The role of atmospheric forcing on the dynamic stability of Greenland's outlet glaciers

Lead Research Organisation: University of Edinburgh
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 2008 and 2009 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

Publications

10 25 50

 
Title Science advisor for the documentary film 'Aquarela' 
Description A film by Aconite Productions and iconic Russian director Victor Kossakovsky about the power, beauty and potentially destructive nature of water in all its forms - with the inevitable links to climate change and environmental warnings. I acted as a scientific (and location) advisor for the glacier and iceberg content of the documentary filmed in Greenland, I am in the credits as a Science Advisor and was invited to the film premier (attending the UK premiere in Glasgow). 
Type Of Art Film/Video/Animation 
Year Produced 2018 
Impact The film premiered at the Venice International film festival. In the UK, it premiered at the Glasgow film festival in Feb 2019. 
URL https://www.scottishfield.co.uk/culture/whatson/enjoy-the-wonders-of-nature-in-the-winter/
 
Description Main Achievements and Outcomes
Between May 2009 and May 2011, we obtained ice motion and surface melt data from GPS sensors located along two ~100 km transects at the western margin of the Greenland Ice Sheet on both land-terminating (Leverett) and tidewater (Kangiata Nunata Sermia - KNS) glacier margins. We also collected data of the hydrological characteristics of the proglacial runoff draining from the land-terminating margin (discharge, e.c. and turbidity). Our research has shown that across a large land-terminating drainage catchment within the Greenland Ice Sheet (GrIS), there is a seasonal upglacier expansion and increase in hydraulic efficiency of the subglacial drainage system, across a catchment >600 km2, to distances >50 km from the ice-sheet margin. This expansion occurs episodically in response to the drainage of surface meltwaters into a hitherto inefficient subglacial drainage system as new input locations become active progressively further upglacier (Objective 2); this system is similar to that observed at Alpine glaciers. These observations provide the first synopsis of seasonal hydrological behaviour in the ablation zone of the GrIS (Bartholomew et al, 2011, GRL). The observations of efficient meltwater routing at the glacier are also

The effect of this meltwater penetration to the ice sheet bed is to perturb the subglacial hydrology at the ice-bed interface causing the ice sheet to flow faster in summer. Our sensors reveal substantial increases in summer motion, of up to 250%, compared with winter background. These motion variations display an upglacier evolution over the course of the summer, with initial velocity enhancement occurring earliest at sites close to the ice margin (Objective 1). The pattern of ice motion and hydrological characteristics of the proglacial runoff in the land-terminating margin confirms that the seasonal evolution in the subglacial drainage system controls basal sliding through hydraulic-ice dynamic forcing mechanisms comparable to those observed at smaller valley glaciers (Bartholomew at al, 2010, Nature Geoscience). Our findings show that the relationship between melt and ice motion varies both at-a-site and between sites during the melt season. At our land terminating transect, we find a strong positive correlation between rates of annual ablation and changes in summer ice motion (Objective 3), with sites nearest the ice sheet margin experiencing greater summer acceleration in ice motion (15-18%) than those above 1000 m elevation (3-8%) (Bartholomew et al, 2011, EPSL). At our tidewater glacier transect, we find that >35 km from the ice-margin, seasonal and shorter-time scale ice flow variations are controlled by surface melt-induced changes in subglacial hydrology but the net effect of the summer speed variations on annual motion is small (~1%) (Sole et al, 2011, JGR) (Objective 4).

The observations of efficient meltwater routing at the glacier bed have profound implications for ice-sheet erosion. Through the collection of sediment flux data (proglacial discharge and suspended sediment concentration) at our land-terminating catchment, we estimate erosion under the catchment occurs at ~4.8 ± 2.6 mm a-1 which is 1 - 2 orders of magnitude greater than previous estimates of erosion rate beneath the Greenland Ice Sheet. Our results suggest that where surface meltwaters are able to access the bed, the rate of erosion by ice sheets is in keeping with the rapid erosion observed at temperate alpine glaciers (Cowton et al, 2012, Geology).

