Ocean-driven and topography-controlled nonlinear glacier retreat during the Holocene: southwestern Ross Sea, Antarctica

Abstract:

Recent grounding-line retreat, dynamic thinning and mass loss in Antarctica has been attributed to oceanic warming. Episodic grounding-line retreat and rapid thinning also occurred in the southwestern Ross Sea during the Holocene, despite seemingly cold ocean temperatures. The style and timing of deglaciation in this region has been difficult to replicate in ice sheet models, partly because the model resolutions used are too coarse to accurately represent the complex bed topography.

We applied regional-scale 2D finite-element ice-flow modelling – constrained by cosmogenic exposure data at two outlet glaciers – to investigate the role of ocean temperature and bed topography in the deglaciation of the southwestern Ross Sea. First, our experiments demonstrate that bed topography controlled the spatial pattern of grounding-line retreat. Topographic pinning points (bedrock mounds and banks) limited the rate of ice loss until retreat progressed beyond a bathymetric threshold. Second, ocean thermal forcing determined the timing of this ice loss. Enhanced ocean-driven melt is required during the Early-to-Mid Holocene in order to replicate the records of deglaciation.

Today, seasonal surface warming and dense High Salinity Shelf Water are responsible for minor ice shelf melt in this region. Enhanced ocean thermal forcing in the Early-to-Mid Holocene more likely supports the idea that warm modified Circumpolar Deep Water was once present and was an important driver of deglaciation. The same driver and controls could also explain episodes of ice loss that are recorded elsewhere on the continental shelf in Antarctica during the Holocene.