Melting, hydrology and ice flow at high elevations of the Greenland Ice Sheet

** FlowState: Swiss National Science Foundation Starting Grant at the University of Lausanne, 2024-2029 **

The shrinkage of the Greenland Ice Sheet is a major source of global sea level rise, affecting millions of inhabitants of coastal areas and exerting major impacts on biogeochemical cycling in Arctic waters. However, 21st century ice sheet mass losses under climate change are uncertain. A critical gap in our understanding is the ice-dynamic behaviour at higher elevations of the ice sheet. If ice flow in these areas speeds up then ice will be fluxed to lower, warmer elevations more rapidly, where it will melt and run off to the ocean more quickly. In recent years substantial surface melting has been observed at higher elevations. This raises the question: is the dynamic stability of higher elevations sensitive to surface meltwater?

In ‘FlowState’, the overarching objective is to quantify the impact of high-elevation surface melting upon the ice sheet’s dynamic stability through the 21st century and beyond. We will measure and then model coupled basal hydrology and ice flow in areas where surface meltwater drains through kilometres-plus thick ice.

The runoff limits of the Greenland Ice Sheet

The aim of this project is to track the changing runoff limits of the GrIS, to understand how changing surface conditions impact upon ice sheet runoff and the global sea level budget. I have led the mapping the runoff limits throughout the satellite era and have undertaken field campaigns to enhance our understanding of the hydrology of icy firn. I advise Nicolas Jullien on his PhD thesis investigating sub-surface ice presence by airborne radar, and I co-supervise Nicole Clerx on her PhD thesis measuring and modelling meltwater transport around the runoff limit. This work is part of the ERC-funded ‘Cassandra’ project awarded to Prof. Horst Machguth.

Darkening of bare ice surfaces of the GrIS

The UK NERC-funded project ‘BLACK and BLOOM’ aimed to unravel the variations in the albedo of the Greenland Ice Sheet as a result of interactions between microbes and particulates. The darker the ice sheet surface is the more it melts, so microbes and particulates could increase the rate at which sea level rise occurs.

As the lead researcher on the upscaling Work Package, I used two main approaches to examine how microbes and particulates control melting:

• In-situ and satellite observations to characterize the reflectivity (albedo) of the ice sheet surface.
• Regional climate modelling to project the potential impact of algal growth and black carbon upon melting of the ice sheet in the future, by including their impact upon albedo in the model scheme.

The project brought together a range of experts in micro-biology, atmospheric chemistry, ice sheet mass balance and remote sensing. We undertook three deep-field campaigns, two to the K-transect and one to Upernavik, to make measurements of algae, black carbon and melting on the ice sheet surface.

The whole project consisted of four work packages delivered across five institutions along with several other partners.

Greenland Ice Sheet margin dynamics

Each summer, areas of the Greenland Ice Sheet’s surface melt. Observations show that this surface meltwater can drain to the bed of the ice sheet via supraglacial lake drainage, moulins and crevasses.

Once this meltwater arrives at the ice sheet bed it changes the amount of friction and contact between the ice and its bed. In turn this allows surface meltwater to affect the speed at which the ice flows downhill.

I examined the impact of this effect over sub-daily and up to decadal timescales. I showed that land-terminating margins in the south-west of the ice sheet have been slowing down over the last 15-20 years in response to increased surface melting.

My findings suggest that at land-terminating margins, increased surface melting caused by projected climate change will not result in ice flow speed-up.

Please see my published papers for more.

Greenland Ice Sheet hydrology

The hydrology of the Greenland Ice Sheet is important not only in modifying ice flow (see above) but also for determining the rate at which meltwater drains into the ocean, and for evacuating sediments and nutrients from beneath the ice sheet.

I have been involved in monitoring the amount of water that drains out the front of Leverett Glacier. I work with colleagues in biogeochemistry to estimate fluxes of iron, phosphorus and other nutrients from the ice sheet.