Phytoplankton community structure in the Arabian Sea during and after the SW monsoon, 1994     

《Deep Sea Research Part II: Topical Studies in Oceanography》1999,46(3-4):655-676

Diatoms, dinoflagellates, coccolithophores, nanoflagellates, picophytoplankton and procaryote algae (Synechococcus spp. and prochlorophytes) were quantified by microscopy and flow cytometry, and their biomass determined, at 12 stations along a 1600 km transect across the Arabian Sea at the end of the SW monsoon in September, and during the inter-monsoon period of November/December 1994. The transect spanned contrasting oceanic conditions that varied from seasonally eutrophic, upwelling waters through mesotrophic, downwelling waters to permanently oligotrophic, stratified waters. The overall diversity of diatoms, dinoflagellates and coccolithophores along the transect was not significantly different between the SW monsoon and inter-monsoon. However, diatoms showed greatest diversity during the SW monsoon and coccolithophores were most diverse during the inter-monsoon. Integrated phytoplankton standing stocks during the SW monsoon ranged from 3 to 9 g C m^-2 in the upwelling eutrophic waters, from 3 to 5 g C m^-2 in downwelling waters, and from 1 to 2 g C m^-2 in oligotrophic waters. Similar phytoplankton standing stocks were found in oligotrophic waters during the inter-monsoon, but were ca. 40% lower compared to the SW monsoon in the more physically dynamic waters. Phytoplankton abundance and biomass was dominated by procaryote taxa. Synechococcus spp. were abundant (often >10⁸ cells l^-1) during both the SW monsoon and inter-monsoon, where the nitrate concentration was ⩾0.1 μ mol l^-1, and often dominated the phytoplankton standing stocks. Prochlorophytes were restricted to oligotrophic stratified waters during the SW monsoon period but were found at all stations along the transect during the inter-monsoon, dominating the phytoplankton standing stocks (>40%) in the oligotrophic region during this period. Of the nano- and micro-phytoplankton, only diatoms contributed significantly to phytoplankton standing stocks, and then only in near-shore upwelling waters during the SW monsoon. There were significant changes in the temporal composition of the phytoplankton community. In nearshore waters a mixed community of diatoms and Synechococcus spp. dominated during the SW monsoon. This gave way to a community dominated by Synechococcus spp. in the intermonsoon. In the downwelling zone, a Synechococcus spp. dominated community was replaced by a mixed procaryote community of Synechococcus spp. and prochlorophytes. In the oligotrophic stratified waters, the mix of procaryote algae was replaced by one dominated by prochlorophytes alone.  相似文献   

The structure of zooplankton communities,in the 2 to 2000 μm size range,in the Arabian Sea during and after the SW monsoon, 1994     

《Deep Sea Research Part II: Topical Studies in Oceanography》1999,46(3-4):815-842

Zooplankton communities, studied in the surface mixed layer on a 1600 m transect across the Arabian Sea, were found to differ in their temporal and spatial response to seasonal forcing. The transect studied, spanned seasonally eutrophic upwelling, mesotrophic downwelling and aseasonal oligotrophic waters. The nano- and microzooplankton communities constituted a relatively constant compartment in the tropical monsoon ecosystem, whilst the mesozooplankton showed a clear response to both upwelling and season. The heterotrophic nanoflagellates were concentrated in the surface mixed layer, except in the eutrophic upwelling waters of the SW monsoon. They reached maximum cell concentrations of 855 ml^-1 during the SW monsoon and a maximum biomass of 8.4 mg C m^-3 during the intermonsoon. Nanozooplankton standing stocks, in the surface mixed layer, ranged between 7 and 333 mg C m^-2, with highest stocks found during the intermonsoon. The microzooplankton community was dominated by Protozoa, particularly aloricate ciliates and heterotrophic dinoflagellates, which accounted for up to 99% in terms of numbers and up to 71% of the biomass. Sarcodines and metazoan nauplii were recorded in lower numbers (<400 l^-1). The microzooplankton were also concentrated in the surface mixed layer during both periods, except in the eutrophic coastal waters during the SW monsoon, when relatively high biomass values were found below the mixed layer depth. Their standing stocks, in the surface mixed layer, ranged between 50 and 182 mg C m^-2, with the highest concentration found in the mesotrophic offshore waters during the late monsoon period. Total mesozooplankton standing stocks, in the surface 100 m, decreased with distance from the coastal to offshore waters and between seasons, decreasing from 1248 to 238 mg C m^-2 during the late SW monsoon and 656–89 mg C m^-2 during the following intermonsoon. The largest size class, of 1000–2000 μm sized organisms, dominated throughout except at the oligotrophic station during the intermonsoon period, when the smallest class, of 200–500 μm, were more important. The shift in size structure from large to small zooplankton occurred in response to a shift in dominance from large to small phytoplankton cells both spatially, along a eutrophic–oligotrophic gradient, and seasonally. These responses are a result of the physical forcing associated with the monsoon seasons in the Arabian Sea.  相似文献   

Seasonal influences on size-fractionated chlorophyll a concentrations and primary production in the north-west Indian Ocean     

