A MODEL STUDY OF SEASONAL MIXED-LAYER PRIMARY PRODUCTION IN THE ARABIAN SEA

We combined a surface irradiance model with a non-spectral photosynthe sis-irradiance model to estimate the daily, average rate of mixed-laye r primary production in the Arabian Sea for the 15th day of months at the end of the northeast monsoon, the southwest monsoon, and the fall and spring inter-monsoons. Our model experiment uses climatologies of cloud cover, mixed-layer thickness, and satellite ocean-color observat ions of phytoplankton biomass. Modelled surface radiation is at an ann ual maximum in May beneath nearly cloud-free skies just prior to the s ummer solstice. The model estimate of surface radiation diminishes thr ough the southwest monsoon over most of the northern Arabian Sea to an annual minimum in August due to intense cloudiness. In agreement with previous ship-based measurements, the photosynthesis-irradiance model predicts that the mixed-layer primary production in the Arabian Sea i s extremely seasonal, and peaks annually during the southwest monsoon to the north-west of the atmospheric Findlater Jet and along the coast of Somalia. Northern Arabian Sea maxima predicted for both the summer and winter monsoons are separated by periods of low mixed-layer prima ry production, the fall and spring inter-monsoons. The annual cycles o f modelled mixed-layer primary production differ by region in the Arab ian Sea due to varying monsoon influence and circulation dynamics.