HR: 16:40h
AN: A14B-03    [Abstracts]
TI: Bio-physical feedbacks in the tropical Pacific
AU: * Timmermann, A
EM: axel@hawaii.edu
AF: IPRC, SOEST, University of Hawaii, 2525 Correa Road, Honolulu, HI 96822 United States
AU: Marzeion, B
EM: benma@nersc.no
AF: Nansen Environmental and Remote Sensing Center, Thormohlensgt. 47, Bergen, 5006 Norway
AU: Jin, F
EM: jff@met.fsu.edu
AF: FSU Department of Meteorology, 404 Love Building, Tallahassee, FL 32306-4520 United States
AU: Murtugudde, R
EM: ragu@essic.umd.edu
AF: ESSIC/UMD, CSS Bldg/Room 2201, College Park, MD 20742 United States
AB: We study the influence of phytoplankton on the tropical Pacific heat budget. A hybrid coupled model for the tropical Pacific is used which is based on a primitive equation reduced gravity multi-layer ocean model, a dynamic ocean mixed layer, an atmospheric mixed layer and a statistical atmosphere. The statistical atmosphere relates deviations of the sea surface temperature from its mean to wind-stress anomalies and allows for the rectification of the annual cycle and the El Ni\~no-Southern Oscillation (ENSO) phenomenon through the positive Bjerknes-feedback. Furthermore, a 9-component ecosystem model is coupled to the physical variables of the ocean. The simulated chlorophyll concentrations can feedback onto the ocean heat budget by their optical properties which modify solar light absorption in the surface layers. It is shown that both, the surface layer concentration as well as the vertical profile of chlorophyll have a significant effect on the simulated mean state, the tropical annual cycle and ENSO. This study supports a previously suggested hypothesis which predicts an influence of phytoplankton concentration of the tropical Pacific climate mean state and its variability. The bio-climate feedback diagnosed here works as follows: Maxima in the subsurface chlorophyll concentrations lead to an enhanced subsurface warming due to the absorption of photosynthetically available shortwave radiation. This warming triggers a deepening of the mixed layer in the eastern equatorial Pacific and eventually a reduction of the surface ocean currents. The weakened south-equatorial current generates an eastern Pacific surface warming. Due to the deepening of the mixed layer, also the strength of the simulated annual cycle is diminished. This in trurn leads to an increase in ENSO variability.
DE: 4215 Climate and interannual variability (3309)
SC: Atmospheric Sciences [A]
MN: 2004 AGU Fall Meeting