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The Amundsen Sea Embayment in West Antarctica is experiencing rapid ice mass loss, resulting in biogeochemical changes via altered nutrient and organic matter supply. However, organic carbon released from melting ice has not yet been accurately quantified. In this paper, we have integrated new dissolved organic carbon (DOC) data obtained close to the melting Dotson Ice Shelf (DIS) with published radiocarbon (Δ14C) data on sinking and suspended particulate organic carbon (POC), sedimentary OC, DOC and dissolved inorganic carbon to quantify the effect of ice melt to the carbon cycle. Elevated DOC concentrations in deep water near the DIS indicate the transport of carbon sources from the ice shelf to the water column at a rate of 4.6 ± 2.0 × 1010 g C yr−1. Furthermore, Δ14C‐DOC measurements suggest there is a possible dark chemoautotrophic production under the influence of meltwater input. The vertical profile of Δ14C in the sedimentary OC from the Sea Ice Zone and the edge of the DIS demonstrates the presence of aged organic carbon sources during warm episodes at ∼11.5 and 15.9 ka BP. Our study indicates that deep water is not only affected by OC discharge from meltwater but also by biological processes due to altered nutrient inputs. Limited data hampers a precise assessment of the influence of meltwater on the carbon cycle. Further sampling in front of the DIS will be beneficial to enhance our understanding of the role of Antarctic Ice Sheet melting in the downstream ecosystem. Plain Language Summary: The Amundsen Sea, in West Antarctica, is experiencing rapid ice melting because of a warming climate. As found in previous studies conducted in these seasonally ice‐free areas, nutrients released from melting ice sheets and upwelled by buoyant melt water stimulate surface primary production, which in return increases the surface uptake of CO2 in these regions. However, the direct release of organic carbon from melting ice has not been accurately quantified. To address this issue, we conducted radiocarbon analysis of dissolved organic carbon in water samples collected near the melting ice shelf in the Amundsen Sea. Available radiocarbon results from sedimentary organic carbon and sinking POC demonstrate that a warming climate may trigger the release of aged organic carbon from subglacial sediments. Our finding indicates the deep water in the regions is going through a biological process under the influence of meltwater input. Further sampling will be needed for the investigation of the role of meltwater in downstream ecosystems. Key Points: Elevated dissolved organic carbon (DOC) concentrations in front of the Dotson Ice Shelf (DIS) indicate an influence from the melting ice shelf and subglacial dischargeΔ14C‐DOC results demonstrate that meltwater has the potential to increase carbon uptake in the water column via chemoautotrophic productionExtra aged organic carbon sources for sedimentary OC in the Amundsen Sea Embayment during the warm episodes at ∼11.5 and 15.9 ka BP [ABSTRACT FROM AUTHOR]

Blue carbon (C) ecosystems (mangroves, salt marshes, and seagrass beds) sequester high amounts of C, which can be respired back into the atmosphere, buried for long periods, or exported to adjacent ecosystems by tides. The lateral exchange of C between a salt marsh and adjacent water is a key factor that determines whether a salt marsh is a C source (i.e., outwelling) or sink in an estuary. We measured salinity, particulate organic carbon (POC), and dissolved organic carbon (DOC) seasonally over eight tidal cycles in a tidal creek at the Chongming Dongtan wetland from July 2017 to April 2018 to determine whether the marsh was a source or sink for estuarine C. POC and DOC fluxes were significantly correlated in the four seasons driven by water fluxes, but the concentration of DOC and POC were positively correlated only in autumn and winter. DOC and POC concentrations were the highest in autumn (3.54 mg/L and 4.19 mg/L, respectively) and the lowest in winter and spring (1.87 mg/L and 1.51 mg/L, respectively). The tidal creek system in different seasons showed organic carbon (OC) export, and the organic carbon fluxes during tidal cycles ranged from –12.65 to 4.04 g C/m2. The intensity showed significant seasonal differences, with the highest in summer, the second in autumn, and the lowest in spring. In different seasons, organic carbon fluxes during spring tides were significantly higher than that during neap tides. Due to the tidal asymmetry of the Yangtze River estuary and the relatively young stage, the salt marshes in the study area acted as a strong lateral carbon source.

