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   

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   

Ectoenzymatic activity in surface waters: A transect from the Mediterranean Sea across the Indian Ocean to Australia     

《Deep Sea Research Part I: Oceanographic Research Papers》2006,53(9):1517-1532

The activities of two hydrolytic enzymes (leucine aminopeptidase and β glucosidase), belonging to the particle-bound enzymatic fraction, were measured in open-sea surface waters. Samples were collected along a transect crossing the Indian Ocean during the early NW monsoon period (November and December 2001). The latitudinal pattern of the ectoenzymatic activities highlighted a generally increasing trend of glycolysis approaching the equator, with significantly higher β glucosidase activity (0.79–3.00 nmol l⁻¹ h⁻¹) within the latitudinal range from 12°N to 16°S. In this area, the surface waters coming from the Indonesian Throughflow and the Bay of Bengal carry a considerable quantity of carbohydrates (38.9–41.9 μg l⁻¹), which stimulated glycolytic activity and its cell-specific rates scaled to bacterial abundance. On the other hand, in the Central Indian Ocean, the proteolytic activity was considerable (0.91–2.03 nmol l⁻¹ h⁻¹), although the particulate proteins did not show significant increases and the dissolved proteinlike signal was one of the lowest of the entire transect (0.7 mg l⁻¹ on average compared to the 1.4–1.6 mg l⁻¹ of the adjacent areas). Therefore, in this area, the two ectoenzymes studied did not respond to the same stimulatory effect (namely the specific substrate concentrations). The time needed for the hydrolysis of macromolecules within the particulate and dissolved organic substrate fractions, although these measures are affected by a number of assumptions starting with the potential nature of the ectoenzymatic determinations, confirms these observations. The Central Indian Ocean displayed the lowest values, from 8 to 26 days for particulate and dissolved organic carbon, respectively. As observed in the equatorial areas of the Atlantic Ocean, the relevant degradation activity of the central area of the Indian Ocean Basin suggests a notable heterotrophy based on a faster turnover of organic substrates.  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   

Community respiration/production and bacterial activity in the upper water column of the central Arctic Ocean     

《Deep Sea Research Part I: Oceanographic Research Papers》2003,50(4):529-542

Community metabolism (respiration and production) and bacterial activity were assessed in the upper water column of the central Arctic Ocean during the SHEBA/JOIS ice camp experiment, October 1997–September 1998. In the upper 50 m, decrease in integrated dissolved oxygen (DO) stocks over a period of 124 d in mid-winter suggested a respiration rate of ∼3.3 nM O₂ h⁻¹ and a carbon demand of ∼4.5 gC m⁻². Increase in 0–50 m integrated stocks of DO during summer implied a net community production of ∼20 gC m⁻². Community respiration rates were directly measured via rate of decrease in DO in whole seawater during 72-h dark incubation experiments. Incubation-based respiration rates were on average 3-fold lower during winter (11.0±10.6 nM O₂ h⁻¹) compared to summer (35.3±24.8 nM O₂ h⁻¹). Bacterial heterotrophic activity responded strongly, without noticeable lag, to phytoplankton growth. Rate of leucine incorporation by bacteria (a proxy for protein synthesis and cell growth) increased ∼10-fold, and the cell-specific rate of leucine incorporation ∼5-fold, from winter to summer. Rates of production of bacterial biomass in the upper 50 m were, however, low compared to other oceanic regions, averaging 0.52±0.47 ngC l⁻¹ h⁻¹ during winter and 5.1±3.1 ngC l⁻¹ h⁻¹ during summer. Total carbon demand based on respiration experiments averaged 2.4±2.3 mgC m⁻³ d⁻¹ in winter and 7.8±5.5 mgC m⁻³ d⁻¹ in summer. Estimated bacterial carbon demand based on bacterial productivity and an assumed 10% gross growth efficiency was much lower, averaging about 0.12±0.12 mgC m⁻³ d⁻¹ in winter and 1.3±0.7 mgC m⁻³ d⁻¹ in summer. Our estimates of bacterial activity during summer were an order of magnitude less than rates reported from a summer 1994 study in the central Arctic Ocean, implying significant inter-annual variability of microbial processes in this region.  相似文献   

Copper complexation by fulvic acid affects copper toxicity to the larvae of the polychaete Hydroides elegans     

