Decadal variabiltiy in Pacific sea surface pCO2
Abstract
An ocean biochemical model is used to study the changes in air-sea CO2 fluxes associated with the 1976/77 shift in the Pacific Ocean. The 1976/77 shift represents the most recent regime shift of the Pacific Decadal Oscillation (PDO), the dominant decadal mode of variability for the Pacific. Although there are insufficient pre-1976 sea surface pCO2 data with which to describe the associated shift in sea surface pCO2, models provide a means whereby this change can be estimated. Here we have used the ORCA2 (version 8.2 of OPA) ocean circulation model to address this question. The model has approximately 2^o resolution globally, but the meridional resolution is increased to 0.5^o near the equator. The ORCA2 ocean circulation model is forced with climatological fields constructed from the years 1961-1970 (cold tropical phase of the PDO), and 1986-1995 (warm tropical phase of the PDO), and run to steady state for each case. It is shown that for the earlier period (1961-1970), there is enhanced entrainment of TCO2- and nutrient-rich mode waters in the equatorial upwelling, relative to the period 1986-1995. This is due primarily to changes in ocean circulation driven by changes in the surface wind forcing, as the trade winds were approximately 25% stronger during the earlier period. Our analysis for the equatorial Pacific focuses on decadal changes in sea surface pCO2, and the extent to which the decreased delivery of TCO2 to the surface layer after 1976 was compensated by decreased export production due to changes in the nutrient supply. We also consider simulated sea surface pCO2 changes in the North Pacific.
- Publication:
-
EGS - AGU - EUG Joint Assembly
- Pub Date:
- April 2003
- Bibcode:
- 2003EAEJA....11622R