《Deep Sea Research Part II: Topical Studies in Oceanography》1999,46(3-4):701-723

Chlorophyll a (chl a) concentrations and primary production by the 0.2–2, 2–18 and >18 μm phytoplankton size-fractions were estimated along a transect in the NW Indian Ocean extending from the coast of Oman to 8°N 68°E during the late SW monsoon and autumn intermonsoonal seasons in 1994. Primary production was estimated using the ¹⁴C technique with either in situ or simulated in situ incubations. During the late monsoon season, maximal chl a and production values were recorded in the coastal upwelling zone with values of 69 mg m^-2 and 3800 mg C m^-2 d^-1, respectively. The maxima, which were distributed patchily in this region, were dominated by the >18 μm size-fraction. Over the remainder of the transect chl a concentrations and production averaged 30 mg m^-2 and 1500 mg C m^-2 d^-1, respectively, with approximately equal contributions by the three size-fractions in the case of chl a at the majority of stations, but in general, with a maximum in production in the 0.2–2 μm fraction. Immediately following cessation of the SW monsoon wind, chl a and production values over the northern part of the transect decreased to values similar to those over the southern part of the transect at the time of the SW monsoon, with the contributions by the three size-fractions being approximately equal. During the following intermonsoonal season, both chl a concentrations and production across the section were dominated by the 0.2–2 μm size-fraction, with average chl a and production values of the order of 20 mg m^-2 and 750 mg C m^-2 d^-1, respectively. Considerable variation in production values, however, was exhibited across the transect. A clearly defined subsurface chl a maximum was only recorded at the southernmost stations of the transect in oligotrophic waters: the feature did not develop universally across the transect during the intermonsoon.  相似文献   

The influence of the south-west monsoon upon the nutrient biogeochemistry of the Arabian Sea     

《Deep Sea Research Part II: Topical Studies in Oceanography》1999,46(3-4):571-591

Variations in the nutrient concentrations were studied during two cruises to the Arabian Sea. The situation towards the end of the southwest monsoon season (September/October 1994) was compared with the inter-monsoonal season during November and December 1994. Underway surface transects showed the influence of an upwelling system during the first cruise with deep, colder, nutrient-rich water being advected into the surface mixed layer. During the southwesterly monsoon there was an area of coastal Ekman upwelling, bringing colder water (24.2°C) into the surface waters of the coastal margin. Further offshore at about 350 km there was an area of Ekman upwelling, as a result of wind-stress curl, north of the Findlater Jet axis; this area also had cooler surface water (24.6°C). Further offshore (>1000 km) the average surface temperatures increased to >27°C. These waters were oligotrophic with no evidence of the upwelling effects observed further inshore. In the upwelling regions nutrient concentrations in the close inshore coastal zone were elevated (NO₃=18 μmol l^-1, PO₄=1.48 μmol l^-1); higher concentrations also were measured at the region of offshore upwelling off the shelf, with a maximum nitrate concentration of 12.5 μmol l^-1 and a maximum phosphate concentration of 1.2 μmol l^-1. Nitrate and phosphate concentrations decreased with increasing distance offshore to the oligotrophic waters beyond 1400 km, where typical nitrate concentrations were 35.0 nmol l^-1 (0.035 μmol l^-1) in the surface mixed layer. A CTD section from the coastal shelf, to 1650 km offshore to the oligotrophic waters, clearly showed that during the monsoon season, upwelling is one of the major influences upon the nutrient concentrations in the surface waters of the Arabian Sea off the coast of Oman. Productivity of the water column was enhanced to a distance of over 800 km offshore. During the intermonsoon period a stable surface mixed layer was established, with a well-defined thermocline and nitracline. Surface temperature was between 26.8 and 27.4°C for the entire transect from the coast to 1650 km offshore. Nitrate concentrations were typically between 2.0 and 0.4 μmol l^-1 for the transect, to about 1200 km where the waters became oligotrophic, and nitrate concentrations were then typically 8–12 nmol l^-1. Ammonia concentrations for the oligotrophic waters were typically 130 nmol l^-1, and are reported for the first time in the Indian Ocean. The nitrogen/phosphorus (N/P) ratios suggest that phytoplankton production was potentially nitrogen-limited in all the surface waters of the Arabian Sea, with the greatest nitrogen limitation during the intermonsoon period.  相似文献   

Basin-scale variability of phytoplankton biomass,production and growth in the Atlantic Ocean     

