Glacial retreat patterns and processes determined from integrated sedimentology and geomorphology records

Although hundreds of cores have been collected on the Antarctic continental shelf over the past five decades, definitive interpretations of depositional environments associated with marine-based ice advance and retreat are hindered by similarities in sediment facies and a lack of geomorphic context. The recent use of an advanced multibeam bathymetry system allows for more detailed ice sheet reconstructions from glacial landforms that were previously not resolved with older generation systems. Here we present results from a recent cruise to the Ross Sea, Antarctica that focuses on integrating sediment facies analyses into a geomorphic framework to confidently determine depositional environments and sedimentological processes since the Last Glacial Maximum. Grain-size analysis, geotechnical properties, and micropaleontology from targeted sediment cores are used to develop improved criteria for making the distinction between subglacial diamictons and ice-proximal diamictons, which can be applied to geomorphically blind sediment cores. Our consideration of geomorphic context while interpreting sediment facies has also allowed us to determine that most debris melted out of the base of paleo-ice shelves in the Ross Sea only 1.2 km seaward of the grounded ice margin. Additionally, we find that agglutinated foraminifera specimens are characteristic of sluggish marine currents and a resulting accumulation of siliceous detritus rich in organic matter; however, calcareous specimens dominate in higher-energy current settings and in ice-proximal environments with lesser amounts of siliceous detritus and associated organic material. Overall, sedimentary successions record contrasting behaviors of the West Antarctic and East Antarctic ice sheets that extended onto the continental shelf during the Last Glacial Maximum. Not only is this coupled geomorphic and sedimentologic approach useful for understanding glacimarine processes and ice-sheet retreat patterns, but it is essential for selecting appropriate facies transitions for chronological constraints of past ice sheet behavior.