AMOR-Bflux porewater and sediment data

Estuarine regions are generally considered a major source of atmospheric CO2 as a result of the high organic carbon (OC) mineralization rates in their water column and sediments. Yet, the intensity of anaerobic respiration processes in the sediments tempered by the reoxidation of reduced metabolites near the sediment-water interface controls the flux of benthic alkalinity. This alkalinity may partially buffer metabolic CO2 generated by benthic OC respiration in sediments. Thus sediments with high anaerobic respiration rates could contribute less to local acidification than previously thought. In this study, a benthic chamber was deployed in the Rhône River prodelta and the adjacent continental shelf (Gulf of Lions, NW Mediterranean) in late summer to assess the fluxes of total alkalinity (TA) and dissolved inorganic carbon (DIC) from the sediment. Concurrently, in situ O2 and pH microprofiles, voltammetric profiles and pore water composition were measured in surface sediments to identify the main biogeochemical processes controlling the net production of alkalinity in these sediments. Benthic TA and DIC fluxes to the water column, ranging between 14 and 74 mmol m-2 d-1 and 18 and 78 mmol m-2 d-1, respectively, were up to 8 times higher than DOU rates (10.4 ± 0.9 mmol m-2 d-1) close to the river mouth, but their intensity decreased offshore, as a result of the decline in OC inputs. In the zone close to the river mouth, pore water redox species indicated that TA and DIC were mainly produced by microbial sulfate and iron reduction. Despite the complete removal of sulfate from pore waters, dissolved sulfide concentrations were low and significant concentration of FeS were found indicating the precipitation and burial of iron sulfide minerals with an estimated burial flux of 12.5 mmol m-2 d-1 near the river mouth. By preventing reduced iron and sulfide reoxidation, the precipitation and burial of iron sulfide increases the alkalinity release from the sediments during the spring and summer months. Under these conditions, the sediment provides a net source of alkalinity to the bottom waters which mitigates the effect of the benthic DIC flux on the carbonate chemistry of coastal waters and weakens the partial pressure of CO2 increase in the bottom waters that would occur if DIC was produced only.

Estuarine regions are generally considered a major source of atmospheric CO2 as a result of the high organic carbon (OC) mineralization rates in their water column and sediments. Yet, the intensity of anaerobic respiration processes in the sediments tempered by the reoxidation of reduced metabolites near the sediment-water interface controls the flux of benthic alkalinity. This alkalinity may partially buffer metabolic CO2 generated by benthic OC respiration in sediments. Thus sediments with high anaerobic respiration rates could contribute less to local acidification than previously thought. In this study, a benthic chamber was deployed in the Rhône River prodelta and the adjacent continental shelf (Gulf of Lions, NW Mediterranean) in late summer to assess the fluxes of total alkalinity (TA) and dissolved inorganic carbon (DIC) from the sediment. Concurrently, in situ O2 and pH microprofiles, voltammetric profiles and pore water composition were measured in surface sediments to identify the main biogeochemical processes controlling the net production of alkalinity in these sediments. Benthic TA and DIC fluxes to the water column, ranging between 14 and 74 mmol m-2 d-1 and 18 and 78 mmol m-2 d-1, respectively, were up to 8 times higher than DOU rates (10.4 ± 0.9 mmol m-2 d-1) close to the river mouth, but their intensity decreased offshore, as a result of the decline in OC inputs. In the zone close to the river mouth, pore water redox species indicated that TA and DIC were mainly produced by microbial sulfate and iron reduction. Despite the complete removal of sulfate from pore waters, dissolved sulfide concentrations were low and significant concentration of FeS were found indicating the precipitation and burial of iron sulfide minerals with an estimated burial flux of 12.5 mmol m-2 d-1 near the river mouth. By preventing reduced iron and sulfide reoxidation, the precipitation and burial of iron sulfide increases the alkalinity release from the sediments during the spring and summer months. Under these conditions, the sediment provides a net source of alkalinity to the bottom waters which mitigates the effect of the benthic DIC flux on the carbonate chemistry of coastal waters and weakens the partial pressure of CO2 increase in the bottom waters that would occur if DIC was produced only.

Disciplines

Chemical oceanography, Environment

Keywords

Coastal sediment, Carbon cycle, alkalinity flux, iron reduction, sulfate reduction, coupled element cycles, oxygen consumption

Location

43.33N, 43.2S, 5.02E, 4.57W

Data

FileSizeFormatProcessingAccess
All data for our AMOR Bflux cruise
113 KoXLS, XLSXProcessed data
Sampling protocols and measurements for AMOR-BFlux cruise
344 KoPDF
Sampling sites during the AMOR-BFlux 2015
332 KoPDF
O2 and pH µ-profils at the interface water-Sediment
666 KoXLS, XLSXProcessed data
How to cite
Rassmann Jens, Eitel Eryn M., Lansard Bruno, Cathalot Cecile, Brandily Christophe, Taillefert Martial, Rabouille Christophe (2019). AMOR-Bflux porewater and sediment data. SEANOE. https://doi.org/10.17882/70376
In addition to properly cite this dataset, it would be appreciated that the following work(s) be cited too, when using this dataset in a publication :
Rassmann Jens, Eitel Eryn M., Lansard Bruno, Cathalot Cecile, Brandily Christophe, Taillefert Martial, Rabouille Christophe (2020). Benthic alkalinity and dissolved inorganic carbon fluxes in the Rhône River prodelta generated by decoupled aerobic and anaerobic processes. Biogeosciences. 17 (1). 13-33. https://doi.org/10.5194/bg-17-13-2020, https://archimer.ifremer.fr/doc/00600/71163/

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