Total Organic Carbon Fluxes Research Articles

マゼラン海峡堆積物に記録された過去13,000年間の 全有機炭素・全窒素フラックス変動

マゼラン海峡堆積物に記録された過去13,000年間の 全有機炭素・全窒素フラックス変動

Carbon fluxes within the epipelagic zone of the Humboldt Current System off Chile: The significance of euphausiids and diatoms as key functional groups for the biological pump

The information from 54 drifting sediment traps deployed between 1997 and 2006 along the Humboldt Current System off Chile (from 19.9°S to 42.2°S) was analyzed to contribute to unveiling the recurrent global-ocean issue of the lack of relationship between gross primary production (GPP) and particulate organic carbon (POC) export below 50 m depth. When the proportion of carbon that effectively sinks is relatively low compared to the carbon being fixed through GPP, a significant amount (average of 32%) of the sinking organic matter is composed of diatoms, regardless of GPP rates. Such a fraction seems to be affected by the physiological state of phytoplankton. In contrast, when the fraction of carbon sinking is high relative to GPP, most of sinking organic matter is composed of euphausid faecal strings. Such a situation occurs at relatively low values of GPP and chlorophyll-a. Most of these high sinking rates of pellets and low phytoplankton biomass occur during summer, when physical conditions favour the presence of phytoplankton blooms, and when the GPP/Biomass ratio indicates healthy phytoplankton physiological conditions. All this evidence supports the assessment of the relevance of euphausiids as key species in the Humboldt Current System pointing to (i) the top–down control that euphausiids are capable of exerting over primary producer biomass, and (ii) euphausiids‘ paramount role on total organic carbon flux over the Concepción continental shelf, regarding both POC export to the sediments and possibly the channelling of GPP directly to higher trophic levels.

Offshore advection of particles within the Cape Blanc filament, Mauritania: Results from observational and modelling studies

This article will review major features of the ‘giant’ Cape Blanc filament off Mauritania with regard to the transport of chlorophyll and organic carbon from the shelf to the open ocean. Within the filament, chlorophyll is transported about 400 km offshore. Modelled particle distributions along a zonal transect at 21°N showed that particles with a sinking velocity of 5 m d −1 are advected offshore by up to 600 km in subsurface particle clouds generally located between 400 m and 800 m water depth, forming an Intermediate Nepheloid Layer (INL). It corresponds to the depth of the oxygen minimum zone. Heavier particles with a sinking velocity of 30 m d −1 are transported from the shelf within the Bottom Layer (BL) of more than 1000 m thickness, largely following the topography of the bottom slope. The particles advected within the BL contribute to the enhanced winter–spring mass fluxes collected at the open-ocean mesotrophic sediment trap site CB-13 (∼200 nm offshore), due to a long distance advection in deeper waters. The lateral contribution to the deep sediment trap in winter–spring is estimated to be 63% and 72% for organic carbon and total mass, respectively, whereas the lateral input for both components on an annual basis is estimated to be in the order of 15%. Biogenic opal increases almost fivefold from the upper to the lower mesotrophic CB-13 trap, also pointing to an additional source for biogenic silica from eutrophic coastal waters. Blooms obviously sink in smaller, probably mesoscale-sized patches with variable settling rates, depending on the type of aggregated particles and their ballast content. Generally, particle sinking rates are exceptionally high off NW Africa. Very high chlorophyll values and a large size of the Cape Blanc filament in 1998–1999 are also documented in enhanced total mass and organic carbon fluxes. An increasing trend in satellite chlorophyll concentrations and the size of the Cape Blanc filament between 1997 and 2008 as observed for other coastal upwelling areas is not documented.

DISSOLVED AND PARTICULATE CARBON IN JAKARTA BAY, INDONESIA

In order to investigate spatial and temporal variability of dissolved organic carbon (DOC) and particulate organic carbon (POC), several samples were collected from five estuaries, inner part and outer part of Jakarta Bay. The samples were collected on 15 and 16 February 2007, a week after heavy flood in Jakarta Area, and on 16 May 2007. DOC concentration in February and May in Jakarta Bay ranged between 100-950 µg-C/l and between 0-850 µg-C/l respectively. POC concentrations ranged between 50-650 µg-C /l and 50-900 µg-C /1 in February and May 2007, respectively. Even though the concentrations between both periods were similar, the load of organic carbon from the land to Jakarta Bay showed a large contrast due to the different amount of freshwater input. The Total organic carbon fluxes from the rivers to the bay in February and May 2007 were 107.6 t d-' C-(ton per day Carbon) and 42.7 t d-1 C, respectively.

