Time and space variations of monsoonal upwelling along the west and east coasts of India

The study of monthly mean local temperature anomaly (LTA defined as the difference between coastal and mid-ocean sea surface temperatures), and Ekman transport along the west and east coasts of India based on 60-year data set of Hastenrath and Lamb (1979) reveals that both LTA and Ekman transport (ME) are found to be high during the summer monsoon. The LTAs are caused by different oceanographic processes; off the southwest coast of India, the positive LTAs are due to upwelling that is driven by the summer monsoonal winds. Along the northern part of the east coast of India the negative LTAs are attributed to the discharges of river water, which also depends on the strength of summer monsoon. Earlier studies on the planktonic foraminifera in the northern Indian Ocean documented that the Globigerinoides bulloides and Neogloboquadrina dutertrei are reliable indicators of upwelling and sea surface salinity, respectively. The existing significant relationships between LTAs and ME during summer monsoon in both the Arabian Sea and Bay of Bengal suggest that the variation in abundance of Globigerina bulloides and Neogloboquadrina dutertrei in the sediment cores of Arabian Sea and Bay of Bengal can trace the intensity of paleoupwelling and river discharge and thereby associated summer monsoon intensity and productivity changes in the northern Indian Ocean.