Reconstruction of relative sea-level changes during the last millennium in northern West Greenland

Abstract

Reconstruction of relative sea-level (RSL) changes around Greenland’s coasts increases our understanding of Greenland Ice Sheet (GIS) retreat since the last glacial maximum, as well as assisting in constraining models of ice sheet behaviour. Understanding earlier ice sheet responses to climate variation will improve predictions of GIS change under various IPCC climate change scenarios, and therefore of Greenland’s likely contribution to global sea level rise from its loss of ice throughout this century. Salt marshes at Upernavik, northern West Greenland were investigated for their elevation range with respect to the tide, diatom assemblages, stratigraphy and sediment organic content (loss on ignition), and samples were dated using 210Pb and AMS 14C. This is further north than this approach has previously been used. Shallow sediment and slow sedimentation rates, related to adverse growing conditions for the halophytic vegetation, limited the precision of results, but RSL rise of 0.3m occurred over the 100 years prior to 2014, with limiting dates showing at least 0.2m rise in the previous 235 years, in agreement with the Huy3 model of GIS evolution. The contrast with recent RSL stability in south- and central West Greenland probably relates to the later deglaciation of the northern GIS and continuing collapse of the North American Ice Complex forebulge. GPS data from Upernavik show 7.81 mm/yr crustal uplift from 2007-2011, probably linked to retreat of Upernaviks Isstrøm 60km east of our field site, but the slow accretion of these marshes is unlikely to be able to demonstrate a change from RSL rise to RSL fall for some time. These marginal northern marshes are positioned mainly above highest astronomical tide (HAT) level, possibly related to sea ice damage below this and low precipitation permitting halophytic vegetation growth further above HAT, but they remain useful sources of RSL data over recent centuries.