ABSTRACT: Regionalism of climate changes in the Northwest North Atlantic, southwestGreenland and eastern Baffin Island areas since 7000 cal. years BP: Marine and terrestrial palynological evidence.

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Abstract

Present-day climate conditions across the subpolar North Atlantic are by no means uniform, and regional scale differences need to be taken into account in paleoclimate studies and for climate and paleoclimate modelling. Over the past few years, paleoclimate studies from both marine and terrestrial records at high latitudes of the North Atlantic and adjacent lands have reported different regional trends in climate changes during the Holocene. Of particular importance is the mid- to late Holocene summer sea-surface temperature (SST) cooling which shows significant differences in the western and eastern North Atlantic, suggesting important changes in surface ocean circulation pattern (e.g. Marchal et al., 2002; Andersen et al., 2004; Moros et al., 2004; de Vernal and Hillaire-Marcel, 2006). The mid-late Holocene climate history is more complex than previously thought (e.g. Steig, 1999) and large uncertainties remain concerning the regional response of terrestrial and marine environments to changes in ocean circulation. Here we use palynological data from marine and lacustrine sediment cores collected in the northwest North Atlantic (northwest Labrador Sea: core HU021, and central North Atlantic: core HU085) and adjacent lands (Baffin Island: Akvaqiak Lake, and southern Greenland: Qipisarqo Lake) to derive climate records spanning about 8000 years for terrestrial and marine ecosystems. The respectivelocation of the terrestrial and marine sedimentary sequences is suitable to address the question of changes in ocean circulation patterns and its impact on continental climates, since they lie in the trajectory of surface ocean currents that play a major role in northward heat fluxes (the North Atlantic Current [NAC] and its westward branch making the West Greenland Current [WGC]) and southward Arctic water flow (Baffin Land [BLC], Labrador [LC] and East Greenland [EGC] currents). Principal component analysis (PCA) is used to summarize the middle to late Holocene succession and variability in pollen and dinocyst assemblages. The first PCA in both lake and marine cores shows strong linear trends in assemblages since 8000 cal. years BP. The first eigenvalue of eastern sites (Qipisarqo and HU085) is two times higher than western sites (Akvaqiak and HU021) indicating much higher amplitude ofchange in pollen and dinocyst assemblages in southwest Greenland and central North Atlantic than in eastern Baffin Island and along the Canadian margin. At all sites there is a pronounced change around the mid-late Holocene transition (i.e., at about 5000 cal. years BP). The transition is abrupt in the central North Atlantic (HU085), whereas it appears more gradual westward, in eastern Baffin Island (Akvaqiak). reconstructed sea-surface and air temperatures from dinocyst and pollen assemblages, respectively (Fig. 2B). The transfer functions used are based on the modern analogue technique. The reference database used for quantitative past ocean conditions includes 60 taxa and 1054 reference sites from mid- to high latitude North Atlantic, NorthPacific and Arctic oceans, and adjacent sub-polar seas (de Vernal and Hillaire-Marcel, 2006). Results show a significant cooling trend of about 6°C in summer and 5°C in winter at the eastern site (HU085), whereas the western site does not show significant change of SST for the last 8000 years. The reference database used for past terrestrial climate reconstruction includes 39 taxa and 831 reference sites from mid- to high latitudes of North America and Greenland (Fréchette et al., in review). Akvaqiak and Qipisarqo lakes show a progressive decrease in July air temperature since 7000 cal. years BP. However, the amplitude of the cooling at Qipisarqo Lake (3.5°C) is much more pronounced than at Akvaqiak Lake, where the cooling trend does not exceed 1°C. The east to west contrast in the amplitude of the mid to late Holocene trend is thus observed in both marine and terrestrial records. The results illustrate the sensitivity of the climate system during a warm inter glacial interval and provide evidence for strong linkages between terrestrial climate and oceanic conditions in the subpolar North Atlantic during the middle to late Holocene. They also point to the decreasing influence of North Atlantic water inflow asmoisture and heat source over southern Greenland, whereas Baffin Island and eastern Canadian margins apparently remained under Arctic influence through the Baffin Land and Labrador currents.

Bibliography of Canadian Geomorphology