Export fluxes of particulate organic carbon in the Chukchi Sea: A comparative study using 234Th/238U disequilibria and drifting sediment traps     

《Marine Chemistry》2007,103(1-2):185-196

Large-volume sampling of ²³⁴Th and drifting sediment trap deployments were conducted as part of the 2004 Western Arctic Shelf–Basin Interactions (SBI) spring (May 15–June 23) and summer (July 17–August 26) process cruises in the Chukchi Sea. Measurements of ²³⁴Th and particulate organic carbon (POC) export fluxes were obtained at five stations during the spring cruise and four stations during the summer cruise along Barrow Canyon (BC) and along a parallel shelf-to-basin transect from East Hanna Shoal (EHS) to the Canada Basin. ²³⁴Th and POC fluxes obtained with in situ pumps and drifting sediment traps agreed to within a factor of 2 for 70% of the measurements. POC export fluxes measured with in situ pumps at 50 m along BC were similar in spring and summer (average = 14.0 ± 8.0 mmol C m^− 2 day^− 1 and 16.5 ± 6.5 mmol C m^− 2 day^− 1, respectively), but increased from spring to summer at the EHS transect (average = 1.9 ± 1.1 mmol C m^− 2 day^− 1 and 19.5 ± 3.3 mmol C m^− 2 day^− 1, respectively). POC fluxes measured with sediment traps at 50 m along BC were also similar in both seasons (31.3 ± 9.3 mmol C m^− 2 day^− 1 and 29.1 ± 14.2 mmol C m^− 2 day^− 1, respectively), but were approximately twice as high as POC fluxes measured with in situ pumps. Sediment trap POC fluxes measured along the EHS transect also increased from spring to summer (3.0 ± 1.9 mmol C m^− 2 day^− 1 and 13.0 ± 6.4 mmol C m^− 2 day^− 1, respectively), and these fluxes were similar to the POC fluxes obtained with in situ pumps. Discrepancies in POC export fluxes measured using in situ pumps and sediment traps may be reasonably explained by differences in the estimated POC/²³⁴Th ratios that arise from differences between the techniques, such as time-scale of measurement and size and composition of the collected particles. Despite this variability, in situ pump and sediment trap-derived POC fluxes were only significantly different at a highly productive station in BC during the spring.  相似文献   

Carbon and biogenic silica export influenced by the Amazon River Plume: Patterns of remineralization in deep-sea sediments     

《Deep Sea Research Part I: Oceanographic Research Papers》2014

The Amazon River Plume delivers freshwater and nutrients to an otherwise oligotrophic western tropical North Atlantic (WTNA) Ocean. Plume waters create conditions favorable for carbon and nitrogen fixation, and blooms of diatoms and their diazotrophic cyanobacterial symbionts have been credited with significant CO₂ uptake from the atmosphere. The fate of the carbon, however, has been measured previously by just a few moored or drifting sediment traps, allowing only speculation about the full extent of the plume's impact on carbon flux to the deep sea. Here, we used surface (0.5 m) sediment cores collected throughout the Demerara Slope and Abyssal Plain, at depths ranging from 1800 to 5000 m, to document benthic diagenetic processes indicative of carbon flux. Pore waters were extracted from sediments using both mm- and cm-scale extraction techniques. Profiles of nitrate (NO₃) and silicate (Si(OH)₄) were modeled with a diffusion-reaction equation to determine particulate organic carbon (POC) degradation and biogenic silica (bSi) remineralization rates. Model output was used to determine the spatial patterns of POC and bSi arrival at the sea floor. Our estimates of POC and Si remineralization fluxes ranged from 0.16 to 1.92 and 0.14 to 1.35 mmol m⁻² d⁻¹, respectively. A distinct axis of POC and bSi deposition on the deep sea floor aligned with the NW axis of the plume during peak springtime flood. POC flux showed a gradient along this axis with highest fluxes closest to the river mouth. bSi had a more diffuse zone of deposition and remineralization. The impact of the Amazon plume on benthic fluxes can be detected northward to 10°N and eastward to 47°W, indicating a footprint of nearly 1 million km². We estimate that 0.15 Tmol C y⁻¹ is remineralized in abyssal sediments underlying waters influenced by the Amazon River. This constitutes a relatively high fraction (~7%) of the estimated C export from the region.; the plume thus has a demonstrable impact on C_org export in the western Atlantic. Benthic fluxes under the plume were comparable to and in some cases greater than those observed in the eastern equatorial Atlantic, the southeastern Atlantic, and the Southern Ocean.  相似文献   

Seasonal and interannual variability in particle fluxes of carbon,nitrogen and silicon from time series of sediment traps at Ocean Station P, 1982–1993: relationship to changes in subarctic primary productivity     

