03 Jun 2022
03 Jun 2022
Status: this preprint is open for discussion.

Influences of iron and manganese cycling on alkalinity in the redox stratified water column of Chesapeake Bay

Aubin Thibault de Chanvalon1,2, George W . Luther2, Emily R. Estes2,a, Jennifer Necker2, Bradley M. Tebo3, Jianzhong Su4,5, and Wei-Jun Cai4 Aubin Thibault de Chanvalon et al.
  • 1Université de Pau et des Pays de l'Adour, E2S UPPA, CNRS, IPREM, Pau, France
  • 2School of Marine Science and Policy, University of Delaware, Lewes, Delaware, 19958 USA
  • 3Division of Environmental and Biomolecular Systems, 3181 SW Sam Jackson Park Road, Portland, OR 97239, USA
  • 4School of Marine Science and Policy, University of Delaware, Newark, Delaware, USA
  • 5State Key Laboratory of Marine Resources Utilization in South China Sea, Hainan University, Haikou, China
  • acurrent address: Department of Chemistry, University of Washington, Seattle, WA 98195-1700

Abstract. The coastal alkalinity cycle controls the global burial of carbonate which modulates the ability of the ocean to trap anthropogenic CO2. Twelve high vertical resolution profiles from the temperate Chesapeake Bay estuary during two summers allow precise description of carbonate dynamics over the salinity and redox gradient along with the measurement of the speciation of most redox sensitive elements. In the presence of oxygen, carbonate dissolution, primary production and aerobic respiration are able to explain the evolution of total alkalinity (TA) versus dissolved inorganic carbon (DIC), once corrected for fresh and oceanic water mixing. A significant flooding event in 2018 prevented the trapping of atmospheric CO2 in the estuary and favoured carbonate dissolution to balance DIC consumption from photosynthesis. In oxygen depleted waters, a particularly high ratio of alkalinity versus DIC occurred (ΔTAex/ΔDICex = 2.4), that has not been previously reported in the literature, and that seemed invariant over the two years. The stoichiometric analysis agrees with Mn measurements to explain this carbonate signature by the critical role of MnO2 reduction followed by Mn carbonate precipitation. Our results underline that Fe and Mn are critical elements of the alkalinity cycle, especially due to their ability to limit the H2S oxidation into SO42- and by favouring sulphur burial.

Aubin Thibault de Chanvalon et al.

Status: open (until 15 Jul 2022)

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  • RC1: 'Comment on egusphere-2022-428', Anonymous Referee #1, 28 Jun 2022 reply

Aubin Thibault de Chanvalon et al.

Aubin Thibault de Chanvalon et al.


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Short summary
The intensity of the oceanic trap of CO2 released by anthropogenic activities depends on the alkalinity brought by the continental weathering. Between ocean and continent, coastal water and estuaries can limit or favour the alkalinity transfer. This study investigate new interactions between dissolved metals and alkalinity in the oxygen depleted zone of estuaries.