Preprints
https://doi.org/10.5194/egusphere-2022-161
https://doi.org/10.5194/egusphere-2022-161
 
07 Apr 2022
07 Apr 2022

Benthic Alkalinity fluxes from coastal sediments of the Baltic and North Seas: Comparing approaches and identifying knowledge gaps

Bryce Van Dam1, Nele Lehmann1,4,7, Mary Zeller3, Andreas Neumann1, Daniel Pröfrock2, Marko Lipka3, Helmuth Thomas1,7, and Michael E. Böttcher3,5,6 Bryce Van Dam et al.
  • 1Helmholtz-Zentrum Hereon, Institute of Carbon Cycles, Geesthacht, Germany
  • 2Helmholtz-Zentrum Hereon, Institute of Coastal Environmental Chemistry, Geesthacht, Germany
  • 3Leibniz Institute for Baltic Sea Research (IOW), Warnemünde, Germany
  • 4Alfred Wegener Institute Helmholtz Centre for Polar and Marine Research, Potsdam, Germany
  • 5Marine Geochemistry, University of Greifswald, Germany
  • 6Interdisciplinary Faculty, University of Rostock, Germany
  • 7University of Oldenburg, Oldenburg, Germany

Abstract. Benthic alkalinity production is often suggested as a major driver of net carbon sequestration in continental shelf ecosystems. However, information and direct measurements of benthic alkalinity fluxes are limited and are especially challenging when biological and dynamic physical forcing causes surficial sediments to be vigorously irrigated. To address this shortcoming, we quantified net sediment-water exchange of alkalinity using a suite of complementary methods, including 1) 224Ra budgeting, 2) incubations with 224Ra and Bromide as tracers, and 3) numerical modelling of porewater profiles. We choose a set of sites in the shallow southern North Sea and western Baltic Sea, allowing us to incorporate frequently occurring sediment classes ranging from coarse sands to muds, and sediment-water interfaces ranging from biologically irrigated and advective to diffusive into the investigations. Sediment-water irrigation rates in the southern North Sea were approximately twice as high as previously estimated for the region, in part due to measured porewater 224Ra activities higher than previously assumed. Net alkalinity fluxes in the Baltic Sea were relatively low, ranging from an uptake of -35 µmol m-2 hr-1 to a release of 53 µmol m-2 hr-1, and in the North Sea from 1 to 33.6 µmol m-2 hr-1. Lower than expected apparent nitrate consumption (potential denitrification), across all sites, is one explanation for our small measured net alkalinity fluxes. Carbonate mineral precipitation and sulfide re-oxidation also appear to play important roles shaping net sediment-water fluxes in the North Sea and Baltic Sea sites, respectively.

Journal article(s) based on this preprint

19 Aug 2022
Benthic alkalinity fluxes from coastal sediments of the Baltic and North seas: comparing approaches and identifying knowledge gaps
Bryce Van Dam, Nele Lehmann, Mary A. Zeller, Andreas Neumann, Daniel Pröfrock, Marko Lipka, Helmuth Thomas, and Michael Ernst Böttcher
Biogeosciences, 19, 3775–3789, https://doi.org/10.5194/bg-19-3775-2022,https://doi.org/10.5194/bg-19-3775-2022, 2022
Short summary

Bryce Van Dam et al.

Interactive discussion

Status: closed

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on egusphere-2022-161', Xinping Hu, 17 Apr 2022
  • RC2: 'Comment on egusphere-2022-161', Anonymous Referee #2, 22 Apr 2022

Interactive discussion

Status: closed

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on egusphere-2022-161', Xinping Hu, 17 Apr 2022
  • RC2: 'Comment on egusphere-2022-161', Anonymous Referee #2, 22 Apr 2022

Peer review completion

AR: Author's response | RR: Referee report | ED: Editor decision
ED: Reconsider after major revisions (13 Jun 2022) by Jack Middelburg
AR by Bryce Van Dam on behalf of the Authors (13 Jun 2022)  Author's response    Author's tracked changes    Manuscript
ED: Referee Nomination & Report Request started (14 Jun 2022) by Jack Middelburg
RR by Xinping Hu (16 Jun 2022)
RR by Anonymous Referee #2 (20 Jun 2022)
ED: Publish subject to minor revisions (review by editor) (21 Jun 2022) by Jack Middelburg
AR by Bryce Van Dam on behalf of the Authors (27 Jun 2022)  Author's response    Author's tracked changes    Manuscript
ED: Publish subject to technical corrections (02 Jul 2022) by Jack Middelburg

Journal article(s) based on this preprint

19 Aug 2022
Benthic alkalinity fluxes from coastal sediments of the Baltic and North seas: comparing approaches and identifying knowledge gaps
Bryce Van Dam, Nele Lehmann, Mary A. Zeller, Andreas Neumann, Daniel Pröfrock, Marko Lipka, Helmuth Thomas, and Michael Ernst Böttcher
Biogeosciences, 19, 3775–3789, https://doi.org/10.5194/bg-19-3775-2022,https://doi.org/10.5194/bg-19-3775-2022, 2022
Short summary

Bryce Van Dam et al.

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The requested preprint has a corresponding peer-reviewed final revised paper. You are encouraged to refer to the final revised version.

Short summary
We quantified sediment-water exchange at shallow sites in the North and Baltic Seas. We found that porewater irrigation rates in the former were approximately twice as high as previously estimated, likely driven by relatively high bio-irrigative activity. In contrast, we found small net fluxes of alkalinity, ranging from -35 µmol m-2 hr-1 (uptake) to 53 µmol m-2 hr-1 (release). We attribute this to low net denitrification, carbonate mineral (re)precipitation and sulfide (re)oxidation.