Chai¹, F., M.-S. Jiang¹, R.T. Barber², R.A. Feely³, R.C. Dugdale⁴, T.-H. Peng⁵, and Y. Chao⁶

¹School of Marine Science, 5471 Libby Hall, University of Maine, Orono, ME 04469, E-mail: fchai@maine.edu, ²Duke University, NSOE Marine Laboratory, 135 Duke Marine Lab Road, Beaufort, NC 28516, ³Ocean Climate Research Division, NOAA/PMEL, 7600 Sand Point Way NE, Seattle WA 98115, ⁴Romberg Tiburon Center, San Francisco State University, PO Box 855, Tiburon CA 94920, ⁵NOAA Atlantic Oceanographic and Meteorological Laboratory, Ocean Chemistry Division, 4301 Rickenbacker Causeway, Miami, FL 33149-1026, and ⁶Jet Propulsion Laboratory, California Institute of Technology, 4800 Oak Grove Drive, Pasadena, CA 91109

Modeled decadal variability of primary productivity and air-sea CO₂ flux in the equatorial Pacific Ocean

The response of primary production and sea-to-air CO₂ flux in the equatorial Pacific to decadal timescale climate variability is investigated using a physical-biogeochemical model forced with COADS wind stress and heat flux. The circulation model resolves decadal variations over the past 40 years with a decrease in the equatorward interior flow and a reduction of 20% in the equatorial upwelling transport since the 1976-77 climate shift. The decreased volume transports causes a rise of sea surface temperature in the equatorial upwelling zone by about 0.7ºC since mid 1970s. Slowdown of the meridional overturning and decrease of the equatorial upwelling transport have significant impacts on marine ecosystem and carbon flux. The modeled primary production and phytoplankton biomass decrease by 10% over the past 40 years mainly due to reduction of upward nutrient flux. Our physical-biogeochemical model results document that the equatorial Pacific sea-to-air CO₂ flux decreased by 20% after the 1976-77 climate shift.