four subjects: the thermohaline circulation, upper
ocean circulation, model constraints, and biogeochemical processes.
Thermohaline Circulation
There is a close coupling of the surface waters in high
latitudes to the deep ocean through the density-driven thermohaline circulation. During the process of
deep-water formation, atmospheric constituents such
as CFCs are introduced into the newly formed water.
In recent years, major advances in our knowledge of
the thermohaline circulation can be attributed to
information derived from transient tracer data, particularly for two reasons. First, the development of
analytical techniques so that oceanographers can
easily produce large quantities of high quality data.
Tracer oceanographers have benefited from multiinvestigator programs like the World Ocean Circulation Experiment. The following highlights some of
the advances that have come about in our understanding of the thermohaline circulation to which
observations of CFCs have contributed:
• Discovery of a new water mass component of
North Atlantic Deep Water (NADW), called Upper
Labrador Sea Water, location of its formation region and contributing processes, and timescales of
eastward spreading along the equator.
• Identification of Denmark Straits Overflow Water
as the primary source of bottom water of the
western subpolar basin.
• Confirmation of the structure and continuity of
the Deep Western Boundary Current throughout
the western North Atlantic Ocean, and extension
into the South Atlantic.
• Extension of the CFCs well into the interior of the
western North Atlantic show the importance of
deep recirculation gyres in ventilating the interior
basins, and in slowing the equatorward transport
to timescales of o30 years with effective spreading rates of 1–2 cm s
À1
.
• Contribution to quantifying formation rates and
decadal climate variability in the Arctic, Greenland and Labrador Seas.
• Estimates for the formation rates of Weddell Sea
Deep and Bottom Waters, production rate of
Antarctic Bottom Water and pathways and timescales for spreading into the North Atlantic.
Upper Ocean Circulation
The use of CFCs for upper ocean processes has involved the application of concentrations to deduce
sources and circulation pathways, and application of
pCFC ages. The following highlights some of the
advances that have come about in our understanding
of the upper ocean circulation to which observations
of CFCs have contributed:
• Identification of the Sea of Okhotsk and Alaskan
Gyre as important location for the ventilation of
North Pacific Intermediate Water, these waters
then spread into the subtropics on a timescale of
o20 years.
• Quantification of the flux of water from the mixed
layer into thermocline and intermediate layers of
the North and South Pacific.
• Contribution to the description of sources and
pathways of water masses transported from the
Pacific through the Indonesian Seas into the Indian Ocean.
• Quantification of the sources of northern and
southern water and the processes needed to ventilate the tropical Pacific and Atlantic, including
advection, diapycnal and vertical mixing.
• Observation that pathways of the most recently
ventilated Antarctic Intermediate Waters are into
the eastern South Indian Ocean, while at that level
there appears to be flow of older waters from the
South Pacific into the western Indian Ocean.
• Quantification of subduction and formation rates
for subtropical underwaters and in the North
Atlantic its interannual variability that is negatively correlated with intermediate waters of the
eastern subpolar gyre.
Model Constraints
In general CFC concentrations and inventories have
been used in comparison with model simulated
concentrations and inventories. The time-dependent
nature of the CFCs provides a stringent test of a
model’s ability to integrate property distributions
over time. The following highlights some of the advances that have come about in our ability to put
constraints on models from the use of CFCs in
models:
• Dilution of CFCs transported by the Deep Western Boundary Current and effect on tracer ages.
• Testing the sensitivity of a model for correct
simulation of formation rates, pathways, and
spreading rates.
• Testing the sensitivity of a model for correct
simulation of ocean model velocity fields.
• Determining the model sensitivity to subgrid scale
mixing for purposes of estimating ventilation
rates.
• The importance of considering seasonal variations
in the upper oceans as part of the tracer boundary
CFCS IN THE OCEAN 161
ocean circulation, model constraints, and biogeochemical processes.
Thermohaline Circulation
There is a close coupling of the surface waters in high
latitudes to the deep ocean through the density-driven thermohaline circulation. During the process of
deep-water formation, atmospheric constituents such
as CFCs are introduced into the newly formed water.
In recent years, major advances in our knowledge of
the thermohaline circulation can be attributed to
information derived from transient tracer data, particularly for two reasons. First, the development of
analytical techniques so that oceanographers can
easily produce large quantities of high quality data.
Tracer oceanographers have benefited from multiinvestigator programs like the World Ocean Circulation Experiment. The following highlights some of
the advances that have come about in our understanding of the thermohaline circulation to which
observations of CFCs have contributed:
• Discovery of a new water mass component of
North Atlantic Deep Water (NADW), called Upper
Labrador Sea Water, location of its formation region and contributing processes, and timescales of
eastward spreading along the equator.
• Identification of Denmark Straits Overflow Water
as the primary source of bottom water of the
western subpolar basin.
• Confirmation of the structure and continuity of
the Deep Western Boundary Current throughout
the western North Atlantic Ocean, and extension
into the South Atlantic.
• Extension of the CFCs well into the interior of the
western North Atlantic show the importance of
deep recirculation gyres in ventilating the interior
basins, and in slowing the equatorward transport
to timescales of o30 years with effective spreading rates of 1–2 cm s
À1
.
• Contribution to quantifying formation rates and
decadal climate variability in the Arctic, Greenland and Labrador Seas.
• Estimates for the formation rates of Weddell Sea
Deep and Bottom Waters, production rate of
Antarctic Bottom Water and pathways and timescales for spreading into the North Atlantic.
Upper Ocean Circulation
The use of CFCs for upper ocean processes has involved the application of concentrations to deduce
sources and circulation pathways, and application of
pCFC ages. The following highlights some of the
advances that have come about in our understanding
of the upper ocean circulation to which observations
of CFCs have contributed:
• Identification of the Sea of Okhotsk and Alaskan
Gyre as important location for the ventilation of
North Pacific Intermediate Water, these waters
then spread into the subtropics on a timescale of
o20 years.
• Quantification of the flux of water from the mixed
layer into thermocline and intermediate layers of
the North and South Pacific.
• Contribution to the description of sources and
pathways of water masses transported from the
Pacific through the Indonesian Seas into the Indian Ocean.
• Quantification of the sources of northern and
southern water and the processes needed to ventilate the tropical Pacific and Atlantic, including
advection, diapycnal and vertical mixing.
• Observation that pathways of the most recently
ventilated Antarctic Intermediate Waters are into
the eastern South Indian Ocean, while at that level
there appears to be flow of older waters from the
South Pacific into the western Indian Ocean.
• Quantification of subduction and formation rates
for subtropical underwaters and in the North
Atlantic its interannual variability that is negatively correlated with intermediate waters of the
eastern subpolar gyre.
Model Constraints
In general CFC concentrations and inventories have
been used in comparison with model simulated
concentrations and inventories. The time-dependent
nature of the CFCs provides a stringent test of a
model’s ability to integrate property distributions
over time. The following highlights some of the advances that have come about in our ability to put
constraints on models from the use of CFCs in
models:
• Dilution of CFCs transported by the Deep Western Boundary Current and effect on tracer ages.
• Testing the sensitivity of a model for correct
simulation of formation rates, pathways, and
spreading rates.
• Testing the sensitivity of a model for correct
simulation of ocean model velocity fields.
• Determining the model sensitivity to subgrid scale
mixing for purposes of estimating ventilation
rates.
• The importance of considering seasonal variations
in the upper oceans as part of the tracer boundary
CFCS IN THE OCEAN 161