Glacial North Atlantic: Sea‐surface conditions reconstructed by GLAMAP 2000

Abstract

[1] The response of the tropical ocean to global climate change and the extent of sea ice in the glacial nordic seas belong to the great controversies in paleoclimatology. Our new reconstruction of peak glacial sea surface temperatures (SSTs) in the Atlantic is based on census counts of planktic foraminifera, using the Maximum Similarity Technique Version 28 (SIMMAX-28) modern analog technique with 947 modern analog samples and 119 well-dated sediment cores. Our study compares two slightly different scenarios of the Last Glacial Maximum (LGM), the Environmental Processes of the Ice Age: Land, Oceans, Glaciers (EPILOG), and Glacial Atlantic Ocean Mapping (GLAMAP 2000) time slices. The comparison shows that the maximum LGM cooling in the Southern Hemisphere slightly preceeded that in the north. In both time slices sea ice was restricted to the north western margin of the nordic seas during glacial northern summer, while the central and eastern parts were ice-free. During northern glacial winter, sea ice advanced to the south of Iceland and Faeroe. In the central northern North Atlantic an anticyclonic gyre formed between 45°and 60°N, with a cool water mass centered west of Ireland, where glacial cooling reached a maximum of >12°C. In the subtropical ocean gyres the new reconstruction supports the glacial-to-interglacial stability of SST as shown by CLIMAP Project Members (CLIMAP) [1981]. The zonal belt of minimum SST seasonality between 2°and 6°N suggests that the LGM caloric equator occupied the same latitude as today. In contrast to the CLIMAP reconstruction, the glacial cooling of the tropical east Atlantic upwelling belt reached up to 6°-8°C during Northern Hemisphere summer. Differences between these SIMMAX-based and published U 37 k -and Mg/Ca-based equatorial SST records are ascribed to strong SST seasonalities and SST signals that were produced by different planktic species groups during different seasons.

Expansion of subarctic water masses in the North Atlantic and Pacific oceans and implications for mid‐Pleistocene ice sheet growth

“…[18] The range of reconstructed SSTs using U 37 K at Site 983 is consistent with reconstructed winter and summer SSTs at the last glacial maximum (around 1 -4°C) [Pflaumann et al, 2003] and with the modern annual SST range at the site (8-11°C) [Conkright et al, 2002]. SSTs using U 37 K 0 are higher than those from U 37 K .…”

Sensitivity of the glacial ocean to Heinrich events from different iceberg sources, as modeled by a coupled atmosphere‐iceberg‐ocean model

“…However, the winter limits of near freezing ocean surface temperatures in the model between 40-50°N are still further south than in the MARGO reconstructions. The modeled sea ice distribution produces sea ice all year round in the Nordic Seas, while this area is thought to have been seasonally ice-free [Pflaumann et al, 2003;Kucera et al, 2005], which also indicates our model is too cold in the northern North Atlantic. Other coupled atmosphere-ocean models from the PMIP project have similar problems obtaining LGM-PD temperature anomalies similar to those of MARGO [Kageyama et al, 2006].…”

The meridional temperature gradient in the eastern North Atlantic during MIS 11 and its link to the ocean–atmosphere system

“…Foraminiferal SSTs for the two polar sites, cores M23063 and MD992277/PS1243, were calculated using a modification of MAT, i.e., SIMMAX (Pflaumann et al, 1996(Pflaumann et al, , 2003. It has been shown that, due to a special approach in calculating similarity indices, SIMMAX may yield quite objective results for the higher latitudes.…”

“…Foraminiferal SSTs for core M23414 were calculated using the North Atlantic subset of the coretop data base as compiled by Pflaumann et al (2003). To reconstruct SSTs at Sites 975 and 958 and their Holocene reference cores (MD95-2043 and 658, respectively) a combined set of 279 samples from the Mediterranean Sea (Kucera et al, 2005 and references therein) and from the Iberian margin (Salgueiro et al, 2008) was added to the aforementioned data base.…”

“…It has been shown that, due to a special approach in calculating similarity indices, SIMMAX may yield quite objective results for the higher latitudes. A total number of 947 coretop samples were used as reference data set (Pflaumann et al, 1996(Pflaumann et al, , 2003.…”