Aims: Although paddy soils are generally characterized by relatively high dissolved organic carbon (DOC) concentrations and fluxes, little is yet known on how water management influences the cycling of this important organic C pool. This work aims at providing insights into the link between DOC cycling during rice cropping and organic C input to the subsoils and export with surface waters, as well as methane (CH) emissions in a temperate paddy soil as a function of different water management practices. Methods: DOC quantity, quality and fluxes, as well as CH emissions were evaluated at field-scale over two cropping seasons for three water management systems including continuous flooding, dry seeding with delayed flooding, and intermittent irrigation. Results: DOC cycling in the different water management systems were strongly linked to the reducing soil conditions resulting from field flooding. In contrast to dry seeding or intermittent irrigation, adoption of continuous flooding not only favoured the accumulation of DOC in the topsoil (>10-20 mg C l), but also enhanced C inputs to the subsoil (33-51 g C m), and exports with surface waters (18-44 g C m). Moreover, changes in DOC quality in paddy soils were linked to a positive feedback on the abiotic release of soil-derived DOC, and substrate availability for CH production. Conclusions: Water management practices in rice paddies strongly affect the temporal trends in DOC quantity and quality over the cropping season, with important implications on organic C fluxes. [ABSTRACT FROM AUTHOR]

Valle de Bravo (VB) is the main water reservoir of the Cutzamala hydraulic system, which provides 40 % of the drinking water consumed in the Mexico City Metropolitan Area and exhibits symptoms of eutrophication. Nutrient (C, N and P) concentrations were determined in two sediment cores to reconstruct the water column trophic evolution of the reservoir and C fluxes since its creation in 1947. Radiometric methods (Pb and Cs) were used to obtain sediment chronologies, using the presence of pre-reservoir soil layers in one of the cores as an independent chronological marker. Mass accumulation rates ranged from 0.12 to 0.56 g cm year and total organic carbon (TOC) fluxes from 122 to 380 g m year. Total N ranged 4.9-48 g m year, and total P 0.6-4.2 g m year. The sedimentary record shows that all three (C, N and P) fluxes increased significantly after 1991, in good agreement with the assessed trophic evolution of VB and with historic and recent real-time measurements. In the recent years (1992-2006), the TOC flux to the bottom of VB (average 250 g m year, peaks 323 g m year) is similar to that found in highly eutrophic reservoirs and impoundments. Over 1/3 of the total C burial since dam construction, circa 70,000 t, has occurred in this recent period. These results highlight the usefulness of the reconstruction of carbon and nutrient fluxes from the sedimentary record to assess carbon burial and its temporal evolution in freshwater ecosystems. [ABSTRACT FROM AUTHOR]

Cold-water corals (CWCs) are key ecosystem engineers in deep-sea benthic communities around the world. Their distribution patterns are related to several abiotic and biotic factors, of which seawater temperature is arguably one of the most important due to its role in coral physiological processes. The CWC Dendrophyllia cornigera has the particular ability to thrive in several locations in which temperatures range from 11 to 17 °C, but to be apparently absent from most CWC reefs at temperatures constantly below 11 °C. This study thus aimed to assess the thermal tolerance of this CWC species, collected in the Mediterranean Sea at 12 °C, and grown at the three relevant temperatures of 8, 12, and 16 °C. This species displayed thermal tolerance to the large range of seawater temperatures investigated, but growth, calcification, respiration, and total organic carbon (TOC) fluxes severely decreased at 8 °C compared to the in situ temperature of 12 °C. Conversely, no significant differences in calcification, respiration, and TOC fluxes were observed between corals maintained at 12 and 16 °C, suggesting that the fitness of this CWC is higher in temperate rather than cold environments. The capacity to maintain physiological functions between 12 and 16 °C allows D. cornigera to be the most abundant CWC species in deep-sea ecosystems where temperatures are too warm for other CWC species (e.g., Canary Islands). This study also shows that not all CWC species occurring in the Mediterranean Sea (at deep-water temperatures of 12-14 °C) are currently living at their upper thermal tolerance limit. [ABSTRACT FROM AUTHOR]

