The role of atmospheric forcing on the dynamic stability of Greenland's outlet glaciers
Lead Research Organisation:
University of Aberdeen
Department Name: Sch of Geosciences
Abstract
This project will quantify the effect of surface generated melt-water fluctuations on ice motion at the margin of the Greenland Ice Sheet (GrIS). More specifically, it will provide data that will enable ice-sheet modellers to improve their predictions of the future contribution of the GrIS to sea level rise in response to a warming world. To achieve this aim requires a dedicated field campaign to the GrIS to investigate seasonal ice flow dynamics and runoff processes along flow parallel transects extending from the ice sheet margin to the equilibrium line altitude (ELA) at both tidewater and land-terminating glaciers. The greatest store of fresh water in the northern hemisphere - equivalent to 7m of eustatic sea level rise - is held within the Greenland Ice Sheet (GrIS), and yet its present and future contribution to sea level is poorly constrained (IPCC, 2007). Recent observations suggest that mass loss near the margin of the GrIS is accelerating through a combination of increased surface melting (e.g. Steffen et al, 2004) and dynamic thinning (e.g. Rignot and Kanagaratnam, 2006). However, the key processes controlling dynamic thinning have yet to be identified (Alley et al, 2005), and in consequence, are not incorporated in the ice-sheet models which form the basis of the IPCC sea level projections. This in part reflects the fact that the satellite data that has revealed the widespread speed-up of glaciers cannot be acquired at the temporal resolution needed to resolve the causal mechanisms. Our present understanding of GrIS mass balance is especially complicated by uncertainties in the sensitivity of ice-marginal dynamics to changes in melt-water induced lubrication resulting from penetration of supraglacial melt-waters to the glacier bed (Zwally et al, 2002). Recent observations on the GrIS Shepherd et al, in review) reveal, over a five day period in July, a strong and direct coupling between surface hydrology and dynamics where diurnal fluctuations in velocity of >100% occur and where maximum daily velocities scale with temperature. Such observations confirm the need to acquire hydrological and dynamic data at high temporal (sub-hourly) and spatial resolution throughout the year to parameterise the coupling between ice melting and flow. This project will collect data at the necessary resolution to quantify the relationship between melt-water production and ice sheet dynamics thereby enabling ice-sheet modellers to improve predictions of the GrIS's response to climate change. We will conduct ground based experiments along two flow-parallel transects at the western margin of the GrIS in adjacent land and marine terminating drainage basins to address the following objectives: 1. Is there a temporal and spatial pattern to any hydrology-dynamic link associated with the seasonal evolution of the supraglacial drainage system (including supraglacial lakes)? 2. Over what area does surface generated meltwater penetrate to the base of the ice sheet? 3. Is there a relationship between the volume of meltwater input at the glacier surface and the magnitude of the dynamic response? 4. Do tidewater and land-terminating glaciers behave differently during the course of a melt-season? Field campaigns will be undertaken during 2009 and 2010 to determine: 1) The rate, extent and duration of melt. 2) The temporal and spatial variations in water volumes stored in and released from supraglacial lakes and delivered to freely draining moulins. 3) The seasonal, diurnal and hourly variations in ice dynamics. 4) The variations in proglacial discharge and water chemistry (at Russell Glacier). As a result of our work, it will be possible to determine whether ice dynamics at the margin of the GrIS is significantly affected by lubrication of the glacier bed following the drainage of surface derived meltwaters. Our results will be delivered to ice sheet modellers to help them constrain predictions for the future of the GrIS
Organisations
People |
ORCID iD |
Douglas Mair (Principal Investigator) |
Publications
Bartholomew I
(2011)
Seasonal variations in Greenland Ice Sheet motion: Inland extent and behaviour at higher elevations
in Earth and Planetary Science Letters
Bartholomew I
(2012)
Short-term variability in Greenland Ice Sheet motion forced by time-varying meltwater drainage: Implications for the relationship between subglacial drainage system behavior and ice velocity
in Journal of Geophysical Research: Earth Surface
Bartholomew I
(2011)
Supraglacial forcing of subglacial drainage in the ablation zone of the Greenland ice sheet GREENLAND SUBGLACIAL HYDROLOGY
in Geophysical Research Letters
Bartholomew I
(2010)
Seasonal evolution of subglacial drainage and acceleration in a Greenland outlet glacier
in Nature Geoscience
Chandler D
(2013)
Evolution of the subglacial drainage system beneath the Greenland Ice Sheet revealed by tracers
in Nature Geoscience
Chandler D
(2021)
Rapid development and persistence of efficient subglacial drainage under 900 m-thick ice in Greenland
in Earth and Planetary Science Letters
Clason C
(2015)
Modelling the transfer of supraglacial meltwater to the bed of Leverett Glacier, Southwest Greenland
in The Cryosphere
Cowton T
(2012)
Rapid erosion beneath the Greenland ice sheet
in Geology
Cowton T
(2013)
Evolution of drainage system morphology at a land-terminating Greenlandic outlet glacier
in Journal of Geophysical Research: Earth Surface
Mair D
(2012)
Glaciology Research update I
in Progress in Physical Geography: Earth and Environment
Shannon SR
(2013)
Enhanced basal lubrication and the contribution of the Greenland ice sheet to future sea-level rise.
