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We have turned the corner on the main CASO sampling loop and are once again heading south. As I write we are at the fourteenth of the 31 CASO stations in this phase of the voyage and have completed the first two legs of the CASO stations over the Antarctic continental slope and rise. The first leg followed a deep canyon running from south to north that drains the bottom water produced in the Mertz polynya region. We found clear evidence that even now, in summer, dense water produced during the winter is spilling off the shelf and cascading down the canyon. The southwards leg that we are now doing, to the east of the Mertz polynya outflow, is a repeat of stations occupied during the BROKE expedition in 1996. Here we are sampling bottom water flowing west from the Ross Sea. In previous work, Steve Rintoull and others showed that the bottom water of the entire Australian – Antarctic Basin became lower in salinity between the early 1970s and 2001. By comparing the bottom water properties on the different legs of CASO, we will be able to determine, first, if the bottom waters are continuing to change, and second, the relative contribution of the Ross Sea and the Mertz polynya to changes in the deep branch of the global overturning circulation. Regards, Martin and Sarah.
Map
A map showing Australia and Antarctica. The map shows the journey of one voyage that has occured in the season, with each route highlighted in a distinct colour.