Description: The Amundsen Sea Embayment of West Antarctica hosts one of the most rapidly changing sectors of the West Antarctic Ice Sheet. With the fastest-flowing ice streams in Antarctica, the region around Pine Island Bay is characterized by rapid ice-sheet thinning and grounding-line retreat. Published surface-exposure data are limited to a few isolated nunataks making it difficult to assess the long-term deglacial history of the area. To address this, we correlate existing records of lateral ice-stream retreat from marine sediment cores with onshore glacial thinning in two key areas of eastern Marie Byrd Land: the Kohler Range and Pine Island Bay. Our 10Be surface-exposure ages are the first from the isolated Kohler Range and show that the nunataks there became ice-free between 8.6 and 12.6 ka. This implies a minimum long-term average thinning rate of 3.3 ± 0.3 cm/yr, which is one order of magnitude lower than recent rates based on satellite data. We also present pre- to early Holocene 10Be surface-exposure ages from two islands located approximately 80 km downstream of the Pine Island Glacier ice-shelf front to constrain the lateral deglacial history in the Pine Island Bay area. This study provides insight into the significance of local ice sheet variations and suggests that the post-LGM history in the Amundsen Sea sector was characterized by glacial thinning as well as lateral retreat in pre- to early Holocene times.

Description: We use cosmogenic nuclide-derived denudation rates from in situ-produced 10Be in river sediment to determine sediment production rates for the central Amazon River and its major tributaries. Recent developments have shown that this method allows calculating denudation rates in large depositional basins despite intermediate sediment storage, with the result that fluxes of the sediment-producing hinterland can now be linked to those discharged at the basins' outlet. In rivers of the central Amazonian plain, sediment of finer grain sizes (125-500 {micro}m) yields a weighted cosmogenic nuclide-derived denudation rate of 0.24 {+/-} 0.02 mm/yr that is comparable to the integrated rate of all main Andean-draining rivers (0.37 {+/-} 0.06 mm/yr), which are the Beni, Napo, Mamore, Ucayali, and Maranon rivers. Coarser-grained sediment (〉500 {micro}m) of central Amazonian rivers is indicative of a source from the tectonically stable cratonic headwaters of the Guyana and Brazilian shields, for which the denudation rate is 0.01-0.02 mm/yr. Respective sediment loads can be calculated by converting these cosmogenic nuclide-derived rates using their sediment-producing areas. For the Amazon River at Obidos, a sediment production rate of [~]610 Mt/yr results; non-Andean source areas contribute only [~]45 Mt/yr. A comparison with published modern sediment fluxes shows similarities within a factor of [~]2 with an average gauging-derived sediment load of [~]1000 Mt/yr at Obidos, for example. We attribute this similar trend in cosmogenic versus modern sediment loads first to the absence of long-term deposition within the basin and second to the buffering capability of the large Amazon floodplain. The buffering capability dampens short-term, high-amplitude fluctuations (climatic variability in source areas and anthropogenic soil erosion) by the time the denudation rate signal of the hinterland is transmitted to the outlet of the basin.