A VARIABLE SINK FOR ATMOSPHERIC CO2 IN SUBTROPICAL MODE WATER OF THE NORTH ATLANTIC

Reference

Bates N.R., A. C. Pequignet, R. J. Johnson and N. Gruber, A Variable Sink for Atmospheric CO2 in
Subtropical Mode Water of the North Atlantic Ocean, Nature, 420, 489-493, 2002.

Abstract
Ocean circulation is an important regulator of the physical uptake of carbon dioxide (CO2) from
the atmosphere. However, the magnitude and variability of CO2 uptake into subtropical mode
waters (STMW’s), that ventilate the shallow depths of the subtropical gyres, are poorly quantified.
Here we report a recent change in the rate of CO2 uptake into the STMW layer of the North
Atlantic Ocean. Since the late 1980’s, CO2 has increased in STMW at a rate double that expected
from equilibrium with increasing atmospheric CO2. We estimate that an extra ~0.6-2.8 Pg (1015 g)
of CO2 has accumulated within the gyre STMW layer, representing ~3-10% (i.e., ~0.03-0.24 Pg C
yr-1) of the net annual ocean uptake of CO22 between 1988 and 2001. The recent change in the
oceanic sink of CO2 into STMW appears coupled to variability of STMW formation and circulation
which in turn is primarily associated with climate variability (i.e. North Atlantic Oscillation, NAO).
Interannual variability in the uptake of CO2 into STMW thus provides another factor and feedback
controlling the global ocean uptake of CO2.

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