Preprints
https://doi.org/10.5194/bg-2021-124
https://doi.org/10.5194/bg-2021-124

  17 May 2021

17 May 2021

Review status: a revised version of this preprint is currently under review for the journal BG.

Ideas and perspectives: Sea-Level Change, Anaerobic Methane Oxidation, and the Glacial-Interglacial Phosphorus Cycle

Bjorn Sundby1,2, Pierre Anschutz3, Pascal Lecroart3, and Alfonso Mucci2 Bjorn Sundby et al.
  • 1ISMER, Université du Québec à Rimouski, Rimouski, QC, Canada H4C 3J9
  • 2GEOTOP and Earth& Planetary Sciences, McGill University, Montreal, QC, Canada H3A 0E8
  • 3Univ. Bordeaux, CNRS, EPOC, EPHE, UMR 5805 F-33615 Pessac, France

Abstract. The oceanic phosphorus cycle describes how phosphorus moves through the ocean, accumulates with the sediments on the seafloor, and participates in biogeochemical reactions. We propose a new two-reservoir scenario of the glacial-interglacial phosphorus cycle. It relies on diagenesis in methane hydrate-bearing sediments to mobilize sedimentary phosphorus and transfer it to the oceanic reservoir during times when falling sea level lowers the hydrostatic pressure on the seafloor and destabilizes methane hydrates. The stock of solid phase phosphorus mobilizable by this process is of the same order of magnitude as the dissolved phosphate inventory of the current oceanic reservoir. The potential, additional flux of phosphate during the glacial period is of the same order of magnitude as pre-agricultural, riverine dissolved phosphate fluxes to the ocean. Throughout the cycle, primary production assimilates phosphorus and inorganic carbon into biomass which, upon settling and burial, returns phosphorus to the sedimentary reservoir. Primary production also lowers the partial pressure of CO2 in the surface ocean, potentially drawing down CO2 from the atmosphere. Concurrent with this slow ‘biological pump’, but operating in the opposite direction, a ’physical pump’ brings metabolic CO2-enriched waters from deep-ocean basins to the upper ocean. The two pumps compete, but the direction of the CO2 flux at the air-sea interface depends on the nutrient content of the deep waters. Because of the transfer of reactive phosphorus to the sedimentary reservoir throughout a glaciation cycle, low phosphorus/ high CO2 deep waters reign at the beginning of a deglaciation, resulting in rapid transfer of CO2 to the atmosphere. The new scenario provides another element to the suite of processes that may have contributed to the rapid glacial-interglacial climate transitions documented in paleo-records.

Bjorn Sundby et al.

Status: final response (author comments only)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on bg-2021-124', Gabriel Filippelli, 22 Jun 2021
    • AC1: 'Reply on RC1', Pierre ANSCHUTZ, 20 Jul 2021
  • RC2: 'Comment on bg-2021-124', David Archer, 25 Jun 2021
    • AC2: 'Reply on RC2', Pierre ANSCHUTZ, 20 Jul 2021
  • RC3: 'Comment on bg-2021-124', Sabine Kasten, 21 Jul 2021
    • AC3: 'Reply on RC3', Pierre ANSCHUTZ, 11 Aug 2021

Bjorn Sundby et al.

Bjorn Sundby et al.

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Short summary
A glacial-interglacial methane-fuelled redistribution of reactive phosphorus between the oceanic and sedimentary phosphorus reservoirs can occur in the ocean when falling sea level lowers the pressure on the seafloor, destabilizes methane hydrates, and triggers the dissolution of P-bearing iron oxides. The mass of phosphate potentially mobilizable from the sediment is similar to the size of the current oceanic reservoir. Hence, this process may play a major role in the marine phosphorus cycle.
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