Understanding causes of changes in Antarctica’s ice shelves using 25 years of continuous satellite radar altimetry

Date & time

1–2pm 14 June 2018

Location

Jaeger 1 Seminar Room, RSES

Speakers

Helen Fricker (UC San Diego)

Event series

Contacts

 Kial Stewart

Antarctic ice loss is accelerating and will soon become the largest contributor to sea-level rise. The Antarctic ice shelves can provide mechanical support to “buttress” the seaward flow of grounded ice, so that ice-shelf thinning and retreat result in enhanced ice discharge to the ocean.  Ice shelves are susceptible to changes in forcing from the atmosphere and the ocean, which both change on a broad range of timescales to modify mass gains and losses at the surface and base. The only viable way to monitor the full extent of the ice shelves while covering the main temporal scales of variability (e.g. interannual-to-decadal) is with satellites. We discuss results from satellite radar altimeter data from four ESA satellites (ERS-1, ERS-2, Envisat, CryoSat-2) to obtain time-series of ice-shelf surface height variations since the early 1990s. We focus on the variability present in the records, providing much more information that can be obtained from linear trends reported in prior studies. The continuous 25-year time series are sufficiently long to resolve patterns of multi-year variability linked to atmospheric and oceanic processes. We show examples of this analysis approach for two regions of Antarctica. The Pacific-sector ice shelves respond strongly to tropical ocean variability, with El Niño events increasing both snowfall and ocean-driven basal melting. The height increase by the added low-density snow exceeds the height decrease by loss of denser basal ice. But mass loss by this basal melting exceeds mass gain from snow, so ice shelves lose mass overall; the opposite occurs during La Niñas. On the Antarctic Peninsula, where several ice shelves have collapsed or significantly retreated in the last three decades, ice shelf heights have increased since 2009, in some cases recovering most of the declines reported previously. We connect this height recovery to reduced summertime melting of the surface, even as the ocean continues to melt the base and remove mass. We expect that the increased thickness of the surface snow layer will reduce the susceptibility of the ice shelf to surface-driven “hydrofracture”, which was linked to earlier collapses of peninsula ice shelves. These examples demonstrate the capability of long and continuous records from satellite altimeters;  allowing us to improve our understanding of the mechanisms involved in ice-shelf changes to the point where we can confidently include this behaviour in models of ice-sheet response to climate changes.

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