Reconstruction of sea-surface temperature, salinity, and sea-ice cover in the northern North Atlantic during the last glacial maximum based on dinocyst assemblages

Abstract

Past sea-surface conditions over the northern North Atlantic during the last glacial maximum were examined from the study of 61 deep-sea cores. The last glacial maximum time slice studied here corresponds to an interval between Heinrich layers H2 and H1, and spanning about 20-16 ka on a 14C time scale. Transfer functions based on dinocyst assemblages were used to reconstruct sea-surface temperature, salinity, and sea-ice cover. The results illustrate extensive sea-ice cover along the eastern Canadian margins and sea-ice spreading, only during winter, over most of the northern North Atlantic. On the whole, much colder winter prevailed, despite relatively mild conditions in August (10-15°C at most offshore sites), thus suggesting a larger seasonal contrast of temperatures than today. Lower salinity than at present is reconstructed, especially along the eastern Canadian and Scandinavian margins, likely because of meltwater supply from the surrounding ice sheets. These reconstructions contrast with those established by CLIMAP on the basis of planktonic foraminifera. These differences are discussed with reference to the stratigraphical frame of the last glacial maximum, which was not the coldest phase of the last glacial stage. The respective significance of dinocyst and foraminifer records is also examined in terms of the thermohaline characteristics of surface waters and the vertical structure of upper water masses, which was apparently much more stratified than at present in the northern North Atlantic, thus preventing deep-water formation.

Cold marine indicators of the late Quaternary: the new dinoflagellate cyst genus Islandinium and related morphotypes

“…Rochon et al (1999, text fig. 9a, 35) extended the known modern distribution of Islandinium minutum into the north temperate realm of the North Atlantic Ocean; and fossil assemblages from Late Glacial Maximum sediments off western Norway are in agreement with this distribution, showing Islandinium minutum (<10%) co-occurring with the tropical to temperate species Lingulodinium machaerophorum (about 4-7%) (de Vernal et al, 2000). Andersen et al (1991) also found small numbers of I. minutum and L. machaerophorum co-occurring in Weichselian deposits from Norway.…”

Laminated sediments preceding Heinrich event 1 in the Northern North Sea and Southern Norwegian Sea: Origin, processes and regional linkage

“…The presence of seasonal sea ice in the region between 20 and 16 cal. ka BP has also been inferred from dinoflagellate cysts analysed from core MD95-2010(de Vernal et al, 2000 and by analysis of planktonic foraminifera assemblages (Weinelt et al, 2003). Thus, the laminations might be the product of a possibly annual cycle where in winter/cooler periods sea ice cover and a reduced input from iceberg melting lead to lower density and thinner layers.…”

Glacier response in the European Alps to Heinrich Event 1 cooling: the Gschnitz stadial

“…Thermohaline circulation in the Norwegian-Greenland Sea was also less vigorous during H1 (Rasmussen et al, 1997;Rasmussen and Thomsen, 2002). Delineation of past permafrost patterns in Europe during intense cold periods, such as the LGM and the Younger Dryas, bears out the association of increased permafrost extent with a cold North Atlantic and abundant pack ice (Renssen and Vandenberghe, 2003) especially in winter (de Vernal et al, 2000). The extremely cold and dry climate that was prevalent during the Gschnitz stadial implies that similar conditions may have existed about 16 000 yr ago.…”