Bathymetry data reveal glaciers vulnerable to ice‐ocean interaction in Uummannaq and Vaigat glacial fjords, west Greenland

Abstract

Marine‐terminating glaciers play a critical role in controlling Greenland's ice sheet mass balance. Their frontal margins interact vigorously with the ocean, but our understanding of this interaction is limited, in part, by a lack of bathymetry data. Here we present a multibeam echo sounding survey of 14 glacial fjords in the Uummannaq and Vaigat fjords, west Greenland, which extends from the continental shelf to the glacier fronts. The data reveal valleys with shallow sills, overdeepenings (>1300 m) from glacial erosion, and seafloor depths 100–1000 m deeper than in existing charts. Where fjords are deep enough, we detect the pervasive presence of warm, salty Atlantic Water (AW) (>2.5°C) with high melt potential, but we also find numerous glaciers grounded on shallow (<200 m) sills, standing in cold (<1°C) waters in otherwise deep fjords, i.e., with reduced melt potential. Bathymetric observations extending to the glacier fronts are critical to understand the glacier evolution.

Exceptional retreat of Novaya Zemlya's marine-terminating outlet glaciers between 2000 and 2013

“…However, rapid retreat was not observed on all lake-terminating glaciers in Patagonia (Sakakibara and Sugiyama, 2014), and the potential for these feedbacks to develop depends on basal topography (e.g. Carr et al, 2015;Porter et al, 2014;Rignot et al, 2016). Consequently, the basal topography would need to be similar for each of the NVZ glaciers to explain the very similar retreat patterns, which is not implausible but perhaps unlikely.…”

Glacier Calving in Greenland

“…Recent asynchronous behaviour of Zachariae Isstrom and Nioghalvfjerdsfjord Glacier is largely attributable to variations in fjord bathymetry, with rapid retreat of the former following its detachment from a shallow sill into deepening water while the latter is retreating slowly along an upward-sloping bed [32]. The increasing availability of bed data now makes it possible to identify vulnerable glaciers from the presence of over-deepened basins beneath their tongues [33].…”

Multibeam bathymetry and CTD measurements in two fjord systems in southeastern Greenland

“…K. Kjeldsen et al: Multibeam bathymetry and CTD measurements in two fjord systems result, many glaciers appear grounded near or at sea level, whereas in reality the glaciers are grounded in deeper waters (Andresen et al, 2014;Rignot et al, 2016).…”

“…The publication of different datasets is continuously improving the bathymetry around Greenland (e.g., Arndt et al, 2015;Fenty et al, 2016;Rignot et al, 2015Rignot et al, , 2016Schumann et al, 2012;Williams et al, 2017), even if it is only based on a suite of single-point observations (Andresen et al, 2014) or inversion of gravity data to obtain bathymetry (Porter et al, 2014). Whereas the topography of the onshore area is more easily determined from air and satellite imagery and altimetry (e.g., Korsgaard et al, 2016;Willis et al, 2015), the relief of the submarine parts is hidden by the water column and can only be determined with hydroacoustic methods or aerial gravimetry.…”