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Significant changes have taken place on Denman Glacier and Shackleton Ice Shelf, which hold a 149-cm SLE (basin C-C′). Denman sped up 16% since the 1970s and the ice shelf sped up by 33% in 1957–1996 and 43% in 1957–2016. The glacier is 10% out of balance. Its neighbor Scott decelerated by 16% in 1957–1996 and 22% in 2000–2008 and sped up by 18% in 2016.
We find that the glacier grounding line experiences a complex pattern of migration with several kilometers retreat at its center, in contrast to a small retreat of the neighboring glaciers, e.g. Scott glacier. The floating section of the glacier experiences vigorous ice melt in contact with the ocean, which suggests the presence of Circumpolar Deep Water (CDW). However, there is no historical oceanographic data near the glacier. The marked increase in ice shelf velocity observed in recent decades could result from the grounding line migration associated with enhanced ice shelf melt. Alternatively, it can be symptomatic of a complex interaction between the fast-moving glacier tongue (Shackleton Ice Shelf) and the surrounding slower moving ice shelves; similarly, to the case of Stancomb-Wills Ice Shelf or Thwaites Ice Shelf.
Some time ago the Denman Glacier ice tongue broke off but remained embedded in the Shackleton ice shelf. That tongue fragment has recently calved a large part.
Denman Glacier is one of the largest in East Antarctica, with a catchment that contains an ice volume equivalent to 1.5 m of global sea-level and which sits in the Aurora Subglacial Basin (ASB). Geological evidence of this basin’s sensitivity to past warm periods,combined with recent observations showing that Denman’s ice speed is accelerating, and its grounding line is retreating along a retrograde slope, have raised the prospect that it could contribute to near-future sea-level rise.The recent changes in the Denman system are important because Denman’s grounding line447 currently rests on a retrograde slope which extends 50 km into its basin (Morlighem et al.,448 2019; Brancato et al., 2020), suggesting clear potential for marine ice sheet instability. Given449 the large catchment size, it has potential to make globally significant contributions to mean sea450 level rise in the coming decades (1.49 m; Morlighem et al., 2020). Crucial to assessing the451 magnitude of any future sea level contributions is improving our understanding of regional452 oceanography, and determining whether the observed changes at Denman are the consequence453 of a longer-term ocean warming. This is in addition to monitoring and understanding the454 potential impact of any future changes in the complex Shackleton/Denman ice shelf system.455 In a wider context our results add to the growing body of evidence that some major East456 Antarctic outlet glaciers, with multi-meter sea-level equivalent catchments have responded to457 changes in ocean-climate forcing over the past 100 years and, therefore, will be sensitive to458 projected future warming.
Mt Sandow nunatak (alt 1380m) 450km west of Casey Station; almost enveloped by the Denman Glacier flowing from the East Antarctic Ice Sheet to the Shackleton Ice Shelf 150km away. Discovered by Mawson’s Western Base Party led by Frank Wild in 1912, pic Greg Barras @AusAntarctic