《Deep Sea Research Part II: Topical Studies in Oceanography》1999,46(11-12):2735-2760

An extended time series of particle fluxes at 3800 m was recorded using automated sediment traps moored at Ocean Station Papa (OSP, 50°N, 145°W) in the northeast Pacific Ocean for more than a decade (1982–1993). Time-series observations at 200 and 1000 m, and short-term measurements using surface-tethered free-drifting sediment traps also were made intermittently. We present data for fluxes of total mass (dry weight), particulate organic carbon (POC), particulate organic nitrogen (PON), biogenic Si (BSi), and particulate inorganic carbon (PIC) in calcium carbonate. Mean monthly fluxes at 3800 m showed distinct seasonality with an annual minimum during winter months (December–March), and maximum during summer and fall (April–November). Fluxes of total mass, POC, PIC and BSi showed 4-, 10-, 7- and 5-fold increases between extreme months, respectively. Mean monthly fluxes of PIC often showed two plateaus, one in May–August dominated by <63 μm particles and one in October–November, which was mainly >63 μm particles. Dominant components of the mass flux throughout the year were CaCO₃ and opal in equal amounts. The mean annual fluxes at 3800 m were 32±9 g dry weight g m⁻² yr⁻¹, 1.1±0.5 g POC m⁻² yr⁻¹, 0.15±0.07 g PON m⁻² yr⁻¹, 5.9±2.0 g BSi m⁻² yr⁻¹ and 1.7±0.6 g PIC m⁻² yr⁻¹. These biogenic fluxes clearly decreased with depth, and increased during “warm” years (1983 and 1987) of the El Niño, Southern Oscillation cycle (ENSO). Enhancement of annual mass flux rates to 3800 m was 49% in 1983 and 36% in 1987 above the decadal average, and was especially rich in biogenic Si. Biological events allowed estimates of sinking rates of detritus that range from 175 to 300 m d⁻¹, and demonstrate that, during periods of high productivity, particles sink quickly to deep ocean with less loss of organic components. Average POC flux into the deep ocean approximated the “canonical” 1% of the surface primary production.  相似文献   

Phytoplankton dynamics in the NE subarctic Pacific     

《Deep Sea Research Part II: Topical Studies in Oceanography》1999,46(11-12):2405-2432

Ocean Station Papa (OSP, 50°N 145°W) in the NE subarctic Pacific is characterised as high nitrate low chlorophyll (HNLC). However, little is known about the spatial extent of these HNLC waters or the phytoplankton dynamics on the basin scale. Algal biomass, production and size-structure data are presented from winter, spring and summer between 1992 and 1997 for five stations ranging from coastal to open-ocean conditions. The inshore stations (P04–P16) are characterised by the classical seasonal cycle of spring and late summer blooms (production >3 g C m⁻² d⁻¹), diatoms are not Fe-stressed, and growth rate is probably controlled by macronutrient supply. The fate of the phytoplankton is likely sedimentation by diatom-dominated spring blooms, with a pelagic recycling system predominating at other times. The offshore stations (P20/OSP) display low seasonality in biomass and production (OSP, mean winter production 0.3 g C m⁻² d⁻¹, mean spring/summer production 0.85 g C m⁻² d⁻¹), and are dominated by small algal cells. Low Fe availability prevents the occurrence of diatom blooms observed inshore. The main fate of phytoplankton is probably recycling through the microbial food web, with relatively low sedimentation compared to inshore. However, the supply of macro- and micro-nutrients to the coastal and open ocean, respectively, may vary between years. Variability in macro-nutrient supply to the coastal ocean may result in decreased winter reserve nitrate, summer nitrate limitation, subsequent floristic shifts towards small cells, and reduced primary production. Offshore, higher diatom abundances are occasionally observed, perhaps indicating episodic Fe supply. The two distinct oceanic regimes have different phytoplankton dynamics resulting in different seasonality, community structure and fate of algal carbon. These differences will strongly influence the biogeochemical signatures of the coastal and open-oceanic NE subarctic Pacific.  相似文献   

Biogenic fluxes in the Cariaco Basin: a combined study of sinking particulates and underlying sediments     

