The Onyx River in The McMurdo Dry Valleys of Antarctica- Long-Term Record Reveals Influence of Climate Teleconnections on Streamflow and Aquatic Ecosystems

The McMurdo Dry Valleys (MDV) of Antarctica is comprised of alpine and terminal glaciers, large expanses of patterned ground, and ice-covered lakes in the valley floors, which are linked by glacial meltwater streams that flow during the austral summer. Precipitation in the MDV is extremely limited and sublimates without contributing to streamflow. Since 1993 the McMurdo Dry Valleys Long-Term Ecological research project, we have operated two stream gauges on the Onyx River, which is the longest river in Antarctica and receives meltwater from piedmont and alpine glaciers. The 45-year Onyx River flow record was begun by the New Zealand Antarctic Program and is the longest continuous environmental record for the McMurdo Dry Valleys. The Onyx record exhibits considerable variation in total annual flows (TAFs), which fluctuate over two orders of magnitude with a mean value of 3.8x10⁶ m³/yr. Many of these streams contain thriving microbial mats comprised of cyanobacteria and endemic diatoms and the lakes support phytoplankton and benthic mat communities in the low-light environment under the 4 to 5 m thick perennial ice-cover. The stream and lake ecosystems responded to a sustained 18-year cool period with low flows, which ended in 2001/02. Three "flood events" have occurred during sunny, warm summers in the past 15 years. Following the first flood event in 2001/02, stream mat biomass was two-fold lower due to scouring and recovered over several years, with lesser declines following the subsequent floods. We diagnosed the relationship between large scale climate variables and the Onyx flows and found clear links to Antarctic Oscillation (AAO). We modeled the interannual variability using a local regression model with two predictors - September-November AAO Index and December-January air temperature. This model accounted for 80% of the interannual flow variance. Analyses suggest that, with the recent trend towards higher AAO indices, the dominant mechanism for high flows in the valleys has shifted to one driven by high incoming radiation.