ABSTRACT A key issue in the study of the carbon cycle is constraining the stocks and fluxes in and between C-reservoirs. Among these, the role and importance of fossil organic carbon (FOC) release by weathering of outcropping sedimentary rocks on continental surfaces is still debated and remains poorly constrained. Our work focuses on FOC fluxes due to chemical and mechanical weathering of marls in two experimental watersheds with typical badlands geomorphology (Draix watersheds, Laval and Moulin, Alpes de Haute Provence, France). Organic matter from bedrock, soil litter and riverine particles are characterized by Rock-Eval 6 pyrolysis. FOC fluxes due to mechanical weathering are then estimated by monitoring the annual particulate solid exports at the outlets of the watersheds (1985-2005 period). FOC fluxes from chemical weathering were calculated using Ca2+ concentrations in dissolved loads (year 2002) to assess the amount of FOC released by the dissolution of the carbonate matrix. Results show that FOC delivery is mainly driven by mechanical weathering, with a yield ranging from 30 to 59 t km-2 yr-1 in the Moulin (0.08 km2) and Laval (0.86 km2) catchments, respectively, (1985-2005 average). The release of FOC attributed to chemical weathering was 2.2 to 4.2 t km-2 for the year 2002. These high FOC fluxes from badlands are similar to those observed in tectonically active mountain catchments. At a regional scale, badland outcropping within the Durance watershed does not exceed 0.25% in area of the Rhône catchment, but could annually deliver 12 000 t yr-1 of FOC. This flux could correspond to 27% of the total particulate organic carbon (POC) load exported by the Rhône River to the Mediterranean Sea. At a global scale, our findings suggest that erosion of badlands may contribute significantly to the transfer of FOC from continental surfaces to depositional environments. Copyright © 2012 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

A mesocosm experiment was conducted for 32 days in an eutrophic pond to study the effects of the bioturbation of the freshwater snail, Bellamya aeruginosa, on the benthic environment and to further understand cycling of organic carbon in water containing algal blooms. Chlorophyll-a (chl-a), phaeopigment, and organic matter contents of sediment, sediment oxygen consumption (SOC), and dissolved organic carbon (DOC) fluxes were determined on day 1, 16, and 32, respectively. The SOC decreased on day 16 and increased on day 32 significantly with the increase in snail density. DOC fluxes showed a net sediment uptake in all enclosures throughout the experiment. DOC fluxes in the high and mid density treatments were lower than those of the control. The concentrations of chl-a and phaeopigment in the sediment increased significantly with snail density, indicating that the presence of snails reduced the biomass of phytoplankton. The results suggest that freshwater snails, B. aeruginosa, could influence the algal biomass (chl-a) of small water bodies by their bioturbation effects on sediment characteristics and the fluxes of organic carbon. A mesocosm experiment was conducted for 32 days in an eutrophic pond to study the effects of the bioturbation of the freshwater snail, Bellamya aeruginosa, on the benthic environment and to further understand cycling of organic carbon in water containing algal blooms. Chlorophyll-a (chl-a), phaeopigment, and organic matter contents of sediment, sediment oxygen consumption (SOC), and dissolved organic carbon (DOC) fluxes were determined on day 1, 16, and 32, respectively. The SOC decreased on day 16 and increased on day 32 significantly with the increase in snail density. DOC fluxes showed a net sediment uptake in all enclosures throughout the experiment. DOC fluxes in the high and mid density treatments were lower than those of the control. The concentrations of chl-a and phaeopigment in the sediment increased significantly with snail density, indicating that the presence of snails reduced the biomass of phytoplankton. The results suggest that freshwater snails, B. aeruginosa, could influence the algal biomass (chl-a) of small water bodies by their bioturbation effects on sediment characteristics and the fluxes of organic carbon. [ABSTRACT FROM AUTHOR]