Significance
Our findings are significant because they provide a conceptual framework to understand the impact of hydrologically-forced velocity variations on the future mass balance of the Greenland Ice Sheet. In particular, the data generated which shows the relationship between the volume of meltwater input at the glacier surface and the magnitude of the dynamic response has now been provided to the ice sheet modelling community, through the EU funded Ice2Sea consortium. The data is being used to improve parameterisations of a sliding law which is being incorporated into a suite of models which will be incorporated into the IPCC 5th report for estimating the contribution from Greenland to sea level rise in a warming world.

All of our original objectives have been achieved (and are referred to above at the most relevant point) and the key findings have been incorporated in the already published peer review journal articles also referred to above (their full details are provided in the JeS "publications summary").

One of our publications (Tedstone et al, PNAS 2013) showed that despite record summer melting over the Greenland Ice Sheet in 2012, the subsequent reduced winter ice motion
resulted in 6% less net annual ice motion in 2012 than in 2009 (an 'average' melt year). Our findings suggest that surface melt-induced acceleration of land-terminating regions of the ice sheet will remain insignificant even under extreme melting scenarios.
Exploitation Route This work was taken forward and applied to remotely sensed satellite data. A paper, published in Nature by Tedstone et al in 2015 revealed that despite warming, landsat data revealed decadal slowdowns across the Greenland Ice Sheet. Tedstone's (PhD student) paper in Nature reveals that parts of the Greenland Ice Sheet are less vulnerable to climate warming than previously thought. A contentious issue, and one with implications for ice sheet stability and sea level rise, has been whether or not an increase in meltwater, in response to climate warming, will accelerate the movement of ice sheets, driving more ice toward the continental margin where it can melt or calve into the ocean. Until now, the link between melt and ice motion has remained equivocal in large part due to the short length of the ice velocity time-series. Using three decades of Landsat imagery for a 170-km land-terminating stretch of the western Greenland Ice Sheet margin, Andrew and colleagues found that more meltwater does not equate to faster ice sheet motion. Rather, despite a 50% increase in surface melting, ice motion decreased in their 8000km2 study region by about 12%.

The study, published in Nature, was carried out in collaboration with the Université Savoie Mont-Blanc in France and the University of Sheffield. Essential to the success of the work was the team in Edinburgh GeoSciences which brought together expertise in remote sensing (Noel Gourmelen who developed the novel technique to exploit the Landsat archive on a previous project) and ice-sheet modelling (Dan Goldberg) to support the previous field based work of Pete Nienow and Andrew Tedstone. The team still have a lot more to do to understand the movement of the sections of the ice sheet which terminate in the ocean, and which have seen acceleration in recent decades.

A NASA news report with more details can be found here: http://landsat.gsfc.nasa.gov/?p=11129
Sectors Aerospace, Defence and Marine,Education,Environment

