Paleoceanographical development off Sisimiut, West Greenland, during the mid- and late Holocene: A multiproxy study

A multiproxy study of paleoceanographic and climatic changes in Holsteinsborg Dyb on the West Greenland shelf shows that the area is sensitive to variations in the mixing between the two components of the West Greenland Current, i.e., the Atlantic Water of the Irminger Current and the Polar Water from the East Greenland Current. A seismic profile illustrates the general development in the area since the deglaciation, and analyses of benthic foraminifera, stable isotopes (δ18O and δ13C), and X-ray fluorescence elemental counts in two cores, covering ca. 6650 and 1100 years, respectively, provide details on the oceanographic changes during the mid- and late Holocene. The chronology is based on 210Pb and AMS 14C age determinations. During the time interval of 6650–1600 cal. yr BP, the bottom waters are characterized by the presence of modified Atlantic Water, with some influence of meltwater, either local or regional. Depleted δ18O values and relatively high Si/Fe ratio suggest warmer conditions from 6650 to 3800 cal. yr BP, corresponding in time to part of the Holocene Thermal Maximum, followed by a general slight cooling with some fluctuation after 3800 cal. yr BP. At 1600 cal. yr BP, there is an abrupt change in almost all investigated proxies. The foraminiferal assemblage and the δ18O values suggest cold, low-salinity bottom-water conditions, and there is indication of seasonal sea-ice cover between 1400 and 1200 cal. yr BP, corresponding in time to the Dark Ages Cold Period and to a minimum in solar irradiance. From ca. 1150 to 580 cal. yr BP, a time interval equivalent to the historical Medieval Warm Period (MWP), the foraminiferal fauna remains indicative of cold, low-salinity bottom waters, but without any indication of sea-ice cover. The influence of Polar Water/meltwater at the sea floor during the MWP is thought to be a result of enhanced mixing of the two components of the West Greenland Current caused by an increase in wind activity during generally positive North Atlantic Oscillation conditions, maybe combined with a displacement of the Irminger Current pathway to the outer shelf. During the Little Ice Age (LIA), there is a strong influence of modified Atlantic Water at the sea floor, related to sea-ice formation and stratification of the water column. After AD 1900, the benthic foraminiferal assemblage suggests a slight increase in Polar Water influence and thereby mixing, even though the environment is not much different from that during the LIA.