《Deep Sea Research Part I: Oceanographic Research Papers》2003,50(6):781-807

The fluxes of total mass, organic carbon (OC), biogenic opal, calcite (CaCO₃) and long-chain C₃₇ alkenones (ΣAlk₃₇) were measured at three water depths (275, 455 and 930 m) in the Cariaco Basin (Venezuela) over three separate annual upwelling cycles (1996–1999) as part of the CARIACO sediment trap time-series. The strength and timing of both the primary and secondary upwelling events in the Cariaco Basin varied significantly during the study period, directly affecting the rates of primary productivity (PP) and the vertical transport of biogenic materials. OC fluxes showed a weak positive correlation (r²=0.3) with PP rates throughout the 3 years of the study. The fluxes of opal, CaCO₃ and ΣAlk₃₇ were strongly correlated (0.6<r²<0.8) with those of OC. The major exception was the lower than expected ΣAlk₃₇ fluxes measured during periods of strong upwelling. All sediment trap fluxes were significantly attenuated with depth, consistent with marked losses during vertical transport. Annually, strong upwelling conditions, such as those observed during 1996–1997, led to elevated opal fluxes (e.g., 35 g m⁻² yr⁻¹ at 275 m) and diminished ΣAlk₃₇ fluxes (e.g., 5 mg m⁻² yr⁻¹ at 275 m). The opposite trends were evident during the year of weakest upwelling (1998–1999), indicating that diatom and haptophyte productivity in the Cariaco Basin are inversely correlated depending on upwelling conditions.The analyses of the Cariaco Basin sediments collected via a gravity core showed that the rates of OC and opal burial (10–12 g m⁻² yr⁻¹) over the past 5500 years were generally similar to the average annual water column fluxes measured in the deeper traps (10–14 g m⁻² yr⁻¹) over the 1996–1999 study period. CaCO₃ burial fluxes (30–40 g m⁻² yr⁻¹), on the other hand, were considerably higher than the fluxes measured in the deep traps (∼10 g m⁻² yr⁻¹) but comparable to those obtained from the shallowest trap (i.e. 38 g m⁻² yr⁻¹ at 275 m). In contrast, the burial rates of ΣAlk₃₇ (0.4–1 mg m⁻² yr⁻¹) in Cariaco sediments were significantly lower than the water column fluxes measured at all depths (4–6 mg m⁻² yr⁻¹), indicating the large attenuation in the flux of these compounds at the sediment–water interface. The major trend throughout the core was the general decrease in all biogenic fluxes with depth, most likely due to post-depositional in situ degradation. The major exception was the relatively low opal fluxes (∼5 g m⁻² yr⁻¹) and elevated ΣAlk₃₇ fluxes (∼2 mg m⁻² yr⁻¹) measured in the sedimentary interval corresponding to 1600–2000 yr BP. Such compositions are consistent with a period of low diatom and high haptophyte productivity, which based on the trends observed from the sediment traps, is indicative of low upwelling conditions relative to the modern day.  相似文献   

Particulate organic carbon in the global ocean derived from SeaWiFS ocean color     

Malgorzata Stramska 《Deep Sea Research Part I: Oceanographic Research Papers》2009,56(9):1459-1470

Satellite remote sensing offers new means of quantifying particulate organic carbon, POC, concentration over large oceanic areas. From SeaWiFS ocean color, we derived 10-year data of POC concentration in the surface waters of the global ocean. The 10-year time series of the global and basin scale average surface POC concentration do not display any significant long-term trends. The annual mean surface POC concentration and its seasonal amplitude are highest in the North Atlantic and lowest in the South Pacific, when compared to other ocean basins. POC anomalies in the North Atlantic, North Pacific, and global concentrations seem to be inversely correlated with El Niño index, but longer time series are needed to confirm this relationship. Quantitative estimates of POC reservoir in the oceanic surface layer depend on the choice of what should represent this layer. Global average POC biomass is 1.34 g m^?2 if integrated over one optical depth, 3.62 g m^?2 if integrated over mixed layer depth, and up to 6.41 g m^?2 if integrated over 200-m layer depth (when assumed POC concentration below MLD is 20 mg m^?3). The global estimate of total POC reservoir in the surface 200-m layer of the ocean is 228.61×10¹³ g. We expect that future estimates of POC reservoir may be even larger, when more precise calculations account for deep-water organic-matter maxima in oligotrophic regions, and POC biomass located just below the seasonal mixed layer in spring and summer in the temperate regions.  相似文献   

High-frequency fluxes of labile compounds in the central Ligurian Sea,northwestern Mediterranean     