A simplified approach to evaluate sedimentary organic matter fluxes and accumulation on the NW Adriatic Shelf (Italy)

Total organic carbon (TOC) and total nitrogen (TN) concentrations and fluxes were estimated in surface sediments of a shelf area in the NW Adriatic Sea (Italy), together with lithology and 210Pb contents at 18 stations during four cruises (1996–1998) carried out offshore of the Po River delta. Mass accumulation rates (MAR) were ∼0.1–0.8 g cm−2 yr−1 and surface concentrations of TOC and TN were within the range of 0.5–1.4 and 0.08–0.19% of dry weight, respectively. Their spatial variability showed a direct correlation with the inputs of suspended matter from the Po River. A simplified approach to calculate average TOC and TN yearly fluxes to surface sediments over the whole area was adopted by subdividing the study area into three zones, selected on the basis of the grain size distributions and of the influence of the Po River discharge, in order to take into account major differences of sedimentological regimes on the shelf. The values of TOC (×103 tC yr−1) and TN (×103 tN yr−1) fluxes for these areas were, respectively, 17.9 and 2.4 near the delta, 45.2 and 6.5 for the intermediate area, and 9.5 and 1.5 for the offshore area.

Distribution, fluxes and bacterial consumption of total organic carbon in a populated Mediterranean Gulf

Saronikos Gulf (Greece) practically constitutes the sea border of the metropolitan city of Athens and the alongshore outskirts, and it receives the treated wastes of ∼4 million people from a point source that discharges on the sea bottom at ∼65 m water depth. Total organic carbon (TOC) was measured in 477 seawater samples collected in the Saronikos Gulf, during 10 cruises, from August 2001 to May 2004 and analyzed with the High Temperature Catalytic Oxidation method (HTCO). TOC concentrations ranged from 49 to 198 μmol C L −1 in agreement with other Mediterranean coastal waters. The highest TOC concentrations were found in the upper waters (0–75 m), whereas in the deeper parts of the Gulf (between 100 and 400 m) TOC concentrations were kept constantly low (49–70 μmol C L −1). A general pattern towards higher TOC concentrations during summer was also observed. Calculations of non-refractory (labile+semi-labile) organic material based on a one-dimensional (1D) conceptual model showed that it corresponds to 33% of the bulk TOC during summer and to 27% during winter. Bacterial production (BP) was measured at selected stations of ∼70–80 m depth using the [ 3H] leucine method. Depth integrated BP values varied from 2.8 to 10.9 mmol m −2 d −1, whereas extraordinary high integrated BP values (126 and 140 mmol m −2 d −1) were observed at the station over the treated sewage outflow. From the turnover time, τ, of the non-refractory TOC by bacteria it was implied that organic matter in the effluents is extremely labile (2–58 days). Moreover, τ values at the other sites showed that during summer non-refractory organic material resisted bacterial degradation (1–8 months), whereas during early spring it was easily degradable (20–50 days). The balance of TOC fluxes for the Inner Gulf for June and September 2003 showed that the Inner Gulf acts as a net producer of TOC during summer. Our results suggest that the presence of the Athens treated sewage outfall does not contribute to the observed summer accumulation of TOC in the Inner Gulf and other causes such as increased bacteria predation and/or nutrient limitation must be responsible.

Biogeochemical records of paleoenvironmental changes in Nainital Lake, Kumaun Himalayas, India

Rapid urbanization and increased tourism around Nainital Lake in the Kumaun Himalayan region in north India has raised concerns about sediment and water pollution. Lead-210 dated sediment cores from the lake represent ~95 years of accumulation and yield a mean sedimentation rate of ~4.7 mm year−1. Total organic carbon (TOC), percent N and S and their atomic C/N and C/S ratios, stable isotopes (δ13C, δ15N, and δ34S), and specific biomarkers (n-alkanes and pigments) were measured in the core. Organic matter is primarily derived from in-lake algal production and TOC flux varies from 1.0 to 3.5 g m−2 year−1. Sediments are anoxic (Eh −328 to −187 mV) and have low (0.10–0.30 g m−2 year−1) N, but high (0.37–1.0 g m−2 year−1) S flux. Shifts in δ13C, δ15N, and δ34S suggest in-lake microbial processes dominated by denitrification and sulfate reduction. The sediments are dominated by short-chain hydrocarbons with low Carbon Preference Index values. The pigments indicate a gradual shift to cyanobacterial domination of the phytoplankton community in recent years. Despite an increase in external input of nutrients, the trophic state of the lake has remained largely unchanged, and the perceived human-induced impacts are limited.

