several decades. These data provide additional validation of
general circulation models, which, in turn, allow a better
identification of the causes and mechanisms of the temporal
variability of
14 C. Figure 4.9 represents the ORCA/IPSL
model simulation of
14 C data measured in one coral from
Bermuda shore (Druffel 1989).
Both the
14 C coral data and the modeled
14 C at the sea
surface show coeval changes, indicating that the model
A
Natural 14 C
ORCA
-80
-120
-140
-160
-180
-200
-240
-80
-120
-140
-160
-180
-200
-240
0
1000
2000
3000
4000
5000
0
1000
2000
3000
4000
5000
Depth (m)
Latitude
-40 -30 -20 -10
0
10
20
Latitude
-40 -30 -20 -10
0
10
20
Fig. 4.8 Observed and simulated
14
C concentration (in ‰) in the
eastern Pacific Ocean. The negative value indicates an aging of the
water bodies compared with the age of the atmosphere. A decrease of
10‰ is equivalent to an aging of about 80 years. A mass of nearly
homogeneous water between −200 and −240‰ occupies the eastern
Pacific Ocean from depths between 2000 and 3500 m. At about 40 °S,
the presence of a more recent water mass, between −180 and −200‰ at
4000 m depth, formed on the edge of the Antarctic continent should be
noted. It corresponds to the Antarctic Bottom Water (AABW)
200
100
0
-100
1950
1960
1970
1980
1990
2000
14
C (‰)
Year A.D.
B
Fig. 4.9 Variations in D
14
C in ‰ (circles) in a banded coral collected
near Bermuda (Druffel 1989), in the subtropical surface waters of the
North Atlantic between 1950 and 1990. Δ
14 C increased rapidly
between 1960 AD and 1965 AD due to the
14
C input into the
atmosphere during the aerial nuclear bomb tests. Results of the
interannual OPA simulation (INT) (8.1) are represented. This simulation highlights the importance of the winds in the atmosphere-ocean
exchanges in the subtropical North Atlantic (Tisnérat, Dutay, personal
communication)
4 Carbon-14
63