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Climate of the Past An interactive open-access journal of the European Geosciences Union
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https://doi.org/10.5194/cp-2020-127
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.
https://doi.org/10.5194/cp-2020-127
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.

  08 Oct 2020

08 Oct 2020

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This preprint is currently under review for the journal CP.

Snapshots of mean ocean temperature over the last 700,000 yr using noble gases in the EPICA Dome C ice core

Marcel Haeberli1, Daniel Baggenstos1, Jochen Schmitt1, Markus Grimmer1, Adrien Michel1,2, Thomas Kellerhals1, and Hubertus Fischer1 Marcel Haeberli et al.
  • 1Climate and Environmental Physics & Oeschger Centre for Climate Change Research, University of Bern, Switzerland, Sidlerstrasse 5, CH-3012 Bern
  • 2Laboratoire des Sciences Cryosphérique, EPFL, ENAC IIE CRYOS GR A0 455 (Bâtiment GR), Station 2, CH-1015 Lausanne

Abstract. Together with the latent heat stored in glacial ice sheets the ocean heat uptake carries the lion’s share of glacial/interglacial changes in the planetary heat content but little direct information on the global mean ocean temperature (MOT) is available to constrain the ocean temperature response to glacial/interglacial climate perturbations. Using ratios of noble gases and molecular nitrogen trapped in the Antarctic EPICA Dome C ice core we are able to reconstruct MOT for peak glacial and interglacial conditions during the last 700,000 years and explore the differences between these extrema. To this end, we have to correct the noble gas ratios for gas transport effects in the firn column and gas loss fractionation processes of the samples after ice core retrieval using the full elemental matrix of N2, Ar, Kr and Xe in the ice and their individual isotopic ratios. The reconstructed MOT in peak glacials is consistently about 3.3 ± 0.4 °C cooler compared to the Holocene. Lukewarm interglacials before the Mid Brunhes event 450 kyr ago are characterized by 1.6 ± 0.4 °C lower temperatures in the ocean than the Holocene, thus, glacial/interglacial amplitudes were only about 50 % of those after the Mid Brunhes event, in line with the reduced radiative forcing by lower greenhouse gas concentrations and their Earth system feedbacks. Moreover, we find significantly increased MOTs at the onset of Marine Isotope Stage 5.5 and 9.3, which are coeval with CO2 and CH4 overshoots at that time. We link these CO2 and CH4 overshoots to a resumption of the Atlantic Meridional Overturning Circulation, which is also the starting point of the release of heat previously accumulated in the ocean during times of reduced overturning.

Marcel Haeberli et al.

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Marcel Haeberli et al.

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Latest update: 24 Oct 2020
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Short summary
Using the temperature dependent solubility of noble gases in ocean water, we reconstruct global mean ocean temperature (MOT) over the last 700 kyr using noble gas ratios in air enclosed in polar ice cores. Our record shows that glacial MOT was about 3 °C cooler compared to the Holocene. Interglacials before 450 kyr ago were characterized by about 1.5 °C lower MOT than the Holocene. In addition, some interglacials show transient maxima in ocean temperature related to changes in ocean circulation.
Using the temperature dependent solubility of noble gases in ocean water, we reconstruct global...
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