《Deep Sea Research Part I: Oceanographic Research Papers》2000,47(5):825-857

The latitudinal distributions of phytoplankton biomass, composition and production in the Atlantic Ocean were determined along a 10,000-km transect from 50°N to 50°S in October 1995, May 1996 and October 1996. Highest levels of euphotic layer-integrated chlorophyll a (Chl a) concentration (75–125 mg Chl m⁻²) were found in North Atlantic temperate waters and in the upwelling region off NW Africa, whereas typical Chl a concentrations in oligotrophic waters ranged from 20 to 40 mg Chl m⁻². The estimated concentration of surface phytoplankton carbon (C) biomass was 5–15 mg C m⁻² in the oligotrophic regions and increased over 40 mg C m⁻² in richer areas. The deep chlorophyll maximum did not seem to constitute a biomass or productivity maximum, but resulted mainly from an increase in the Chl a to C ratio and represented a relatively small contribution to total integrated productivity. Primary production rates varied from 50 mg C m⁻² d⁻¹ at the central gyres to 500–1000 mg C m⁻² d⁻¹ in upwelling and higher latitude regions, where faster growth rates (μ) of phytoplankton (>0.5 d⁻¹) were also measured. In oligotrophic waters, microalgal growth was consistently slow [surface μ averaged 0.21±0.02 d⁻¹ (mean±SE)], representing <20% of maximum expected growth. These results argue against the view that the subtropical gyres are characterized by high phytoplankton turnover rates. The latitudinal variations in μ were inversely correlated to the changes in the depth of the nitracline and positively correlated to those of the integrated nitrate concentration, supporting the case for the role of nutrients in controlling the large-scale distribution of phytoplankton growth rates. We observed a large degree of temporal variability in the phytoplankton dynamics in the oligotrophic regions: productivity and growth rates varied in excess of 8-fold, whereas microalgal biomass remained relatively constant. The observed spatial and temporal variability in the biomass specific rate of photosynthesis is at least three times larger than currently assumed in most satellite-based models of global productivity.  相似文献   

Seasonal dynamics of primary and new production in the northern South China Sea: The significance of river discharge and nutrient advection     

《Deep Sea Research Part I: Oceanographic Research Papers》2006,53(6):971-986

Biochemical and productivity measurements and nutrient enrichment experiments were conducted on three cruises in summer and two cruises in winter on the shelf and the basin of the northern South China Sea (SCS) between 2001 and 2004. Phytoplankton production, in terms of depth-integrated new production (INP) or depth-integrated primary production (IPP), was higher in winter than in summer and on the shelf than in the basin. In winter, with deepening of the mixed layer, nitrate from the shallow nitracline that characterized the SCS waters was made available in the surface and supported the highest production of the year. Averaged INP measured in winter (0.25 g C m⁻² d⁻¹) was about twice the summer average (0.12 g C m⁻² d⁻¹) and was 0.19 g C m⁻² d⁻¹ on the shelf compared with 0.15 g C m⁻² d⁻¹ in the basin. In winter, average INP on the shelf was higher than the basin (0.34 versus 0.21 g C m⁻² d⁻¹); whereas in summer, averaged INP on the shelf (0.13 g C m⁻² d⁻¹) and the basin (0.11 g C m⁻² d⁻¹) were similar. While averaged IPP measured in the basin was higher in winter than in summer (0.53 versus 0.35 g C m⁻² d⁻¹), IPP on the shelf showed little temporal variation (0.82 in winter versus 0.84 g C m⁻² d⁻¹ in summer). Considerable spatial and inter-annual variation in production was measured in the shelf waters during summer, which could be linked to discharge volume and plume flow direction of the Zhujiang River. While the shelf waters in summer were mostly nitrogen starved or nitrogen and phosphorus co-limited, excessive river runoff may cause the nutritive state to shift to phosphorus deficiency. Waters with low surface salinities and high fluorescence from riverine mixing could be found extending from the Zhujiang mouth to as far as offshore southern Taiwan after a typhoon passed the northern SCS and brought heavy rainfall. Overall, both nutrient advection in winter and river discharge from the China coast in summer made new nitrogen available and shaped the dynamics of phytoplankton production in these oligotrophic waters.  相似文献   

Picophytoplankton dynamics and production in the Arabian Sea during the 1995 Southwest Monsoon     

《Deep Sea Research Part II: Topical Studies in Oceanography》1999,46(8-9):1745-1768

Phytoplankton community structure is expected to shift to larger cells (e.g., diatoms) with monsoonal forcing in the Arabian Sea, but recent studies suggest that small primary producers remain active and important, even in areas strongly influenced by coastal upwelling. To better understand the role of smaller phytoplankton in such systems, we investigated growth and grazing rates of picophytoplankton populations and their contributions to phytoplankton community biomass and primary productivity during the 1995 Southwest Monsoon (August–September). Environmental conditions at six study stations varied broadly from open-ocean oligotrophic to coastal eutrophic, with mixed-layer nitrate and chlorophyll concentrations ranging from 0.01 to 11.5 μM NO₃ and 0.16 to 1.5 μg Chl a. Picophytoplankton comprised up to 92% of phytoplankton carbon at the oceanic stations, 35% in the diatom-dominated coastal zone, and 26% in a declining Phaeocystis bloom. Concurrent in situ dilution and ¹⁴C-uptake experiments gave comparable ranges of community growth rates (0.53–1.05 d⁻¹ and 0.44–1.17 d⁻¹, to the 1% light level), but uncertainties in C:Chl a confounded agreement at individual stations. Microzooplankton grazing utilized 81% of community phytoplankton growth at the oligotrophic stations and 54% at high-nutrient coastal stations. Prochlorococcus (PRO) was present at two oligotrophic stations, where its maximum growth approached 1.4 d⁻¹ (two doublings per day) and depth-integrated growth varied from 0.2 to 0.8 d⁻¹. Synechococcus (SYN) growth ranged from 0.5 to 1.1 d⁻¹ at offshore stations and 0.6 to 0.7 d⁻¹ at coastal sites. Except for the most oligotrophic stations, growth rates of picoeukaryotic algae (PEUK) exceeded PRO and SYN, reaching 1.3 d⁻¹ offshore and decreasing to 0.8 d⁻¹ at the most coastal station. Microzooplankton grazing impact averaged 90, 70, and 86% of growth for PRO, SYN, and PEUK, respectively. Picoplankton as a group accounted for 64% of estimated gross carbon production for all stations, and 50% at high-nutrient, upwelling stations. Prokaryotes (PRO and SYN) contributed disproportionately to production relative to biomass at the most oligotrophic station, while PEUK were more important at the coastal stations. Even during intense monsoonal forcing in the Arabian Sea, picoeukaryotic algae appear to account for a large portion of primary production in the coastal upwelling regions, supporting an active community of protistan grazers and a high rate of carbon cycling in these areas.  相似文献   

