PMEL Programs and Plans
Accomplishments in FY 99 and Plans for FY 00
CFC Tracer and Large-Scale Ocean Circulation Program
Accomplishments in FY 99
The PMEL Chlorofluorocarbon CFC Tracer Program studies ocean circulation
and mixing processes
by measuring the distribution of dissolved 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 99, the PMEL CFC Tracer Group continued work on improving
techniques for analyzing CFCs, and techniques of storing seawater
samples
in glass ampules.
The CFC group worked on the analyses of data collected on a
multi-institutional
oceanographic
expedition in the southwestern Pacific on the NOAA Ship Discoverer
(CGC96),
as part of the World Ocean
Circulation
Experiment (WOCE) and on 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 seventh year of a NOAA supported program
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 efforts
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 evaluate models of oceanic uptake of anthropogenic Carbon Dioxide, as
part of the
OACES and
Ocean Carbon Modeling
Intercomparison Programs. 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 00
-
Improve analytical techniques for measuring CFCs in the atmosphere and
ocean.
-
Develop improved techniques for the long-term storage of dissolved CFC
samples.
-
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 the NA24N expedition.
-
Take the lead on the synthesis of the CFC data collected as part of the
WOCE Hydrographic Progam
Pacific One-Time Survey,
in collaboration 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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