Sinking rates and ballast composition of particles in the Atlantic Ocean: implications for the organic carbon fluxes to the deep ocean

Abstract. The flux of materials to the deep sea is dominated by larger, organic-rich particles with sinking rates varying between a few meters and several hundred meters per day. Mineral ballast may regulate the transfer of organic matter and other components by determining the sinking rates, e.g. via particle density. We calculated particle sinking rates from mass flux patterns and alkenone measurements applying the results of sediment trap experiments from the Atlantic Ocean. We have indication for higher particle sinking rates in carbonate-dominated production systems when considering both regional and seasonal data. During a summer coccolithophorid bloom in the Cape Blanc coastal upwelling off Mauritania, particle sinking rates reached almost 570 m per day, most probably due the fast sedimentation of densely packed zooplankton fecal pellets, which transport high amounts of organic carbon associated with coccoliths to the deep ocean despite rather low production. During the recurring winter-spring blooms off NW Africa and in opal-rich production systems of the Southern Ocean, sinking rates of larger particles, most probably diatom aggregates, showed a tendency to lower values. However, there is no straightforward relationship between carbonate content and particle sinking rates. This could be due to the unknown composition of carbonate and/or the influence of particle size and shape on sinking rates. It also remains noticeable that the highest sinking rates occurred in dust-rich ocean regions off NW Africa, but this issue deserves further detailed field and laboratory investigations. We obtained increasing sinking rates with depth. By using a seven-compartment biogeochemical model, it was shown that the deep ocean organic carbon flux at a mesotrophic sediment trap site off Cape Blanc can be captured fairly well using seasonal variable particle sinking rates. Our model provides a total organic carbon flux of 0.29 Tg per year down to 3000 m off the NW African upwelling region between 5 and 35° N. Simple parameterisations of remineralisation and sinking rates in such models, however, limit their capability in reproducing the flux variation in the water column.

DOWNCORE DISTRIBUTION OF LIVING CALCAREOUS FORAMINIFERA AND STABLE ISOTOPES IN THE WESTERN BARENTS SEA

The density and vertical distribution of living calcareous foraminifera have been studied in six box cores from the shelf depressions in the Western Barents Sea in relation to total organic carbon content and flux to the seafloor, primary production, sedimentation rates, bottom-water masses and stable isotopes. It appears that at least several infaunal species—like Melonis barleeanus , Islandiella norcrossi and perhaps Nonionellina labradorica , Cribroelphidium excavatum clavatum and Cassidulina reniforme —might penetrate down to 8–10 cm below the sediment surface searching for a favorable microhabitat. A deep penetration of some living specimens, notably epifaunal Cibicides lobatulus , into the sediment might result from bioturbation and survival inside polychaete tubes. The highest foraminiferal abundances (up to 130–240 sp/50 cm3) of the six cores were found in the most productive areas on the West Spitsbergen shelf and in the mouth of the Isfjorden (Svalbard) and likely resulted from fast sedimentation and mass accumulation rates of marine organic matter. These factors seemed to be responsible for deeper penetration and habitat depth of the above-mentioned species on the shelf as compared to the northern Barents Sea continental slope. However, the abundance of living calcareous foraminifera on the slope was much higher than in our study, probably due to a greater flux of particulate organic matter produced during the seasonal phytoplankton bloom along the ice-edge margin. In general, more depleted δ18O values (of unstained foraminifera) are found in the box cores obtained beneath pure Atlantic water compared to those beneath cooler bottom water. Estimated δ18O disequilibrium effects for Nonionellina labradorica (0.28‰), Cibicides lobatulus (−0.76‰) and Melonis barleeanus (−0.41‰) support previous findings for these species.

