Pathways of ocean heat towards Pine Island and Thwaites grounding lines

Abstract

In the Amundsen Sea, modified Circumpolar Deep Water (mCDW) intrudes into ice shelf cavities, causing high ice shelf melting near the ice sheet grounding lines, accelerating ice flow, and controlling the pace of future Antarctic contributions to global sea level. The pathways of mCDW towards grounding lines are crucial as they directly control the heat reaching the ice. A realistic representation of mCDW circulation, however, remains challenging due to the sparsity of in-situ observations and the difficulty of ocean models to reproduce the available observations. In this study, we use an unprecedentedly high-resolution (200 m horizontal and 10 m vertical grid spacing) ocean model that resolves shelf-sea and sub-ice-shelf environments in qualitative agreement with existing observations during austral summer conditions. We demonstrate that the waters reaching the Pine Island and Thwaites grounding lines follow specific, topographically-constrained routes, all passing through a relatively small area located around 104°W and 74.3°S. The temporal and spatial variabilities of ice shelf melt rates are dominantly controlled by the sub-ice shelf ocean current. Our findings highlight the importance of accurate and high-resolution ocean bathymetry and subglacial topography for determining mCDW pathways and ice shelf melt rates.

Revealing the former bed of Thwaites Glacier using sea-floor bathymetry

“…It is clear from our results that the increased spatial resolution of the MBES data is critical for capturing the high-frequency bathymetric variability on the inner continental shelf seaward of TG, which is necessary to understand warm water incursions into sub-ice shelf cavities (Figs. 8, S5;Nakayama et al, 2019). The strong correlation of our observations with interpretations of the present bed conditions of TG and, therefore, the robustness of this deglaciated terrain as an analogue for the modern bed, further demonstrates that more information can be gleaned from this type of marine dataset (i.e.…”

“…3a); oceanographic measurements and models confirm that this deep acts as a pathway for CDW towards grounding lines in western Pine Island Bay ( Fig. 2a) (Dutrieux et al, 2014;Nakayama et al, 2019).…”

“…The need for high-resolution bathymetry was underscored by recent predictive modelling studies of Antarctic outlet glaciers, which conclude that the shape of the ice-shelf cavity and knowledge of small, kilometre-scale pinning points are both key to improving predictions of ice-sheet retreat and sea-level change (Berger et al, 2016;Favier et al, 2016). Similarly, the latest high-resolution ocean models demonstrate that warm deep water reaches the grounding zone of TG through topographically-constrained pathways, again highlighting the critical need for high-resolution bathymetry in making accurate predictions (Nakayama et al, 2019).…”

Revealing the former bed of Thwaites Glacier using sea-floor bathymetry: implications for warm-water routing and bed controls on ice flow and buttressing

“…1) (e.g. Nitsche et al, 2007;Walker et al, 2007;Jacobs et al, 2012;Nakayama et al, 2013). Landward of the MBES data coverage that existed prior to this study, gravity inversions had indicated the presence of a NE-SWtrending ridge on which the EIS is pinned (Rignot, 2001;Tinto and Bell, 2011;Millan et al, 2017).…”

“…Regional bathymetry for the Amundsen Sea Embayment and location of Thwaites Glacier (TG), West Antarctica. Bathymetry is from IBCSO (Arndt et al, 2013); arrows show observed (solid) and inferred (dashed) pathways for CDW across the continental shelf towards the grounding zones of Pine Island, Thwaites and Smith glaciers (following Nakayama et al, 2013;Dutrieux et al, 2014) and along the Dotson-Getz trough (Ha et al, 2014). PIT is Pine Island Trough; PITE is Pine Island Trough East; PITW is Pine Island Trough West; TGT is Thwaites Glacier Tongue; EIS is Eastern Ice Shelf; other ice shelves (I.S.)…”