New world map of sea-surface temperature and sea-ice extent during the Last Glacial Maximum

Apr 13, 2021

The basis for GLOMAP is data obtained from deep-sea sediment cores. Photo: MARUM - Center for Marine Environmental Sciences, University of Bremen; V. Diekamp

Researchers use maps to visualize their data. Using paleodata from the international MARGO project ("Multiproxy Approach for the Reconstruction of the Glacial Ocean Surface") on temperatures near the sea surface, a team led by Dr. André Paul from MARUM - Center for Marine Environmental Sciences at the University of Bremen and the Alfred Wegener Institute has created a new map: GLOMAP ("Glacial Ocean Map"). In addition to temperatures, this monthly world map includes a new synthesis of paleo-sea ice data.

GLOMAP shows how sea surface temperatures and sea ice changed at the time of the Last Glacial Maximum (LGM) as compared to today, and it provides the basis for future simulations of the atmospheric circulation with climate models. Such models help researchers visualize climate changes and test them against additional, independent data from the past.

The paleodata are based on samples obtained from deep-sea sediment cores. In particular, abundances of planktonic microorganisms were used for GLOMAP. In addition, biomarker data were taken into account to reconstruct the paleo-sea ice distribution in the Arctic. However, there are gaps in sampling. Data points exist only where deep-sea cores could be obtained. Therefore, sufficient data are not available for all ocean areas.

Therefore, for GLOMAP, the authors applied a new method from physical oceanography for the first time to create a comprehensive representation of mean sea-surface conditions for the time period between 23,000 to 19,000 years ago from the sparse and scattered data. Data gaps were filled using statistical relationships so that a complete coverage of the world ocean could be achieved. The method also provided an indication of the uncertainty in temperature change, which depends on data coverage and errors in the raw data.

The temperature change averaged over the entire world ocean provides an estimate of the sensitivity of the climate system to changes in the Earth's radiative budget due to the large continental ice sheets and the decrease in greenhouse gas concentrations during the LGM. Currently, global warming due to a doubling of the atmospheric CO2 concentration is assumed to range between 2.6 and 4.1 °C. Paleodata such as GLOMAP argue for a value in the middle of this range and against a very high climate sensitivity.

Original publication:

André Paul, Stefan Mulitza, Rüdiger Stein, Martin Werner: A global climatology of the ocean surface during the Last Glacial Maximum mapped on a regular grid (GLOMAP), Clim. Past, 17, 805–824, https://doi.org/10.5194/cp-17-805-2021, 2021.

The Glacial Ocean Map (GLOMAP) of temperature differences in °C between the Last Glacial Maximum and today for winter in the northern hemisphere. The colored data points reflect the temperature differences reconstructed at the locations of 600 sediment cores and included in the statistical analysis. The yellow-brownish areas near Antarctica and in the Arctic indicate the sea-ice extent, which was also reconstructed.