Christoph Mayer

Present and past climate control on fjord glaciations in Greenland: Implications for IRD‐deposition in the sea

Calving of icebergs is the dominant ablation mechanism for large outlet glaciers from the Greenland ice sheet except in northernmost Greenland where bottom melting from floating glaciers dominates. This difference is controlled by present climate conditions. Glacial geological evidence indicates that the transition between the associated types of fjord-glaciations moved north-south in response to past climate change. In cold periods, local melt-out of debris from the bottom of an increasing number of floating glaciers reduces the potential for iceberg transport of IRD. Thus, the marine IRD signal of Greenland origin is not a simple cold climate signal. Our findings are discussed in the context of the ongoing debate about the kind of ice transporting IRD - icebergs or sea ice.

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

Seismic depth soundings on Nioghalvfjerdsfjor- den Glacier (NFG), NE Greenland, reveal an overdeepened trough under thefloating glacier. The maximum depth of the trough reaches more than 900m below sea level. Mass balance calculations indicate considerable ice loss due to strong subglacial melting with a mean melt rate of 8ma 1 . The geometry of the cavity and water mass characteristics from CTD measurements suggest the existence of a well de- ned regional circulation system. Warm, saline and rather densewaterfollows theinwardinclining basalslope through the deep valley of Dijmphna Sund towards the grounding line. Shallow ridges at the eastern glacier front prevent this watermassenteringfromthatdirection. Thecomparatively cold, fresh 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 semi permanent sea ice cover in this region. Cold water masses upwelling in the Northeast Water Polynia and detected by satellite remote sensing are very likely influenced and mod- ied by the subglacial melt water production.