The subglacial cavity and implied dynamics under Nioghalvfjerdsfjorden Glacier, NE-Greenland

Seismic depth soundings on Nioghalvfjerdsfjorden Glacier (NFG), NE Greenlan d, reveal an overdeepened trough under the Boating glacier. The maximum dep th of the trough reaches more than 900 m below sea level. Mass balance calc ulations indicate considerable ice loss due to strong subglacial melting wi th a mean melt rate of 8 m a-l The geometry of the cavity and water mass ch aracteristics from CTD measurements suggest the existence of a well defined regional circulation system. Warm, saline and rather dense water follows t he inward inclining basal slope through the deep valley of Dijmphna Sund to wards the grounding line. Shallow ridges at the eastern glacier front preve nt this water mass entering from that direction. The comparatively cold, fr esh and less dense melt water follows the subglacial ice topography leaving the cavity through the gaps towards the east. The abundance of subglacial melt water east of NFG is most probably one of the main reasons for the sem i permanent sea ice cover in this region. Cold water masses upwelling in th e Northeast Water Polynia and detected by satellite remote sensing are very likely influenced and modified by the subglacial melt water production.