《Marine environmental research》2008,65(5):563-573

Copper toxicity is influenced by a variety of environmental factors including dissolved organic matter (DOM). We examined the complexation of copper by fulvic acid (FA), one of the major components of DOM, by measuring the decline in labile copper by anodic stripping voltammetrically (ASV). The data were described using a one-site ligand binding model, with a ligand concentration of 0.19 μmol site mg⁻¹ C, and a log K′ of 6.2. The model was used to predict labile copper concentration in a bioassay designed to quantify the extent to which Cu–FA complexation affected copper toxicity to the larvae of marine polychaete Hydroides elegans. The toxicity data, when expressed as labile copper concentration causing abnormal development, were independent of FA concentration and could be modeled as a logistic function, with a 48-h EC₅₀ of 58.9 μg l⁻¹. However, when the data were expressed as a function of total copper concentration, the toxicity was dependent on FA concentration, with a 48-h EC₅₀ ranging from 55.6 μg l⁻¹ in the no-FA control to 137.4 μg l⁻¹ in the 20 mg l⁻¹ FA treatment. Thus, FA was protective against copper toxicity to the larvae, and such an effect was caused by the reduction in labile copper due to Cu–FA complexation. Our results demonstrate the potential of ASV as a useful tool for predicting metal toxicity to the larvae in coastal environment where DOM plays an important role in complexing metal ions.  相似文献   

Winter and spring phytoplankton composition and production in a shallow eutrophic Baltic lagoon     

《Estuarine, Coastal and Shelf Science》2005,62(1-2):169-181

Taxonomic composition and productivity of winter and spring phytoplankton in a eutrophic estuary have been investigated in order to elucidate the carbon flux under conditions of limitation by physical factors – light and temperature. In spite of the important differences in nutrients, solar radiation and water temperature between winter and spring season, mean concentrations of particulate organic carbon were equal to 13.2 and 13.0 mgC l⁻¹, respectively. Chlorophyll a averaged at 79 μgChl l⁻¹ in winter, that is 69% of spring. Although community respiration accounted for only 6–26% of light saturated photosynthesis, integrated net primary production of the 1.2 m deep water column was negative until April. High attenuation of the water body (K_o = 2.9 m⁻¹) lead to a negative carbon balance (net heterotrophy) below 35 cm for all sampling dates. Thus, the high winter POC and phytoplankton values can only originate from summer or autumn primary production. This assumption was supported by a carbon loss rate of just 3% of total organic carbon per day for the whole water column. The composition of phytoplankton was very constant through both seasons: 39% Chlorophyceae, 33% Cyanobacteria and 25% Bacillariophyceae. As expected, phytoplankton was low light acclimated, having high α values (slope of light limited photosynthesis), but moderate maximum photosynthesis rates at saturating irradiances, which were heavily affected by temperature. Calculation of net carbon flux yet showed net heterotrophy of the Bodden waters in winter and early spring were caused by external physical limitation (low surface irradiance and low temperature) in combination with a high light attenuation of the water body.  相似文献   

Monitoring suspended particulate matter fluxes and patterns with the AVHRR/NOAA-11 satellite: application to the Bay of Biscay     

《Deep Sea Research Part II: Topical Studies in Oceanography》1999,46(10):2029-2055

AVHRR/NOAA-11 satellite images of the C1 (580–680 nm) and C2 (725–1100 nm) channels were used to quantify the suspended particulate matter discharged into the ocean by the Gironde estuary (France). The calibration method is based on a comparison between satellite values (AVHRR reflectances) and suspended particulate matter (SPM) concentrations at the sea surface, measured in situ. To correct the aerosol variations a C1-C2 image subtraction is applied. However, when the SPM concentration is greater than about 15 mg l⁻¹, the C2 channel image is affected by water turbidity and the C1-C2 correction cannot be used. The C1 channel is more sensitive, and we were able to distinguish SPM concentration variations greater than 0.5 mg l⁻¹. A subtraction of two images recorded with a 24 h interval was carried out to evaluate vertical and horizontal fluxes. The residual image shows the quantity of particles leaving the surface layer. To assess horizontal displacements, turbid fronts were mapped by means of an image gradient analysis. Major and minor fronts recorded each day, superimposed to outline displacements (gradients and orientations), were displaced from the Gironde estuary to the West and the Northwest.During the ECOFER cruises (1989–1991), several AVHRR scenes were processed using an atmospheric correction based on the low SPM concentrations (“ocean pixel subtraction”). Generally, surface particulate matter is confined to the inner continental shelf. Higher values were observed during the ECOFER 4 cruise. Suspended particulate matter concentrations with the maximum extension appeared during the ECOFER 1 cruise. Concentrations were very low during the ECOFER 5 cruise, even in the lower estuary. This was due to low summer discharges that occurred during the dry period of 1988–1991 in France. During these surveys, estimated SPM concentrations were less than 1.5 mg l⁻¹ in the ECOFER area.  相似文献   

