24 Jan 2023
24 Jan 2023
Status: this preprint is currently under review for the journal CP.

Effects of LGM sea surface temperature and sea ice extent on the isotope-temperature slope at polar ice core sites

Alexandre Cauquoin1, Ayako Abe-Ouchi2, Takashi Obase2, Wing-Le Chan3, André Paul4, and Martin Werner5 Alexandre Cauquoin et al.
  • 1Institute of Industrial Science (IIS), The University of Tokyo, Kashiwa, Japan
  • 2Atmosphere and Ocean Research Institute (AORI), The University of Tokyo, Kashiwa, Japan
  • 3Research Center for Environmental Modeling and Application, Japan Agency for Marine-Earth Science and Technology (JAMSTEC), Yokohama, Japan
  • 4MARUM – Center for Marine Environmental Sciences and Department of Geosciences, University of Bremen, Bremen, Germany
  • 5Alfred Wegener Institute (AWI), Helmholtz Centre for Polar and Marine Sciences, Bremerhaven, Germany

Abstract. Stable water isotopes in polar ice cores are widely used to reconstruct past temperature variations over several orbital climatic cycles. One way to calibrate the isotope-temperature relationship is to apply the present-day spatial relationship as a surrogate for the temporal one. However, this method leads to large uncertainties because several factors like the sea surface conditions or the origin and the transport of water vapor influence the isotope-temperature temporal slope. In this study, we investigate how the sea surface temperature (SST), the sea ice extent and the strength of the Atlantic Meridional Overturning Circulation (AMOC) affect these temporal slopes in Greenland and Antarctica for Last Glacial Maximum (LGM, ~21 000 years ago) to preindustrial climate change. For that, we use the isotope-enabled atmosphere climate model ECHAM6-wiso, forced with a set of sea surface boundary condition datasets based on reconstructions (e.g., GLOMAP) or MIROC 4m simulation outputs. We found that the isotope-temperature temporal slopes in East Antarctic coastal areas are mainly controlled by the sea ice extent, while the sea surface temperature cooling affects more the temporal slope values inland. Mixed effects on isotope-temperature temporal slopes are simulated in West Antarctica with sea surface boundary conditions changes, because the transport of water vapor from the Southern Ocean to this area can dampen the influence of temperature on the changes of the isotopic composition of precipitation and snow. In the Greenland area, the isotope-temperature temporal slopes are influenced by the sea surface temperatures very near the coasts of the continent. The greater the LGM cooling off the coast of southeast Greenland, the larger the temporal slopes. The presence or absence of sea ice very near the coast has a large influence in Baffin Bay and the Greenland Sea and influences the slopes at some inland ice cores stations. We emphasize that the extent far south of the sea ice is not so important. On the other hand, the seasonal variations of sea ice distribution, especially its retreat in summer, influence the water vapor transport in this region and the modeled isotope-temperature temporal slopes in the eastern part of Greenland. A stronger LGM AMOC decreases LGM to preindustrial isotopic anomalies in precipitation in Greenland, degrading the isotopic model-data agreement. The AMOC strength does not modify the temporal slopes over inner Greenland, and only a little on the coasts along the Greenland Sea where the changes in surface temperature and sea ice distribution due to the AMOC strength mainly occur.

Alexandre Cauquoin et al.

Status: open (until 21 Mar 2023)

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Alexandre Cauquoin et al.

Alexandre Cauquoin et al.


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Short summary
Stable water isotopes are tracers of climate processes occurring in the hydrological cycle. They are widely used to reconstruct the past variations of polar temperature before the instrumental era thanks to their measurements in ice cores. However, the relationship between measured isotopes and temperature has still large uncertainties. In our study, we investigate how the sea surface conditions (temperature, sea ice, ocean circulation) impact this relationship for a cold to warm climate change.