in Proceedings of the National Academy of Sciences of the United States of America
Sole A
(2011)
Seasonal speedup of a Greenland marine-terminating outlet glacier forced by surface melt-induced changes in subglacial hydrology
in Journal of Geophysical Research
Sole A
(2013)
Winter motion mediates dynamic response of the Greenland Ice Sheet to warmer summers
in Geophysical Research Letters
Tedstone AJ
(2013)
Greenland ice sheet motion insensitive to exceptional meltwater forcing.
in Proceedings of the National Academy of Sciences of the United States of America
Description | Multi-annual record of seasonal variations in ice dynamics, air temperature and melt were measured from a land-terminating margin of the Greenland Ice Sheet (Leverett/Rusell Glacier catchment) to high elevation regions of accumulation area over a 150 km transect. Simultaneous measurements of pro-glacial river discharge and water quality throughout three summer melt seasons were used to infer seasonal evolution in the sub-glacial drainage system of the ice sheet. Seasonal and spatial variations in ice sheet dynamics explained with recourse to evidence of subglacial hydrological drainage evolution driven by varying atmospheric conditions. The seasonal growth and drainage of supraglacial lakes is critical in driving short-term variations in ice velocity in high elevation regions of the ice sheet. Insights into the key hydro-dynamic coupling processes were gained from analyses of the data and through comparison with model output over a range of timescales from diurnal to inter-annual. Warmer summers were associated with faster summer ice velocities, but lower autumn/fall velocities. Annual velocities were therefore not significantly higher during warmer summers. Warm summers caused increase melt magnitude and extent and higher summer surface velocities. However, we infer that greater melt also created a more efficient, low-water pressure subglacial drainage system which delayed the re-establishment of the "winter" high pressure drainage system. The prolonging of the low-pressure system suppressed autumn velocities by an amount sufficient to negate the enhanced summer velocity increase. The dynamics and hydrology of a large marine terminating tidewater glacier (Kangiata Nunata Sermia, KNS) were investigated between 30-80 km from its calving margin. We show that seasonal variations in the dynmics of the interior regions of tidewater glaciers are more strongly influenced by atmospherically driven surface melting and the development and drainage of supra-glacial lakes, than by variations in icebeg calving rates at the marine terminus. |
Exploitation Route | Our findings will be of particular interest to glaciological modellers seeking to project how ice sheets and glaciers will react to the generation of increased volumes of glacial meltwater which may be expected as a consequence of climate warming. |
Sectors | Environment |
Description | Our findings have been used by the ice sheet modelling community to parameterise the effects of potential future increases in the inputs of surface meltwater to the bed of glaciers and ice sheets on glacier flow velocities and hence to better understand how significant this effect may be on the mass balance of ice masses. Changes in the mass loss of the Earth's glaciers and ice sheets is a major contributor to changes in global sea levels and is therefore an important aspect of efforts to account for and identify the sources of ongoing and future sea level change. |
First Year Of Impact | 2013 |
Sector | Environment |
Impact Types | Societal,Policy & public services |
Description | Calving Glaciers: Longterm Validation and Evidence |
Amount | £238,775 (GBP) |
Organisation | The Leverhulme Trust |
Sector | Charity/Non Profit |
Country | United Kingdom |
Start | 02/2015 |
End | 01/2018 |