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Projects

Using Earth Observations to Unravel the Greenland Dark Zone

Jim McQuaid (School of Earth & Environment, Leeds), Duncan Quincey (School of Geography, Leeds) & Amelie Kirchgaessner (British Antarctic Survey)

The poles are said to be the barometer of the planet and it is critical we understand the processes which are impacting them at this time. The melting of the Greenland icesheet is estimated to have contributed to 16% of planetary sea level change since the early 1990s. In recent times there has been considerable interest in the south west region of the Greenland Icesheet where there has been quite noticeable darkening which in turn leads to an acceleration of surface melting in this region.

A very recent report from the IMBIE project used satellite data from a 26 year period to conclude that Greenland is losing ice seven times faster than it was in the 1990s. We urgently need to improve our understanding of the multitude of processes which contribute to the melting of the icesheet and subsequent discharge of meltwater into the ocean.

We already know that airborne material being deposited to the surface is a major driver of this darkening, however a major NERC project; Black and Bloom, has recently investigated the different components beyond just this transported material which contribute to the reduction of the surface albedo in this area. The so-called bio-albedo system, which co-exists with the deposited material actually consolidating it, goes through seasonal cycles and as the topmost surface melts in the polar spring revealing these algal colonies once more the accelerated melting is quickly re-established.

The Black and Bloom project has already gathered a wealth of compositional data from field samples. Isotopic analyses have shown that a significant fraction is very local, having recirculated onto the icesheet against the surface katabatic winds, further evidence of the complexity of atmosphere above the icesheet, both closeto the surface as well as in the free troposphere above.

This project will provide the opportunity to undertake a multi-scale analysis combining earth observations alongside an atmospheric dispersion model (FLEXPART) to produce climatologies for the entire Greenland icesheet. In this studentship you will use optical satellite observations to detect the formation of melt ponds local to the dark zone to be  tracked though the full annual cycle.  This will shed light on how local changes in albedo affect the formation, persistence and ultimately their lifetime, all of which are tied to water runoff from the icesheet.

Existing fine-spatial resolution satellite sensors (e.g. Planet, Sentinel) will provide the opportunity to do this at unprecedented spatial and temporal resolutions and capture the variability often ignored in coarse resolution approaches, as well as test ideas around the potential expansion of this darkening into other zones of the ice sheet. New sensors (e.g. SWOT) may give novel insights into lake water level fluctuations and how they respond to changes in surrounding ice surface characteristics, and historic patterns will be established from the long archive of SPOT and Landsat sensors using commonly applied (e.g. NDWI, spectral unmixing) approaches.

FIELDWORK OPPORTUNITY – There is also the possibility of making ground observations using arrays of time-lapse cameras, to characterise the local-scale evolution (albedo and roughness) of the ice surface, and track the distribution of algal communities as the melt-season progresses. These observations will be coupled with the dispersion modelling to track when and where materials impact this part of the ice sheet. The FLEXPART model will be run using the new ERA5 reanalysis data which provides a new high resolution capability back to 1950, this will allow detailed investigations to be conducted as to changes in circulation patterns over this region and assess the sources of the long range transported materials.

This studentship will be closely integrated into the recently funded €11m Deep Purple project, this is a team lead by Prof Martyn Tranter (Bristol) which builds upon the Black and Bloom project which has already provided significant insights into the process which are driving the dramatic darkening around the south western zone of the Greenland Icesheet.

 

In addition to changes in the ablation zone of the icesheet, the warming/cooling effect of arctic clouds are in a very fine balance, optically thin clouds can impose a measured warming as was observed in summer 2012 when an optically thin layer persisted over the Greenland icesheet for a period, the layer was sufficiently insulating that the surface layer warmed causing an unprecedented melt across the entire icesheet, estimated at close to 100% of the icesheet was above 0 °C for several days.  There are many hypotheses as to the range of and sources of the atmospheric aerosols which contribute to the budget of so called cloud condensation nuclei (CCN) which for the ‘seed’ for cloud formation.

Understanding the delivery mechanisms of aerosols which contribute to the cloud systems over the icesheet will provide critical insight into the Greenland system.   This work will be conducted alongside the a major NERC/NSF initiative; Greenland Aerosol Cloud Experiment (GrACE) which has began making some of the most comprehensive coupled observations of aerosols and clouds on the icesheet. GrACE includes a suite of instruments providing vertical profiles of water/ice, ice crystals habit and other cloud properties, these will also be compared to profiles generated by satellite observations.

Coupled to GrACE, this project will undertake a comprehensive study of the airmasses which impact on the icesheet identifying case studies for closer inspection. Our climatologies will be used to explore further the meteorological systems which will then allow the observational dataset to be further exploited.