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Chlorofluorocarbon Tracer Program

The PMEL Chlorofluorocarbon (CFC) Tracer Program has been using dissolved CFCs as tracers of ocean circulation and mixing processes. Studies of the entry of CFCs and other transient tracers into the ocean provide a unique description of the time-integrated circulation of the ocean on decadal time scales. The central goals of the CFC program are to document the entry of these compounds into the world ocean, by means of repeat long-line hydrographic sections at 5-year intervals, and to use these observations to help test and evaluate ocean-atmosphere models. The development and testing of such models is critical for understanding the present state of the ocean-atmosphere system, quantifying the ocean's role in the uptake of climatically important trace gases such as CO, and improving predictions of climate change for the coming century. The 5-year repeat section program for CFCs and carbon dioxide (and other tracers), begun at PMEL in the 1980s, serves as a prototype for a long-term system for monitoring and detecting change in the ocean on decadal time scales. In FY 94, the PMEL CFC Tracer group organized and helped successfully complete a multi-institutional oceanographic expedition on NOAA ship Discoverer, as part of WOCE. This section (designated WOCE line P18) extended along 1030 1100W from 670S to 230N, and included more than 184 stations. The full suite of recommended WOCE measurements were included on this expedition, and the quality of the data collected should fully meet all WOCE standards. The P18 section was a repeat of a section previously occupied by NOAA in 1989. The PMEL CFC Tracer group also participated in WOCE line P21W, a 2-month expedition in the central and western Pacific. This work represents a major contribution by NOAA to the WOCE program. The PMEL CFC Tracer group helped establish a dissolved-nutrient program at PMEL, and supported an analytical facility for the high-accuracy measurement of dissolved oxygen. These measurements are critical in understanding and interpreting the tracer and carbon distributions observed along the hydrographic sections. The third year of a NOAA Atlantic Climate Change Program (ACCP)-supported program to monitor variability of dense water formation and ventilation processes in the Greenland-Iceland-Norwegian Seas, using CFCs and helium/tritium as tracers was completed.

PMEL tracer and hydrographic datasets were put into digital format and made accessible via the Internet. Collaborative programs were continued with researchers at the NOAA/ERL Geophysical Fluid Dynamics Laboratory (GFDL) to utilize the CFC datasets in numerical models of ocean circulation. A new collaborative program was begun with researchers at the National Center for Atmospheric Research (NCAR) to utilize CFC data in global eddy-resolving models of ocean circulation.

Work continued on the development of techniques for the long-term storage of dissolved CFC samples and on the improvement of analytical techniques for measuring CFCs in the atmosphere and ocean.
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