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

Event type: 
Seminar
Date: 
12 June 2018
Time: 
2.00 - 3.00 pm
Location: 

Climate Change Research Centre, Seminar Room, Mathews Building 4th floor, UNSW, Sydney

Presenter: 
Helen Fricker
Scripps Institution of Oceanography, UC San Diego, USA
Host: 
Climate Change Research Centre, UNSW

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. Results from satellite radar altimeter data will be discussed 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. They 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. They 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. They connect this height recovery to reduced summertime melting of the surface, even as the ocean continues to melt the base and remove mass. They 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 to improve the understanding of the mechanisms involved in ice-shelf changes to the point where researchers can confidently include this behaviour in models of ice-sheet response to climate changes.

 

Brief Biography: Helen Fricker is a Professor of Geophysics in the Cecil H. and Ida M. Green Institute of Geophysics and Planetary Physics at Scripps Institution of Oceanography at UC San Diego. Her research focuses on ice sheets in Antarctica and Greenland and their role in the climate system. She uses a combination of satellite radar and laser altimetry and other remote-sensing data to understand ice sheet processes. Professor Fricker is widely recognized for her discovery of active sub-glacial lakes, and she has shown that these lakes form dynamic hydrologic systems, where one lake can drain into another in a short period of time. She is also known for her innovative research into Antarctic ice shelf mass budget processes such as iceberg calving and basal melting and freezing.