Primary productivity,differential size fraction and pigment composition responses in two Southern Ocean in situ iron enrichments     

《Deep Sea Research Part I: Oceanographic Research Papers》2007,54(5):747-773

Two in situ iron-enrichment experiments were conducted in the Pacific sector of the Southern Ocean during summer 2002 (SOFeX). The “north patch,” established within the Subantarctic Zone (∼56°S), was characterized by high nitrate (∼21 mmol m⁻³) but low silicic acid (2 mmol m⁻³) concentrations. North patch iron enrichment increased chlorophyll (Chl) by 12-fold to 2.1 mg m⁻³ and primary productivity (PP_EU) by 8-fold to 188 mmol C m⁻² d⁻¹. Surprisingly, despite low silicic acid concentrations, diagnostic pigment and size-fraction composition changes indicated an assemblage shift from prymnesiophytes toward diatoms. The “south patch,” poleward of the Southern Boundary of the Antarctic Circumpolar Current (SBACC) (∼66°S), had high concentrations of nitrate (∼27 mmol m⁻³) and silicic acid (64 mmol m⁻³). South patch iron enrichment increased Chl by 9-fold to 3.8 mg m⁻³ and PP_EU 5-fold to 161 mmol C m⁻² d⁻¹ but, notably, did not alter the phytoplankton assemblage from the initial composition of ∼50% diatoms. South patch iron addition also reduced total particulate organic carbon:Chl from ∼300 to 100; enhanced the presence of novel non-photosynthetic, but fluorescent, compounds; and counteracted a decrease in photosynthetic performance as photoperiod decreased. These experiments show unambiguously that in the contemporary, high nitrate Southern Ocean increasing iron supply increases primary productivity, confirming the initial premise of the Martin Iron Hypothesis. However, despite a 5-fold increase in PP_EU under iron-replete conditions in late summer, the effect of iron on annual productivity in the Southern Ocean poleward of the SBACC is limited by seasonal ice coverage and the dark of polar winter.  相似文献   

Dry atmospheric deposition and diazotrophy as sources of new nitrogen to northwestern Mediterranean oligotrophic surface waters     

《Deep Sea Research Part I: Oceanographic Research Papers》2007,54(11):1859-1870

Atmospheric dry deposition of nitrogen (N) and dinitrogen (N₂) fixation rates were assessed in 2004 at the time-series DYFAMED station (northwestern Mediterranean, 43°25′N, 7°52′E). The atmospheric input was monitored over the whole year. Dinitrogen fixation was measured during different seasonal trophic states (from mesotrophy to oligotrophy) sampled during nine cruises. The bioavailability of atmospherically deposited nutrients was estimated by apparent solubility after 96 h. The solubility of dry atmospheric N deposition was highly variable (from ∼18% to more than 96% of total N). New N supplied to surface waters by the dry atmospheric deposition was mainly nitrate (NO₃⁻) (∼57% of total N, compared to ∼6% released as ammonium (NH₄⁺)). The mean bioavailable dry flux of total N was estimated to be ∼112 μmol m⁻² d⁻¹ over the whole year. The NO₃⁻ contribution (70 μmol NO₃⁻ m⁻² d⁻¹) was much higher than the NH₄⁺ contribution (1.2 μmol NH₄⁺ m⁻² d⁻¹). The N:P ratios in the bioavailable fraction of atmospheric inputs (122.5–1340) were always much higher than the Redfield N:P ratio (16). Insoluble N in atmospheric dry deposition (referred to as “organic” and believed to be strongly related to anthropogenic emissions) was ∼40 μmol m⁻² d⁻¹. N₂ fixation rates ranged from 2 to 7.5 nmol L⁻¹ d⁻¹. The highest values were found in August, during the oligotrophic period (7.5 nmol L⁻¹ at 10 m depth), and in April, during the productive period (4 nmol L⁻¹ d⁻¹ at 10 m depth). Daily integrated values of N₂ fixation ranged from 22 to 100 μmol N m⁻² d⁻¹, with a maximum of 245 μmol N m⁻² d⁻¹ in August. No relationship was found between the availability of phosphorus or iron and the observed temporal variability of N₂ fixation rates. The atmospheric dry deposition and N₂ fixation represented 0.5–6% and 1–20% of the total biological nitrogen demand, respectively. Their contribution to new production was more significant: 1–28% and 2–55% for atmospheric dry deposition and N₂ fixation, respectively. The dry atmospheric input was particularly significant in conditions of water column stratification (16–28% of new production), while N₂ fixation reached its highest values in June (46% of new production) and in August (55%).  相似文献   