《Deep Sea Research Part I: Oceanographic Research Papers》2000,47(3):533-556

Sinking particles were collected every 4 h with drifting sediment traps deployed at 200 m depth in May 1995 in a 1-D vertical system during the DYNAPROC observations in the northwestern Mediterranean sea. POC, proteins, glucosamine and lipid classes were used as indicators of the intensity and quality of the particle flux. The roles of day/night cycle and wind on the particle flux were examined. The transient regime of production from late spring bloom to pre-oligotrophy determined the flux intensity and quality. POC fluxes decreased from, on average, 34 to 11 mg m⁻² d⁻¹, representing 6–14% of the primary production under late spring bloom conditions to 1–2% under pre-oligotrophic conditions. Total protein and chloroplast lipid fluxes correlated with POC and reflected the input of algal biomass into the traps. As the season proceeded, changes in the biochemical composition of the exported material were observed. The C/N ratio rose from 7.8 to 12. Increases of serine (10–28% of total proteins), total lipids (7–9 to 14–28% of POC) and reserve lipids (1–5 to 5–22% of total lipids) were noticeable, whereas total protein content in POC decreased (20–27 to 18–7%). N-acetyl glucosamine, a tracer of fecal pellet flux, showed that zooplankton grazing was a major vector of downward export during the decaying bloom. Against this background pattern, episodic events specifically increased the flux, modifying the quality and the settling velocity of particles. Day/night signals in biotracers (POC, N-acetyl glucosamine, protein and chloroplast lipids) showed that zooplankton migrations were responsible for sedimentation of fresh material through fast sinking particles (V=170–180 m d⁻¹) at night. Periodic signatures of re-processed material (high lipolysis and bacterial biomass indices) suggested that other zooplankton fecal pellets or small aggregates, probably of lower settling velocities (V<170 m d⁻¹), contributed to the flux during calm periods. At the beginning of the experiment, during the development of a prymnesiophyte bloom in the upper layers, the sterol signal with no periodicity enabled us to estimate high particle settling velocities (⩾600 m d⁻¹) likely related to large aggregate formation. A wind event increased biotracer fluxes (POC, protein, chloroplast lipids). The rapid transmission of surface signals through extremely fast sinking particles could be a general feature of particle fluxes in marine areas unaffected by horizontal advection.  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   

Downward transport of organic carbon by diel migratory micronekton in the western equatorial Pacific:: its quantitative and qualitative importance     

《Deep Sea Research Part I: Oceanographic Research Papers》2001,48(8):1923-1939

Using simultaneous sampling with a commercial-sized trawl, a zooplankton net, and a sediment trap, we evaluated the contribution of vertically migrating micronekton to vertical material transport (biological pump) at two stations (3°00′N, 146°00′E and 3°30′N, 145°20′E) in the western equatorial North Pacific. The gravitational sinking particulate organic carbon flux out of the euphotic zone was 54.8 mg C m⁻² day⁻¹. The downward active carbon flux by diel migrant mesozooplankton was 23.53 and 9.97 mg C m⁻² day⁻¹, and by micronekton 4.40 and 2.26mg C m⁻² day⁻¹ at the two stations. Assuming that the micronekton sampling efficiency of the trawl was 14%, we corrected the downward carbon flux due to micronekton respiration to 29.9 and 15.2mg C m⁻² day⁻¹, or 54.6 and 27.7% of the sinking particle flux at the two stations. The corrected micronekton gut fluxes were 1.53 and 0.97mg C m⁻² day⁻¹. The role of myctophid fish fecal matter as a possible food resource for deep-sea organisms, based on its fatty acid and amino acid analysis, is discussed.  相似文献   

Three-year assessment of particulate organic carbon fluxes in Amundsen Gulf (Beaufort Sea): Satellite observations and sediment trap measurements     

Alexandre Forest  Simon Bélanger  Makoto Sampei  Hiroshi Sasaki  Catherine Lalande  Louis Fortier 《Deep Sea Research Part I: Oceanographic Research Papers》2010,57(1):125-142

Surface concentrations and vertical fluxes of particulate organic carbon (POC) were assessed in the Amundsen Gulf (southeastern Beaufort Sea, Arctic Ocean) over the years 2004 to 2006 by using ocean color remote-sensing imagery and sequential sediment traps moored over the ca. 400 m isobath. Environmental conditions (sea ice, wind) and oceanographic variables (temperature, salinity, fluorescence and currents) were investigated to explain the variability of POC data. Annual downward POC fluxes in 2004, 2005 and 2006 cumulated, respectively, to 3.3, 4.2 and 6.0 g C m^?2 yr^?1 at ～100 m depth, and to 1.3, 2.2 and 3.3 g C m^?2 yr^?1 at ～210 m depth. The fraction of settling POC attributable to autochthonous processes occurring at or next to ice break-up was estimated to be 75–84% of the 100 m annual fluxes and to be 61–75% of the 210 m fluxes. Over the three ice-reduced seasons, distinct scenarios between ice conditions, surface POC pools and vertical POC export at 100 m were identified: (1) in 2004, despite a normal ice break-up, a weak primary production was measured and low vertical fluxes were collected as old ice moved across the region; (2) in 2005, a lengthened ice-free period allowed an extended season of surface POC production near-shore, while an intermediate increase of vertical fluxes was recorded offshore; and (3) in 2006, a late ice melt gave rise to a pulsed ice edge bloom and to large vertical fluxes also associated with extra ice-flushed material. Linear regressions of vertical POC fluxes against satellite-derived surface POC concentrations suggested that the pelagic POC retention in the upper 100 m of the Amundsen Gulf ranged from ca. 70% to 90% depending on the timing of ice cover melt. Regardless of the inter-annual variability, the estimated fraction of the surface POC reservoir reaching the 210 m water depth was reduced to ～5%. Therefore, as the Arctic Ocean warms up, our results support the expectation that the increasing extent of the seasonal ice zone will promote the POC pathways that benefit pelagic webs rather than benthic communities.  相似文献   

