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Climate of the Past An interactive open-access journal of the European Geosciences Union
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© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.

  10 Aug 2020

10 Aug 2020

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This preprint is currently under review for the journal CP.

Can we reconstruct the formation of large open ocean polynyas in the Southern Ocean using ice core records?

Hugues Goosse1, Quentin Dalaiden1, Marie G. P. Cavitte1, and Liping Zhang2,3 Hugues Goosse et al.
  • 1Earth and Life Institute, Université catholique de Louvain, Louvain-la-Neuve, Belgium
  • 2NOAA/Geophysical Fluid Dynamics Laboratory, Princeton, New Jersey, USA
  • 3University Corporation for Atmospheric Research, Boulder, Colorado

Abstract. Large open-ocean polynyas, defined as ice-free areas within the sea ice pack, have been observed only rarely over the past decades in the Southern Ocean. In addition to smaller recent events, an impressive sequence occurred in the Weddell Sea in 1974, 1975 and 1976 with openings of more than 300,000 km2 that lasted the full winter. Those big events have a huge impact on the sea ice cover, deep-water formation and more generally on the Southern Ocean and the Antarctic climate. However, we have no estimate of the frequency of the occurrence of such large open-ocean polynyas before the 1970s. Our goal here is to test if polynya activity could be reconstructed using continental records, and specifically, observations derived from ice cores. The fingerprint of big open-ocean polynyas is first described in reconstructions based on data from weather stations, in ice cores for the 1970s and in climate models. It shows a clear signal, characterized by a surface air warming and increased precipitation in coastal regions adjacent to the eastern part of the Weddell Sea where several high-resolution ice cores have been collected. The signal of isotopic composition of precipitation is more ambiguous and we thus base our reconstructions on surface mass balance records only. A first reconstruction is obtained by performing a simple average of standardized records. Given the similarity between the observed signal and the one simulated in models, we also use data assimilation to reconstruct past polynya activity. The impact of open ocean polynyas on the continent is not large enough compared to the changes due, for instance, to atmospheric variability to detect without ambiguity the polynya signal and additional observations would be required to discriminate clearly the years with and without open ocean polynya. It is thus reasonable to consider that, in these preliminary reconstructions, some high accumulation events may be wrongly interpreted as the consequence of polynya formation while some years with polynya formation may be missed. Nevertheless, our reconstructions suggest that big open ocean polynyas, such as the ones that were observed in the 1970s, are rare events, occurring at most a few times per century. Century-scale changes in polynya activity are also likely but our reconstructions are unable to assess precisely this aspect at this stage.

Hugues Goosse et al.

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Hugues Goosse et al.

Hugues Goosse et al.


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Publications Copernicus
Short summary
Polynyas are ice-free oceanic areas surrounded by sea ice. Small polynyas are regularly observed in the Southern Ocean, but large open ocean polynyas such as the one observed in the Weddell Sea in the 1970s, were rare over the past decades. Using records from available ice cores in Antarctica, we confirm that those events were also rare over the past centuries but the information provided by existing data is not sufficent to precisely characterize the timing of past polynya opening.
Polynyas are ice-free oceanic areas surrounded by sea ice. Small polynyas are regularly observed...