Fate of biogenic carbon in the upper 200 m of the central Greenland Sea     

《Deep Sea Research Part II: Topical Studies in Oceanography》1999,46(6-7):1497-1509

Sedimentation of particulate carbon from the upper 200–300 m in the central Greenland Sea from August 1993 to June 1995 was less than 2 g C m⁻² yr⁻¹. Daily rates of sedimentation of particulate organic carbon reached highest values of about 18 mg m⁻² d⁻¹ in fall 1994. For total particulate material, maximum rates of sedimentation of about 250 mg m⁻² d⁻¹ were recorded in spring and fall 1994. For chlorophyll equivalent, highest rates of sedimentation of about 140 μg m⁻² d⁻¹ were recorded in spring 1994. As reported in related investigations, the transient accumulation of DOC in surface waters during summer, as well as respiration and mortality of deep overwintering zooplankton stocks, appeared to dominate the fate of photosynthetically fixed organic carbon. The above processes may account for roughly 43 g C m⁻² in the upper 200 m of the central Greenland Sea. For comparison, the seasonal deficit in dissolved inorganic carbon was reported to be about 23 g C m⁻² in the upper 20 m of surface water, and estimates for new annual production were reported to be about 57 g C m⁻². In our investigation, the biological carbon pump was not unusually effective in transporting carbon out of the productive surface layer.  相似文献   

Time-series observation of POC fluxes estimated from 234Th in the northwestern North Pacific     

《Deep Sea Research Part I: Oceanographic Research Papers》2007,54(7):1070-1090

Time-series measurements of ²³⁴Th activities and particulate organic carbon (POC) concentrations were made at time-series stations (K1, K2, K3, and KNOT) in the northwestern North Pacific from October 2002 to August 2004. Seasonal changes in POC export fluxes from the surface layer (∼100 m) were estimated using ²³⁴Th as a tracer. POC fluxes varied seasonally from approximately 0 to 180 mg C m⁻² d⁻¹ and were higher in spring–summer than in autumn–winter. The export ratio (e-ratio) ranged from 6% to 55% and was also higher in spring–summer. Annual POC fluxes were estimated to be 31 g C m⁻² y⁻¹ in the subarctic region (station K2) and 23 g C m⁻² y⁻¹ in the region between the subarctic and subtropical gyres (station K3). POC fluxes and e-ratios in the northwestern North Pacific were much higher than those in most other oceans. The annual POC flux corresponded to 69% of annual new production estimated from the seasonal difference of the nutrient in the Western Subarctic Gyre (45 g C m⁻² y⁻¹). These results indicate that much of the organic carbon assimilated in the surface layer of the northwestern North Pacific is transferred to the deep ocean in particulate form. Our conclusions support previous reports that diatoms play an important role in the biological pump.  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   

Vertical flux of particulate Al,Fe, Pb,and Ba from the upper ocean estimated from 234Th/238U disequilibria     

《Deep Sea Research Part I: Oceanographic Research Papers》2005,52(8):1477-1488

The vertical sinking flux of particulate Al, Fe, Pb, and Ba from the upper 250 m of the Labrador Sea has been estimated from measurements of ²³⁴Th/²³⁸U disequilibrium and the respective metal/²³⁴Th ratios in >53 μm size particles. ²³⁴Th-derived particulate metal fluxes include in situ scavenged metals, labile lithogenic metals, and metals derived from external input (e.g., atmospheric supply). In contrast to the POC/²³⁴Th ratio, particle size-fractionated (0.4–10 μm, 10–53 μm, and >53 μm) Al/²³⁴Th, Fe/²³⁴Th and Pb/²³⁴Th, and Ba/²³⁴Th ratios generally increase with depth and exhibit no systematic change with particle diameter. Sinking fluxes of particulate Al (2.47–22.3 μmol m⁻² d⁻¹), Fe (2.69–16.3 μmol m⁻² d⁻¹), Pb (2.85–70 nmol m⁻² d⁻¹), and Ba (0.13–2.1 μmol m⁻² d⁻¹) at 50 m (base of the euphotic zone) and 100 m (base of the mixed layer) are largely within the range of previous sediment trap results from other ocean basins. Estimates of the upper ocean residence time of Al (0.07–0.28 yr) and Pb (0.8–2.9 yr) are short compared to previously reported values. The settling rate of >53 μm particles calculated from the ²³⁴Th data ranges from 14 to 38 m d⁻¹.  相似文献   