Ascending and descending particle flux from hydrothermal plumes at Endeavour Segment,Juan de Fuca Ridge     

《Deep Sea Research Part I: Oceanographic Research Papers》2001,48(4):1093-1120

Bio-acoustic surveys and associated zooplankton net tows have documented anomalously high concentrations of zooplankton within a 100 m layer above the hydrothermal plumes at Endeavour Segment, Juan de Fuca Ridge. These and other data suggest that congregating epi-plume zooplankton are exploiting a food substrate associated with the hydrothermal plume. Ascending, organic-rich particles could provide a connection. Consequently, two paired sequentially sampling ascending and descending particle flux traps and a current meter were deployed on each of three moorings from July 1994 to May 1995. Mooring sites included an on-axis site (OAS; 47°57.0′N, 129°05.7′W) near the main Endeavour vent field, a “down-current” site 3 km west of the main vent field (WS), and a third background station 43 km northeast of the vent field (ES). Significant ascending and descending particle fluxes were measured at all sites and depths. Lipid analyses indicated that ascending POC was derived from mid-depth and deep zooplankton whereas descending POC also contained a component of photosynthetically derived products from the sea surface. Highest ascending POC fluxes were found at the hydrothermal plume-swept sites (OAS and WS). The limited data available, however, precludes an unequivocal conclusion that hydrothermal processes contribute to the ascending flux of organic carbon at each site. Highest ascending to descending POC flux ratios were also found at WS. Observed trends in POC, PMn/PTi, and PFe/PTi clearly support a hydrothermal component to the descending flux at the plume-swept WS site (no descending data was recovered at OAS) but not at the background ES site. Alternative explanations for ascending particle data are discussed. First-order calculations for the organic carbon input (5–22 mg C m⁻² d⁻¹) required to sustain observed epi-plume zooplankton anomalies at Endeavour are comparable both to measured total POC flux to epi-plume depths (2–5 mg C m⁻² d⁻¹: combined hydrothermal and surface derived organic carbon) and to estimates of the total potential in situ organic carbon production (2–9 mg C m⁻² d⁻¹) from microbial oxidation of hydrothermal plume H₂, CH₄ and NH₄⁺.  相似文献   

Spatial and temporal variability of POC in the northeast Subarctic Pacific     

《Deep Sea Research Part II: Topical Studies in Oceanography》1999,46(11-12):2699-2733

Particulate organic carbon (POC) concentrations from 0 to 1000 m were quantified in size-fractionated particulate matter samples obtained by the multiple unit large volume in situ filtration system (MULVFS) in 1996 and 1997 along the 1600 km long “line P” transect from continental slope waters near southern Vancouver Island to Ocean Station PAPA (OSP, 50°N, 145°W). Regression of in situ POC vs. beam attenuation coefficient, c, from a simultaneously deployed 1-m pathlength SeaTech transmissometer gave slope, intercept and r² values of 6.15±0.19×10⁻⁵ m⁻¹ (nmol C l⁻¹)⁻¹, 0.363±0.003 m⁻¹, and 0.951 (n=145), respectively. This result agreed within several percent of calibrations obtained from two 2600-km-long transects of the equatorial Pacific in 1992 (Bishop, 1999). Data from other, more frequently deployed transmissometers were standardized against the 1-m instrument, and the combined optical data set was used to document POC variability at finer spatial and temporal scales than could be sampled directly using either conventional water bottle casts or MULVFS. Published bottle POC vs. c relationships show much more variability and remain problematic. Along the line P transect in the salinity-stratified upper 100 m, POC isolines shoaled from winter to summer in concert with seasonal stratification. At the same time, POC was progressively enriched in subeuphotic zone waters to depths greater than 500 m. Near-surface POC fields sampled in the winter time showed strong temporal POC variability over time scales of days as well as between years. POC concentrations at OSP in February 1996 were higher than those found at any other time of year. Less variability was found along line P in other seasons. In May 1996, kilometer-scale spatial variability of POC at OSP was small; dawn vs. dusk variations of c were used to calculate 0–100 m POC turnover times shorter than 6 d. Calculations also suggest that 25–50% of primary productivity was expressed as dissolved organic carbon at OSP in May 1996.  相似文献   

Primary productivity,bacterial productivity and nitrogen uptake in response to iron enrichment during the SEEDS II     

《Deep Sea Research Part II: Topical Studies in Oceanography》2009,56(26):2755-2766

