Ocean Circulation and Geochemistry
Transient Tracers: Chlorofluorocarbons and Carbon Tetrachloride
E. Peter Jones and Fiona A. McLaughlin
The cloud of international concern over the growing anthropogenic releases of
refrigerants, aerosols and solvents and their impact on climate and the ozone
layer, ironically, has had a silver lining for oceanographers. The measurement
of chlorofluorocarbons (CFCs) and carbon tetrachloride (CCl4) in seawater,
from the surface to the bottom, provides a tool for tracing water masses since
they were last at the sea surface with a time clock that spans most of this
century. Such data give important information about the various layers within
the ocean, for example: Are they rapidly flushed or isolated? Are the waters
transported from other oceans or nearby shelves? These are important ques-
tions in Arctic Ocean research, as they relate directly to the transport of contam-
inants--such as organochlorines and radionuclides--to the Arctic food chain.
Measuring CCl4 may also contribute to understanding the ocean's ability
to absorb carbon dioxide, a critical question for those attempting to predict
global warming. CCl4 can be used as a surrogate for estimating levels of atmo-
spheric carbon dioxide, as both compounds have been increasing in the atmo-
sphere in a similar fashion since the turn of the century. The depth at which
CCl4 is found in the ocean thus signals the depth at which anthropogenic
carbon dioxide, produced in the twentieth century, is found.
AOS-94 provided an opportunity to measure a suite of CFCs (CFC-12,
CFC-11 and CFC-113) and CCl4 on a transect crossing the Arctic Ocean.
Samples were collected at almost all oceanographic stations at almost all sam-
pling depths, typically 36 from the surface to the bottom, using the rosette
sampler. The samples were analyzed using a standard purge-and-trap gas chrom-
atograph.
Previous cruises sampled different regions in different years: the Nansen
Basin in 1987, the Nansen and Amundsen Basins and the North Pole in 1991,
and the southwestern Canada Basin in 1993. The latter cruise yielded infor-
mation suggesting that the structure and circulation of water masses in the
Arctic Ocean may be undergoing a major change. AOS-94 CFC data will
allow us to determine the rate, magnitude and extent of these changes.
Although results are preliminary, certain key features are evident. CFC and
E. Peter Jones is from the Bedford Institute of Oceanography in Dartmouth, Nova Scotia, Canada. Fiona McLaugh-
lin is from the Institute of Ocean Sciences in Sidney, British Columbia, Canada.
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