Preprints
https://doi.org/10.5194/cpd-11-3597-2015
https://doi.org/10.5194/cpd-11-3597-2015

  10 Aug 2015

10 Aug 2015

Review status: this preprint was under review for the journal CP but the revision was not accepted.

Impact of the oceanic geothermal heat flux on a glacial ocean state

M. Ballarotta1,2, F. Roquet2,3, S. Falahat2,4, Q. Zhang1,2, and G. Madec5,6 M. Ballarotta et al.
  • 1Department of Physical Geography, Stockholm University, Stockholm, Sweden
  • 2Bolin Centre for Climate Research, Stockholm University, Stockholm, Sweden
  • 3Department of Meteorology, Stockholm University, Stockholm, Sweden
  • 4Department of Environmental Science and Analytical Chemistry, Stockholm University, Stockholm, Sweden
  • 5Sorbonne Universités (UPMC, Université Paris 06)-CNRS-IRD-MNHN, LOCEAN Laboratory, Paris, France
  • 6National Oceanography Centre, Southampton, Marine Systems Modelling Group, Southampton, UK

Abstract. The oceanic geothermal heating (OGH) has a significant impact on the present-day ocean state, but its role during glacial periods, when the ocean circulation and stratification were different from those of today, remains poorly known. In the present study, we analyzed the response of the glacial ocean to OGH, by comparing ocean simulations of the Last Glacial Maximum (LGM, ∼ 21 ka ago) including or not geothermal heating. We found that applying the OGH warmed the Antarctic Bottom Waters (AABW) by ∼ 0.4 °C and increased the abyssal circulation by 15 to 30 % north of 30° S in the deep Pacific and Atlantic basins. The geothermally heated deep waters were then advected toward the Southern Ocean where they upwelled to the surface due to the Ekman transport. The extra heat transport towards Antarctica acted to reduce the amount of sea ice contributing to the freshening of the whole AABW overturning cell. The global amount of salt being conserved, this bottom freshening induced a salinification of the North Atlantic and North Pacific surface and intermediate waters, contributing to the deepening of the North Atlantic Deep Water. This indirect mechanism is responsible for the largest observed warming, found in the North Atlantic deep western boundary current between 2000 and 3000 m (up to 2 °C). The characteristic time scale of the ocean response to the OGH corresponds to an advective time scale (associated with the overturning of the AABW cell) rather than a diffusive time scale. The OGH might facilitate the transition from a glacial to an inter-glacial state but its effect on the deep stratification seems insufficient to drive alone an abrupt climate change.

M. Ballarotta et al.

 
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Status: closed
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AC: Author comment | RC: Referee comment | SC: Short comment | EC: Editor comment
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M. Ballarotta et al.

M. Ballarotta et al.

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Short summary
We investigate the impact of the ocean geothermal heating (OGH) on a glacial ocean state using numerical simulations. We found that the OGH is a significant forcing of the abyssal ocean and thermohaline circulation. Applying the OGH warms the Antarctic Bottom Water by ~0.4°C and strengthens the deep circulation by 15% to 30%. The geothermally heated waters are advected from the Indo-Pacific to the North Atlantic basin, indirectly favouring the deep convection in the North Atlantic.