Primary productivity (PP), bacterial productivity (BP) and the uptake rates of nitrate and ammonium were measured using isotopic methods (¹³C, ³H, ¹⁵N) during a mesoscale iron (Fe)-enrichment experiment conducted in the western subarctic Pacific Ocean in 2004 (SEEDS II). PP increased following Fe enrichment, reached maximal rates 12 days after the enrichment, and then declined to the initial level on day 17. During the 23-day observation period, we observed the development and decline of the Fe-induced bloom. The surface mixed layer (SML) integrated PP increased by 3-fold, but was smaller than the 5-fold increase observed in the previous Fe-enrichment experiment conducted at almost the same location and season during 2001 (SEEDS). Nitrate uptake rates were enhanced by Fe enrichment but decreased after day 5, and became lower than ammonium uptake rates after day 17. The total nitrogenous nutrient uptake rate declined after the peak of the bloom, and accumulation of ammonium was obvious in the euphotic layer. Nitrate utilization accounted for all the requirements of N for the massive bloom development during SEEDS, whereas during SEEDS II, nitrate accounted for >90% of total N utilization on day 5, declining to 40% by the end of the observation period. The SML-integrated BP increased after day 2 and peaked twice on days 8 and 21. Ammonium accumulation and the delayed heterotrophic activity suggested active regeneration occurred after the peak of the bloom. The SML-integrated PP between days 0 and 23 was 19.0 g C m⁻². The SML-integrated BP during the same period was 2.6 g C m⁻², which was 14% of the SML-integrated PP. Carbon budget calculation for the whole experimental period indicated that 33% of the whole (particulate plus dissolved) PP (21.5 g C m⁻²) was exported below the SML and 18% was transferred to the meso-zooplankton (growth). The bacterial carbon consumption (43% of the whole PP) was supported by DOC or POC release from phytoplankton, zooplankton, protozoa and viruses. More than a half (56%) of the whole PP in the Fe patch was consumed within the SML by respiration of heterotrophic organisms and returned to CO₂.  相似文献   

Fluxes and exchange of suspended sediment in tidal inlets draining a degraded mangrove forest in Kenya     

《Estuarine, Coastal and Shelf Science》2003,56(3-4):655-667

This study focuses on sediment exchange in the degraded Mwache mangrove forest wetland located in southern Kenya. It involved measurement of total and particulate organic suspended sediment concentrations (TSSC and POSC), tidal water elevation and current velocities. Results showed that in the heavily degraded backwater zone mangrove forest, the ebb and flood tide total sediment fluxes were of same order of magnitude, however, flood tide sediment fluxes were slightly higher than the ebb ones. In the moderately degraded frontwater zone mangrove forest, the flood tide sediment fluxes were more than 50% higher than the ebb tide fluxes. The peak net sedimentation in the highly degraded backwater zone was 4 g m⁻² tide⁻¹ but that in the moderately degraded frontwater zone was 63 g m⁻² tide⁻¹. In the frontwater zone of the mangrove forest, the peak instantaneous ebb tide sediment flux was 3206 kg tide⁻¹ equivalent to 35.6 g m⁻² tide⁻¹ and the flood one 8574 kg tide⁻¹ (95 g m⁻² tide⁻¹). The peak instantaneous flood and ebb tide particulate organic sediment (POS) fluxes in the frontwater zone mangrove forest were 1316 kg tide⁻¹ (15 g m⁻² tide⁻¹) and 587 kg tide⁻¹ (6.5 g m⁻² tide⁻¹), respectively. The peak ebb and flood tide sediment fluxes in the backwater mangrove forest were 3206 kg tide⁻¹ (36 g m⁻² tide⁻¹) and 3305 kg tide⁻¹ (36.7 g m⁻² tide⁻¹), respectively. In case of POS fluxes in the backwater zone mangrove forest, the peak flood period POS flux was 969 kg tide⁻¹ (10.7 g m⁻² tide⁻¹) while the ebb period one was 484 kg tide⁻¹ (5.4 g m⁻² tide⁻¹). In both highly degraded backwater and moderately degraded frontwater zone of the mangrove forest, there is net import of sediments. However, the net import is relatively lower in the backwater zone forest where the trapping efficiency is 27%. In the moderately degraded frontwater zone of the mangrove forest, the sediment trapping efficiency is 65%. The net sediment import occurs mainly in periods of high river discharge in both neap and spring tides, but occurs only in spring tides during dry season. The net accretion rates in the backwater and frontwater zone mangrove forests are 0.25 and 3.5 cm year⁻¹, respectively.  相似文献   

Regional variations in the fluxes of foraminifera carbonate,coccolithophorid carbonate and biogenic opal in the northern Indian Ocean     

