oceanographic parameter on another parameter can
be difficult to discern directly from data. These research questions are better investigated with numerical ocean models. Before an ocean model result can
be taken seriously, however, the model must demonstrate reasonable ability to simulate current conditions. This generally requires that various model
inputs or variables be ‘tuned’ or calibrated to match
measured distributions and rates. Radiocarbon is the
only common measurement that can be used to
calibrate the various rates of abyssal processes in
general circulation models. M. Fiadeiro carried out
the first numerical simulation for the abyssal Pacific
and used the GEOSECS
14 C data to calibrate the
model. J.R. Toggweiler extended this study using a
global model.
Both the Fiadeiro and Toggweiler models, and all
subsequent models that include the deep water D
14
C,
are of coarse resolution owing to current computer
limitations. As the much larger WOCE
14 C data set
becomes available, the failure of these models, especially in detail, becomes more evident. Toggweiler’s model, for example, has advective mixing in the
Southern Ocean that is significantly greater than
supported by data. Additionally, the coarse resolution of the model prevents the formation of, or at
least retards the importance of, deep western
boundary currents. Significant model deficiencies
appear when the bomb14 C distribution and integrals
at the time of GEOSECS and WOCE are compared
with data.
During the last 10 years the number and variety of
numerical ocean models has expanded greatly, in
large part because of the availability and speed of
modern computers. The Ocean Carbon Model
Intercomparison Project (OCMIP) brought ocean
modelers together with data experts in the first organized effort to compare model results with data,
with the long-term goals of understanding the processes that cause model differences and of improving
the prediction capabilities of the models. The unique
aspect of this study was that each participating group
Latitude
Depth (m)
60°S
60°S
40°S
40°S
20°S
20°S
0
0
20°N
20°N
40°N
40°N
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60°N
1000
600
200
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_ 40
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100
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_ 220
_ 200
_ 180
_ 160
_ 140
_ 120
_ 100
_ 80
_ 60
Depth (m)
1000
600
200
0
800
400
800
400
Figure 11 Upper thermocline meridional sections along 1521 W in the central Pacific. (A) The same measured data as in Figure 5C
(B) An estimate of thermocline D
14
C values prior to the invasion of bomb-produced radiocarbon.
_ 240
_ 220
_ 200
_ 180
_ 160
140
160
180
200
Δ
14 C (ppt)
Apparent oxygen utilization ( mol kg )
μ
_ 1
Figure 12 Apparent oxygen utilization plotted against
measured D
14
C for WOCE Pacific Ocean samples taken at
depths greater than 4000 m and north of 401S. The slope of the
line ( À 0.83170.015) can be used to estimate an approximate
oxygen utilization rate of 0.1 mmol kg
À1 y
À1 if steady state and no
mixing with other water masses is assumed.
246 RADIOCARBON
be difficult to discern directly from data. These research questions are better investigated with numerical ocean models. Before an ocean model result can
be taken seriously, however, the model must demonstrate reasonable ability to simulate current conditions. This generally requires that various model
inputs or variables be ‘tuned’ or calibrated to match
measured distributions and rates. Radiocarbon is the
only common measurement that can be used to
calibrate the various rates of abyssal processes in
general circulation models. M. Fiadeiro carried out
the first numerical simulation for the abyssal Pacific
and used the GEOSECS
14 C data to calibrate the
model. J.R. Toggweiler extended this study using a
global model.
Both the Fiadeiro and Toggweiler models, and all
subsequent models that include the deep water D
14
C,
are of coarse resolution owing to current computer
limitations. As the much larger WOCE
14 C data set
becomes available, the failure of these models, especially in detail, becomes more evident. Toggweiler’s model, for example, has advective mixing in the
Southern Ocean that is significantly greater than
supported by data. Additionally, the coarse resolution of the model prevents the formation of, or at
least retards the importance of, deep western
boundary currents. Significant model deficiencies
appear when the bomb14 C distribution and integrals
at the time of GEOSECS and WOCE are compared
with data.
During the last 10 years the number and variety of
numerical ocean models has expanded greatly, in
large part because of the availability and speed of
modern computers. The Ocean Carbon Model
Intercomparison Project (OCMIP) brought ocean
modelers together with data experts in the first organized effort to compare model results with data,
with the long-term goals of understanding the processes that cause model differences and of improving
the prediction capabilities of the models. The unique
aspect of this study was that each participating group
Latitude
Depth (m)
60°S
60°S
40°S
40°S
20°S
20°S
0
0
20°N
20°N
40°N
40°N
60°N
60°N
1000
600
200
0
. . . . . . . .
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_ 200
_ 160
_ 120
_ 80
_ 40
0
40
80
100
100
Latitude
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_ 220
_ 200
_ 180
_ 160
_ 140
_ 120
_ 100
_ 80
_ 60
Depth (m)
1000
600
200
0
800
400
800
400
Figure 11 Upper thermocline meridional sections along 1521 W in the central Pacific. (A) The same measured data as in Figure 5C
(B) An estimate of thermocline D
14
C values prior to the invasion of bomb-produced radiocarbon.
_ 240
_ 220
_ 200
_ 180
_ 160
140
160
180
200
Δ
14 C (ppt)
Apparent oxygen utilization ( mol kg )
μ
_ 1
Figure 12 Apparent oxygen utilization plotted against
measured D
14
C for WOCE Pacific Ocean samples taken at
depths greater than 4000 m and north of 401S. The slope of the
line ( À 0.83170.015) can be used to estimate an approximate
oxygen utilization rate of 0.1 mmol kg
À1 y
À1 if steady state and no
mixing with other water masses is assumed.
246 RADIOCARBON