Laminated sediments from the central Peruvian continental slope: A 500 year record of upwelling system productivity, terrestrial runoff and redox conditions

Sedimentological studies including X-ray digital analyses, mineralogy, inorganic contents, and organic geochemistry on cores of laminated sediments accumulated in the oxygen minimum zone of the central Peruvian margin reveal variable oceanographic and climate conditions during the last 500 yr. Coherent upcore variations in sedimentological and geochemical markers in box cores taken off Pisco (B0405-6) and Callao (B0405-13) indicate that variability in the climate proxies examined has regional significance. Most noteworthy is a large shift in proxies at ∼1820 AD, as determined by 210Pb and 14C radiometric dating. This shift is characterized by an increase in total organic carbon (TOC) in parallel with an abrupt increase in the enrichment factor for molybdenum Mo indicating a regional intensification of redox conditions, at least at the sediment water interface. In addition there was lower terrestrial input of quartz, feldspar and clays to the margin. Based on these results, we interpret that during several centuries prior to 1820, which corresponds to the little ice age (LIA), the northern Humboldt current region was less productive and experienced higher terrestrial input related to more humid conditions on the continent. These conditions were probably caused by a southward displacement of the inter-tropical convergence zone and the subtropical high pressure cell during the LIA. Since 1870, increases in TOC and terrigenous mineral fluxes suggest an increase of wind-driven upwelling and higher productivity. These conditions continued to intensify during the late 20th century, as shown by instrumental records of wind forcing.

Increased organic C and N leaching in a northern boreal river basin in Finland

Increasing trends in dissolved organic carbon concentrations in small lakes and streams have been reported across Europe and North America. Several hypotheses have been proposed, of which decreasing mineral acidity has recently been considered to be the most likely cause. The near‐natural, northern Simojoki river basin (3160 km2) is located in the northern boreal zone in Finnish Lapland. Human impacts are minor with only limited forest management, low atmospheric deposition, and declining sulfate and H+ deposition over recent decades. Here we show that multiple effects (changes both in hydrological dynamics and in climate) explain increasing long‐term total organic carbon (TOC) and total organic nitrogen (TON) fluxes in the river. Strong fluctuation was observed in the TOC concentration time series during the studied 43 year time period from 1962 to 2005. Statistically significant upward trends were detected for TON concentration and flow of the river during 1976–2005. The average TOC and TON flux increased by 38% and 42%, respectively, during the 1990s compared with the 1980s. The annual runoff was 27% higher during the 1990s than during the 1980s, accounting for only part of the increase in the TOC and TON outputs. Hydrological fluctuations, including longer drought/wet periods, are important. For example the drought period of 1994–1997 with low concentrations was followed by high TOC and TON concentration peaks and strong leaching fluxes during the period 1998–2000. Average soil temperatures in winter (January–April) in the 1990s were 1.6–2.1°C higher than in the 1980s. This increase may have contributed to increasing trends in organic N concentrations particularly during winter low flow, because of increased organic matter decomposition rates during the dormant season. These changes in decomposition rates might further intensify in warmer climatic conditions.

Climate's control of intra‐annual and interannual variability of total organic carbon concentration and flux in two contrasting boreal landscape elements

Large spatial and temporal variations in stream total organic carbon (TOC) concentration and export occurred during an 11‐year observation period (1993–2003) in a boreal headwater catchment. TOC flux and concentration patterns from mire‐ and forest‐dominated subcatchments differed (mean annual flux 8.2 g m−2 a−1 versus 5.8 g m−2 a−1). Temporal variations in stream TOC concentrations in both landscape types were primarily driven by variations in streamflow, with the mire stream generally diluting by half with increased runoff during spring flood and TOC from the forested landscape increasing during runoff peaks irrespective of season. Average TOC concentration in the mire stream in the snow‐free season increased with increased seasonal precipitation from around 20 to 40 mg L−1 but then dropped to around 35 mg L−1 during very wet years. Average snow‐free season TOC concentration at the forested site remained stable when summer precipitation was below average but then increased from 10 to around 25 mg L−1 during exceptionally wet years. For both the forested subcatchment and the whole catchment, TOC concentrations increased during the warm summer months during wet years, but no such increase occurred during dry years. Interannual variations in TOC flux were primarily driven by variations during the snow‐free period. Wet years decreased the relative TOC export from the mire and favored the relative export of TOC from areas dominated by forest, an observation that also held true on a larger scale when similar landscape types were considered. Predicted climate change in rainfall and temperature patterns will affect the amount and character of TOC exported downstream from boreal landscapes with a mix of forest and mire.

