PMEL Programs and Plans
Accomplishments in FY 97 and Plans for FY 98
Figures (a) CFC-11 section at 170W in 1996, and
(b) CFC-11 levels from observations (top) and
from a coupled climate model (bottom).
CFC Tracer and Large-Scale Ocean Circulation Program
Accomplishments in FY 97
The PMEL CFC Tracer Program studies ocean circulation and mixing
processes by measuring the distribution of dissolved
chlorofluorocarbons (CFCs) in the ocean. Key long-term goals are to
document the entry of CFCs from the atmosphere into the world ocean
by means of repeat long-line hydrographic sections at decadal
intervals, and to use these observations to help test and evaluate
ocean-atmosphere models. Comparisons of CFC data from repeat sections
highlight regions, such as the North Atlantic between 1988 and 1993,
where intermediate and deep waters can rapidly take up anthropogenic
gases such as carbon dioxide on decadal time-scales.
The development and testing of models 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 Carbon Dioxide, and improving predictions of
climate change for the coming century.
During FY 97, the PMEL CFC Tracer Group completed work on
determining the solubilities of carbon tetrachloride in
seawater.
The CFC group worked on the analyses of data collected on a
multi-institutional oceanographic expedition in the southwest Pacific
on the NOAA Ship Discoverer (CGC96), as part of the World Ocean
Circulation Experiment (WOCE) and planned for a long zonal section
in the North Atlantic. A variety of physical, chemical and
biological measurements were made on these expeditions. The CFC data
obtained on these expeditions highlight the rapid uptake of atmospheric
gases into these regions, and the CFC signals carried equatorward in
abyssal currents of North Atlantic Deep Water, and Antarctic Bottom
Water.
The fifth year of a NOAA Atlantic Climate Change Program (ACCP) supported
study 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. These studies have shown that the
rate of formation of new Greenland Sea Deep Water (GSDW) during the 1980s
and early 1990s was drastically lower than that in the 1970s. The
near-cessation of the production of this cold, dense water mass by deep
convective processes may be the result of decadal-scale changes in surface
conditions in the central Greenland Sea.
Collaborative programs begun with researchers at the NOAA/ERL
Geophysical Fluid Dynamics Laboratory (GFDL) and at the National Center for
Atmospheric Research (NCAR) to utilize the CFC datasets in numerical models
of ocean circulation were expanded to include groups involved in the use
of CFCs and other tracers to evauate models of oceanic uptake of anthropogenic
Carbon Dioxide, as part of the Ocean Carbon Modeling Intercomparison Program.
Such comparison studies are critical if we are to have confidence in the
ability of such models to predict possible changes in the earth's climate
due to release of greenhouse gases or other anthropogenic activities.
CFC Tracer and Large-Scale Ocean Circulation Program
Plans for FY 98
- Improve analytical techniques for measuring CFCs in the atmosphere and
ocean.
- Develop improved techniques for the long-term storage of dissolved CFC
samples.
- Complete CFC measurements on the trans-Atlantic section along 24 N (NA24N)
- Continue the program to monitor annual variability of dense water
formation and ventilation process in the Greenland-Iceland-Norwegian
Seas, using CFCs and helium/tritium as tracers.
- Complete analyses of data collected on CGC96 and NA24N expeditions.
- Take the lead on the synthesis of the CFC data collected as
part of the WOCE Hydrographic Progam Pacific One-Time Survey(8), in
colloboration with other investigators.
- Work jointly with other investigators on a global synthesis of the WOCE
CFC data sets.
- Continue interactions with modelers and utilize the CFC results to help
evaluate and improve the ability of numerical models to realistically
simulate oceanic ventilation processes as well as carbon uptake and
transport.
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