Reconstruction of Early Holocene West Greenland Ice Sheet and West Greenland Current Using Radiocarbon Dating and Foraminiferal Assemblages

Benthic foraminiferal assemblages from two marine sediment cores on the West Greenland continental shelf are used to investigate changes in the Greenland Ice Sheet (GIS) and the West Greenland Current (WGC) during the early to mid Holocene. Analyzed cores (343300, HU2008-029-070PC,TC) are members of a transect of cores extending from the mouth of Jakobshavn Isbrae in Disko Bay to the slope of the continental shelf. Jakobshavn Isbrae is the largest West Greenland ice stream and drains 6.5% of the GIS. The use of marine sediment cores to constrain the maximum extent of Jakobshavn and its retreat is a relatively new technique. Basal dates from these sediment cores indicate the initial retreat may have been much earlier than previously believed (11.1 cal ka BP at the bay mouth), and more rapid on the shelf than inside the bay (basal date of 11.8 cal ka BP on the outer shelf). Insight into the cause and timing of this retreat is obtained from the microfossil foraminiferal record. Foraminifers are single celled protists that construct shells of CaCO₃ and agglutinated particles. They can be used as paleoclimate proxies due the dependence of species prevalence on temperature, surface conditions and nutrient availability (most nutrients being carried in by the WGC). Species indicative of cooled Atlantic water (Cassidulina neoteritis and C. reniforme) in these cores suggest that subsurface intrusion of relatively warm Atlantic water may have played a role in this rapid deglaciation. As present ice stream retreat has also been tied to warmed subsurface waters, improving our understanding of this past behavior may help elucidate changes in the WGC and GIS today.