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

摘要

Warm, subtropical-originating Atlantic water (AW) has been identified as aprimary driver of mass loss across the marine sectors of the Greenland IceSheet (GrIS), yet the specific processes by which this water mass interactswith and erodes the calving front of tidewater glaciers is frequently modelledand much speculated upon but remains largely unobserved. We present a suite offjord salinity, temperature, turbidity versus depth casts along withglacial runoff estimation from Rink and Store glaciers, two major marineoutlets draining the western sector of the GrIS during 2009 and 2010. Wecharacterise the main water bodies present and interpret their interactionwith their respective calving fronts. We identify two distinct processes ofice–ocean interaction which have distinct spatial and temporal footprints:(1) homogenous free convective melting which occurs across the calving frontwhere AW is in direct contact with the ice mass, and (2) localised upwelling-driven melt by turbulent subglacial runoff mixing with fjord water whichoccurs at distinct injection points across the calving front. Throughout thestudy, AW at 2.8 ± 0.2 °C was consistently observed incontact with both glaciers below 450 m depth, yielding homogenous,free convective submarine melting up to ~200 m depth. Abovethis bottom layer, multiple interactions are identified, primarily controlledby the rate of subglacial fresh-water discharge which results in localisedand discrete upwelling plumes. In the record melt year of 2010, the StoreGlacier calving face was dominated by these runoff-driven plumes which ledto a highly crenulated frontal geometry characterised by large embayments atthe subglacial portals separated by headlands which are dominated bycalving. Rink Glacier, which is significantly deeper than Store has a largerproportion of its submerged calving face exposed to AW, which results in auniform, relatively flat overall frontal geometry.