 
Description The data generated which shows the relationship between the volume of meltwater input at the glacier surface and the magnitude of the dynamic response has now been used by the ice sheet modelling community, through the EU funded Ice2Sea consortium. The data has been used to improve parameterisations of a sliding law which has been incorporated into a suite of models with relevance to the IPCC for estimating the contribution from Greenland to sea level rise in a warming world (Shannon et al, 2013). Several activities have been undertaken to promote our work and findings to the public which include: 1) Exhibition on our Greenland research at "Our Dynamic Earth", Edinburgh's five-star visitor attraction. Our research team initiated, set-up and hosted an exhibition entitled "On Thin Ice" at 'Our Dynamic Earth' in Edinburgh. The exhibition was held over four days in October (17-20 Oct 2011) to coincide with the Scottish schools half term. We had an exclusive exhibition space where we presented our work investigating the stability of the Greenland Ice Sheet. The exhibition was aimed at children but had something for all ages and included videos, photos, posters (full academic and 'child friendly'), jigsaws, hands on exhibits (e.g. equipment and clothing) and discussants. The exhibition was fronted by NERC PDRAs (Sole and de la Pena) and PhD students (Bartholomew and Cowton). The exhibition had ~800-1000 visitors over the four days. More information available at: http://www.deadlinenews.co.uk/2011/10/14/picture-special-stunning-greenland-images-launch-science-exhibition/ http://www.ed.ac.uk/schools-departments/geosciences/news/news?StoryID=704&cw_xml=newsFullStory.html 2) Panel discussant after showing of the film 'Burning Ice' at the Edinburgh International Film Festival. The film 'Burning Ice' follows a group of artists and scientists who visit Greenland to witness the physical threat of climate change and develop a cultural response. This film was shown at the Edinburgh International Film Festival at the Edinburgh Filmhouse on 21/6/11. Following the film, attended by ~100 members of the public, there was a 30 min question and answer session with 3 expert panelist 'discussants' of whom grant PI Dr Peter Nienow was one. The other panellists were Rob Edwards (Environment Editor for the Sunday Herald) and Malcolm Fleming (Media & Public Relations Manager for Oxfam in Scotland). 3) We have presented our work at a number of public meetings including: i) Nienow gave a lecture to the Scottish Hydrological Society at the Royal Society of Edinburgh in 2011: "Investigating the hydrology of the Greenland Ice Sheet" ii) Bartholomew presented a lecture to the Cowper Society in Berkhamsted, Herts in Feb 2011: "Investigating the hydrology and dynamics of the Greenland Ice Sheet". iii) Nienow was involved in an Exhibit at the Science museum concerning the stability of the Greenland Ice Sheet and is quoted (with attached photo) in the exhibition and on the Science museum web site: http://antenna.sciencemuseum.org.uk/science-now/new-climate-science-tz/points-of-view/ iv) The findings from our work published in Nature Geosciences in May 2010, resulted in an Edinburgh University press release which was picked up by Reuters and other media outlets. In addition, the research featured in the University of Edinburgh's Annual Report as an example of the topical, important and cutting edge research being carried out by the University. In Sept 2016, PWN was asked by Professor Louise Heathwaite, the Chief Scientific Adviser Rural Affairs and Environment for The Scottish Government to provide her with some text and slides that highlight what the critical science challenges are for the Arctic from the perspective of the cryosphere, and how our scientific research and broader science in Scotland is contributing to helping solve them. This material was then used by Professor Heathwaite to prepare a science briefing note for the Scottish First Minister, Nicola Sturgeon, for the FM to use in a keynote speech to the 'Arctic Circle Forum' in Reykjavik, Iceland on October 6th 2016, in which she signalled the critical role of scientific evidence in supporting decision-making in relation to policies associated with climate change.
First Year Of Impact 2016
Sector Education,Environment,Government, Democracy and Justice
Impact Types Cultural,Societal,Policy & public services

 
Description Feedback to the Chief Scientific Adviser Rural Affairs and Environment for The Scottish Government
Geographic Reach Multiple continents/international 
Policy Influence Type Gave evidence to a government review
 
Title Greenland ice motion data 
Description The database includes ice velocity data collected as part of this NERC grant and is stored at the Polar Data Centre as Tedstone, A. & Nienow, P. "Ice motion measurements, south-west Greenland Ice Sheet" v2 (2018) Polar Data Centre, Natural Environment Research Council, UK. doi:10.5285/1f69fba3-4c62-47ad-8119-08cfeec05e46 
Type Of Material Database/Collection of data 
Year Produced 2017 
Provided To Others? Yes  
Impact The data is being used by other researchers including citation in: Koziol et al, The Cryosphere, 11, 2783-2797, 2017. Incorporating modelled subglacial hydrology into inversions for basal drag. 
URL http://doi.org/ch3p
 
