The WOCE programme is providing extensive
data for analysing the fate of this throughflow
water within the Indian Ocean.
5.8.4 Outlook
The WOCE tracer survey provided the most extensive, global, high-quality data sets for a variety of
transient and ‘steady-state’ tracers. The integration
of tracer data collection into a major oceanographic programme that observed the ocean circulation with many variables in a coherent fashion
has never been achieved before. This offers the
possibility to extract a wealth of new results on
the physical climate system and biogeochemical
processes.
Preliminary examination of the data reveals
many features that will shed new light on global
and regional elements of the ocean circulation.
Some of the early results discussed above,
although mostly qualitative and semiquantitative
in nature, are indicative of the rich set of results
that we expect to obtain from the WOCE multitracer data set. Present efforts are directed at a
synthesis of the individual data sets on a global
scale. Future work will include combining the
tracer data with other measurements performed
during WOCE to address a variety of global and
regional oceanographic problems along the lines of
those presented in this contribution. Additionally,
there will be targeted efforts to integrate the tracer
data into the set of variables used to advance the
performance of global circulation models (see
Willebrand and Haidvogel, Chapter 7.2). Many of
these efforts will go on in parallel, i.e. results from
WOCE tracer studies will be produced on a continuous basis even if the nature of the studies will
vary.
The use of tracer inventories provides an independent means of estimating water mass formation rates. In contrast to current meter arrays or
hydrographic sections across strong boundary
flows, tracer inventories represent the integrated
effects of water mass formation from all sources
on decadal time scales, and the results are less susceptible to shorter-term fluctuations on the mean
water mass formation rate. The development and
refinement of techniques for estimating water mass
formation rates using tracer inventories are still in
the early stages. Significant improvements are
anticipated as more data become available, and
techniques are being refined for estimating inventories from these data. Significant improvements
are also possible by advancing our understanding of the boundary conditions for input and
export of tracers in the water masses. Detailed
comparisons of observational data sets with model
simulations should also provide insight of mutual
benefit.
In terms of deriving oceanographic information
that complements that from other methods, we are
only at the beginning of exploiting the deep helium
tracer field. Thus far most of the analysis has been
descriptive in nature rather than quantitative.
However, the helium field has now been mapped
in sufficient detail to allow direct comparison with
models that include tracer transport equations, as
well as helium sources and sinks (e.g. Farley et al.,
1995). Future work should refine these modelling
efforts and expand them to include inverse modelling studies, either on a regional or basin scale.
The combination of the helium isotope data with
hydrographic and other tracer data from the
WOCE survey and augmenting studies will provide valuable insights into ocean circulation and
mixing.
The extensive tracer data set collected as part of
WOCE offers the opportunity to study in greater
detail than was previously possible the formation
rates of dense waters around Antarctica. This
should help to improve our understanding of
the subsequent mixing processes that occur as
these deep and bottom waters move away from
Antarctica. It also represents a key element in
studies of the long-term variability of deep and
bottom water in the Southern Ocean (Broecker
et al., 1999).
Tracers have been used extensively in the past to
constrain rates of biogeochemical processes.
Recently transient tracers have been used directly in
the calculation of the ocean uptake of anthropogenic CO 2 (Gruber et al., 1996; Wallace, Chapter
6.3). In addition, a number of three-dimensional
global models are being developed and used to
simulate key ocean circulation processes, and to
provide predictive capabilities for possible future
changes related to climate variability (Böning and
Semtner, Chapter 2.2; Willebrand and Haidvogel,
Chapter 7.2). The ability of these models to simulate realistically water mass formation rates, and
estimate the uptake of important atmospheric trace
gases (such as CO 2 ) in the Southern Ocean, must
SECTION 5 FORMATION AND TRANSPORT OF WATER MASSES
450
data for analysing the fate of this throughflow
water within the Indian Ocean.
5.8.4 Outlook
The WOCE tracer survey provided the most extensive, global, high-quality data sets for a variety of
transient and ‘steady-state’ tracers. The integration
of tracer data collection into a major oceanographic programme that observed the ocean circulation with many variables in a coherent fashion
has never been achieved before. This offers the
possibility to extract a wealth of new results on
the physical climate system and biogeochemical
processes.
Preliminary examination of the data reveals
many features that will shed new light on global
and regional elements of the ocean circulation.
Some of the early results discussed above,
although mostly qualitative and semiquantitative
in nature, are indicative of the rich set of results
that we expect to obtain from the WOCE multitracer data set. Present efforts are directed at a
synthesis of the individual data sets on a global
scale. Future work will include combining the
tracer data with other measurements performed
during WOCE to address a variety of global and
regional oceanographic problems along the lines of
those presented in this contribution. Additionally,
there will be targeted efforts to integrate the tracer
data into the set of variables used to advance the
performance of global circulation models (see
Willebrand and Haidvogel, Chapter 7.2). Many of
these efforts will go on in parallel, i.e. results from
WOCE tracer studies will be produced on a continuous basis even if the nature of the studies will
vary.
The use of tracer inventories provides an independent means of estimating water mass formation rates. In contrast to current meter arrays or
hydrographic sections across strong boundary
flows, tracer inventories represent the integrated
effects of water mass formation from all sources
on decadal time scales, and the results are less susceptible to shorter-term fluctuations on the mean
water mass formation rate. The development and
refinement of techniques for estimating water mass
formation rates using tracer inventories are still in
the early stages. Significant improvements are
anticipated as more data become available, and
techniques are being refined for estimating inventories from these data. Significant improvements
are also possible by advancing our understanding of the boundary conditions for input and
export of tracers in the water masses. Detailed
comparisons of observational data sets with model
simulations should also provide insight of mutual
benefit.
In terms of deriving oceanographic information
that complements that from other methods, we are
only at the beginning of exploiting the deep helium
tracer field. Thus far most of the analysis has been
descriptive in nature rather than quantitative.
However, the helium field has now been mapped
in sufficient detail to allow direct comparison with
models that include tracer transport equations, as
well as helium sources and sinks (e.g. Farley et al.,
1995). Future work should refine these modelling
efforts and expand them to include inverse modelling studies, either on a regional or basin scale.
The combination of the helium isotope data with
hydrographic and other tracer data from the
WOCE survey and augmenting studies will provide valuable insights into ocean circulation and
mixing.
The extensive tracer data set collected as part of
WOCE offers the opportunity to study in greater
detail than was previously possible the formation
rates of dense waters around Antarctica. This
should help to improve our understanding of
the subsequent mixing processes that occur as
these deep and bottom waters move away from
Antarctica. It also represents a key element in
studies of the long-term variability of deep and
bottom water in the Southern Ocean (Broecker
et al., 1999).
Tracers have been used extensively in the past to
constrain rates of biogeochemical processes.
Recently transient tracers have been used directly in
the calculation of the ocean uptake of anthropogenic CO 2 (Gruber et al., 1996; Wallace, Chapter
6.3). In addition, a number of three-dimensional
global models are being developed and used to
simulate key ocean circulation processes, and to
provide predictive capabilities for possible future
changes related to climate variability (Böning and
Semtner, Chapter 2.2; Willebrand and Haidvogel,
Chapter 7.2). The ability of these models to simulate realistically water mass formation rates, and
estimate the uptake of important atmospheric trace
gases (such as CO 2 ) in the Southern Ocean, must
SECTION 5 FORMATION AND TRANSPORT OF WATER MASSES
450