iSTAR-D: The contribution to sea-level rise from the Amundsen Sea sector of Antarctica

The notions of a warming climate, melting ice and rising sea levels are firmly rooted in the public consciousness. In fact, today, while sea level is rising at some 3 cm per decade, the great ice sheets of Greenland and Antarctica are only contributing a small component, perhaps some 0.5 cm per decade. Nonetheless, it is also established that their contribution to sea level rise is accelerating, by perhaps as much as 0.1 cm per year. In Antarctica, this acceleration is result, in part, of the warming Antarctic Peninsula, but of greater concern, because of the vast quantities of ice backed up in their basins, are the Amundsen sector ice streams; one of which, the Pine Island Glacier, has quadrupled its mass loss in the past decade. What we know about the behavior of these large ice sheets has been established over the past two decades through measurements from successive Earth-orbiting satellites: ERS-1, ERS-2, ENVISAT, GRACE and most recently CryoSat-2. Equally, the satellite estimates remain uncertain; an uncertainty that, as concern increases as to the magnitude of the rising contribution, it is increasingly important to close down. This proposal aims to attack this problem directly for the Amundsen sector ice streams.

The uncertainties arise because the satellites do not directly observe the mass loss of the ice sheets. There are three different instruments and techniques, satellite altimetry, satellite gravimetry, and SAR interferometry, and each of them contains a bete noir. Satellite altimetry measurements cannot distinguish changes in density from changes in mass. Satellite gravimetry cannot distinguish those changes due to mass loss from the ice from those due to the motion of the underlying solid Earth. SAR interferometry is reliant on an uncertain combination of patchy surface measurements and forecast models. These uncertainties can only be unraveled by other, ground observations that, together with the satellite measurements, can provide a complete picture of the mass loss. This proposal aims to provide these 'missing' measurements, of snow accumulation, of density, and solid Earth motion, over the two decades of the satellite measurements, for the Amundsen sector ice streams.

At its heart is a 800 km traverse of the Pine Island glacier basin in the austral summers of 2012/3 and 2013/4. Two tracked vehicles, will progress around the tributaries of the Pine Island Glacier, carrying with them scientists and their equipment. Through a combination of shallow and deeper ice cores, along the traverse, we will obtain a continuous record of the snowfall and its density. We will extrapolate the dated, annual accumulation layers and their density throughout the traverse through an airborne over-flight of a very high resolution, 'snow' radar. In parallel, a separate party, flying out from Union Glacier in West Antarctica, will make annual visits from 2012/3 to rare exposures of the Earth's crust ('nunataks' ) south of the Pine Island Basin. Using automated GPD stations attached to the nunataks, the motion of the solid Earth can be determined.

These observations will be used to, first, evaluate the quality of the models of Antarctic accumulation, density and solid Earth motion that are presently used with the satellite data. With this information, we will be able to determine the errors in the historical (from 1992) and on-going series of altimeter, SAR and gravimeter satellites. Second, the data we collect (and other data of Project Partners and beyond) will be used to update these models. Finally, we will generate the best estimate of the contribution to sea level, and its trend in time, throughout the Amundsen sector basins of the West Antarctic ice sheet. The result will also, when combined with the outcome of the 'sister' program of ISTAR-D, provide the best available prediction into the future of these great glacier basins.

This proposal (ISTAR-D) is aimed at determining the recent past, and present contribution to sea level of the Amundsen sector drainage basins. It will run along side the second activity of this NERC opportunity, ISTAR-C, that will focus on the dynamical behaviour of the sector's ice streams. Together, the two activities will provide the best knowledge, and prediction of this sector's contribution to sea level. We intend to pursue a common impact plan with ISTAR-C, as our contribution to the wider impact plan of the ISTAR program as a whole. The following groups are identified as key stakeholders in iSTAR-C/D science, and will be specifically targeted by our Knowledge Exchange activities:

1. Intergovernmental Panel on Climate Change (IPCC). The IPCC is by far the most authoritative group synthesising scientific knowledge and predictions of sea-level rise. It is therefore essential that l group synthesising and delivering sea-level rise projections to policy-makers, it is essential that iSTAR-C/D science is delivered to IPCC. Science to be included in the IPCC 5th Assessment Report has to be submitted for peer review by July, 2012, iSTAR-C/D science will only be available to subsequent reports. Since IPCC reports relies almost exclusively on peer-reivewed literature, delivery to IPCC must be achieved through such publications. PI ISTAR-C is a Coordinating Lead Author for IPCC 4th and 5th Assessment Report, and can direct ISTAR-C and -D investigators to ensure ISTAR C and D fully contribute to the IPCC.
2. UK Environment Agency. Because of limitations of the IPCC sea-level rise projections, the UK Environment Agency have found the need to develop its own UK specific sea-level rise scenarios. These were developed in conjunction with the Hadley Centre and BAS. A regular dialogue with the key Programme Managers at the Environment Agency (e.g. TE2100) will ensure that the Environment Agency is fully able to use science outcomes.
3. Living With Environmental Change (LWEC). LWEC is a UK government initiative to optimize the coherence and effectiveness of UK environmental research funding and ensure government, business and society have the foresight, knowledge and tools to mitigate, adapt to and capitalise on environmental change. The ISTAR-C PI currently leads an Accredited Activity ("Ice sheets and sea-level rise") within the Living With Environment Change programme (LWEC). Early discussions, indicate that the activities described in iSTAR-C/D are welcome as a substantial addition to this activity. LWEC is proving to be an effective method of delivery to UK government departments and iSTAR-C/D will be well-positioned to contribute, especially to the activities such as LWEC's development of the UK First Flood Research Strategy .
4. Space and Meteorological Operational Agencies & Supply Industry. The CryoSat-2 radar design, that originated with the ISTAR-D PI, has been adopted as standard for future European operational meteorological and oceanographic satellites, and in particular the GMES Sentinel 3 and NOAA/Eumetsat/CNES Jason-CS missions. ISTAR-D will provide the proving ground for the scientific data processing of these data. The ISTAR-D PI is actively involved in the provision, with industry, of ground processing software for these missions.