SPATIAL AND TEMPORAL VARIABILITY OF SEDIMENT FLUX TO BAYS AND FJORDS ALONG A BROAD LATITUDINAL TRANSECT FROM CENTRAL PATAGONIA TO THE ANTARCTIC PENINSULA

Theory suggests that glacial erosion and sediment flux to fjords and bays should decrease with colder climatic conditions due to larger extent of cold-based ice (less water availability) and decreased ice speed. Here we present quantitative evidence to test this hypothesis over millennial timescales using data from nine glacially influenced fjords and bays across a broad latitudinal transect, from central-western Patagonia (46°S) to the Antarctic Peninsula (65°S). We acquired dense grids of high-resolution seismic and swath bathymetry data along with sediment cores during several cruises to these areas. Seismic data are used to subdivide basin fill into sedimentary units and map units within each basin. We then calculate volumes of each unit and use radiocarbon ages to constrain their ages. The results reveal significant variability in sediment flux, both spatially and temporally, within and among different bays and fjords. These differences reflect numerous factors that regulate sediment supply and dispersal in these settings.

We use our estimates of sediment fill volumes to calculate basin-average erosion rate (Ç) for each study area. This was completed by dividing the rock-equivalent volumes by effective drainage basin area and total estimated time span of accumulation for each unit. Erosion rates span two orders of magnitude, from 0.02 mm/yr for Lapeyrère Bay on Anvers Island, Antarctica (~64.5°S), to 0.83 mm/yr for San Rafael Glacier in northern Patagonia (~46.5°S). The latitudinal decrease of millennial Ç along the study transect is ~5% per degree latitude and is interpreted to result primarily from the decrease in temperature and meltwater production with increasing latitude.

Despite variability of terrigenous flux, known variations in climatological and glaciological parameters, and a clear latitudinal trend in Ç, the silt-sized fraction of each individual fjord record (measured using laser particle size analysis of core samples) is surprisingly uniform in post-LGM sediment. Silt size varies among different fjords, however, indicating that bedrock geology is a primary control on grain size. Basins that drain volcanic island landscapes, for example, range from 60 to 75 vol % silt, whereas basins that drain granitic landscapes range from 70 to 80 vol % silt in post-LGM sediment.