WHAT DOES THE NEARLY 50-YEAR RECORD OF STREAMFLOW ON THE ONYX RIVER, ANTARCTICA TELL US ABOUT RECENT CLIMATE DYNAMICS?

The Onyx River is the largest in Antarctica, flowing 32 km from Lake Brownworth to Lake Vanda in Wright Valley for 8-12 weeks per year. The New Zealand Antarctic Programme began gauging the Onyx just upstream of terminus in 1968 (Onyx River @ Vanda). A few years later, a second gauge was installed near its source (Onyx River @ Lower Wright). These ~5 decades of data collection provide a unique opportunity to study the controls on flow generation and seasonal flow dynamics in this system. In most years, more water flows past the Lower Wright gauge than the Vanda gauge indicating substantial evaporative (transmission) loss along its length. This is confirmed by synoptic water sampling for stable isotopes and water chemistry, which indicate an enriching pattern downstream. Flow generation is controlled by surface energy balance on source glaciers. Recent analyses demonstrate that high flow seasons since 2002 are associated with a positive AAO (Antarctic Oscillation), and low flow years over the entire record are coincident with negative AAO. In addition, high flow seasons in the last decade are associated with the regional presence of a strong ozone hole. Lake Vanda is a closed basin lake, and so water level is controlled greatly by the Onyx inflow, the primary source of water to the lake. Since 1972, lake level has risen over 10 m, serving as a ‘long-term memory’ of Onyx River dynamics. The Onyx River flow records are an invaluable resource for studying the recent past climate dynamics in the Dry Valleys region of Antarctica.