Microzooplankton grazing impact in the Western Arctic Ocean     

《Deep Sea Research Part II: Topical Studies in Oceanography》2009,56(17):1264-1273

Microzooplankton grazing impact on phytoplankton was assessed using the Landry–Hassett dilution technique in the Western Arctic Ocean during spring and summer 2002 and 2004. Forty experiments were completed in a region encompassing productive shelf regions of the Chukchi Sea, mesotrophic slope regions of the Beaufort Sea off the North Slope of Alaska, and oligotrophic deep-water sites in the Canada Basin. A variety of conditions were encountered, from heavy sea-ice cover during both spring cruises, moderate sea-ice cover during summer of 2002, and light to no sea ice during summer of 2004, with a concomitant range of trophic conditions, from low chlorophyll-a (Chl-a; <0.5 μg L⁻¹) during heavy ice cover in spring and in the open basin, to late spring and summer shelf and slope open-water diatom blooms with Chl-a >5 μg L⁻¹. The microzooplankton community was dominated by large naked ciliates and heterotrophic gymnodinoid dinoflagellates. Significant, but low, rates of microzooplankton herbivory were found in half of the experiments. The maximum grazing rate was 0.16 d⁻¹ and average grazing rate, including experiments with no significant grazing, was 0.04±0.06 d⁻¹. Phytoplankton intrinsic growth rates varied from the highest values of about 0.4 d⁻¹ to the lowest values of zero to slightly negative growth, on average 0.16±0.15 d⁻¹. Light limitation in spring and post-bloom senescence during summer were likely explanations of observed low phytoplankton growth rates. Microzooplankton grazing consumed 0–120% (average 22±26%) of phytoplankton daily growth. Grazing and growth rates found in this study were low compared to rates reported in another Arctic system, the Barents Sea, and in major geographic regions of the world ocean.  相似文献   

Enhancement of particulate organic carbon export flux induced by atmospheric forcing in the subtropical oligotrophic northwest Pacific Ocean     

Chin-Chang Hung  Gwo-Ching Gong  Wang-Chen Chung  Wei-Ting Kuo  Fu-Chen Lin 《Marine Chemistry》2009,113(1-2):19-24

The effects of extreme atmospheric forcing on the export flux of particulate organic carbon (POC) in the warm oligotrophic nitrogen-limited northwest Pacific Ocean were examined in 2007 during the spring Asian dust storm period. Several strong northeast monsoon events (maximum sustained wind speeds approaching 16.7 m s^? 1, and gusts up to 19.0 m s^? 1) accompanied by dust storms occurred during a 1-month period. The cold stormy events decreased surface water temperature and induced strong wind-driven vertical mixing of the water column, resulting in nutrient entrainment into the mixed layer from subsurface waters. As a result, the export flux of POC ranged from 49 to 98 (average value = 71 ± 16) mg m^? 2 day^? 1, approximately 2–3 times greater than average values in other seasons. As dry and wet deposition of nitrogen attributable to Asian dust storm events does not account for the associated increases in POC stocks in this N-limited oligotrophic oceanic region, the enhancement of POC flux must have been caused by nutrient entrainment from subsurface waters because of the high winds accompanying the dust storm events.  相似文献   

Bacterioplankton and phytoplankton biomass and production during summer stratification in the northwestern Mediterranean Sea     