Title Ice motion measurements, south-west Greenland Ice Sheet 
Description From May 2009 to May 2013, seven dual-frequency GPS receivers were deployed along a 120 km-long transect in the south-west of the Greenland Ice Sheet. Two additional dual-frequency GPS receivers were deployed perpendicular to longitudinal ice flow at ~14 km inland: one 5 km distant from June 2011 to May 2013, and another 2.5 km distance from May 2012 to May 2013. Each receiver recorded position observations every 10 seconds or 30 seconds (depending on configuration), enabling resolution of horizontal and vertical ice motion. Sites were powered by solar panels and operated 24 hours a day during summer but shut down in the autumn. Absolute ice displacements at each site were obtained for each summer and winter period in the absence of continuous measurements. Position measurements were kinematically corrected relative to an off-ice base station using TRACK (Chen, 1999). Daily velocities were then obtained by differencing across 24-hour periods, whilst continuous velocities were obtained through application of a sliding 6-hour differencing window. At each GPS site we also measured (1) the near-surface air temperature every 15 minutes year-round, (2) net seasonal ablation using ablation stakes, and (3) at several selected sites melt rates using sonic ranging sensors. This version 1 of the dataset has been succeeded by a new version with ice motion records at 1-day resolution rather than 2-day resolution. In other respects the dataset has not changed. 
Type Of Material Database/Collection of data 
Year Produced 2017 
Provided To Others? Yes  
 
Title Ice motion measurements, south-west Greenland Ice Sheet (version 2) 
Description From May 2009 to May 2013, seven dual-frequency GPS receivers were deployed along a 120 km-long transect in the south-west of the Greenland Ice Sheet. Two additional dual-frequency GPS receivers were deployed perpendicular to longitudinal ice flow at ~14 km inland: one 5 km distant from June 2011 to May 2013, and another 2.5 km distance from May 2012 to May 2013. Each receiver recorded position observations every 10 seconds or 30 seconds (depending on configuration), enabling resolution of horizontal and vertical ice motion. Sites were powered by solar panels and operated 24 hours a day during summer but shut down in the autumn. Absolute ice displacements at each site were obtained for each summer and winter period in the absence of continuous measurements. Position measurements were kinematically corrected relative to an off-ice base station using TRACK (Chen, 1999). Daily velocities were then obtained by differencing across 24-hour periods, whilst continuous velocities were obtained through application of a sliding 6-hour differencing window. At each GPS site we also measured (1) the near-surface air temperature every 15 minutes year-round, (2) net seasonal ablation using ablation stakes, and (3) at several selected sites melt rates using sonic ranging sensors. This version 2 of the dataset updates the previously 2-day temporal resolution of the ice motion records to 1-day resolution. In other respects the dataset has not changed. 
Type Of Material Database/Collection of data 
Year Produced 2018 
Provided To Others? Yes  
 
Title Proglacial discharge measurements, Leverett Glacier, south-west Greenland (2009-2012) 
Description Measurements of water discharge, suspended sediment concentration and electrical conductivity during the melt seasons of 2009, 2010, 2011 and 2012 in the proglacial river draining from the tongue of Leverett Glacier, a land-terminating glacier in the south-west of the Greenland Ice Sheet. The measurements were made in a stable bedrock section approximately 2 km downstream from the glacier terminus. Data loggers recorded measurements every 15 minutes from approximately May to August each year. Water depth (stage) was converted to discharge (Q) using season-specific ratings curves derived from repeat dye-dilution injections undertaken across the stage values. Suspended sediment concentration (SSC) was obtained by calibrating turbidity sensor readings with sediment samples taken in-situ and then filtered, dried and weighed. Electrical conductivity (EC) was recorded using a water conductivity probe; the data were filtered for bad values and corrected for temperature, but no smoothing was applied. These version 2 files are presented as CSV lists, with some summary metadata included as comments at the start of each file; they essentially contain the same data as the previous version files. 
Type Of Material Database/Collection of data 
Year Produced 2017 
Provided To Others? Yes  
 
Description Boat of Garten 'Boat talks' - 'The stability of the Greenland Ice Sheet' 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach Regional
Primary Audience Public/other audiences
Results and Impact I was invited to give a talk to the series of talks at Boat of Garten entitled 'Boat talks' - 'The stability of the Greenland Ice Sheet'
Year(s) Of Engagement Activity 2018
URL https://www.eventbrite.co.uk/e/boat-talks-the-stability-of-the-greenland-ice-sheet-with-professor-pe...
 
