EGU22-9308, updated on 28 Mar 2022
EGU General Assembly 2022
© Author(s) 2022. This work is distributed under
the Creative Commons Attribution 4.0 License.

Severe cooling of the Atlantic thermocline during the last glacial

Marleen Lausecker1, Freya Hemsing1, Thomas Krengel1, Julius Förstel1, Andrea Schröder-Ritzrau1, Evan Cooper Border1, Covadonga Orejas2, Jürgen Titschak3,4, Claudia Wienberg3, Dierk Hebbeln3, Anne-Marie Wefing5, Paolo Montagna6, Eric Douville7, Lelia Matos8, Jacek Raddatz9, and Norbert Frank1
Marleen Lausecker et al.
  • 1Institute of Environmental Physics, Heidelberg University, Heidelberg, Germany
  • 2Instituto Español de Oceanografía, Centro Oceanográfico de Gijón (IEO, CSIC), Gijón, Spain
  • 3MARUM – Center for Marine Environmental Sciences, University of Bremen, Bremen, Germany
  • 4Marine Research Department, Senckenberg am Meer, Wilhelmshaven, Germany
  • 5Institute of Biogeochemistry and Pollutant Dynamics, ETH Zürich, Zürich, Switzerland
  • 6Institute of Polar Sciences (ISP-CNR), Bologna, Italy
  • 7Laboratoire des Sciences du Climat et de l'Environnement, LSCE/IPSL, Gif-sur-Yvette, France
  • 8Portuguese Institute for the Ocean and Atmosphere (IPMA), Lisbon, Portugal
  • 9Institute of Geosciences, Goethe University Frankfurt, Frankfurt am Main, Germany

The mean cooling of the global ocean during the Last Glacial Maximum (LGM) was recently estimated to 2.6°C using noble gases trapped in ice cores (1). The ocean, however, is highly heterogeneous with respect to its internal temperature varying both in latitude and water depth. While temperature changes in the deep ocean are small at about 2 - 3 °C (1,2), the upper ocean is more dynamic. Regional temperature anomalies of up to 7°C are predicted during the LGM compared to modern interior ocean temperature by global ocean circulation models (3). Due to the temperature drop to near freezing conditions and the global increase in salinity from ice sheet growth, the oceans’ deep interior became strongly haline stratified (2). Temperatures of the glacial ocean thermocline are, however, less well constrained.

Here, thermocline temperature reconstructions since the last glacial based on the Li/Mg ratio in cold-water coral skeletons are presented. The coral samples, collected from 300 - 1200 m water depths from different sites in the Atlantic (43°N to 25°S), reveal synchronous 5 - 7°C cooling during the last glacial period compared to today, as well as a dramatic shoaling of the thermocline. At the end of the LGM, warming of the upper thermocline ocean occurred early in the southern hemisphere followed by a fluctuating warming and thermocline deepening in the northern Hemisphere. This supports the oceanic climate seesaw proposed by Stocker and Johnson in 2003 (4). We thus propose dramatic changes in the export of polar waters towards the Equator and an enhanced subsurface ocean stratification leading to a mostly polar Atlantic with a shallow permanent thermocline during the glacial.



1) Bereiter et al., Nature 553, 39-44 (2018).
2) Adkins et al., Science 298, 1769-1773 (2002).
3) Ballarotta et al., Clim. Past 9, 2669-2686 (2013).
4) Stocker and Johnsen, Paleoceanography 18, 1087 (2003).

How to cite: Lausecker, M., Hemsing, F., Krengel, T., Förstel, J., Schröder-Ritzrau, A., Border, E. C., Orejas, C., Titschak, J., Wienberg, C., Hebbeln, D., Wefing, A.-M., Montagna, P., Douville, E., Matos, L., Raddatz, J., and Frank, N.: Severe cooling of the Atlantic thermocline during the last glacial, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-9308,, 2022.