Physical-Biogeochemical Interaction Linkages associated with the Arabian Sea Monsoons: Climate Trend or Decadal Variablity?

Interannual variation in satellite-based ocean color observations from the early SeaWiFS era revealed increases in surface chlorophyll of the Arabian Sea, which have been attributed to stronger coastal upwelling during the summer monsoon as a result of retreating glaciers and reduced albedo in Central Asia associated with anthropogenic warming. On longer time scales, warmer periods of the Holocene have been characterized by a northward shift of the intertropical convergence zone (ITCZ), especially in the South Asian Monsoon sector, thereby increasing the strength and northward extension of summer monsoon rains. The marine sediment record indicates increased monsoonal upwelling in the Arabian Sea during such warming periods associated with increased denitrification in the oxygen minimum zone. Recent data analyses showed a decrease of oxygen and an increase of nitrite concentrations in the northern part of the Arabian Sea during the last 50 years, which could also be related to a strengthening of the summer monsoon and a northward shift of the ITCZ. Through the use of remote sensing observations, nutrient data, sediment trap time series, and high-resolution sedimentary records, we investigate whether recent changes in Arabian Sea productivity, upwelling intensity, sea surface temperature and denitrification are related to decadal variability or global warming trends. These observational assets are applied to characterize both the winter and summer monsoon periods in order to comprehensively examine how seasonal biogeochemical variability in the Arabian Sea has responded to these influences.