Direct observations of submarine melt and subsurface geometry at a tidewater glacier

Abstract

Ice loss from the world’s glaciers and ice sheets contributes to sea level rise, influences ocean circulation, and affects ecosystem productivity. Ongoing changes in glaciers and ice sheets are driven by submarine melting and iceberg calving from tidewater glacier margins. However, predictions of glacier change largely rest on unconstrained theory for submarine melting. Here, we use repeat multibeam sonar surveys to image a subsurface tidewater glacier face and document a time-variable, three-dimensional geometry linked to melting and calving patterns. Submarine melt rates are high across the entire ice face over both seasons surveyed and increase from spring to summer. The observed melt rates are up to two orders of magnitude greater than predicted by theory, challenging current simulations of ice loss from tidewater glaciers.

Meltwater Intrusions Reveal Mechanisms for Rapid Submarine Melt at a Tidewater Glacier

“…Further evidence for the importance of the horizontal velocity field is found in the sonar-derived melt rates from Sutherland et al (2019). Terminus-averaged melt rates were observed to be 4 times higher in August than in May, whereas standard plume-melt theory predicts that ambient melt rates should be slightly higher in May.…”

Distinct Frontal Ablation Processes Drive Heterogeneous Submarine Terminus Morphology

“…Furthermore, large uncertainties remain for estimates of outlet discharge in Greenland fjords, which have been constrained using fjord water properties (Chauché et al, 2014;Jackson et al, 2017;Stevens et al, 2016) and can strongly influence near-glacier circulation and melt rates (Carroll et al, 2015;Fried et al, 2015;Slater et al, 2018). In addition, ambient melting (outside of discharge outlets) may be an important source of terminus melt that is not well understood (Slater et al, 2018;Sutherland et al, 2019;Wagner et al, 2019). Ultimately, the connection between frontal ablation and terminus morphology is largely unknown, which limits our ability to parameterize the complete fjord-terminus-glacier system in coupled ocean-ice models.…”

How Oceanic Melt Controls Tidewater Glacier Evolution

“…Only recently, observations from tidewater and freshwater glaciers during summer conditions have been published. These studies illustrate that many calving fronts exhibit ice feet, which occasionally reach lengths exceeding 100 m (Bendtsen et al, ; Fried et al, , ; Slater et al, ; Sugiyama et al, ; Sutherland et al, ; Rignot et al, ). The shapes and extents of these documented terminus geometries show strong similarities with our model results.…”

“…In a recent sophisticated modeling study, Todd et al () also demonstrated a direct influence of submarine melting on the evolution of Store Gletscher. However, their approach only allowed for a fully vertical calving front after ice break‐off, and any buoyant submerged ice was removed as soon as it formed, which is not fully consistent with observations (Hunter & Powell, ; Fried et al, ; Motyka, ; O'Neel et al, ; Sugiyama et al, ; Sutherland et al, ; Warren et al, ). The presence of submerged ice induces buoyancy forces (Benn et al, ; Warren et al, ) that alter the stresses near the calving front and consequently the calving process.…”