HR: 0800h
AN: OS31A-0557    [Abstracts]
TI: Decadal Variations in Ecosystem, Biogeochemistry and Carbon Cycle in the Equatorial Pacific: A Model Study
AU: * Wang, X
EM: wwang@essic.umd.edu
AF: University of Maryland/ESSIC, 2207 Computer and Space Sciences Building, College Park, MD 20742 United States
AU: Christian, J
EM: Jim.Christian@ec.gc.ca
AF: Canadian Centre for Climate Modelling and Analysis, University of Victoria, Victoria, BC V8W 2Y2 Canada
AU: Murtugudde, R
EM: ragu@essic.umd.edu
AF: University of Maryland/ESSIC, 2207 Computer and Space Sciences Building, College Park, MD 20742 United States
AU: Busalacchi, A
EM: tonyb@essic.umd.edu
AF: University of Maryland/ESSIC, 2207 Computer and Space Sciences Building, College Park, MD 20742 United States
AB: The equatorial Pacific Ocean is known to undergo significant physical, biological, and chemical changes on seasonal (e.g., upwelling), interannual (e.g., El Ni\~{n}o and La Ni\~{n}a), and decadal time scales (e.g., the Pacific Decadal Oscillation). We undertook a study to investigate special and temporal variations in ecosystem, biogeochemistry, and carbon cycle using a basin-scale 3-dimensional physical-ecosystem-carbon model forced by 6-day mean surface wind-stresses from the NCEP. The model is able to capture the surface chlorophyll variability observed in the SeaWiFS, showing significant seasonal-to-interannual variability in biogeochemical fields. Moreover, simulations indicate pronounced decadal variations and regime shift in the high-nitrate low-chlorophyll (HNLC) region of the equatorial Pacific over the past 50 years. The largest decadal variations in the mixed layer depth (MLD) were found in the central equatorial Pacific where mid-year MLDs vary from approximately 60 m prior to 1970 to about 40 m post 1980, which results in weakening of nutrient supply through entrainment during the period of 1980-2000. The model simulated remarkable increase in zooplankton biomass but slight decrease in phytoplankton biomass in surface waters of the central/eastern equatorial Pacific after the 1976/7 phase shift. Modeled primary productivity and new production declined by approximately 5 mmol C m$^{-2}$ d$^{-1}$ during 1980-2000 relative to 1955-1975 in the HNLC. While delta-pCO$_{2}$ increased in most parts of region after the shift, sea-air CO$_{2}$ flux dropped in the east but increased in the west of $150\deg$W after the shift.
DE: 4805 Biogeochemical cycles (1615)
DE: 4806 Carbon cycling
DE: 4815 Ecosystems, structure and dynamics
DE: 4845 Nutrients and nutrient cycling
DE: 4215 Climate and interannual variability (3309)
SC: Ocean Sciences [OS]
MN: 2004 AGU Fall Meeting