5.8.1 Background
During the past decades, natural and anthropogenic
trace substances such as tritium (
3
H), radiocarbon
(
14
C), or Chlorofluorocarbons (CFCs) have been
used in studies of the dynamics of natural systems,
and as an analogue for the penetration of anthropogenic CO 2 into the ocean. Early applications of
tracers to studies of the ocean were directed at
determination of circulation patterns and mean residence times of specific water masses, as well as
estimates of mixing coefficients (e.g. Begemann and
Libby, 1957; Broecker et al., 1960; Munk, 1966;
Münnich and Roether, 1967; Craig, 1969; Rooth
and Östlund, 1972; Gammon et al., 1982). These
exploratory studies suggested that tracers add significantly to our understanding of the oceanic circulation. In order to exploit this potential fully, the
first global tracer study, the GEochemical Ocean
SECtions Study (GEOSECS; Craig and Turekian,
1980; see Broecker and Peng, 1982, for summary of
GEOSECS tritium and
14
C results), was launched as
part of the International Decade of Ocean Exploration (IDOE). GEOSECS explored a large set of
ocean tracers for studies of physical, chemical and
biological processes in the ocean. Its success, manifested in a host of new results, led to the design of
the Transient Tracers in the Ocean (TTO) programme. In contrast to GEOSECS, TTO was
restricted to the Atlantic Ocean (NAS, North
Atlantic Study; TAS, Tropical Atlantic Study;
SAVE, South Atlantic Ventilation Experiment). It
was a more focused programme than GEOSECS
(smaller number of tracers), designed to resolve
oceanographic features and processes at a much
higher resolution than achieved during GEOSECS.
It demonstrated that a very close coordination of
tracer programmes with physical oceanography
studies is required for full utilization of the tracer
data.
During the final stages of TTO, plans for the
World Ocean Experiment (WOCE) were developed. As part of its World Hydrographic Programme (WHP), especially during the One-Time
Survey, a set of tracers was measured on a global
scale with unprecedented spatial resolution (both
lateral and vertical). The original implementation
plan (WCRP, 1988a) included a larger number of
tracers (CFCs,
3 H/
3
He,
14 C,
39 Ar, stable isotopes
of water, helium isotopes,
228 Ra,
90 Sr,
137 Cs,
85
Kr)
than could actually be measured systematically
(CFCs,
3 H/
3
He,
14 C, H 2
18
O/H 2
16 O, helium isotopes). Although both carbon tetrachloride (CCl 4 )
and CFC-113 have distinctly different atmospheric
release histories from CFC-11 and CFC-12, and
offer the potential to provide additional valuable
information on time-dependent processes (including deep water formation) in the ocean, measurements of these compounds were made on only a
small subset of the WHP One-Time Survey cruises.
This was due in part to difficulties in analysing
these compounds (especially CFC-113) in seawater
samples, and to concerns about the non-conservative behaviour of CCl 4 in seawater (Wallace et al.,
1994). Nevertheless, the resulting multitracer data
set, which presently is under evaluation, exceeds
those obtained from pre-WOCE tracer studies by a
5.8
Transformation and Age of Water Masses
P. Schlosser, J. L. Bullister, R. Fine,W. J. Jenkins, R. Key, J. Lupton,
W. Roether and W. M. Smethie, Jr
431
OCEAN CIRCULATION AND CLIMATE
Copyright © 2001 Academic Press
ISBN 0-12-641351-7
All rights of reproduction in any form reserved
CHAPTER
During the past decades, natural and anthropogenic
trace substances such as tritium (
3
H), radiocarbon
(
14
C), or Chlorofluorocarbons (CFCs) have been
used in studies of the dynamics of natural systems,
and as an analogue for the penetration of anthropogenic CO 2 into the ocean. Early applications of
tracers to studies of the ocean were directed at
determination of circulation patterns and mean residence times of specific water masses, as well as
estimates of mixing coefficients (e.g. Begemann and
Libby, 1957; Broecker et al., 1960; Munk, 1966;
Münnich and Roether, 1967; Craig, 1969; Rooth
and Östlund, 1972; Gammon et al., 1982). These
exploratory studies suggested that tracers add significantly to our understanding of the oceanic circulation. In order to exploit this potential fully, the
first global tracer study, the GEochemical Ocean
SECtions Study (GEOSECS; Craig and Turekian,
1980; see Broecker and Peng, 1982, for summary of
GEOSECS tritium and
14
C results), was launched as
part of the International Decade of Ocean Exploration (IDOE). GEOSECS explored a large set of
ocean tracers for studies of physical, chemical and
biological processes in the ocean. Its success, manifested in a host of new results, led to the design of
the Transient Tracers in the Ocean (TTO) programme. In contrast to GEOSECS, TTO was
restricted to the Atlantic Ocean (NAS, North
Atlantic Study; TAS, Tropical Atlantic Study;
SAVE, South Atlantic Ventilation Experiment). It
was a more focused programme than GEOSECS
(smaller number of tracers), designed to resolve
oceanographic features and processes at a much
higher resolution than achieved during GEOSECS.
It demonstrated that a very close coordination of
tracer programmes with physical oceanography
studies is required for full utilization of the tracer
data.
During the final stages of TTO, plans for the
World Ocean Experiment (WOCE) were developed. As part of its World Hydrographic Programme (WHP), especially during the One-Time
Survey, a set of tracers was measured on a global
scale with unprecedented spatial resolution (both
lateral and vertical). The original implementation
plan (WCRP, 1988a) included a larger number of
tracers (CFCs,
3 H/
3
He,
14 C,
39 Ar, stable isotopes
of water, helium isotopes,
228 Ra,
90 Sr,
137 Cs,
85
Kr)
than could actually be measured systematically
(CFCs,
3 H/
3
He,
14 C, H 2
18
O/H 2
16 O, helium isotopes). Although both carbon tetrachloride (CCl 4 )
and CFC-113 have distinctly different atmospheric
release histories from CFC-11 and CFC-12, and
offer the potential to provide additional valuable
information on time-dependent processes (including deep water formation) in the ocean, measurements of these compounds were made on only a
small subset of the WHP One-Time Survey cruises.
This was due in part to difficulties in analysing
these compounds (especially CFC-113) in seawater
samples, and to concerns about the non-conservative behaviour of CCl 4 in seawater (Wallace et al.,
1994). Nevertheless, the resulting multitracer data
set, which presently is under evaluation, exceeds
those obtained from pre-WOCE tracer studies by a
5.8
Transformation and Age of Water Masses
P. Schlosser, J. L. Bullister, R. Fine,W. J. Jenkins, R. Key, J. Lupton,
W. Roether and W. M. Smethie, Jr
431
OCEAN CIRCULATION AND CLIMATE
Copyright © 2001 Academic Press
ISBN 0-12-641351-7
All rights of reproduction in any form reserved
CHAPTER