Calculating Freshwater Input from Iceberg Melt in Greenlandic Fjords by Combining In Situ Observations of Iceberg Movement with High Resolution Satellite Imagery

Abstract:

Understanding fjord circulation in Greenland’s outlet glacial fjords is crucial to explaining recent temporal and spatial variability in glacier dynamics, as well as freshwater transport on the continental shelf. The fjords are commonly assumed to exhibit a plume driven circulation that draws in warmer and saltier Atlantic-origin water toward the glacier at depth. Freshwater input at glacier termini directly drives this circulation and significantly influences water column stratification, which indirectly feeds back on the plume driven circulation. Previous work has focused on freshwater inputs from surface runoff and submarine melting, but the contribution from iceberg melt, a potentially important freshwater source, has not been quantified. Here, we develop a new technique combining in situ observations of movement from iceberg-mounted GPS units with multispectral satellite imagery from Landsat 8. The combination of datasets allows us to examine the details of iceberg movement and quantify mean residence times in a given fjord. We then use common melt rate parameterizations to estimate freshwater input for a given iceberg, utilizing novel satellite-derived iceberg distributions to scale up to a fjord-wide freshwater contribution. We apply this technique to Rink Isbræ and Kangerlussuup Sermia in west Greenland, and Helheim Glacier in southeast Greenland. The analysis can be rapidly expanded to look at other systems as well as seasonal and interannual changes in how icebergs affect the circulation and stratification of Greenland’s outlet glacial fjords. Ultimately, this work will lead to a more complete understanding of the wide range of factors that control the observed regional variability in Greenland’s glaciers.