Decadal Changes in Dissolved Chlorofluorocarbons Along 150°W in the Pacific Ocean

Two hydrographic sections (P16S, extending from 71°S to 17°S, and P16N, extending from 17°S to 56°N) nominally along 150°W in the Pacific Ocean, were occupied in 2005 in 2006, respectively, as part of the CLIVAR Global Repeat Hydrography Program. These sections repeated sections occupied along 150°W in 1991 as part of the World Ocean Circulation Experiment (WOCE). Full water column CTD profiles were collected at each station. A suite of physical and chemical measurements were made along the sections. Dissolved chlorofluorocarbon (CFC) concentrations in the water column generally increased along the section between 1991 and 2005-2006, with the leading edge of the CFC transient deepening in the water column. The CFC concentrations at abyssal depths along the southern end of the section showed substantial increases between 1991 and 2005-2006. The largest increases in concentrations (and CFC partial pressures) were observed in Sub-Antarctic Mode Waters in the Southern Hemisphere. Significant changes in a number of other water mass properties, including dissolved oxygen and dissolved inorganic carbon (DIC) were observed in the upper waters along the sections between the 1991 and 2005-2006 occupations. In addition to the CFCs, a pilot study was made to measure sulfur hexafluoride (SF6) along P16N in 1996. This man-made compound has been increasing rapidly in the atmosphere and measurements of its penetration in the water column offers the potential, together with the CFCs, to allow improved estimates to be made of the ventilation time-scales, transit time distributions and the uptake of anthropogenic CO2 in the waters of this region.