BASIN SCALE DENUDATION RATES IN A POLAR DESERT

Chemical weathering of geologic materials is an important geomorphologic process and long term climate moderator. While temperate and tropical regions are well known with respect to weathering rates, assessments of global climate change require a priori knowledge of chemical weathering in all environmental endmembers to gauge climate moderation effects. Here we apply a uranium isotope mass balance model to rocks associated with stream drainages in Taylor Valley, Antarctica, to assess chemical weathering rates. Taylor Valley is a polar desert and represents an important endmember. Ephemeral stream fed by alpine glaciers flow for six to ten weeks during the austral summer. The stream channels and associated hyporheic zones are the sites of chemical weathering in these environments. The mass balance model assumes that uranium will move through and be contained in three reservoirs, rocks, sediments, and stream water. Uranium concentrations and (234U/238U) activity ratios were determined for stream waters, sediments and representative basin rocks. Denudation rates in Taylor Valley with varied with discharge and stream length and rates within an order of magnitude of a Brazilian river were found in some streams.