Investigating controls on flow variability in Greenland's tidewater glaciers: the impact of runoff on fjord circulation and termini melt rates

The greatest store of fresh water in the northern hemisphere - equivalent to ~7m of sea level rise - is held within the Greenland Ice Sheet (GrIS). In the last decade, it has become clear that the ice sheet is losing mass and has become a significant contributor to global sea-level rise. The rate of mass loss has accelerated in the last decade and the ice sheet is now contributing about 1 mm/yr to sea level rise. This behaviour is a result of: 1) dramatic increases in the speed of many large outlet ('tidewater') glaciers, thereby increasing ice flux to the sea; and 2) substantial increases in both melt rates and the area of the ice sheet experiencing summer melting thereby increasing runoff from the ice-sheet surface to the ocean. These increases in ice motion and surface melt rate have been linked with warmer air and ocean temperatures over and around Greenland. A major concern for policymakers, society and scientists is how the GrIS will continue to react to the temperature rises that are predicted during the coming centuries. However, to better understand ice sheet sensitivity to projected global warming, the processes which affect how ocean terminating glaciers flow and discharge into the sea must be better understood.

This project will improve our understanding of why tidewater glaciers are losing mass at an accelerating rate. Recent observations suggest warmer ocean temperatures have resulted in tidewater glacier acceleration through a process known as 'dynamic thinning'; here warm ocean waters access the front of tidewater glaciers causing them to thin by enhanced melting and to retreat through increased rates of iceberg calving. However, while ocean waters off the coast of Greenland have warmed in the last decade, it is unclear how these warm waters actually access the front of glaciers which are often located at the head of long narrow fjords tens of kilometres from the warm ocean shelf waters. An increasingly popular theory contends that summer meltwater runoff from the glaciers establishes fjord circulation whereby strong ouflow of meltwater down the fjord sets up an opposing flow drawing in the warm water from the coastal shelf. As the runoff increases, the fjord circulation strength and thus volume of warm offshore water drawn into the fjord also increases. This theory is supported by some observations of water flow and temperature in fjords but the sensitivity of the process has not been tested.

This proposal aims to address this limitation by investigating how variations in glacial runoff perturb fjord circulation and thus the submarine melt rate and dynamic behaviour of tidewater glaciers. More specifically, the project will use a previously tested model (the Bergen Ocean Model (BOM)) to determine how variations in fjord geometry and meltwater runoff affect the seasonal delivery of 'warm' shelf waters to the marine termini of tidewater glaciers. The project will achieve this by:

1) Running a suite of fjord modeling experiments using a range of synthetic model parameters and boundary conditions (e.g. fjord geometry (length, width, depth); runoff volume; coastal ocean temperature) which will be varied systematically to establish the sensitivity of along-fjord heat transportation (and thus tidewater terminus melt-rates) to the different parameters.

2) Investigating the extent to which decadal (2000-2009) changes in glacier runoff and offshore ocean temperatures can explain observed changes in glacier margin position at ten tidewater glaciers along Greenland's east coast

3) Investigating how projected ocean and atmospheric warming by 2100 will affect the along-fjord heat transportation and thus terminus melt-rates at our ten 'test-case' glaciers.

Through the delivery of these objectives, the project will make a fundamental contribution to our understanding of how the GrIS will likely respond dynamically to future climate change and specifically, changes in atmospheric and ocean temperatures.

1. Potential users

a) Environmental agencies with statutory duties to monitor and plan for flooding risk (e.g. Environment Agency, Scottish Environmental Protection Agency (SEPA)). The outcomes from the proposed research (advancing our understanding of future Greenland Ice Sheet (GrIS) ice loss and sea level contributions) could be used to predict UK coastal flooding.

b) Environmental Protection (UK) to ensure that their lobbying role is well informed in terms of current activities and research outcomes in the area of climate change and sea level rise. Information sources for government, politicians and policy-makers (e.g. SPICE - Scottish parliamentary information resource to provide briefing notes to MSPs).

c) The Scottish Government's Coordinated Agenda for Marine, Environment and Rural Affairs Science (CAMERAS).

d) Scotland and Northern Ireland Forum For Environmental Research (SNIFFER) and the Scottish Climate Change Impacts Partnership (SCCIP) which aims to increase the resilience of organisations and infrastructure in Scotland to meet the challenges and opportunities presented by the impacts of climate change.

e) General public: sea level rise will affect everyone. Nienow has given numerous public talks and interviews with the media on ice sheet stability and sea level rise including presenting at the British Science Festival in Aberdeen in 2012.

f) Learned societies who are involved in reviewing the state of the scientific evidence base and providing advice to policy-makers, including The Royal Society, the Royal Society of Edinburgh, the Royal Geographical Society (with Institute of British Geographers), the Royal Scottish Geographical Society and the Scottish Hydrological Society (who Nienow has already given an invited talk to on Greenland Ice Sheet hydrology and dynamics).

2. Specific/existing links
a) The proposed meeting between with the Scottish Government's environmental policy makers and their science advisors will build on the relationship between Alliance for Geoscience, Environment and Society (SAGES) and the Scottish Government.

b) The Dynamic Earth Exhibition follows a successful exhibition organized by Sole and Cowton in 2011, and will build on the existing good working relationship between Dynamic Earth and the School of Geosciences at the University of Edinburgh (see LoS from Dynamic Earth).

c) The proposed Climate Change Workshop at the RGS will build on an existing relationship since Sole ran a similar workshop for secondary school children at the RGS as part of Science Week in 2007 focusing on the role of the cryosphere in the climate system.

3. Economic impacts
a) Furthering our understanding of future GrIS ice loss will reduce uncertainties associated with predictions of sea level rise allowing more effective planning and protection against coastal flooding in low-lying areas such as South East Asia, small islands in the Pacific, and coastal cities, such as Mumbai and London.

b) Improving our understanding of how the GrIS will respond to climate change will enable more robust predictions of potential changes to the North Atlantic thermo-haline circulation which ultimately provides the UK with warmer temperatures than other regions at comparable latitudes. This will inform planning for significant shifts in the UK's climate.

4. Public policy or legislatory impacts
a) Evidence-based policy making: The proposed meeting between with the Scottish Government's environmental policy makers and their science advisors will provide a forum for the research findings to be presented directly to policy makers.

5. Quality of life and public good impacts
a) Increasing public engagement with research and related societal issues. The Dynamic Earth exhibition and Cafe Scientifique session will present the research findings in an engaging and understandable manner. It is hoped that this will help to engage the general public and lead to changes in their daily routines.