Bathymetric models and their limitations beneath the ice shelves of Dronning Maud Land, East Antarctica.

Abstract:

The majority of Antarctica’s ice sheets are stabilized by their floating components, the ice shelves. An increase in ice shelf mass loss by calving, surface melting and/or basal melting can lead to an increased drainage of the corresponding ice sheet. This contributes to global sea level rise. The process of basal melting beneath ice shelves largely depends on ice-ocean interactions involving the exchange of water and heat. To understand these fully, it is vital to attain consistently-reliable bathymetric models. We have constructed bathymetric models beneath the ice shelves of Dronning Maud Land by inverting airborne gravity data, tied where available to known depth reference points. These models reveal a pattern in which the seafloor beneath the ice shelves is cut by deep glacial troughs that are partially isolated from the deep ocean interiors by shallow sills close to the continental shelf breaks. The sills lie shallower than the average Warm Deep Water thermocline in the ocean off Dronning Maud Land, and therefore currently shield the ice shelves from a potential cause of significant basal melting. Gravity anomalies in areas of high topographic gradients are strongly affected by the nearby topographic density contrasts that those gradients cause. This is equally true for bathymetric gradients such as continental slopes. These topographic effects tend to cause bathymetric models to be anomalously shallow at the foot of the slope and anomalously deep near the crest, where Dronning Maud Land’s protective sills are found. The steeper the slope, the more pronounced these effects become. Integrating topographic corrections into the bathymetric modeling process yields improvements in accurately depicting these high bathymetric gradients, and should thus more confidently highlight those sills and ice shelves that may be most exposed to ongoing changes in the thermal structure of the Southern Ocean.