《Deep Sea Research Part I: Oceanographic Research Papers》1999,46(6):985-1019

We examined bacterioplankton biomass and heterotrophic production (BHP) during summer stratification in the northwestern Mediterranean in four successive stratification seasons (June–July of 1993–1996). Values of phytoplankton biomass and primary production were determined simultaneously so that the data sets for autotrophic and heterotrophic microbial plankton could be compared. Three standard stations were set along a transect from Barcelona to the channel between Mallorca and Menorca, representing coastally influenced shelf waters, frontal waters over the slope front, and open sea waters. Conversion factors from ³H-leucine incorporation to BHP were empirically determined and varied between 0.29 and 3.25 kg C mol^-1. Bacterial biomass values were among the lowest found in any marine environment. BHP values (between 0.02 and 2.5 μg C L^-1 d^-1) were larger than those of low nutrient low chlorophyll areas such as the Sargasso Sea and lower than those from high nutrient low chlorophyll areas such as the equatorial Pacific. Growth rates of bacterioplankton were highest at the slope front (0.20 d^-1) and lowest at the open sea station (0.04 d^-1). Phytoplankton growth rates were similar at the three stations (∼0.50 d^-1). Integrated values of bacterioplankton biomass, BHP and bacterial growth rates did not show significant differences among years, but differences between the three stations were clearly significant. Phytoplankton biomass, primary production, and phytoplankton growth rates did not show significant differences either with year or with station. As a consequence the bacterioplankton to phytoplankton biomass (BB/BPHY) and production (BHP/PP) ratios varied from the coastal to the open sea stations. The BB/BPHY ratio was 0.98 at the coast and ∼0.70 at the other two stations. These ratios are similar to those found in other oligotrophic marine environments. The BHP/PP ratio was 0.83 at the coast, 0.36 at the slope and 0.09 at the open sea station. The last value is also similar to values found in other oligotrophic marine environments. Vertical distribution of these ratios was also examined.The comparison of microbial parameters at the three stations indicates a different kind of relationship between bacterioplankton and phytoplankton in oligotrophic open sea waters and in coastal, nutrient-richer waters. According to such parameters and to the values of the BB/BPHY and BHP/PP ratios, open waters in the northwestern Mediterranean (despite their relatively short distance from the shore) were intermediate between the extremely oligotrophic waters of the eastern Mediterranean or the Sargasso Sea and the more productive waters of the equatorial Pacific.  相似文献   

Atmospheric input of dissolved inorganic phosphorus and silicon to the coastal northwestern Mediterranean Sea: Fluxes,variability and possible impact on phytoplankton dynamics     

《Deep Sea Research Part I: Oceanographic Research Papers》2005,52(11):2005-2016

One hundred twelve rainwater samples collected from 1986 to 2003 at the signal station of Cap Ferrat (France, NW Mediterranean coast) were analysed for phosphate and silicate contents. This sampling site is affected by a European urban-dominated background material, with episodic Saharan dust inputs. The input of dissolved inorganic phosphorus (DIP) and dissolved inorganic silicon (DISi) was calculated. The most significant loadings of DIP and DISi were selected in order to assess their potential impact on phytoplankton dynamics, particularly in oligotrophic conditions, when surface waters are nutrient-depleted. The theoretical new production triggered by DIP and DISi inputs (NP_atmo) was estimated through Redfield calculations. The maximum theoretical DIP-triggered NP_atmo was up to 670 mg C m⁻² in October, at the end of the oligotrophic period (135 mg C m⁻³ in the 5 m-thick surface layer). During the same period, the daily integrated primary production measured at the DYFAMED site (NW Mediterranean Sea) was on average 219 mg C m⁻² d⁻¹ within the 0–100 m depth water column, while the mean daily primary production in the 5 m-thick surface layer was 1.6 mg C m⁻³ d⁻¹. However, high NP_atmo due to high DIP inputs might be episodically limited by lower DISi inputs, which may consequently lead to episodic preferential growth of non-siliceous phytoplanktonic species.  相似文献   

Organic carbon flux and remineralization in surface sediments from the northern North Atlantic derived from pore-water oxygen microprofiles     

《Deep Sea Research Part I: Oceanographic Research Papers》2001,48(2):529-553

Organic carbon fluxes through the sediment/water interface in the high-latitude North Atlantic were calculated from oxygen microprofiles. A wire-operated in situ oxygen bottom profiler was deployed, and oxygen profiles were also measured onboard (ex situ). Diffusive oxygen fluxes, obtained by fitting exponential functions to the oxygen profiles, were translated into organic carbon fluxes and organic carbon degradation rates. The mean C_org input to the abyssal plain sediments of the Norwegian and Greenland Seas was found to be 1.9 mg C m⁻² d⁻¹. Typical values at the seasonally ice-covered East Greenland continental margin are between 1.3 and 10.9 mg C m⁻² d⁻¹ (mean 3.7 mg C m⁻² d⁻¹), whereas fluxes on the East Greenland shelf are considerably higher, 9.1–22.5 mg C m⁻² d⁻¹. On the Norwegian continental slope C_org fluxes of 3.3–13.9 mg C m⁻² d⁻¹ (mean 6.5 mg C m⁻² d⁻¹) were found. Fluxes are considerably higher here compared to stations on the East Greenland slope at similar water depths. By repeated occupation of three sites off southern Norway in 1997 the temporal variability of diffusive O₂ fluxes was found to be quite low. The seasonal signal of primary and export production from the upper water column appears to be strongly damped at the seafloor. Degradation rates of 0.004–1.1 mg C cm⁻³ a⁻¹ at the sediment surface were calculated from the oxygen profiles. First-order degradation constants, obtained from C_org degradation rates and sediment organic carbon content, are in the range 0.03–0.6 a⁻¹. Thus, the corresponding mean lifetime of organic carbon lies between 1.7 and 33.2 years, which also suggests that seasonal variations in C_org flux are small. The data presented here characterize the Norwegian and Greenland Seas as oligotrophic and relatively low organic carbon deep-sea environments.  相似文献   

Plankton net community production and dark respiration in the Arabian Sea during September 1994     

