| Summary: | © The Author(s), 2017. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Annals of Glaciology 58 (2017): 107-117, doi:10.1017/aog.2017.19. Jakobshavn Isbræ, which terminates in Ilulissat Icefjord, has undergone rapid retreat and is currently the largest contributor to ice-sheet mass loss among Greenland’s marine terminating glaciers. Accelerating mass loss is increasing fresh water discharge to the ocean, which can feed back on ice melt, impact marine ecosystems and potentially modify regional and larger scale ocean circulation. Here we present hydrographic observations, including inert geochemical tracers, that allow the first quantitative description of the glacially-modified waters exported from the Jakobshavn/Icefjord system. Observations within the fjord suggest a deep-reaching overturning cell driven by glacial buoyancy forcing. Modified waters containing submarine meltwater (up to 2.5 ± 0.12%), subglacial discharge (up to 6 ± 0.37%) and large portions of entrained ocean waters are seen to exit the fjord and flow north. The exported meltwaters form a buoyant coastal gravity current reaching to 100 m depth and extending 10 km offshore. We gratefully acknowledge support from WHOI’s Ocean and Climate Change Institute, the WHOI Doherty Postdoctoral Scholarship, the US National Science Foundation grant NSF OCE-1536856, and the leaders and participants of the Advanced Climate Dynamics Summer School (SiU grant NNA-2012/10151). Ship-based CTD data are freely available from the NOAA National Centers for Environmental Information, discoverable with Accession Number 0162649. Expendable CTD data are included in the Supplementary Material.
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