Defining models of glacial isostatic adjustments in West Antarctica and the Antarctic (UKANET): better constraints on Earth structure and uplift

We aim to decrease the uncertainty associated with the measurement of ice mass change in West Antarctica by addressing our lack of knowledge of Earth structure and accuracy of present-day uplift rates. Ice loss from the West Antarctic Ice Sheet (WAIS) currently accounts for around 10% of present-day global sea-level rise. Moreover, this region is undergoing accelerated ice loss. Accurate projections for the evolution of WAIS are currently hindered by uncertainties in measurements of present-day ice mass change.

Two key methods for deriving this change are satellite gravimetry, which determines changes in Earth's gravity field due to surface mass redistribution, and altimetry, which measures modifications to the height of the ice surface. Crucially, both of these techniques are susceptible to errors introduced by correcting for the uplift response of the solid Earth to past ice mass loss, a process known as Glacial Isostatic Adjustment (GIA).

GIA models require information relating to the regional deglaciation history and the rheological properties of the solid Earth. In most GIA models only 1D global averages of Earth structure are taken in to account; this is a gross oversimplification.

We propose to determine (i) 3D Earth structure in West Antarctica and Antarctic Peninsula through a new passive seismological experiment and (ii) present-day uplift rates through the extension of a NERC-funded GPS network in the Peninsula and new spatially extensive satellite radar interferometry data (InSAR). We will deploy 10 broadband seismometers for 2 years, adjacent to a contemporaneous 2 year POLENET deployment, to estimate 3D variations in Earth rheology by determining S-wave velocity-depth models down to depths of 400 km. Seismic data have never been collected in the southern Antarctic Peninsula region of West Antarctica, and hence very little is known about its Earth structure.

The determination of lithospheric structure will also improve our understanding of the tectonic evolution of the region. We propose a 3 year PDRA to carry out the fieldwork and seismological research. Long time series of surface deformation measurements are important to our understanding of uplift rates due to GIA. A network of 10 GPS sites has been deployed in the southern Antarctic Peninsula since 2009 under a now terminating NERC/AFI grant. At minor additional financial cost, but with significant scientific benefit, we propose to operate this network for a further 2 years.

Our Project Partner Matt King (University of Tasmania) will oversee the processing of these data. The seismic structure results will be incorporated into a 3D GIA model as an addition to CI Whitehouse's Fellowship work; a 1.5 year PDRA will combine the GIA and deformation results to more tightly constrain past and present ice mass change in the southern Antarctic Peninsula and West Antarctica.

While the sparse network of GPS will constrain the deformation pattern on a broad scale, we expect smaller wavelength variability in deformation due to present-day ice mass change. Therefore, we plan to apply satellite radar interferometry (InSAR) to the rock outcrops in West Antarctica to increase the spatial sampling of the deformation field by orders of magnitude. Because distances between rock outcrops can be large, the spatial variability of the tropospheric radar propagation delay during interferometric processing has to be estimated from weather models.

We propose to test these assumptions with a local field deployment of 6 GPS in the Antarctic Peninsula. The timing of this grant proposal is critical as 1) BAS logistics are already in place for the funded 2 year iStar programme in the south of the region; 2) US POLENET seismometers will temporarily be positioned to the south and significantly extend our station coverage; 3) the grant supporting the GPS network is ending.

Impact

The main beneficiaries of knowledge arising from this project are policy makers, such as the Intergovernmental Panel on Climate Change (IPCC) and the UK Environment Agency (EA), charged with policy and planning related to robust projections of future sea level rise. The Living With Environmental Change (LWEC) initiative, established by the UK government, could use the outputs from this research to improve the capacity of government, business and society to mitigate and adapt to environmental change.

We aim to benefit the general public by furthering their understanding of uncertainty in science using GIA models, ice mass balance and sea level rise as our proxies. We hope to extend this theme out to industry and policy makers in government. We will demonstrate how scientific research can be used to address and reduce uncertainty, but also explain why uncertainty is inherent in the science of sea level rise.

How will they benefit from the research?

This research will help to reduce the uncertainty associated with projections of future sea level rise and the subsequent risk associated with sea-defence planning and coastal adaptation.

Our results will evidence and support UK's own sea-level projections, which EA have been developing in conjunction with the Hadley Centre and British Antarctic Survey (BAS) as a response to limitations in the global projections of the IPCC. The IPCC AR5 is currently in draft, and will be published in 2013/14. It will include specific sea-level rise projections to 2100 that will be based almost exclusively on the evidence provided in the peer-reviewed literature. The papers coming out our project will hopefully influence subsequent IPCC drafts.

Grant

NE/L006065/1