Abstract
Abstract. The floating ice shelves and glacier tongues which fringe the Antarctic continent are important because they help buttress ice flow from the ice sheet interior. Dynamic feedbacks associated with glacier calving have the potential to reduce buttressing and subsequently increase ice flow into the ocean. However, there are few high temporal resolution studies on glacier calving, especially in East Antarctica. Here we use ENVISAT ASAR wide swath mode imagery to investigate monthly glacier terminus change across six marine-terminating outlet glaciers in Porpoise Bay (76° S, 128° E), Wilkes Land (East Antarctica), between November 2002 and March 2012. This reveals a large near-simultaneous calving event in January 2007, resulting in a total of ∼ 2900 km2 of ice being removed from glacier tongues. We also observe the start of a similar large near-simultaneous calving event in March 2016. Our observations suggest that both of these large calving events are driven by the break-up of the multi-year sea ice which usually occupies Porpoise Bay. However, these break-up events appear to have been driven by contrasting mechanisms. We link the 2007 sea ice break-up to atmospheric circulation anomalies in December 2005 weakening the multi-year sea ice through a combination of surface melt and a change in wind direction prior to its eventual break-up in January 2007. In contrast, the 2016 break-up event is linked to the terminus of Holmes (West) Glacier pushing the multi-year sea ice further into the open ocean, making the sea ice more vulnerable to break-up. In the context of predicted future warming and the sensitivity of sea ice to changes in climate, our results highlight the importance of interactions between landfast sea ice and glacier tongue stability in East Antarctica.
Highlights
Iceberg calving is an important process that accounts for around 50 % of total mass loss to the ocean in Antarctica (Depoorter et al, 2013; Rignot et al, 2013)
First pattern is shown by Holmes (West) Glacier, which advances a total of ∼ 13 km throughout the observation period, with no evidence of any major iceberg calving that resulted in substantial retreat of the terminus beyond the measurement error (±500 m)
Between January and April 2007, Frost Glacier, Glacier 1, Glacier 2, and Holmes (East) Glaciers all underwent a large near-simultaneous calving event. This led to 1300 km2 of ice being removed from glaciers in Porpoise Bay, we note the disintegration of a major tongue from an unnamed glacier further west, which contributed a further 1600 km2
Summary
Iceberg calving is an important process that accounts for around 50 % of total mass loss to the ocean in Antarctica (Depoorter et al, 2013; Rignot et al, 2013). Dynamic feedbacks associated with retreat and/or thinning of buttressing ice shelves or floating glacier tongues can result in an increased discharge of ice into the ocean (Rott et al, 2002; Rignot et al, 2004; Wuite et al, 2015; Fürst et al, 2016). In Antarctica, major calving events can be broadly classified into two categories: the discrete detachment of large tabular icebergs (e.g. Mertz Glacier tongue: Massom et al, 2015) or the spatially extensive disintegration of floating glacier tongues or ice shelves into numerous smaller icebergs (e.g. Larsen A and B ice shelves; Rott et al, 1996; Scambos et al, 2009). Despite some well-documented ice-shelf collapses (Scambos et al, 2003; Banwell et al, 2013) and major individual calving events
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