Characteristics of ocean waters reaching Greenland's glaciers

Abstract

Interaction of Greenland's marine-terminating glaciers with the ocean has emerged as a key term in the ice-sheet mass balance and a plausible trigger for their recent acceleration. Our knowledge of the dynamics, however, is limited by scarcity of ocean measurements at the glacier/ocean boundary. Here data collected near six marine-terminating glaciers (79 North, Kangerdlugssuaq, Helheim and Petermann glaciers, Jakobshavn Isbrae, and the combined Sermeq Kujatdleq and Akangnardleq) are compared to investigate the water masses and the circulation at the ice/ocean boundary. Polar Water, of Arctic origin, and Atlantic Water, from the subtropical North Atlantic, are found near all the glaciers. Property analysis indicates melting by Atlantic Water (AW; found at the grounding line depth near all the glaciers) and the influence of subglacial discharge at depth in summer. AW temperatures near the glaciers range from 4.58 8C in the southeast, to 0.168C in northwest Greenland, consistent with the distance from the subtropical North Atlantic and cooling across the continental shelf. A review of its offshore variability suggests that AW temperature changes in the fjords will be largest in southern and smallest in northwest Greenland, consistent with the regional distribution of the recent glacier acceleration.

The sensitivity of the Greenland Ice Sheet to glacial–interglacial oceanic forcing

“…First, we analyse the sensitivity of the model to different constant (in space and time) B ref values applied at the base of the ice-sheet marine margins. Due to the scarcity of submarine melt observations along the GrIS coasts, and since the only available estimates have focused on few very rapid tidewater Greenland glaciers that cannot be representative of the basal melt rate for the entirety of GrIS marine areas (Rignot et al, 2010;Motyka et al, 2011;Straneo et al, 2012;Xu et al, 2013;Enderlin and Howat, 2013;Fried et al, 2015;Rignot et al, 2016;Wilson et al, 2017), we assume presentday basal melting rates for Greenland comparable to those from Antarctic ice shelves . The range of values of B ref is set between 0 and 40 m a −1 , while κ is set to zero to make the ocean contribution constant in time.…”

Ice–ocean interaction and calving front morphology at two west Greenland tidewater outlet glaciers

“…In NW Greenland, two distinct phases of dynamic ice loss (1985-1990 and 2005-2010) across the Melville Coast have been attributed to oceanic rather than atmospheric forcing (Kjaer et al, 2012). An implicit assumption in these studies is that warm AW comes into direct contact with the marine termini of large tidewater outlet glaciers draining the ice sheet (Holland et al, 2008;Kjaer et al, 2012;Motyka et al, 2011;Rignot et al, 2010;Straneo et al, 2012). Yet to date few observational studies have been focused on the actual ice-ocean interface, in particular on the specific controls governing submarine melt rates and the concomitant mass and energy exchanges which determine outlet glacier and fjord dynamics alike (Hubbard, 2011).…”

“…SgFW is very difficult to measure in its original state due to the vigorous mixing which occurs on its injection from the portal (Salcedo-Castro et al, 2011;Xu et al, 2012Xu et al, , 2013. Hence, SgFW is reasonably assumed to have the basic characteristics of θ = 0 • C and S = 0 PSU (Mortensen et al, 2013;Straneo et al, 2012). (Fig.…”

“…In the θ-S diagram, the mixed water mass resulting from submarine melting of the glacier will fall on the Gade-slope joining the water, driving the melt and the virtual water type with characteristics θ = θ eff and S = 0. A similar identification procedure can be applied to track runoff mixing and resulting mixed water mass as it will follow a line joining the ambient water and the fresh runoff water (θ = 0 • C; S = 0 • C) (Mortensen et al, 2013;Straneo et al, 2011Straneo et al, , 2012) (hereafter called the runoff slope). If both submarine melting and runoff mixing are affecting the same water parcel, the resulting mixed water mass will have a θ-S gradient proportional to the theoretical slope of each process (Mortensen et al, 2013).…”

“…Following Straneo et al (2011Straneo et al ( , 2012, the horizontal inflection in the θ-S diagram is used to define the second apex of the runoff slope (Fig. 3) and gives a theoretical value of ∼ 0.05 • C PSU −1 and 0.04 • C PSU −1 respectively.…”