《Deep Sea Research Part II: Topical Studies in Oceanography》1999,46(3-4):745-765

Plankton community net and gross production and dark respiration were determined from in vitro changes in dissolved inorganic carbon and dissolved oxygen during September 1994 along a southeast offshore transect in the Arabian Sea. Surface rates of gross production decreased from 17±0.7 mmol C m^-3 d^-1 at a coastal upwelling station to 3±0.8 mmol C m^-3 d^-1 at the most offshore station. The euphotic zone at the time of sampling was predominantly heterotrophic, with integrated net community production values ranging from 15±7 mmol C m^-2 d^-1 inshore to −253±32 mmol C m^-2 d^-1 offshore. Calculations of the respiration attributable to the major plankton groups could account for 61–87% of the dark community respiration measured at the inshore stations, but only 15–26% of the community respiration determined offshore. Comparison of the fluxes of dissolved inorganic carbon and oxygen revealed a tendency for higher respiratory quotients than those calculated for organic metabolism prevailing at the offshore stations.  相似文献   

Benthic fluxes in a tidal salt marsh creek affected by fish farm activities: Río San Pedro (Bay of Cádiz,SW Spain)     

S. Ferrón  T. Ortega  J.M. Forja 《Marine Chemistry》2009,113(1-2):50-62

Benthic fluxes of dissolved inorganic carbon, total alkalinity, oxygen, nutrients, nitrous oxide and methane were measured in situ at three sites of Río San Pedro salt marsh tidal creek (Bay of Cádiz, SW Spain) during three seasons. This system is affected by the discharges of organic carbon and nutrients from the surrounding aquaculture installations. Sediment oxygen uptake rates and inorganic carbon fluxes ranged respectively from 16 to 79 mmol O₂ m^? 2 d^? 1 and from 48 to 146 mmol C m^? 2 d^? 1. Benthic alkalinity fluxes were corrected for the influence of NH₄⁺ and NO₃^? + NO₂^? fluxes, and the upper and lower limits for carbon oxidation rates were inferred by considering two possible scenarios: maximum and minimum contribution of CaCO₃ dissolution to corrected alkalinity fluxes. Average C_ox rates were in all cases within ± 25% of the upper and lower limits and ranged from 40 to 122 mmol C m^? 2 d^? 1. Whereas carbon mineralization did not show significant differences among the sites, C_ox rates varied seasonally and were correlated with temperature (r² = 0.72). During winter and spring denitrification was estimated to account for an average loss of 46% and 75%, respectively, of the potentially recyclable N, whereas during the summer no net removal was observed. A possible shift from denitrification to dissimilatory nitrate reduction to ammonium (DNRA) during this period is argued. Dissolved CH₄ and N₂O fluxes ranged from 5.7 to 47 μmol CH₄ m^? 2 d^? 1 and 4.3 to 49 μmol N–N₂O m^? 2 d^? 1, respectively, and represented in all cases a small fraction of total inorganic C and N flux. Overall, about 60% of the total particulate organic matter that is discharged into the creek by the main fish farm facility is estimated to degrade in the sediments, resulting in a significant input of nutrients to the system.  相似文献   

Bacterioplankton activity in the surface waters of the Arabian Sea during and after the 1994 SW monsoon     

《Deep Sea Research Part II: Topical Studies in Oceanography》1999,46(3-4):767-794

Bacterial biomass and production were measured on two cruises to the northwestern Arabian Sea in 1994; the first cruise took place towards the end of the SW monsoon in September, and the second cruise during the inter-monsoon period in November and December. Although phytoplankton production was significantly higher during the monsoon, bacterial numbers showed little difference. Bacteria were most abundant in the euphotic zone and highest bacterial numbers were measured during the monsoon period in the Gulf of Oman and the shelf waters off southern Oman; in these regions, numbers ranged from 0.9 to 1.6×10⁹ bacteria l^-1. On both cruises, bacteria were less abundant in the euphotic zone of the central Arabian Sea and typically ca 0.8×10⁹ cells l^-1 were present. The majority of bacteria (80–95%) were small cocci that were larger (median diameter 0.40 μm) during the monsoon period than the inter-monsoon, when the cells had a diameter of 0.36 μm; there was no comparable change in cell dimensions of bacteria present as rods. Bacterial production was measured by the incorporation of ³H-thymidine and ³H-leucine. On both cruises, uptake rates were highest on the Omani shelf and decreased offshore. In the central Arabian Sea, thymidine incorporation rates were similar in the monsoon and inter-monsoon periods, but higher rates of leucine incorporation were measured during the monsoon period. Bacterial production was a relatively small proportion of phytoplankton production in both periods sampled; bacterial production was equivalent to between 10 and 30% of the daily primary production in the Arabian Sea.  相似文献   

Monsoon-controlled export fluxes to the interior of the Arabian Sea     

《Deep Sea Research Part II: Topical Studies in Oceanography》1999,46(8-9):1859-1902

