Modelling the retreat of the Uummannaq ice stream system, central west Greenland.

Abstract

I aim to understand what controlled the retreat pattern of the Uummannaq ice stream (UISS) during the last deglaciation. Evidence for the pattern of retreat is recorded in marine bathymetric and sedimentological data in the central trough (Ó Cofaigh et al., 2013). On land, on the islands that sit within the fjord (Ubekendt and Karrat) and on the fjord margins, geomorphological evidence records the thinning of the ice surface through time (Roberts et al., 2013; Lane et al., 2014). These records are set within a chronological framework of radiocarbon and cosmogenic dates, which suggest that the ice stream was grounded close to the continental shelf edge at the Last Glacial Maximum, and had begun rapid retreat by 17ka BP. However, it is unclear what controlled the retreat pattern identified in the Uummannaq system.
Modelling the UISS using a 1-D numerical model provides the opportunity to combine the chronology and geometries inferred from the landforms and to test the influence of various controls upon the retreat of the ice stream. The model has the capability to dynamically and robustly simulate grounding line retreat behaviour over millennial timescales (Jamieson et al., 2014). Marine geophysical data and dates from islands are used to constrain the numerical model and sensitivity tests are conducted to explore its response to a range of forcing patterns. The model retreat is simulated from a steady-state LGM configuration and was subjected to a series of retreat perturbations forced independently or simultaneously by either rising sea level, sub marine melting, ice temperature and surface melt. Comparing the simulated behaviour of the UISS against the geomorphological and cosmogenic exposure evidence for ice surface thinning onshore confirms that the UISS responds non-linearly to the applied forcings. This is likely to be because of the influence of topographic controls in the system, which appears to be the key modulator of retreat. Ice temperature and climate also have an impact on retreat and thinning of the UISS, but ultimately, a combination of sea level rise, submarine melt, increasing atmospheric temperatures are needed to reconstruct the retreat of the UISS that fits with the geomorphic evidence presented.