which pumps water down into the upper thermocline over more than half the ocean surface area, a reservoir much larger than that of the mixed layer alone, The connections between the upper-thermocline reservoir and the deep ocean may indeed require very long time constants, but the carbon and heat budgeting on the decadal time scale must account properly for the potentially large reservoir directly beneath the mixed layer.

Simple model calculations involving Ekman pumping from the mixed layer into the intermediate waters of the order of 10–20 cm/day1 and estimates of mixing coefficients for the intermediate waters from tracer studies (Östlund et al., 1974; National Science Foundation, 1979) suggest that the upper-thermocline reservoir communicates effectively with the mixed layer on time scales of several decades. Therefore, the effective thermal capacity of the ocean for absorbing heat on these time scales is nearly an order of magnitude greater than that of the mixed layer alone.* If this reservoir is indeed involved, it could delay the attainment of ultimate global thermal equilibrium by the order of a few decades. It would also increase the rate at which the ocean can take up carbon from the air and might at least partially account for the current discrepancies between the observed rise in atmospheric CO2 and the estimated rise due to the anthropogenic input of CO2 into the air.

*

The existence of the Ekman pumping underlies all the generally accepted ideas about the physics of the general circulation of the oceans. The order of magnitude estimated above (10–20 cm/day) is consistent with a variety of oceanographic data, including wind stress, chemical tracers, and local heat-budget calculations.



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