Abstract: The aim of this study is to explore the contribution of living phytoplankton carbon to vertical fluxes in a coastal upwelling system as a key piece to understand the coupling between primary production in the photic layer and the transfer mechanisms of the organic material from the photic zone. Between April 2004 and January 2005, five campaigns were carried out in the Ría de Vigo (NW Iberian Peninsula) covering the most representative oceanographic conditions for this region. Measurements of particulate organic carbon (POC), chlorophyll-a (chl a), phaeopigments (phaeo), and identification of phytoplankton species were performed on the water column samples and on the organic material collected in sediment traps. The POC fluxes measured by the sediment traps presented no seasonal variation along the studied period ranging around a mean annual value of 1085±365mgm−2 d−1, in the upper range of the previously reported values for other coastal systems. The fact that higher POC fluxes were registered during autumn and winter, when primary production rates were at their minimum levels points to a dominant contribution of organic carbon from resuspended sediments on the trap collected material. On the contrary, fluxes of living phytoplankton carbon (Cphyto) and chl a clearly presented a seasonal trend with maximum values during summer upwelling (546mgm−2 d−1 and 22mgchl a m−2 d−1, respectively) and minimum values during winter (22mgm−2 d−1 and 0.1mgchl a m−2 d−1, respectively). The contribution of Cphyto to the vertical flux of POC ranged between 2% and 49% in response to the pelagic phytoplankton community structure. Higher values of Cphyto fluxes were registered under upwelling conditions which favour the dominance of large chain-forming diatoms (Asterionellopsis glacialis and Detonula pumila) that were rapidly transferred to the sediments. By contrast, Cphyto fluxes decreased during the summer stratification associated with a pelagic phytoplankton community dominated by single-cell diatoms and flagellates. Minimal Cphyto fluxes were observed during the winter mixing conditions, when the presence of the benthic specie Paralia sulcata in the water column also points toward strong sediment resuspension. [Copyright &y& Elsevier]

A seasonal flux study was carried out in the eastern Gotland Basin, a stratified waterbody, to describe the vertical transport of trace metals (Al, Fe, Mn, Cd, Pb, Cu, Zn, Ni, As) in particulate phases through the pycnocline. A sediment trap was deployed between December 1999 and February 2001 in 120-m depth below the pycnocline. The trap was changed quarterly, sampling periods ranged between 6 and 8 days. To characterise the water column, vertical CTD profiles (suspended particulate matter (SPM), salinity, oxygen, hydrogen sulfide) and the determination of trace metals in the dissolved and particulate phases were performed parallel to the trap experiment.The leakage of the sampling bottles was between 9% and 15%. With the exception of nickel, the blank for the investigated metals in the sodium azide poisoned stock solution was in the range between 1% and 16% in relation to the mean trace metal concentrations in the supernatant. The mean resolution (annual average) of trace metals in the supernatant in relation to the total metal concentration in the sample bottle was 53% for Cd, 49% for Mn, 26% for Cu, 14% for Zn, 15% for Ni and 2% for Fe.The vertical distribution of Mn and Fe in the water column was mainly influenced by the seasonal variability of the distance between pycnocline and redoxcline. Concentrations of suspended particulate matter (SPM) in the water column ranged between 0.05 and 0.75 mg/dm3 with season and depth.During winter, the composition of the trap material is dominated by lithogenic fractions of aluminium and iron, while during summer, particulate organic material (POM) is the main compound with 63% of the total mass flux. Elevated trace metal contents (Zn, As, Fe, Mn, Pb) related to the particle mass were observed in suspended particulate matter (SPM) of the water column in February 2001, which was attributed to the lateral transport of material from the river Memel.A continuous increase of the enrichment factors (EF) in the trap material was noticed from December 1999 to November 2000 with highest values for the time period July 2000–November 2000 for Cd (280), Zn (87) and Ni (13) probably due to the low lithogenic Al content and the enhanced elimination of the metals by degradation products of cyanoblooms. Lead shows decreasing EF during the same time period which we think is a result of the “dilution effect” with particles of mainly biogenic origin.Total mass fluxes ranged between 1 and 200 mg/m2 day; significant seasonal variations were not observed. This result is discussed in connection with under/overtrapping and in relation to the change of the redox conditions in the depth horizon of the deployed trap. Significant correlation exists between the fluxes of Pb/Al, As/Al, Fe/Al, Cd/Corg, Cu/Corg, Zn/Corg and Ni/Corg. [Copyright &y& Elsevier]