Increased Terrestrial to Ocean Sediment and Carbon Fluxes in the Northern Chesapeake Bay Associated With Twentieth Century Land Alteration

We calculated Chesapeake Bay (CB) sediment and carbon fluxes before and after major anthropogenic land clearance using robust monitoring, modeling and sedimentary data. Four distinct fluxes in the estuarine system were considered including (1) the flux of eroded material from the watershed to streams, (2) the flux of suspended sediment at river fall lines, (3) the burial flux in tributary sediments, and (4) the burial flux in main CB sediments. The sedimentary maximum in Ambrosia (ragweed) pollen marked peak land clearance (~1900 a.d.). Rivers feeding CB had a total organic carbon (TOC)/total suspended solids of 0.24 ± 0.12, and we used this observation to calculate TOC fluxes from sediment fluxes. Sediment and carbon fluxes increased by 138–269% across all four regions after land clearance. Our results demonstrate that sediment delivery to CB is subject to significant lags and that excess post-land clearance sediment loads have not reached the ocean. Post-land clearance increases in erosional flux from watersheds, and burial in estuaries are important processes that must be considered to calculate accurate global sediment and carbon budgets.

Riverine inputs of total organic carbon and suspended particulate matter from the Pearl River Delta to the coastal ocean off South China

A total of 1008 samples were collected from the eight major riverine runoff outlets in the Pearl River Delta (PRD) during 2005−2006 to estimate the fluxes of total organic carbon (TOC) to the coastal ocean off South China. The average dissolved organic carbon (DOC) concentration was 1.67 mg/L with a range of 1.38−2.13 mg/L. Concentrations of particulate organic carbon (POC) ranged from 2.66−4.12% of total suspended particulate matter (SPM). The fluxes of TOC and SPM from the PRD via the eight outlets were 9.2 × 10 5 and 2.5 × 10 7 tons/yr, respectively. Temporal variations in POC and DOC were observed at all outlets due to the large variability in runoff levels because of the seasonality of rainfall, and the riverine discharge amount was an important factor controlling TOC flux. The net contribution of organic carbon from the PRD to the coastal ocean represented approximately 0.1−0.2% of total organic carbon transported by rivers worldwide.

Manipulation of Snow in Small Headwater Catchments at Storgama, Norway: Effects on Leaching of Total Organic Carbon and Total Organic Nitrogen

Projected increases in winter temperature due to future climate change may cause decreased snow accumulation at lower and intermediate altitudes in northern temperate regions. The resulting changes in soil temperature and water regime may affect the leaching of total organic carbon (TOC) and total organic nitrogen (TON). We manipulated the snow cover of small headwater catchments in a montane heathland area of southern Norway to quantify its effect on concentrations and fluxes of TOC and TON in runoff. Manipulations included snow removal, to promote soil frost, and insulation, to prevent soil frost. Snow removal resulted in increased TOC and TON concentrations, but decreased fluxes. Insulation caused a slight decrease in concentrations and fluxes of TOC. Our experiments show that a change in snow depth, and thus soil temperature, is not likely to have serious effects on TOC and TON leaching in the montane heathland area studied.

Effect of Climate Change on Flux of N and C: Air-Land-Freshwater-Marine Links: Synthesis

Projected climate change might increase the deposition of nitrogen by about 10% to seminatural ecosystems in southern Norway. At Storgama, increased precipitation in the growing season increased the fluxes of total organic carbon (TOC) and total organic nitrogen (TON) in proportion to the water flux. In winter, soil temperatures near 0 degrees C, common under a snowpack, induced higher runoff of inorganic nitrogen (N) and lower runoff of TOC. By contrast, soil temperatures below freezing, caused by little snow accumulation (expected in a warmer world), reduced runoff of inorganic N, TON, and TOC. Long-term monitoring data showed that reduced snowpack can cause either decreased or increased N leaching, depending on interactions with N deposition, soil temperature regime, and winter discharge. Seasonal variation in TOC was mainly climatically controlled, whereas deposition of sulfate and nitrate (NO3) explained the long-term TOC increase. Upscaling to the river basin scale showed that the annual flux of NO3 will remain unchanged in response to climate change projections.

Manipulation of Precipitation in Small Headwater Catchments at Storgama, Norway: Effects on Leaching of Organic Carbon and Nitrogen Species

Projected changes in climate in Southern Norway include increases in summer and autumn precipitation. This may affect leaching of dissolved organic matter (DOM) from soils. Effects of experimentally added extra precipitation (10 mm week) during the growing season of 3 years (2004-2006) to small headwater catchments at Storgama (59 degrees 0'N, 550-600 m a.s.l.) on leaching of total organic carbon (TOC) and total organic nitrogen (TON) were assessed. Extra precipitation did not have a significant effect on average TOC and TON concentrations in runoff. Thus, fluxes of TOC and TON increased nearly proportionally with water fluxes. This suggests that a store of adsorbed and potentially mobile TOC and TON in catchment soils buffers the concentration of DOM in runoff. The size and dynamics of the pool of TOC and TON depends on the balance between production and leaching rates. Infrequent short droughts had only small effects on TOC and TON fluxes in runoff from the reference catchments.