As a part of the US-JGOFS Arabian Sea Process Study (ASPS), we deployed a mooring array consisting of 16 Mark-7G time-series sediment traps on five moorings, each in the mesopelagic and interior depths in the western Arabian Sea set along a transect quasi-perpendicular to the Omani coast. The array was deployed for 410 days to cover all monsoon and inter-monsoon phases at 4.25-, 8.5- or 17-day open-close intervals, all of which were synchronized at 17-day periods. Total mass flux, fluxes of organic, inorganic carbon, biogenic Si and lithogenic Al (mg m⁻² day⁻¹) were obtained from samples representing 667 independent periods. The average total mass fluxes estimated in the interior depth along this sediment trap array at Mooring Stations 1–5 (MS-1–5) during 1994-5 ASPS were 147, 235, 221, 164 and 63 mg m⁻² day⁻¹, respectively. Mass fluxes during the southwest (SW) Monsoon were always larger than during the northeast (NE) Monsoon at all divergent zone stations, but the difference was insignificant at the oligotrophic station, MS-5. Four major pulses of export flux events, two each at NE Monsoon and SW Monsoon, were observed in the divergent zone; these events dominated in quantity production of the annual mass flux, but did not dominate temporally. Export pulses were produced by passing eddies and wind-curl events, but the direct processes to produce individual export blooms at each station were diversified and highly complex. The onset of these pulses was generally synchronous throughout the divergent zone. Export pulses associated with specific biogeochemical signatures such as the ratio of elevated biogenic Si to inorganic carbon indicate a supply of deep water to the euphotic layer in varying degrees. The variability of mass fluxes at the oligotrophic station, MS-5, also represented both monsoon events, but with far less amplitude and without notable export pulses.  相似文献   

Microbial respiration in the Levantine Sea: evolution of the oxidative processes in relation to the main Mediterranean water masses     

《Deep Sea Research Part I: Oceanographic Research Papers》2001,48(10):2147-2159

First data on microbial respiration in the Levantine Sea are reported with the aim of assessing the distribution of oxidative processes in association with the main Mediterranean water masses and the changing physical structure determined by the Eastern Mediterranean Transient. Respiratory rates, in terms of metabolic carbon dioxide production, were estimated from measured electron transport system activities in the polygonal area of the Levantine Sea (32.5–36.5 N Latitude, 26.0–30.25 E Longitude) and at Station Geo’95, in the Ionian Sea (35°34.88 N; 17°14.99 E). At the Levantine Sea, the mean carbon dioxide production rate decreased from the upper to the deeper layers and varied from 22.0±12.4 μg C h⁻¹ m⁻³ in the euphotic layer to 1.30±0.5 μg C h⁻¹ m⁻³ in the depth range between 1600 and 3000 m. Significant differences were found among upper, intermediate and bottom layers. The euphotic zone supported a daily carbon dioxide production of 96.6 mg C d⁻¹ m⁻² while the aphotic zone (between 200 and 3000 m) sustained a 177.1 mg C d⁻¹ m⁻² carbon dioxide production. In Station Geo’95, the carbon dioxide production rates amounted to 170.4 and 102.2 mg C d⁻¹ m⁻² in the euphotic and aphotic zones, respectively. The rates determined in the identified water masses showed a tight coupling of respiratory processes and Mediterranean circulation patterns. The increasing respiratory rates in the deep layers of the Levantine Sea are explained by the introduction of younger waters recently formed in the Aegean Sea.  相似文献   

Biogeochemical study of a coccolithophore bloom in the northern Bay of Biscay (NE Atlantic Ocean) in June 2004     

J. Harlay  A.V. Borges  C. Van Der Zee  B. Delille  R.H.M. Godoi  L.-S. Schiettecatte  N. Roevros  K. Aerts  P.-E. Lapernat  L. Rebreanu  S. Groom  M.-H. Daro  R. Van Grieken  L. Chou 《Progress in Oceanography》2010,86(3-4):317-336

The present paper synthesizes data obtained during a multidisciplinary cruise carried out in June 2004 at the continental margin of the northern Bay of Biscay. The data-set allows to describe the different stages of a coccolithophore bloom dominated by Emiliania huxleyi. The cruise was carried out after the main spring phytoplankton bloom that started in mid-April and peaked in mid-May. Consequently, low phosphate (PO₄ < 0.2 μM) and silicate (DSi < 2.0 μM) concentrations, low partial pressure of carbon dioxide (pCO₂) and high calcite saturation degree in surface waters combined with thermal stratification, probably favoured the blooming of coccolithophores. During the period of the year our cruise was carried out, internal tides induce enhanced vertical mixing at the continental shelf break leading to the injection of inorganic nutrients to surface waters that probably trigger the bloom. The bloom developed as the water-column stratified and as the water mass was advected over the continental shelf, following the general residual circulation in the area. The most developed phase of the bloom was sampled in a remote sensed high reflectance (HR) patch over the continental shelf that was characterized by low chlorophyll-a (Chl-a) concentration in surface waters (<1.0 μg L^?1), high particulate inorganic carbon (PIC) concentration (～8 μmol L^?1) and coccolithophore abundance up to 57 × 10⁶ cells L^?1. Transparent exopolymer particles (TEP) concentrations ranged between 15 and 75 μg C L^?1 and carbon content of TEP represented up to 26% of the particulate organic carbon (POC; maximum concentration of 15.5 μmol L^?1 in the upper 40 m). Integrated primary production (PP) ranged between 210 and 680 mg C m^?2 d^?1 and integrated calcification (CAL) ranged between 14 and 140 mg C m^?2 d^?1, within the range of PP and CAL values previously reported during coccolithophore blooms in open and shelf waters of the North Atlantic Ocean. Bacterial protein production (BPP) measurements in surface waters (0.3–0.7 μg C L^?1 h^?1) were much higher than those reported during early phases of coccolithophore blooms in natural conditions, but similar to those during peak and declining coocolithophorid blooms reported in mesocosms. Total alkalinity anomalies with respect to conservative mixing (ΔTA) down to ?49 μmol kg^?1 are consistent with the occurrence of biogenic precipitation of calcite, while pCO₂ remained 15–107 μatm lower than atmospheric equilibrium (372 μatm). The correlation between ΔTA and pCO₂ suggested that pCO₂ increased in part due to calcification, but this increase was insufficient to overcome the background under-saturation of CO₂. This is related to the biogeochemical history of the water masses due to net carbon fixation by the successive phytoplankton blooms in the area prior to the cruise, hence, the investigated area remained a sink for atmospheric CO₂ despite calcification.  相似文献   

