South-East Greenland Trough Experiment

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The stability of the GrIS, and its likely future contribution to sea level rise, is widely discussed by the scientific community, media, general public and policy makers. This attention has arisen because recent results have shown unexpected changes to the ice sheet; meaning that it is contributing to sea level rise at faster rates than scientists have expected. Glaciers in Greenland have recently undergone a synchronous retreat with associated thinning and acceleration of their flow. An example is Jakobshavn Isbrae, which is a major glacier on the west coast. In the late 1990s it accelerated, a response that has been linked to an increase in the warm ocean water that entered the glacier's fjord. Further examples of glacial acceleration triggered by ocean warming are identified in the south-east of Greenland, notably the Helheim and Kangerdlugssuaq Glaciers. However, the very latest results show that these glaciers have now slowed down. This acceleration and slowing response is coincident with changes in the oceanic waters outside of the fjords (warming and then cooling). There is mounting evidence that there is a critical link between ocean temperatures and glacier dynamics which in turn are the primary control of the Greenland Ice Sheet to sea-level rise. Tidewater glaciers discharge into deep fjords which are themselves connected to the ocean by deep troughs (or canyons) that cut across the shallow continental shelf. Clearly the fjords and troughs are an important component in understanding how ocean waters are delivered to the glacier. Whilst there is increasing observational effort in the fjords, there have been no studies of the hydrography of the cross-shelf troughs. Yet it is through these troughs that the warm ocean water is delivered to the mouth of the fjords. In essence, the troughs are currently an oceanographic 'black box'. An important requirement to be able to develop our understanding of ocean-glacier interactions is to be able to accurately model the adjacent shelves. This requires observations of the troughs in a bid to understand and quantify the process within the 'black box'. In this project we will focus on the major cross-shelf trough that transports warm oceanic waters to the fjord of Kangerdlugssuaq Glacier. Some previous, sparse observations have noted the presence of warm water carried through this trough yet there have been no systematic observations made. We will collect data on bathymetry, distribution of the water masses, flow rates and heat transport through the trough. These are the parameters essential for validating numerical models of the shelf. We will also make measurement of the turbulence and estimate the rate at which heat is lost along the length of the trough. This is important as it ultimately determines how much heat will be delivered into the fjord. Analysing and quantifying the oceanographic processes within troughs will provide a basis for interpreting satellite imagery of the Sea Surface Temperature (SST) of the region which then enables analysis of conditions back to 1992, which is approximately the same timescale as we have glacier velocities for. We would then be able to interpret archived SST data with a clearer appreciation of the underlying hydrographic processes and assess the effect on glacier velocities. Ultimately the goal of the scientific community is to be able to offer better predictions of key parameters like sea level. Understanding the oceanic drivers behind changes in glacier dynamics is key to better future prediction of Greenland's contribution to sea-level rise. The data from this project will be ideal for the development of future coupled of ice sheet-ocean models.