AMOR-Bflux porewater and sediment data

Date 2019-11-19
Temporal extent 2015-09-04 -2015-09-14
Author(s) Rassmann Jens1, Eitel Eryn M.2, Lansard Bruno1, Cathalot CecileORCID3, Brandily Christophe3, Taillefert Martial2, Rabouille Christophe1
Affiliation(s) 1 : Laboratoire des Sciences du Climat et de l’Environnement, LSCE/IPSL,CEA-CNRS-UVSQ-Université Paris Saclay, 91198 Gif-sur-Yvette, France
2 : School of Earth and Atmospheric Sciences; Georgia Institute of Technology, GA 30332-0340 Atlanta, USA
3 : IFREMER, Laboratoire Environnement Profond, 29280 Plouzané, France
DOI 10.17882/70376
Publisher SEANOE
Keyword(s) Coastal sediment, Carbon cycle, alkalinity flux, iron reduction, sulfate reduction, coupled element cycles, oxygen consumption

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.

Licence CC-BY
Acknowledgements The authors thank the captain and crews of the RV Tethys II for their support at sea and Bruno Bombled for his technical help on-board and in the laboratory. We thank Gael Monvoisin for the analysis of sulfate samples at GEOPS (Paris-Sud University), Joel Craig and Olivia Studebaker for the analysis of nutrients and AVS at Georgia Tech, and Celine Liorzou for the ICP-AES measurements at Pôle Spéctrométrie Océan in Brest. The authors would also like to thank Jack Middelburg for handling the manuscript and two anonymous reviewers for their constructive comments that helped improve an earlier version of the manuscript. Finally, we are grateful to Sabine Kasten, Sandra Arndt, and Andrew Dale for interesting discussions about the interactions of AOM with carbonates and iron minerals and sediment dynamics. This research was funded by the project Mistrals/MERMEX-Rivers, the French State programme "Investissement d'avenir" ran by the National Research Agency (AMORAD project ANR-11-RSNR-0002) and the National Science Foundation (OCE-1438648).
File Size Format Processing Access
All data for our AMOR Bflux cruise 113 KB XLS, XLSX Processed data Open access
Sampling protocols and measurements for AMOR-BFlux cruise 344 KB PDF Open access
Sampling sites during the AMOR-BFlux 2015 332 KB PDF Open access
O2 and pH µ-profils at the interface water-Sediment 666 KB XLS, XLSX Processed data Open access
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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.

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. Publisher's official version : , Open Access version :