《Deep Sea Research Part I: Oceanographic Research Papers》2006,53(2):271-293

Mass fluxes of diatom opal, planktonic foraminifera carbonate and coccolithophorid carbonate were measured with time-series sediment traps at six sites in the Arabian Sea, Bay of Bengal and Equatorial Indian Ocean (EIOT). The above fluxes were related to regional variations in salinity, temperature and nutrient distribution. Annual fluxes of diatom opal range between 3 and 28 g m⁻² yr⁻¹, while planktonic foraminifera carbonate fluxes range between 6 and 23 g m⁻² yr⁻¹ and coccolithophorid carbonate fluxes range between 4 and 24 g m⁻² yr⁻¹. Annual planktonic foraminifera carbonate to coccolithophorid carbonate ratios range between 0.8 and 2.2 and coccolithophorid carbonate to diatom opal ratios range between 0.5 and 3.3.In the western Arabian Sea, coccolithophorids are the major contributors to biogenic flux during periods of low nutrient concentrations. Coccolithophorid carbonate fluxes decrease and planktonic foraminiferal carbonate and diatom opal fluxes increase when nutrient-rich upwelled waters are advected over the trap site. In the oligotropic eastern Arabian Sea, coccolithophorid carbonate fluxes are high throughout the year. Planktonic foraminiferal carbonate fluxes are the major contributors to biogenic flux in the EIOT. In the northern and central Bay of Bengal, when surface salinity values drop sharply during the SW monsoon, there is a drastic reduction in planktonic foraminiferal carbonate fluxes, but coccolithophorid carbonate and diatom opal fluxes remain steady or continue to increase. Distinctly higher annual molar Si_bio/C_inorg (>1) and C_org/C_inorg (>1.5) ratios are observed in the northern and central Bay of Bengal mainly due to lower foraminiferal carbonate production as a result of sharp salinity variations. We can thus infer that the enhanced freshwater supply from rivers should increase oceanic CO₂ uptake. Its silicate supply favours the production of diatoms while the salinity drop produces conditions unfavourable for most planktonic foraminifera species.  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   

Particulate organic carbon export fluxes and size-fractionated POC/234Th ratios in the Ligurian,Tyrrhenian and Aegean Seas     

《Deep Sea Research Part I: Oceanographic Research Papers》2006,53(11):1810-1830

Measurements of ²³⁴Th/²³⁸U disequilibria and particle size-fractionated (1, 10, 20, 53, 70, 100 μm) organic C and ²³⁴Th were made to constrain estimates of the export flux of particulate organic C (POC) from the surface waters of the Ligurian, Tyrrhenian and Aegean Seas in March–June 2004. POC exported from the surface waters (75–100 m depth) averaged 9.2 mmol m⁻² d⁻¹ in the Ligurian and Tyrrhenian Seas (2.3±0.5–14.9±3.0 mmol m⁻² d⁻¹) and 0.9 mmol m⁻² d⁻¹ in the Aegean Sea. These results are comparable to previous measurements of ²³⁴Th-derived and sediment-trap POC fluxes from the upper 200 m in the Mediterranean Sea. Depth variations in the POC/²³⁴Th ratio suggest two possible controls. First, decreasing POC/²³⁴Th ratios with depth were attributed to preferential remineralization of organic C. Second, the occurrence of maxima or minima in the POC/²³⁴Th ratio near the DCM suggests influence by phytoplankton dynamics. To assess the accuracy of these data, the empirical ²³⁴Th-method was evaluated by quantifying the extent to which the ²³⁴Th-based estimate of POC flux, P_POC, deviates from the true flux, F_POC, defined as the p-ratio (p-ratio=P_POC/F_POC=S_Th/S_POC, where S=particle sinking rate). Estimates of the p-ratio made using Stokes’ Law and the particle size distributions of organic C and ²³⁴Th yield values ranging from 0.93–1.45. The proximity of the p-ratio to unity implies that differences in the sinking rates of POC- and ²³⁴Th-carrying particles did not bias ²³⁴Th-normalized POC fluxes by more than a factor of two.  相似文献   

Lithogenic and biogenic particle fluxes on the Lomonosov Ridge (central Arctic Ocean) and their relevance for sediment accumulation: Vertical vs. lateral transport     

