Preprints
https://doi.org/10.5194/bg-2021-244
https://doi.org/10.5194/bg-2021-244

  22 Sep 2021

22 Sep 2021

Review status: this preprint is currently under review for the journal BG.

Dissolution of a submarine carbonate platform by a submerged lake of acidic seawater

Matthew P. Humphreys1, Erik H. Meesters2, Henk de Haas3, Szabina Karancz1, Louise Delaigue1, Karel Bakker1, Gerard Duineveld1, Siham de Goeyse1, Andi Haas4, Furu Mienis1, Sharyn Ossebaar1, and Fleur C. van Duyl4 Matthew P. Humphreys et al.
  • 1Department of Ocean Systems (OCS), NIOZ Royal Netherlands Institute for Sea Research, PO Box 59, 1790 AB Den Burg (Texel), the Netherlands
  • 2Wageningen Marine Research, Wageningen University and Research, PO Box 57, 1780 AB Den Helder, the Netherlands
  • 3National Marine Facilities (NMF), NIOZ Royal Netherlands Institute for Sea Research, PO Box 59, 1790 AB Den Burg (Texel), the Netherlands
  • 4Department of Marine Microbiology and Biogeochemistry (MMB), NIOZ Royal Netherlands Institute for Sea Research, PO Box 59, 1790 AB Den Burg (Texel), the Netherlands

Abstract. Submarine sinkholes are found on carbonate platforms around the world. They are thought to form and grow when groundwater interactions generate conditions corrosive to carbonate minerals. Because their morphology can restrict mixing and water exchange, the effects of biogeochemical processes can accumulate such that the sinkhole water properties considerably diverge from the surrounding ocean. Studies of sinkhole waters can therefore reveal new insights into marine biogeochemical cycles, thus sinkholes can be considered as 'natural laboratories' where the response of marine ecosystems to environmental variations can be investigated. We conducted the first measurements in recently discovered sinkholes on Luymes Bank, part of Saba Bank in the Caribbean Netherlands. Our measurements revealed a plume of gas bubbles rising from the seafloor in one of the sinkholes, which contained a constrained body of dense, low-oxygen ([O2] = 60.2 ± 2.6 μmol · kg−1), acidic (pHT = 6.24 ± 0.01) seawater that we term the 'acid lake'. Here, we investigate the physical and biogeochemical processes that gave rise to and sustain the acid lake, the chemistry of which is dominated by the bubble plume. We determine the provenance and fate of the acid lake’s waters, which we deduce must be continuously flowing through. We show that the acid lake is actively dissolving the carbonate platform, so the bubble plume may provide a novel mechanism for submarine sinkhole formation and growth. It is likely that the bubble plume is ephemeral and that other currently non-acidic sinkholes on Luymes Bank have previously experienced ‘acid lake’ phases. Conditions within the acid lake are too extreme to represent coming environmental change on human timescales but in some respects reflect the bulk ocean billions of years ago. Other Luymes Bank sinkholes host conditions analogous to projections for the end of the 21st century and could provide a venue for studies on the impacts of anthropogenic CO2 uptake by the ocean.

Matthew P. Humphreys et al.

Status: open (until 10 Nov 2021)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on bg-2021-244', Anonymous Referee #1, 11 Oct 2021 reply

Matthew P. Humphreys et al.

Matthew P. Humphreys et al.

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Short summary
A series of submarine sinkholes were recently discovered on Luymes Bank, part of Saba Bank, a carbonate platform in the Caribbean Netherlands. Here, we investigate the waters inside these sinkholes for the first time. One of the sinkholes contained a body of dense, low-oxygen and low-pH water, which we call the 'acid lake'. We use measurements of seawater chemistry to work out what processes were responsible for forming the acid lake, and discuss the consequences for the carbonate platform.
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