47
Descriptive Oceanography
where h is the average height of the water column (3200 m), and A is the area of the ocean
(3.23 10 8 km 2 ) (V deep = h A). The values of ( 14 C/ C) Atlantic /( 14 C/ C) Pacific = 1.20 ± 0.03 can be used
to estimate the ventilation time of deep Pacific water:
t = V deep / R mix = [( 14 C/ C) surface /( 14 C/ C) deep – 1] λ
(1.10)
Using λ = 8200 yr, one obtains a mean residence time of about 1600 ± 250 years.
More recent studies have divided the oceans into a number of boxes in an attempt
to determine the age of the different water masses. A sketch of the box model with the
values for the estimated rates of exchange is shown in Figure 1.55. The 14 C work from
the GEOSECS program has been used to give us a look at the deep- water circulation
in the world oceans (Stuiver, Quay, and Ostlund, 1983). Most of the deep- water formation takes place in the North Atlantic. The average residence time for water in the North
Atlantic is about 246 yr, which is the youngest of the oceans. The major source of this
North Atlantic deep water is from the Norwegian Sea. This deep water flows over the
1000
3000
Depth (m)
5000
0
ABW
NIW
W
DWM
DWV
DW
AABW
AABW
SIW
SIW
DWL
ABW
80°N
60°
40°
20°N
0°
20°S
40°
60°
80°S
Figure 1.52
Characteristic water masses in the Atlantic Ocean. W = warm water sphere; NIW = subarctic intermediate
water; SIW = subantarctic intermediate water; DW = deep water; DWU = deep water, upper; DWM = deep water,
middle; DWL = deep water, lower; ABW = Arctic bottom water; AABW = Antarctic bottom water.
1000
3000
Depth (m)
5000
0
NIW
W
W
DW
DW
AABW
SIW
AABW
58°N
40°
20°N
0°
20°S
40°
60°
80°S
Figure 1.53
Characteristic water masses in the Pacific Ocean. W = warm water sphere; NIW = subarctic intermediate water;
SIW = subantarctic intermediate water; DW = deep water; AABW = Antarctic bottom water.