Abstract
Abstract. Warm, subtropical-originating Atlantic water (AW) has been identified as a primary driver of mass loss across the marine sectors of the Greenland Ice Sheet (GrIS), yet the specific processes by which this water mass interacts with and erodes the calving front of tidewater glaciers is frequently modelled and much speculated upon but remains largely unobserved. We present a suite of fjord salinity, temperature, turbidity versus depth casts along with glacial runoff estimation from Rink and Store glaciers, two major marine outlets draining the western sector of the GrIS during 2009 and 2010. We characterise the main water bodies present and interpret their interaction with their respective calving fronts. We identify two distinct processes of ice–ocean interaction which have distinct spatial and temporal footprints: (1) homogenous free convective melting which occurs across the calving front where AW is in direct contact with the ice mass, and (2) localised upwelling-driven melt by turbulent subglacial runoff mixing with fjord water which occurs at distinct injection points across the calving front. Throughout the study, AW at 2.8 ± 0.2 °C was consistently observed in contact with both glaciers below 450 m depth, yielding homogenous, free convective submarine melting up to ~200 m depth. Above this bottom layer, multiple interactions are identified, primarily controlled by the rate of subglacial fresh-water discharge which results in localised and discrete upwelling plumes. In the record melt year of 2010, the Store Glacier calving face was dominated by these runoff-driven plumes which led to a highly crenulated frontal geometry characterised by large embayments at the subglacial portals separated by headlands which are dominated by calving. Rink Glacier, which is significantly deeper than Store has a larger proportion of its submerged calving face exposed to AW, which results in a uniform, relatively flat overall frontal geometry.
Highlights
Introduction and backgroundThe west Greenland current advects deep (> 400 m), warm (> 3 ◦C) and saline (> 34.8 PSU – practical salinity units) Atlantic water around the south coast of Greenland, transferring large fluxes of thermal energy of a subtropical origin into this sensitive polar environment (Christoffersen et al, 2012; Holland et al, 2008; Kjær et al, 2012; Mortensen et al, 2011; Ribergaard, 2007; Sutherland et al, 2013)
The pycnocline at the lower interface of the Surface water (SW) appears to act as a barrier to buoyant upwelling waters (Sect. 4.4) often constraining them below the SW
We suggest that notch cutting and the resulting headlands along the ice front are related to the presence of localised plume-induced melting of the ice front where Subglacial fresh water (SgFW) is released from subglacial portals (Figs. 8 and 9)
Summary
Introduction and backgroundThe west Greenland current advects deep (> 400 m), warm (> 3 ◦C) and saline (> 34.8 PSU – practical salinity units) Atlantic water around the south coast of Greenland, transferring large fluxes of thermal energy of a subtropical origin into this sensitive polar environment (Christoffersen et al, 2012; Holland et al, 2008; Kjær et al, 2012; Mortensen et al, 2011; Ribergaard, 2007; Sutherland et al, 2013). The frontal dynamics of tidewater outlet glaciers draining the Greenland Ice Sheet (GrIS) can be profoundly influenced by Atlantic water (AW), which has the potential to directly access their. 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; Kjær et al, 2012; Motyka et al, 2011; Rignot et al, 2010; Straneo et al, 2012). 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)
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