GLAMAP2000
Glacial Atlantic Mapping and Prediction

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Objectives

GLAMAP2000 is a joint effort to reconstruct Atlantic sea-surface temperatures (SST) during the Last glacial maximum (LGM). Contributing institutes are GEOMAR, Kiel for the Arctic, University of Kiel for the North Atlantic, University of Bremen for the South Atlantic, and Alfred Wegener Institute (AWI), Bremerhaven, for the Southern Ocean.

Method

The reconstruction is based on about 180 sediment cores with d18O stratigraphy of which 30 cores were AMS 14C dated. The LGM time slice was defined at the fairly stable d18O maximum 18-15 14C ka, equal to about 22-18 calendar ka, in ultrahigh-resolution records from the North Atlantic. Sedimentation rates and the quality of the age models led to six categories of sediment records. The worst category was discarded. Summer and winter SST values were derived from planktonic foraminifera census counts via the SIMMAX modern analog technique and the Imbrie-Kipp technique. From diatom and radiolarian census counts summer SST values where estimated using the Imbrie-Kipp technique only. At each site the various SST estimates within the LGM time slice were averaged.

First results

As compared to the CLIMAP (1981) reconstruction our new SST patterns confirm
  1. a southward shift of the northern subpolar front to about 45°N,
  2. a constant SST level in the subtropical gyres of both the North and South Atlantic, and
  3. a disappearance of most of the temperate zones in both hemispheres.

Different from CLIMAP the new patterns reveal ice-free conditions in the eastern Nordic Seas during LGM summer up to north of Svalbard and a sea-ice cover only reaching down to west of Ireland during winter. In the tropical divergence zone the LGM SST decreased much stronger than estimated by CLIMAP, by 5-8°C during boreal summer and 4.5-6.5°C during austral summer (CLIMAP: 4-5°C and 0-2°C, respectively). Finally, the zonal SST anomalies in the eastern coastal upwelling zones were weaker off northwest Africa, but more pronounced off southwest Africa than at CLIMAP, possibly due to a major glacial interhemispheric asymmetry in trade winds.

Contributors

  • GEOMAR, Research Center for Marine Geoscienes:
    M. Hüls, Nørgaard-Pedersen, R. Spielhagen, J. Thiede
  • IfG, Institut für Geowissenschaften an der Universität Kiel:
    C. Hohnemann, M. Hüls, G. Kähler, T. Kiefer, M. Maslin, U. Pflaumann, M. Sarnthein, H. Schulz, S. van Kreveld, E. Vogelsang, M. Weinelt
  • GeoB, Fachbereich Geowissenschaften an der Universität Bremen:
    H. Arz, B. Donner, W. Hale, S. Mulitza, S. Niebler, J. Pätzold, R. Sieger, G. Wefer
  • AWI, Alfred Wegener Institute for Polar and Marine Research:
    A. Abelmann, U. Brathauer, B. Censarek, R. Gersonde, U. Zielinski

References