Outlet glacier dynamics and bathymetry at Upernavik Isstrøm and Upernavik Isfjord, North-West Greenland

Abstract

During the past decades, the Greenland ice sheet has experienced a marked increase in mass loss resulting in an increased contribution to global sea-level rise. The three largest outlet glaciers in Greenland have increased their discharge, accelerated, thinned and retreated between 1996 and 2005. After 2005 most of them have slowed down again although not to previous levels. Geodetic observations suggest that rapid increase in mass loss from the north-western part of the ice sheet occurred during 2005–2010 (Kjeldsen et al. 2013). Warming of the subsurface water masses off Greenland may have triggered the acceleration of outlet glaciers from the ice sheet (Straneo & Heimbach 2013). The North Atlantic subpolar gyre, which transports water to South-East and West Greenland via the warm Irminger Current, warmed in the mid-1990s. Increased inflow of warm subpolar waters likely led to increased submarine melting of tidewater glaciers. Climate, glacier configuration and fjord bathymetry play fundamental roles for outlet glacier dynamics and thus knowledge of these parameters is warranted. In particular, the bathymetry of a fjord gives important information about the exchange between fjord waters close to marine-terminating glaciers and the shelf and ocean. However, only sparse bathymetric data are available for the majority of fjords in Greenland. The International bathymetry chart for the Arctic Ocean (IBCAO) does not provide adequate data for the fjords and gives the impression that water depths in fjords are typically <200 m. Here we present the first detailed bathymetric data from Upernavik Isfjord in North-West Greenland, which were obtained during a cruise led by the Geological Survey of Denmark and Greenland in August 2013. The purpose of the cruise was to retrieve sediment cores, collect hydrographic data and map the bathymetry of the fjord. In this paper, we also estimate retreat rates of the Upernavik Isstrøm since 1849 and evaluate them in the context of climate variability, glacier setting and fjord bathymetry.