A sediment and organic carbon budget for the greater Strait of Georgia     

《Estuarine, Coastal and Shelf Science》2003,56(3-4):845-860

Recent efforts to construct global ocean budgets for carbon have recognized the importance of continental margins. In this study, we constructed budgets for the Strait of Georgia, a temperate, North American west coast basin that receives the inflow of one of the world's major rivers. Drawing from published and unpublished data, we have estimated the magnitude of the various sources and sinks of fresh water, sediment and organic carbon.The Fraser River is the dominant source of fresh water and particles to the strait, contributing approximately 73% of the 158×10⁹ m³ year⁻¹ of water and 64% of the 30×10⁹ kg year⁻¹ of particles. Other rivers supply most of the remainder, while rain, groundwater and anthropogenic sources of water and particles are negligible in comparison. Fresh water escapes the Strait of Georgia through Juan de Fuca Strait, but particulate inputs are approximately balanced by sedimentation within the greater Strait of Georgia, implying almost complete trapping of particles.Dissolved and particulate organic carbon are derived mainly from in situ primary production (855×10⁶ kg year⁻¹) and from the Fraser River (550×10⁶ kg year⁻¹). Other rivers contribute 200×10⁶ kg year⁻¹ of organic carbon, and anthropogenic sources (ocean dumping, sewage, pulp mills and aquaculture) a further 119×10⁶ kg year⁻¹. Particulate organic carbon is predominantly buried (428×10⁶ kg year⁻¹) or oxidized (90×10⁶ kg year⁻¹) in the sediments of the strait. About 70% of the organic carbon that enters or is produced in the strait is dissolved. Most of the dissolved organic carbon is oxidized within the strait (784×10⁶ kg year⁻¹), but the remainder (400×10⁶ kg year⁻¹) is exported to the Pacific Ocean. Although the particulate organic carbon budget by itself implies net autotrophy, dissolved organic carbon oxidation may make the Strait of Georgia slightly net heterotrophic.  相似文献   

Effects of mesoscale phytoplankton variability on the copepods Neocalanus flemingeri and N. plumchrus in the coastal Gulf of Alaska     

《Deep Sea Research Part I: Oceanographic Research Papers》2006,53(2):321-332

The copepods Neocalanus flemingeri and N. plumchrus are major components of the mesozooplankton on the shelf of the Gulf of Alaska, where they feed, grow and develop during April–June, the period encompassing the spring phytoplankton bloom. Satellite imagery indicates high mesoscale variability in phytoplankton concentration during this time. Because copepod ingestion is related to food concentration, we hypothesized that phytoplankton ingestion by N. flemingeri and N. plumchrus would vary in response to mesoscale variability of phytoplankton. We proposed that copepods on the inner shelf, where the phytoplankton bloom is most pronounced, would be larger and have more lipid stores than animals collected from the outer shelf, where phytoplankton concentrations are typically low. Shipboard feeding experiments with both copepods were done in spring of 2001 and 2003 using natural water as food medium. Chlorophyll concentration ranged widely, between 0.32 and 11.44 μg l⁻¹ and ingestion rates varied accordingly, between 6.0 and 627.0 ng chl cop⁻¹ d⁻¹. At chlorophyll concentrations<0.50 μg l⁻¹, ingestion is always low, <40 ng cop⁻¹ d⁻¹. Intermediate ingestion rates were observed at chlorophyll concentrations between 0.5 and 1.5 μg l⁻¹, and maximum rates at chlorophyll concentrations>1.5 μg l⁻¹. Application of these feeding rates to the phytoplankton distribution on the shelf allowed locations and time periods of low, intermediate and high daily feeding to be calculated for 2001 and 2003. A detailed cross-shelf survey of body size and lipid store in these copepods, however, indicated they were indistinguishable regardless of collection site. Although the daily ingestion of phytoplankton by N. flemingeri and N. plumchrus varied widely because of mesoscale variability in phytoplankton, these daily differences did not result in differences in final body size or lipid storage of these copepods. These copepods efficiently dealt with small and mesoscale variations in their food environment such that mesoscale structure in phytoplankton did not affect their final body size.  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   

