Bottom Water Export from the western Ross Sea

Time series of Antarctic Bottom Water (AABW) export, a water mass of global importance, reveal a surprising degree of variability. Here we present the results of a 4-year mooring array within the outflow of AABW from the Ross Sea Sector: Cape Adare Long Term Mooring (CALM) program, February 2007 to January 2011. All measured properties show a pronounced seasonal signal, as well as considerable interannual variability. In particular, minima in potential temperature and a maxima in both speed and salinity at the bottom instruments occur during the austral fall, March-May, suggesting that seasonal variability originates mainly from the shelf/slope exchange of High Salinity Shelf Water (HSSW) of the western Ross Sea's Drygalski Trough, during the summer months. By contrast, bottom water whose T/S indicate a source further east within the Ross Sea has much more limited seasonal variability, but still appears to contribute significantly to the outflow of AABW off Cape Adare. The more eastern source imposes a weak secondary bottom speed maximum and potential temperature minimum in austral spring, November, but lacks relatively high salinity, and may be indicative of AABW drawn from the Ice Shelf Water (ISW) in the central Ross Sea. Longer time series observations of AABW export at select sites around Antarctica will no doubt reveal a broad spectrum of variability, enabling more quantitative, observationally based, coupling of AABW behavior to broad regional forcing.