper and deep ocean processes were carried out in the Northwestern Indian Ocean (Arabian Sea) within the framework of JGOFS and related projects in order to improve our understanding of the marine carbon cycle and the ocean’s role as a reservoir for atmospheric CO₂. The results show a pronounced monsoon-driven seasonality with enhanced organic carbon fluxes into the deep-sea during the SW Monsoon and during the early and late NE Monsoon north of 10°N. The productivity is mainly regulated by inputs of nutrients from subsurface waters into the euphotic zone via upwelling and mixed layer-deepening. Deep mixing introduces light limitation by carrying photoautotrophic organisms below the euphotic zone during the peak of the NE Monsoon. Nevertheless, deep mixing and strong upwelling during the SW Monsoon provide an ecological advantage for diatoms over other photoautotrophic organisms by increasing the silica concentrations in the euphotic zone. When silica concentrations fall below 2 μmol l⁻¹, diatoms lose their dominance in the plankton community. During diatom-dominated blooms, the biological pathway of uptake of CO₂ (the biological pump) appears to be more efficient than during blooms of other organisms, as indicated by organic carbon to carbonate carbon (rain) ratios. Due to the seasonal alternation of diatom and non-diatom dominated exports, spatial variations of the annual mean rain ratios are hardly discernible along the main JGOFS transect.Data-based estimates of the annual mean impact of the biological pump on the fCO₂ in the surface water suggest that the biological pump reduces the increase of fCO₂ in the surface water caused by intrusion of CO₂-enriched subsurface water by 50–70%. The remaining 30 to 50% are attributed to CO₂ emissions into the atmosphere. Rain ratios up to 60% higher in river-influenced areas off Pakistan and in the Bay of Bengal than in the open Arabian Sea imply that riverine silica inputs can further enhance the impact of the biological pump on the fCO₂ in the surface water by supporting diatom blooms. Consequently, it is assumed that reduced river discharges caused by the damming of major rivers increase CO₂ emission by lowering silica inputs to the Arabian Sea; this mechanism probably operates in other regions of the world ocean also.  相似文献   

Compositions and transport of lipid biomarkers through the water column and surficial sediments of the equatorial Pacific Ocean   总被引：2，自引：0，他引：2  

Stuart G. Wakeham  John I. Hedges  Cindy Lee  Michael L. Peterson  Peter J. Hernes 《Deep Sea Research Part II: Topical Studies in Oceanography》1997,44(9-10)

A systematic investigation of fluxes and compositions of lipids through the water column and into sediments was conducted along the U.S. JGOFS EgPac transect from l2°N to l5°S at 140°W. Fluxes of lipids out of the euphotic zone varied spatially and temporally, ranging from ≈0.20 – 0.6 mmol lipid-C m⁻² day⁻¹. Lipid fluxes were greatly attenuated with increasing water column depth, dropping to 0.002-0.06 mmol lipid-C m⁻² day⁻¹ in deep-water sediment traps. Sediment accumulation rates for lipids were ≈ 0.0002 – 0.00003 mmol lipid-C m⁻² day⁻¹. Lipids comprised ≈ 11–23% of C_org in net-plankton, 10–30% in particles exiting the euphotic zone, 2–4% particles in the deep EgPac, and 0.1-1 % in sediments. Lipids were, in general, selectively lost due to their greater reactivity relative to bulk organic matter toward biogeochemical degradation in the water column and sediment. Qualitative changes in lipid compositions through the water column and into sediments are consistent with the reactive nature of lipids. Fatty acids were the most labile compounds, with polyunsaturated fatty acids (PUFAs) being quickly lost from particles. Branchedchain C₁₅ and C₁₇ fatty acids increased in relative abundance as particulate matter sank and was incorporated into the sediment, indicating inputs of organic matter from bacteria. Long-chain C₃₉ alkenones of marine origin and long-chain C₂₀-C₃₀ fatty acids, alcohols and hydrocarbons derived from land plants were selectively preserved in sediments. Compositional changes over time and space demonstrate the dynamic range of reactivities among individual biomarker compounds, and hence of organic matter as a whole. A thorough understanding of biogeochemical reprocessing of organic matter in the oceanic water column and sediments is, thus, essential for using the sediment record for reconstructing past oceanic environments.  相似文献   

Inorganic carbon in the central California upwelling system during the 1997–1999 El Niño–La Niña event     

