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Surveys were conducted seaward of all the major drainage outlets of the Antarctic ice sheet from the Pennell Coast, northVictoria Land, to Marguerite Bay, Antarctic Peninsula. The results show that the ice sheet extended onto the outer shelf. Glacial troughs occur offshore of all major glacial outlets.Where the substrate is crystalline bedrock, ice flow tended to follow the structural grain of the bedrock, deposited little sediment and eroded the underlying bedrock. Where ice flowed over relatively soft, more easily eroded, sedimentary strata, the direction of ice flow was more directly offshore, and depositional features characterize the sea-floor. In these areas the signature of the grounded ice consists of till deposits and large-scale geomorphic features. Drumlins occur within the region of contact between crystalline and sedimentary substrates. The different geological substrates are interpreted to have exerted a fundamental control on the behavior of past ice sheets. The troughs in the areas of bedrock composed of sedimentary substrate are interpreted to have been occupied by relatively fast-flowing ice, ice streams, and the troughs in the areas of crystalline substrate are interpreted to have been occupied by slower-moving ice. The area between these two zones was characterized by ice acceleration and is marked by drumlins.

Glacial erosion is fundamental to our understanding of the role of Cenozoic-era climate change in the development of topography worldwide, yet the factors that control the rate of erosion by ice remain poorly understood. In many tectonically active mountain ranges, glaciers have been inferred to be highly erosive, and conditions of glaciation are used to explain both the marked relief typical of alpine settings and the limit on mountain heights above the snowline, that is, the glacial buzzsaw. In other high-latitude regions, glacial erosion is presumed to be minimal, where a mantle of cold ice effectively protects landscapes from erosion. Glacial erosion rates are expected to increase with decreasing latitude, owing to the climatic control on basal temperature and the production of meltwater, which promotes glacial sliding, erosion and sediment transfer. This relationship between climate, glacier dynamics and erosion rate is the focus of recent numerical modelling, yet it is qualitative and lacks an empirical database. Here we present a comprehensive data set that permits explicit examination of the factors controlling glacier erosion across climatic regimes. We report contemporary ice fluxes, sliding speeds and erosion rates inferred from sediment yields from 15 outlet glaciers spanning 19 degrees of latitude from Patagonia to the Antarctic Peninsula. Although this broad region has a relatively uniform tectonic and geologic history, the thermal regimes of its glaciers range from temperate to polar. We find that basin-averaged erosion rates vary by three orders of magnitude over this latitudinal transect. Our findings imply that climate and the glacier thermal regime control erosion rates more than do extent of ice cover, ice flux or sliding speeds.

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