PMEL Programs and Plans
Accomplishments in FY 96 and Plans for FY 97
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 96
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. 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 Carbon Dioxide, and improving predictions of climate change for
the coming century.
During FY 96, the PMEL CFC Tracer group helped organize and participated in
a multi-institutional oceanographic
expedition in the southwest Pacific on the NOAA Ship Discoverer,
as part of the World Ocean Circulation Experiment (
WOCE). A variety of physical, chemical and biological measurements were
made on this expedition. The CFC
data obtained on this expedition highlight the rapid uptake of atmospheric
gases into the ocean in this region, and the deep CFC signal being carried northward
into the abyssal Pacific Ocean by Antarctic Bottom Waters.
The fourth 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 were continued 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. Results of a comparison of
CFC observations in the ocean with the results of a coupled
ocean-atmosphere numerical model has been published. Such tests 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 97
- Develop improved techniques for the long-term storage of dissolved CFC samples.
- Improve analytical techniques for measuring CFCs in the atmosphere and ocean.
- Determine
the solubilities of CFCs and carbon tetrachloride in seawater.
- 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.
- Take the lead on the initial synthesis of the CFC data collected as part of the WOCE
Hydrographic Progam Pacific One-Time Survey, in colloboration with other investigators.
- 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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