G. E. Friederich  P. M. Walz  M. G. Burczynski  F. P. Chavez 《Progress in Oceanography》2002,54(1-4)

Sea surface pCO₂ was monitored during 49 cruises from February 1997 to December 1999 along a section perpendicular to the central California Coast. Continuous measurements of the ocean–atmosphere difference of pCO₂ were made on a mooring in the same region from July 1997 to December 1999. The El Niño/La Niña cycle of 1997–1999 had a significant influence on local ocean–atmosphere CO₂ transfer. During the warm anomaly associated with El Niño, upwelling was suppressed and average sea surface pCO₂ was below atmospheric level. High rainfall and river runoff in the late winter and early spring of 1998 produced areas where pCO₂ was depressed by as much as 100 μatm. A flux ranging from 0.3 to 0.7 mol C m⁻² y⁻¹ from the atmosphere into the ocean was estimated for the El Niño period from wind and ΔpCO₂ data. Temperatures and upwelling returned to near normal in the summer of 1998, but a cold anomaly developed during autumn of that year. Temperature and pCO₂ data indicate that upwelling continued throughout much of the 1998–1999 winter and intensified significantly in the spring of 1999. During strong upwelling events, the estimate of ocean to atmosphere flux approached rates of 50 mol C m⁻² y⁻¹. The estimate for the average CO₂ flux from July 1998 to July 1999 was 1.5–2.2 mol C m⁻² y⁻¹ from the ocean to the atmosphere. While the flux estimate for the El Niño time period may be applicable to a larger area, the high ocean to atmosphere fluxes during La Niña might be the result of sampling near a zone of intense upwelling.  相似文献   

Denitrification in the Arabian Sea: A 3D ecosystem modelling study     

Thomas R. Anderson  Vladimir A. Ryabchenko  Michael J.R. Fasham  Victor A. Gorchakov 《Deep Sea Research Part I: Oceanographic Research Papers》2007,54(12):2082-2119

A three-dimensional hydrodynamic-ecosystem model was used to examine the factors determining the spatio-temporal distribution of denitrification in the Arabian Sea. The ecosystem model includes carbon and nitrogen as currencies, cycling of organic matter via detritus and dissolved organic matter, and both remineralization and denitrification as sinks for material exported below the euphotic zone. Model results captured the marked seasonality in plankton dynamics of the region, with characteristic blooms of chlorophyll in the coastal upwelling regions and central Arabian Sea during the southwest monsoon, and also in the northern Arabian Sea during the northeast monsoon as the mixed layer shoals. Predicted denitrification was 26.2 Tg N yr⁻¹,the greatest seasonal contribution being during the northeast monsoon when primary production is co-located with the zone of anoxia. Detritus was the primary organic substrate consumed in denitrification (97%), with a small (3%) contribution by dissolved organic matter. Denitrification in the oxygen minimum zone was predicted to be fuelled almost entirely by organic matter supplied by particles sinking vertically from the euphotic zone above (0.73 mmol N m⁻² d⁻¹) rather than from lateral transport of organic matter from elsewhere in the Arabian Sea (less than 0.01 mmol N m⁻² d⁻¹). Analysis of the carbon budget in the zone of denitrification (north of 10°N and east of 55°E) indicates that the modelled vertical export flux of detritus, which is similar in magnitude to estimates from field data based on the ²³⁴Th method, is sufficient to account for measured bacterial production below the euphotic zone in the Arabian Sea.  相似文献   

Seasonal and spatial variation in abundance and egg production of Paracalanus parvus (Copepoda: Calanoida) in/out Jiaozhou Bay, China     

X.H. Sun  S. Sun  C.L. Li  G.T. Zhang 《Estuarine, Coastal and Shelf Science》2008,79(4):637-643

The spatial distribution of stage-specific abundance and reproduction of the copepod Paracalanus parvus were studied from October 2005 to September 2006 in the Jiaozhou Bay. This copepod occurred continuously in this bay throughout the year. The species reached the lowest abundance in April and peaked in June. From October to December, distribution center mainly occurred in offshore water and at the mouth of the bay. In winter, early copepodites and adults gradually decreased and till February, most of the population was only comprised of CIV–CV stages. Overwintering copepodites matured in March and males tended to mature before female. From May to September, each stage occurred in the population and gradually reached high abundance. Temperature and chlorophyll a (Chl-a) concentration in the three stations can't clearly explain the seasonal variation in stage-specific abundance, so we surmised the important effect of the Yellow Sea. Egg production rate (EPR) reached its lowest in winter and peaked in June at 60.8 eggs female⁻¹ day⁻¹ in nearshore water. In the warming period, EPR in nearshore water was statistically higher and EPR > 10 eggs female⁻¹ day⁻¹ lasted longer than that in offshore water, showing the importance of nearshore water for recruitment of P. parvus. Our study showed that EPR was positively related to temperature and total chlorophyll a in offshore water and mouth of the bay. In nearshore water, the relationships between EPR and temperature and Chl-a in three size fractions were not the same as those in offshore water, suggesting complicated ecosystem in such a eutrophic area in warming period.  相似文献   

Nutrient flux into an intense deep chlorophyll layer in a mode-water eddy     

James R. Ledwell  Dennis J. McGillicuddy Jr.  Laurence A. Anderson   《Deep Sea Research Part II: Topical Studies in Oceanography》2008,55(10-13):1139

