Airborne investigation of bathymetric sills in Godthåbsfjord, Greenland - results from IcePOD and Operation IceBridge

The bathymetry of Greenlandic fjords is an important boundary condition for understanding circulation within the fjord. This in turn is crucial to the understanding of ocean-ice interactions at the margins of the Greenland ice sheet. Marine-based surveys have identified sills at the heads of many of these fjords, and demonstrated their importance to the circulation patterns within the fjords themselves. The inaccessibility of much of the Greenland fjord system leaves many regions poorly surveyed, with important data gaps remaining in the interior of the fjords. Airborne surveys provide a valuable platform for the study of fjord dynamics by offering wide coverage and the ability to survey otherwise inaccessible regions of fjords. In this study we combine results from Operation IceBridge gravity surveys with visible and infrared imagery from the IcePOD project to investigate circulation, transport, and mixing in Godthåbsfjord, Greenland, at the calving front of Kangiata Nunâta Sermia. The bathymetry of this fjord has been well mapped, but information is sparse from the inner 13 km where the fjord is filled with icebergs. Gravity data show a 4 mGal positive anomaly 10 km from the calving front. Models constrained by the gravity anomaly over a known sill further up the fjord give this newly identified sill a predicted depth of approximately 100 m. IcePOD is a multi-instrument pod flown on an LC130 operated by the New York Air National Guard. During test flights in the summer of 2013 multiple passes were made of the inner, iceberg-filled part of Godthåbsfjord with both visible and infra-red cameras. Here we compare the movement of ice within the fjord with modelled bathymetry from IceBridge to investigate the circulation of the inner part of the fjord.