《Deep Sea Research Part I: Oceanographic Research Papers》2007,54(8):1256-1272

Investigations of lithogenic and biogenic particle fluxes using long-term sediment traps are still very rare in the northern high latitudes and are restricted to the arctic marginal seas and sub-arctic regions. Here data on the variability of fluxes of lithogenic matter, CaCO₃, opal, and organic carbon and biomarker composition from the central Arctic Ocean are presented for a 1-year period. The study was carried out on material obtained from a long-term mooring system equipped with two multi-sampling traps, at 150 and 1550 m depth, and deployed on the southern Lomonosov Ridge close to the Laptev Sea continental margin from September 1995 to August 1996. In addition, data from surface sediments were included in the study. Annual fluxes of lithogenic matter, CaCO₃, opal, and particulate organic carbon were 3.9, 0.8, 2.6, and 1.5 g m⁻² y⁻¹, respectively, in the shallow trap and 11.3, 0.5, 2.9, and 1.05 g m⁻² y⁻¹, respectively, in the deep trap.Both the shallow and the deep trap showed significant variations in vertical flux over the year. Higher values were found from mid-July to the end of October (total mass flux of 75–130 mg m⁻² d⁻¹ in the shallow trap and 40–225 mg m⁻² d⁻¹ in the deep trap). During all other months, fluxes were fairly low in both traps (most total mass flux values <10 mg m⁻² d⁻¹). The interval of increased fluxes can be separated into (1) a mid-July/August maximum caused by increased primary production as documented in high abundances of marine biomarkers and diatoms and (2) a September/October maximum caused by increased influence of Lena River discharge indicated by maximum lithogenic flux and large amounts of terrigenous/fluvial biomarkers in both traps. During September/October, total mass fluxes in the deep trap were significantly higher than in the shallow trap, suggesting a lateral sediment flux at greater depth. The lithogenic flux data also support the importance of sediment input from the Laptev Sea for the sediment accumulation on the Lomonosov Ridge on geological time scales, as indicated in sedimentary records from this region.  相似文献   

High primary productivity and f-ratio in summer in the Ulleung basin of the East/Japan Sea     

《Deep Sea Research Part I: Oceanographic Research Papers》2013

To better understand the cause of high summer primary productivity in the Ulleung Basin located in the southwest part of the East/Japan Sea, the spatial dynamics of primary, new, and regenerated productivities (PP, NP, and RP) were examined along the path of the Tsushima Warm Current system in summer 2008. We compared hydrographic and chemical parameters in the Ulleung Basin with those of the Kuroshio Current in the Western Pacific Ocean and the East China Sea. In summer, integrated primary productivity (IPP, 0.37–0.96 g C m⁻² d⁻¹) and integrated new productivity (INP, 26–221 mg N m⁻² d⁻¹) within the euphotic zone in the Ulleung Basin were higher than those in the East China Sea and the Western Pacific Ocean (0.17–0.28 g C m⁻² d⁻¹, 2−5 mg N m⁻² d⁻¹, respectively). In contrast, there was no pronounced spatial variation in integrated regenerated productivity (IRP, 43–824 mg N m⁻² d⁻¹). Strong positive correlations between IPP and INP (also the f-ratio), and between nitrate uptake rate in the mixed layer and nitrate upward flux through the top of pycnocline in summer in the Ulleung Basin imply that the high IPP was mainly supported by supply of nitrate from the underlying water in the euphotic zone. Shallowing of the pycnocline depth as the current enters the East/Japan Sea facilitates nitrate supply from the nutrient-replete cold water immediately below the pycnocline through nitrate upward flux. A subsurface maximum in PP at or above the pycnocline and a high f-ratio further support the importance of this source of nitrate for maintaining the high summer PP in the Ulleung Basin. In comparison, the high PP layer was observed at the surface in the following fall and spring in the Ulleung Basin. Our results demonstrate the importance of hydrographic features in enhancing PP in this oligotrophic Tsushima Warm Current system.  相似文献   

Biomass size-spectra of macrobenthic communities in the oxygen minimum zone off Chile     

《Estuarine, Coastal and Shelf Science》2005,62(1-2):217-231

Estimates of macrofaunal secondary production and normalized biomass size-spectra (NBSS) were constructed for macrobenthic communities associated with the oxygen minimum zone (OMZ) in four areas of the continental margin off Chile. The presence of low oxygen conditions in the Humboldt Current System (HCS) off Chile was shown to have important effects on the size structure and secondary production of the benthic communities living in this ecosystem. The distribution of normalized biomass by size was linear (log₂–log₂ scale) at all stations. The slope of the NBSS ranged from −0.481 to −0.908. There were significant differences between the slopes of the NBS-spectra from the stations located in the OMZ (slope = −0.837) and those located outside the OMZ (slope = −0.463) (p < 0.05). The results of this study suggest that low oxygen conditions (<0.5 ml L⁻¹) appear to influence biomass size-spectra, because small organisms are better able to satisfy their metabolic demands. The annual secondary production was higher off central Chile (6.8 g C m⁻² y⁻¹) than off northern Chile (2.02 g C m⁻² y⁻¹) and off southern Chile (0.83 g C m⁻² y⁻¹). A comparison with other studies suggests that secondary production in terms of carbon equivalents was higher than in other upwelling regions.  相似文献