Moored Observations for the Forced Upper Ocean Dynamics Experiment in the Arabian Sea.

The year-long mooring records in the Arabian Sea 15 deg 30N61 deg 30E show clearly the semi-annual biological response to the northeast and southwest monsoons. Each monsoon causes the mixed layer to deepen, but for the northeast monsoon, convective processes dominate, while during the southwest monsoon, the mixed layer deepens via wind-induced mixing. During both mixing periods, chlorophyll declines, and then increases as the water column stratifies. The annual cycle of chlorophyll variability at the mooring site the climatological center of the Findlater Jet generally follows the mixed layer depth. Strong diel variability in phytoplankton and particle variables were observed, and coherence analysis indicated that these were modulated more by water column processes e.g., changes in the mixed layer depth than by solar variability. We have demonstrated the utility of moored sensor systems in an unforgiving environment. The high-resolution data are extremely useful to those trying to understand the drivers for seasonal variability in productivity. The seasonal variability in productivity is crucial to interpret the export of carbon from the surface ocean to depth. The results will fuel consideration of the importance of diel processes in determining the activities of plankton.