• Trevor Platt

      Articles written in Journal of Earth System Science

    • A model study of seasonal mixed-layer primary production in the Arabian Sea

      John Brock Shubha Sathyendranath Trevor Platt

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      We combined a surface irradiance model with a non-spectral photosynthesisirradiance model to estimate the daily, average rate of mixed-layer 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 observations of phytoplankton biomass.

      Modelled surface radiation is at an annual maximum in May beneath nearly cloud-free skies just prior to the summer solstice. The model estimate of surface radiation diminishes through 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 is 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 primary production, the fall and spring inter-monsoons. The annual cycles of modelled mixed-layer primary production differ by region in the Arabian Sea due to varying monsoon influence and circulation dynamics.

    • New production and mixed-layer physics

      Shubha Sathyendranath Trevor Platt

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      We treat the ocean carbon cycle as a coupled physical-biogeochemical process. The interactions between mixed-layer dynamics and growth of phytoplankton in the layer are discussed, and the formal relationship between phytoplankton accumulation and new production is examined. A coupled biological-physical model is presented for studying the classical spring bloom in the N. Atlantic, and possible differences in the mechanisms that drive the seasonal phytoplankton blooms in the N. Atlantic and the Arabian Sea are discussed. Finally, recommendations are made for observational programs to improve our understanding of the biologically-mediated carbon cycle in the Arabian Sea.

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