Heterogenous Retreat And Ice Melt Of Thwaites Glacier, West Antarctica - Science Advances
Abstract
The glaciers flowing into the Amundsen Sea Embayment, West Antarctica, have undergone acceleration and grounding line retreat over the past few decades that may yield an irreversible mass loss. Using a constellation of satellites, we detect the evolution of ice velocity, ice thinning, and grounding line retreat of Thwaites Glacier from 1992 to 2017. The results reveal a complex pattern of retreat and ice melt, with sectors retreating at 0.8 km/year and floating ice melting at 200 m/year, while others retreat at 0.3 km/year with ice melting 10 times slower. We interpret the results in terms of buoyancy/slope-driven seawater intrusion along preferential channels at tidal frequencies leading to more efficient melt in newly formed cavities. Such complexities in ice-ocean interaction are not currently represented in coupled ice sheet/ocean models.
The Antarctic Ice Sheet is changing rapidly and contributing notably to global sea level rise (1, 2). With 1.2-m potential sea level equivalent, the Amundsen Sea Embayment (ASE) sector of West Antarctica is a dominant contributor to sea level rise at present and for decades to come (3–5). Thwaites Glacier accounts for one-third of the mass loss from the ASE (6). The fast-flowing main trunk of Thwaites accelerated by 0.8 km/year, or 33%, between 1973 and 1996, and another 33% between 2006 and 2013 (7). Between 1970–2003 and 2010–2013, ice discharge increased at a rate of 2.2 Gt/year2, and the rate quadrupled in 2003–2010 (9.5 Gt/year2). More recently, parts of the glacier have been observed to thin as much as 4 m/year (8).
As bed topography beneath Thwaites is several hundreds of meters below sea level at the grounding line and is getting deeper inland (retrograde bed slope), this sector may be prone to rapid retreat (9, 10). Several studies have suggested that the glacier is already in a stage of collapse and the retreat is unstoppable (3, 4, 11). The rate of grounding line retreat is controlled by bed topography, dynamic ice thinning, and ice shelf melt by warm, salty circumpolar deep water (CDW), with ice shelf melt playing a critical role (12). The grounding line retreated at 0.6 to 0.9 km/year between 1996 and 2011 along the glacier sides and the main trunk, respectively (Fig. 1) (4). There has been no adequate interferometric synthetic aperture radar (InSAR) data after 2011 to observe the grounding line retreat (13, 14).
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In the rapidly moving main trunk of Thwaites (Fig. 1 and fig. S1), the grounding line migrates at tidal scales over a zone 2.5 km wide in 2016–2017 versus 0.5 km wide in 1996. A larger migration zone is explained by the flatter bed topography at the 2016–2017 grounding line (16) versus 1996, similar to what is observed on Pine Island Glacier (15). The average retreat rate in 2011–2017 is 3.6 ± 1.2 km/year or 0.6 ± 0.2 km/year, which is 20% less than in 1992–2011 (0.8 km/year). Several areas of local grounding vanished since 2011. Their presence revealed a shallow water column, with the ice shelf scraping over a rough bed (17–19). Their disappearance indicates rapid ice thinning and ungrounding. Within the 2016–2017 grounding zone, we detect ephemeral pinning points, a few kilometers in diameter, where the ice shelf alternatively scrapes over the bed and lifts off the bed (fig. S1). Ephemeral points disappear with time, indicating vigorous formation of new cavities.
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http://advances.sciencemag.org/content/5/1/eaau3433