Decadal changes in ventilation of the abyssal Southwest Pacific ocean from repeated CFC and new SF6 measurements

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Oceanic distributions of anthropogenic trace gases provide critical measures of how quickly the ocean interacts with the atmosphere, and its anthropogenic changes, that are difficult to obtain otherwise. Tracer data have been used by scientists to identify large-scale patterns and rates of variability in ventilation, and are critical for validation of climate models. This project will result in high-quality, full water column, tracer data sets which will be available to the broader community via the internet. In addition, the study will train a graduate student in the analytical methods, interpretation, and modeling of these data.The US Repeat Hydrography program includes 6 meridional sections that cross the Antarctic Circumpolar Current and extend into Antarctic waters. The chlorofluorocarbon/sulfur hexafluoride measurements are classified as Level 1 data - of the highest priority - and have been funded through both the National Science Foundation and the National Oceanic and Atmospheric Administration on all of these sections. The zonal spacing between these sections ranges from 25 to 120 degrees of longitude, with the largest gap between 90°E and 150°W. There are two meridional sections in this region that are carried out by the Australians - SR3 along 140°E between Tasmania and Antarctica, and P15S along 170°W between 70°S and the equator. While the Australians carry out most of the Level 1 measurements, they do not have a sea-going chlorofluorocarbon laboratory. To fill this gap in 2001 and 2008/2009, the University of Washington and National Oceanic and Atmospheric Administration-Pacific Marine Environmental Laboratory with support from the National Science Foundation and the National Oceanic and Atmospheric Administration, collaborated with the Australians to make chlorofluorocarbon measurements on both sections. This proposed research will continue the collaboration, measuring chlorofluorocarbons/ sulfur hexafluoride along P15S (April - June 2016) and SR3 (December 2016 - January 2017). This project will collect the data and interpret tracer distributions in context of changes to the ventilation of deep and bottom waters.