Abstract

We use extensive sedimentary and marine geophysical data to derive sediment volume-based millennial time-scale glacial erosion rates (E) from glacially influenced fjords and bays across a broad latitudinal transect, from central Patagonia (46 degrees S) to the Antarctic Peninsula (65 degrees S), and to determine how glacial erosion rates change with increasing latitude and decreasing atmospheric temperatures. We also calculate million-year time-scale erosion rates for the western Antarctic Peninsula cordillera and inner continental shelf from seismic stratigraphic analysis of the continental margin. These results are complemented by erosion rates derived from existing thermochronology data sets (apatite fission-track and apatite [U-Th]/He) for both Patagonia and the Antarctic Peninsula regions. Despite considerable regional variability, our results show a clear trend of decreasing (E) over bar with increasing latitude. Millennial (E) over bar values span two orders of magnitude, from 0.02 mm/yr for Illiad glacier on Anvers Island, Antarctica (similar to 64.5 degrees S), to 0.83 mm/yr for San Rafael glacier in northern Patagonia (similar to 46.5 degrees S). Regional averages are three times higher for the Patagonian areas than the Antarctic Peninsula areas. This trend is interpreted to result from a general decrease in temperature and water availability at the ice-bedrock interface. For the Antarctic Peninsula study sites, erosion rates are highly clustered around 0.1 mm/yr, with the exception of Maxwell Bay, for which the (E) over bar value is 0.36 mm/yr. In Patagonia, erosion rates are more variable than in the Antarctic Peninsula, with (E) over bar ranging between 0.14 mm/yr (Europa glacier area) and 0.83 mm/yr (San Rafael glacier area). This regional variability in (E) over bar is interpreted as due to differences in hypsometry and bedrock resistance to erosion. Million-year time-scale (E) over bar values derived from thermochronology ages also decrease with latitude, with maximum values decreasing from similar to 0.9-1.1 mm/yr north of 46 degrees S to similar to 0.1-0.2 mm/yr south of 48 degrees S in Patagonia, and reaching similar to 0.2-0.3 mm/yr in the Antarctic Peninsula. The sediment-based million year time-scale (E) over bar estimates for the western Antarctic Peninsula cordillera indicate that glacial erosion rates increased by 25%-30% after 5.3 Ma, from similar to 0.09 mm/yr (5.3-9.5 Ma) to similar to 0.11-0.12 mm/yr ( 5.3 Ma). For Patagonia, the decrease in long-term erosion rates south of similar to 46 degrees S is interpreted to result from relatively long periods of slow glacial erosion associated with the ice masses having been colder (subpolar) on the southern Patagonian cordillera, and having eroded at rates comparable to those we obtained for the Antarctic Peninsula. These long-term erosion rates are 1-2 orders of magnitude lower than estimates based on recent sediment yields, highlighting the transient nature of high-sediment-flux events. However, our sediment volume-derived millennial time-scale (E)over bar> closely approximates the maximum values of tectonic time-scale (E) over bar values derived from thermochronology ages. Our combined millennial and million-year time-scale glacial erosion data quantify the significant decrease in rates of glacially driven denudation at geological (tectonic) and millennial time scales with increasing latitude from Patagonia to the Antarctic Peninsula, highlighting the influence of climate on mountain denudation.