U.S. Dept. of Commerce / NOAA / OAR / PMEL / OCRD
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.