Latitudinal distribution of microbial plankton abundance,production, and respiration in the Equatorial Atlantic in autumn 2000     

《Deep Sea Research Part I: Oceanographic Research Papers》2005,52(5):861-880

Phytoplankton and bacterial abundance, size-fractionated phytoplankton chlorophyll-a (Chl-a) and production together with bacterial production, microbial oxygen production and respiration rates were measured along a transect that crossed the Equatorial Atlantic Ocean (10°N–10°S) in September 2000, as part of the Atlantic Meridional Transect 11 (AMT 11) cruise. From 2°N to 5°S, the equatorial divergence resulted in a shallowing of the pycnocline and the presence of relatively high nitrate (>1 μM) concentrations in surface waters. In contrast, a typical tropical structure (TTS) was found near the ends of the transect. Photic zone integrated ¹⁴C primary production ranged from ∼200 mg C m⁻² d⁻¹ in the TTS region to ∼1300 mg C m⁻² d⁻¹ in the equatorial divergence area. In spite of the relatively high primary production rates measured in the equatorial upwelling region, only a moderate rise in phytoplankton biomass was observed as compared to nearby nutrient-depleted areas (22 vs. 18 mg Chl-a m⁻², respectively). Picophytoplankton were the main contributors (>60%) to both Chl-a biomass and primary production throughout the region. The equatorial upwelling did not alter the phytoplankton size structure typically found in the tropical open ocean, which suggests a strong top-down control of primary producers by zooplankton. However, the impact of nutrient supply on net microbial community metabolism, integrated over the euphotic layer, was evidenced by an average net microbial community production within the equatorial divergence (1130 mg C m⁻² d⁻¹) three-fold larger than net production measured in the TTS region (370 mg C m⁻² d⁻¹). The entire region under study showed net autotrophic community metabolism, since respiration accounted on average for 51% of gross primary production integrated over the euphotic layer.  相似文献   

Monsoonal influence on the distribution of phytoplankton pigments in the Arabian Sea     

《Deep Sea Research Part II: Topical Studies in Oceanography》1999,46(3-4):677-699

Variations in the distribution of chemotaxonomic pigments were monitored in the Arabian Sea and the Gulf of Oman at the end of the SW monsoon in September 1994 and during the inter-monsoon period in November/December 1994 to determine the seasonal changes in phytoplankton composition. The Gulf of Oman was characterized by sub-surface chlorophyll maxima at 20-40 m during both seasons, and low levels of divinyl chlorophyll a indicated that prochlorophytes did not contribute significantly to the total chlorophyll a. Prymnesiophytes (19′-hexanoyloxyfucoxanthin), diatoms (fucoxanthin) and chlorophyll b containing organisms accounted for most of the phytoplankton biomass in September, while prymnesiophytes dominated in November/December. In the Arabian Sea in September, high total chlorophyll a concentrations up to 1742 ng l^-1 were measured in the coastal upwelling region and a progressive decline was monitored along the 1670 km offshore transect to oligotrophic waters at 8°N. Divinyl chlorophyll a was not detected along this transect except at the two most southerly stations where prochlorophytes were estimated to contribute 25–30% to the total chlorophyll a. Inshore, the dominance of fucoxanthin and/or hexanoyloxyfucoxanthin indicated that diatoms and prymnesiophytes generally dominated the patchy phytoplankton community, with zeaxanthin-containing Synechococcus also being important, especially in surface waters. At the southern oligotrophic localities, Synechococcus and prochlorophytes dominated the upper 40 m and prymnesiophytes were the most prominent at the deep chlorophyll maximum. During the inter-monsoon season, total chlorophyll a concentrations were generally half those measured in September and highest levels were found on the shelf (1170 ng l^-1). Divinyl chlorophyll a was detected at all stations along the Arabian Sea transect, and we estimated that prochlorophytes contributed between 3 and 28% to the total chlorophyll a, while at the two oligotrophic stations this proportion increased to 51–52%. While procaryotes were more important in November/December than September, eucaryotes still accounted for >50% of the total chlorophyll a. Pigment/total chlorophyll a ratios indicated that 19′-hexanoyloxyfucoxanthin-containing prymnesiophytes were the dominant group, although procaryotes accounted for 65% at the two southerly oligotrophic stations.  相似文献