Description Exhibitions at our Dynamic Earth, Edinburgh 
Form Of Engagement Activity Participation in an activity, workshop or similar
Part Of Official Scheme? No
Geographic Reach Regional
Primary Audience Schools
Results and Impact We undertook two outreach events to showcase our research to the public at the geosciences museum Our Dynamic Earth in Edinburgh. The first of these (March 15th, 2016) was attended by a number of secondary school groups, while the second (October 16-17th 2016) was aimed at families. We presented images and videos to showcase our research, and discussed the underlying science and policy questions with visitors to the exhibition.
Year(s) Of Engagement Activity 2016
 
Description Midlothian Science Festival talk at IKEA - 'The Greenland Ice Sheet in a warming world'. 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach Local
Primary Audience Public/other audiences
Results and Impact About 30 members of the public attended my talk, 'The Greenland Ice Sheet in a warming world' at IKEA as part of the Midlothian Science Festival.
Year(s) Of Engagement Activity 2018
URL https://midlothiansciencefestival.com/event/climate-change-greenlands-ice-sheet/
 
Description Research seminar 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach National
Primary Audience Postgraduate students
Results and Impact Seminar to Bristol University School of Geography on Greenland research and tidewater glaciers
Year(s) Of Engagement Activity 2020
 
Description Royal Society of Edinburgh - 'Winter Wonders' public event - talk and discussion. 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach Local
Primary Audience Public/other audiences
Results and Impact Royal Society of Edinburgh - 'Winter Wonders' public event - talk and discussion. Invited talk with Prof David Sugden whom spoke about Antartica, I spoke about the Greenland Ice Sheet and we discussed and answered questions from the floor.
Year(s) Of Engagement Activity 2018
URL https://www.scottishfield.co.uk/culture/whatson/enjoy-the-wonders-of-nature-in-the-winter/
 
Description Science advisor to "Aquarela", a cinematic climate science documentary 
Form Of Engagement Activity A broadcast e.g. TV/radio/film/podcast (other than news/press)
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Public/other audiences
Results and Impact I contributed expert glacial knowledge to the film/documentary 'Aquarela' on water, ice and climate change - I am acknowledged in the credits and attended the UK premier as a guest
Year(s) Of Engagement Activity 2019
URL https://www.theguardian.com/film/2019/dec/11/aquarela-review-victor-kossakovsky-climate-crisis-docum...
 
Description Talk at Art Festival 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach National
Primary Audience Public/other audiences
Results and Impact Talk and panellist at Sonica-Cryptic Art Festival, Glasgow Centre for Contemporary Art (CCA) - 'Are we at the Tipping Point?'. Talk focussed on whether the Greenland Ice Sheet is at a tipping point regarding ice mass loss in response to climate change. The talk and panel was linked to an art installation at the Sonica-Cryptic Art Festival by artist Kathy Hinde that was addressing ice mass loss and climate change issues. The Art Festival wanted a scientist to discuss the issues regarding ice mass loss and climate change.
Year(s) Of Engagement Activity 2017
URL http://sonic-a.co.uk/talks-tours-workshops/
 
Description Talk at Kingussie High School - 'Climate change, ice-sheets and satellites' 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach Local
Primary Audience Schools
Results and Impact Invited talk at Kingussie High School to their S4 and S5 Geography Higher class - 'Climate change, ice-sheets and satellites'
Year(s) Of Engagement Activity 2019
 
Description Talk at a science festival 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach Regional
Primary Audience Public/other audiences
Results and Impact Evening talk at IKEA, Edinburgh as part of the Midlothian Science Festival entitled 'Science in Extreme Conditions'. Talk focussed on investigations of Greenland Ice Sheet stability, especially with respect to the importance of collecting hard won field based data sets to support the science.
Year(s) Of Engagement Activity 2017
 
Description Talk to the Probus Club of Lomond, Drymen - 'The stability of the Greenland Ice Sheet' 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach Regional
Primary Audience Public/other audiences
Results and Impact Invited to give a talk to the Probus Club of Lomond in Drymen, Scotland - talk title 'The stability of the Greenland Ice Sheet'
Year(s) Of Engagement Activity 2018