An intense deep chlorophyll layer in the Sargasso Sea was reported near the center of an anticyclonic mode-water eddy by McGillicuddy et al. [2007. Eddy–wind interactions stimulate extraordinary mid-ocean plankton blooms, Science, accepted]. The high chlorophyll was associated with anomalously high concentrations of diatoms and with a maximum in the vertical profile of ¹⁴C primary productivity. Here we report tracer measurements of the vertical advection and turbulent diffusion of deep-water nutrients into this chlorophyll layer. Tracer released in the chlorophyll layer revealed upward motion relative to isopycnal surfaces of about 0.4 m/d, due to solar heating and mixing. The density surfaces themselves shoaled by about 0.1 m/d. The upward flux of dissolved inorganic nitrogen, averaged over 36 days, was approximately 0.6 mmol/m²/d due to both upwelling and mixing. This flux is about 40% of the basin wide, annually averaged, nitrogen flux required to drive the annual new production in the Sargasso Sea, estimated from the oxygen cycle in the euphotic zone, the oxygen demand below the euphotic zone, and from the ³He excess in the mixed layer. The observed upwelling of the fluid was consistent with theoretical models [Dewar, W.K., Flierl, G.R., 1987. Some effects of wind on rings. Journal of Physical Oceanography 17, 1653–1667; Martin, A.P., Richards, K.J., 2001. Mechanisms for vertical nutrient transport within a North Atlantic mesoscale eddy. Deep-Sea Research II 48, 757–773] in which eddy surface currents cause spatial variations in surface stress. The diapycnal diffusivity at the base of the euphotic zone was 3.5±0.5×10⁻⁵ m²/s. Diapycnal mixing was probably enhanced over more typical values by the series of storms passing over the eddy during the experiment and may have been enhanced further by the trapping of near-inertial waves generated within the eddy.  相似文献   

Effect of iron enrichment on the dynamics of transparent exopolymer particles in the western subarctic Pacific   总被引：1，自引：0，他引：1  

Neelam Ramaiah  Shigenobu Takeda  Ken Furuya  Takeshi Yoshimura  Jun Nishioka  Tatsuo Aono  Yukihiro Nojiri  Keiri Imai  Isao Kudo  Hiroaki Saito  Atsushi Tsuda 《Progress in Oceanography》2005,64(2-4):253

Dynamics of transparent exopolymer particles (TEP) was studied during the first in situ iron-enrichment experiment conducted in the western subarctic Pacific in July–August 2001, with the goal of evaluating the contribution of TEP to vertical flux as a result of increased primary production following iron enrichment in open ocean ecosystems. Subsequent to the enhancement of phytoplankton production, we observed increase in TEP concentration in the surface layer and sedimentation of organic matter beneath it. Vertical profiles of TEP, chlorophyll a (Chl a) and particulate organic carbon (POC) were obtained from six depths between 5 and 70 m, from a station each located inside and outside the enriched patch. TEP and total mass flux were estimated from the floating sediment traps deployed at 200 m depth. Chl a and TEP concentrations outside the patch varied from 0.2 to 1.9 μg L⁻¹ and 40–60 μg XG equiv. L⁻¹, respectively. Inside the patch, Chl a increased drastically from day 7 reaching the peak of 19.2 μg L⁻¹ on day 13, which coincided with the TEP peak of 189 μg XG equiv. L⁻¹. TEP flux in the sediment trap increased from 41 to 88 mg XG equiv. m⁻² d⁻¹, with 8–14% contribution of TEP to total mass flux. This forms the basic data set on ambient concentrations of TEP in the western subarctic Pacific, and evaluation of the effect of iron enrichment on TEP.  相似文献   

Seasonal appearance ofProchlorococcus in Suruga Bay,Japan in 1992–1993     

Shimada  A.  Nishijima  M.  Maruyama  T. 《Journal of Oceanography》1995,51(3):289-300

Seasonal appearance ofProchlorococcus was studied by flow cytometry in Suruga Bay, Japan in 1992–1993.Prochlorococcus cells were in high concentrations (>1×10⁴ cells ml^–1) from July to October 1992 and September 1993, when the water temperature was over 20°C. The 16S rRNA of the isolated cells showed 98.5% sequence homology with that ofP. marinus (Sargasso strain), indicating that they are the same species. The former has a high divinyl-chlorophyll (DV-Chl.)a/b ratio similar to the Mediterranean strain and different from the Sargasso strain. Maximum concentration ofProchlorococcus at the surface water was 2.5×10⁴ cells ml^–1 in August 1992 and their DV-Chl.a accounted for 4.0% of the total chlorophylla. A decrease in cell density to less than 5×10³ cells ml^–1 was observed from December to May with an exceptional rise in January 1993. WhileProchlorococcus showed a maximum concentration of 3.6×10⁴ cells ml^–1 at 10 m depth in September 1992, phycoerythrin (PE)-richSynechococcus spp. were dominant with their maximum concentration of 2.2×10⁵ cells ml^–1 in the same water body. On the other hand, phycocyanin (PC)-richSynechococcus spp. and the larger phytoplankters showed maximum concentrations in the surface waters in May and June. BothProchlorococcus and PE-richSynechococcus showed their lowest concentrations in April. A significant positive correlation was obtained between cell concentrations of the PE-richSynechococcus andProchlorococcus.  相似文献