Coupling between SW monsoon‐related surface and deep ocean processes as discerned from continuous particle flux measurements and correlated satellite data

Abstract

Particle flux data obtained by time series sediment traps deployed at water depths of approximately 3000 m in the western, central, and eastern Arabian Sea since 1986 were compared with wind speeds derived from measurements made by microwave radiometer flying on polar orbiting satellites and sea surface temperatures (SSTs) provided by the Physical Oceanography Distributed Active Archive Center at Jet Propulsion Laboratory. This comparison has allowed us to trace the link between the oceanographic and biological processes related to the development of the SW monsoon with the pattern and interannual variability of particle fluxes to the interior of the Arabian Sea. We could recognize the well‐known upwelling systems along the coasts of Somalia and Oman as well as open ocean upwelling at the beginning of the SW monsoon. Both open ocean upwelling and coastal upwelling off Oman cause a cooling of surface waters at our western and central Arabian Sea stations. When SSTs fall below their long‐term average, an increase in fluxes which are dominated by coccolithophorid‐derived carbonates occurs. The timing of this increase is determined by the rate of surface water cooling. Further intensification of upwelling as the SW monsoon progresses causes additional increases in biogenic opal fluxes denoting diatom blooms in the overlying waters. The total fluxes during this period are the highest measured in the open Arabian Sea. At the central Arabian Sea location the fluxes are only randomly affected by these blooms. The particle flux in the eastern Arabian Sea is as high as in the central Arabian Sea but is influenced by a weaker upwelling system along the Indian coast. The observed interannual variability in the pattern of particle fluxes during the SW monsoons is most pronounced in the western Arabian Sea. This is controlled by the intensity of the upwelling systems on the one hand and the transport of cold, nutrient‐poor, south equatorial water into the Oman region on the other. The latter effect, which is strongest during the SW monsoon with highest recorded wind speeds, reduces the influence of upwelling and the related particle fluxes at the western Arabian Sea station, where highest fluxes occur during SW monsoons with moderate wind speeds. Thus coastal and open ocean upwelling are most effective in transferring biogenic matter to the deep sea during the SW monsoons of intermediate strength.

Spatiotemporal variations of nitrogen isotopic records in the Arabian Sea

“…1a). Contrary to higher denitrification in the northeastern AS, the export production is always higher in the northwestern AS throughout a year (Rixen et al, 1996). Such decoupling between productivity and denitrification was attributed to the oxygen supply by intermediate water exchange besides primary productivity oxygen demand (Pichevin et al, 2007).…”

Diatoms and their influence on the biologically mediated uptake of atmospheric CO<sub>2</sub> in the Arabian Sea upwelling system

“…The SW winds (SW monsoon) form a tropospheric jet (Findlater Jet) extending almost parallel to the Arabian coast (Fig. 1, Findlater, 1977;Rixen et al, 1996). The monsoon winds and the deserts surrounding the western and northern parts of the Arabian Sea lead to dust inputs into the Arabian Sea, which are among the highest in the world ocean Fung, 1994, 1995).…”

“…The monsoon winds and the deserts surrounding the western and northern parts of the Arabian Sea lead to dust inputs into the Arabian Sea, which are among the highest in the world ocean Fung, 1994, 1995). Rixen et al (1996). Red squares indicate the U.S. JGOFS (Honjo et al, 1999) and the red circles the long-term Indo/German sediment trap sites in the western and central Arabian Sea (Rixen et al, 2002).…”

Seasonal and interannual variations in the nitrogen cycle in the Arabian Sea

“…Sea surface temperatures (SSTs) were used as an indicator of upwelling strength (Rixen et al, 1996). However, its use is problematic since the impact of global warming, through mixing and deep water formation, penetrates into the Fig.…”