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   

Sulfate reduction in Black Sea sediments: in situ and laboratory radiotracer measurements from the shelf to 2000 m depth     

《Deep Sea Research Part I: Oceanographic Research Papers》2001,48(9):2073-2096

Sulfate reduction rate measurements by the ³⁵SO₄²⁻ core injection method were carried out in situ with a benthic lander, LUISE, and in parallel by shipboard incubations in sediments of the Black Sea. Eight stations were studied along a transect from the Romanian shelf to the deep western anoxic basin. The highest rates measured on an areal basis for the upper 0–15 cm were 1.97 mmol m⁻² d⁻¹ on the shelf and 1.54 mmol m⁻² d⁻¹ at 181 m water depth just below the chemocline. At all stations sulfate reduction rates decreased to values <3 nmol cm⁻³ d⁻¹ below 15 cm depth in the sediment. The importance of sulfate reduction relative to the total mineralization of organic matter was very low, 6%, on the inner shelf, which was paved with mussels, and increased to 47% on the outer shelf at 100 m depth. Where the oxic–anoxic interface of the water column impinged on the sea floor at around 150 m depth, the contribution of sulfate reduction increased from >50% just above the chemocline to 100% just below. In the deep sea, mean sulfate reduction rates were 0.6 mmol m⁻² d⁻¹ corresponding to an organic carbon oxidation of 1.3 mmol m⁻² d⁻¹. This is close to the mean sedimentation rate of organic carbon over the year in the western basin. A comparison with published data on sulfate reduction in Black Sea sediments showed that the present results tend to be higher in shelf sediments and lower in the deep-sea than most other data. Based on the present water column H₂S inventory and the H₂S flux out of the sediment, the calculated turnover time of H₂S below the chemocline is 2100 years.  相似文献   

Particle sedimentation patterns in the eastern Fram Strait during 2000–2005: Results from the Arctic long-term observatory HAUSGARTEN     

Eduard Bauerfeind  Eva-Maria Nöthig  Agnieszka Beszczynska  Kirsten Fahl  Lars Kaleschke  Kathrin Kreker  Michael Klages  Thomas Soltwedel  Christiane Lorenzen  Jan Wegner 《Deep Sea Research Part I: Oceanographic Research Papers》2009,56(9):1471-1487

Since 2000 long-term measurements of vertical particle flux have been performed with moored sediment traps at the long-term observatory HAUSGARTEN in the eastern Fram Strait (79°N/4°E). The study area, which is seasonally covered with ice, is located in the confluence zone of the northward flowing warm saline Atlantic water with cold, low salinity water masses of Arctic origin. Current projections suggest that this area is particularly vulnerable to global warming. Total matter fluxes and components thereof (carbonate, particulate organic carbon and nitrogen, biogenic silica, biomarkers) revealed a bimodal seasonal pattern showing elevated sedimentation rates during May/June and August/September. Annual total matter flux (dry weight, DW) at ～300 m depth varied between 13 and 32 g m^?2 a^?1 during 2000 and 2005. Of this total flux 6–13% was due to CaCO₃, 4–21% to refractory particulate organic carbon (POC), and 3–8% to biogenic particulate silica (bPSi). The annual flux of all biogenic components together was almost constant during the period studied (8.5–8.8 g m^?2 a^?1), although this varied from 27% to 67% of the total annual flux. The fraction was lowest in a year characterized by the longest duration of ice coverage (91 and 70 days for the calendar year and summer season, May–September, respectively). Biomarker analyses revealed that organic matter originating from marine sources was present in excess of terrigenious material in the sedimented matter throughout most of the study period. Fluxes of recognizable phyto- and protozooplankton cells amounted up to 60×10⁶ m^?2 d^?1. Diatoms and coccolithophorids were the most abundant organisms. Diatoms, mainly pennate species, dominated during the first years of the investigation. A shift in the composition occurred during the last year when numbers of diatoms declined considerably, leading to a dominance of coccolithoporids. This was also reflected in a decrease in the sedimentation of bPSi. The sedimentation of biogenic matter, however, did not differ from the amount observed during the previous years. Among the larger organisms, pteropods at times contributed significantly to both the total matter and CaCO₃, fluxes.  相似文献