Projected Stream Water Fluxes of NO3and Total Organic Carbon from the Storgama Headwater Catchment, Norway, under Climate Change and Reduced Acid Deposition

Fluctuations in the 20-year record of nitrate (NO3) and total organic carbon (TOC) concentrations and fluxes in runoff at the small headwater catchment Storgama, southern Norway, were related to climate and acid deposition. The long-term decline in NO3 related to reduced NO3 deposition and increased winter discharge, whereas the long-term increase in TOC related to reduced sulfur deposition. Multiple regression models describing long-term trends and seasonal variability in these records were used to project future concentrations given scenarios of climate change and acid deposition. All scenarios indicated reduced NO3 fluxes and increased TOC fluxes; the largest projected changes for the period 2071-2100 were -86% and +24%, respectively. Uncertainties are that the predicted future temperatures are considerably higher than the historical record. Also, nonlinear responses of ecosystem processes (nitrogen [N] mineralization) to temperature, N-enrichment of soils, and step-changes in environmental conditions may affect future leaching of carbon and N.

Organic matter dynamics and budgets in the turbidity maximum zone of the Seine Estuary (France)

Organic matter was studied in the turbidity maximum zone (TMZ) of the Seine Estuary during 8 tidal cycles from April to October in 2001, 2002 and 2003, covering a salinity range from 0 to 27. The hydrological conditions were quite varied (extremely wet in 2001, unusually dry in 2003). A particularly striking feature is the high organic matter content in the suspended solids (SS) of the Seine estuary (4–5%). By determining micro-organism activity and organic carbon partitioning, either linked to particles or in dissolved forms, and estimating the TMZ water volumes, together with SS, we extrapolated these activities and stocks to the whole TMZ. Carbon metabolism in the TMZ and fluxes upstream of the TMZ were compared on the dates of field surveys, and the routes and fate of carbon in the TMZ were quantified in order to learn about the trophic status of this estuarine zone in terms of autotrophy vs. heterotrophy. The upstream total organic carbon (TOC) fluxes (48% of particulate organic carbon (POC), 52% of dissolved organic carbon (DOC) on average) varied fourfold between the surveys, reaching the highest value of 280 TC d −1 during the wet summer of 2001; and the lowest value of about 70 TC d −1 in August 2003. Whereas nearly all of the DOC flux entering the TMZ reaches the coastal marine zone, mostly (at least 85%) in a refractory form, the POC accumulates in the TMZ of the estuarine channel, particle exportation being negligible. In the TMZ, biodegradation of DOC was, on average, much less (only a 2% decrease in the BDOC/DOC ratio between the TMZ upstream and downstream fluxes) than biodegradation of POC (11%). A simplified model of the TMZ (LIFT- Lumped Idealisation of the ecological Functioning in estuarine Turbidity maximum) was constructed for investigating the dynamics of organic matter on a seasonal scale. The agreement between observation and calculation allowed us to run sensitivity tests using new constraints; reductions of the upstream fluxes of phytoplankton and organic carbon showed that the high content of organic matter, originating mostly from the domestic effluents of the Paris conurbation, can explain the high organic content of the Seine estuary TMZ.

Particle fluxes and δ15N variation of sinking particles in the central Bransfield Strait (Antarctica)

Sediment-trap deployment in the central Bransfield Strait during 1999/2000 shows distinct seasonal variation of particle fluxes, in which more than 99% of total annual flux occurred during a limited time. A more positive relationship between biogenic silica and total organic carbon fluxes in the intermediate-water sediment trap demonstrates that the surface-water production (mainly diatoms) played an important role in the supply of biogenic particles during the short period. The low δ15N values of particulate organic particles are attributed to high nitrate concentration in the Antarctic surface waters. The gradual increasing δ15N values in the bottom-water trap from the productive to unproductive season are likely associated with a switch in source from diatom aggregates to some remains of zooplankton, supplement to the horizontal contribution of lithogenic particles presumably from nearby shallow environment. Thus, the δ15N enrichment of sinking particles in the bottom-water trap during December to early February seems to be due to the laterally transported materials, assuming that the δ15N values decrease with depth in the Antarctic Polar Frontal region.