Impact of the Indian Ocean temperature - phytoplankton feedback on
simulated South Asia climate
Abstract
A regional Earth System Model has been implemented for the South Asia
region. We investigate the effect of the marine biogeochemical feedback
which affects the attenuation of the short-wave radiation upon the
regional climate. In the experiment where the feedback is activated the
average SST is lower over most of the domain. The greatest deviations
(more than 1°C) in SST between the two runs occur in the summer period
during the phytoplankton bloom. A significant cooling of subsurface
layers occurs and the thermocline shifts upward compared to the Jerlov
type absorption. The phytoplankton primary production and its deviation
in the feedback-based simulation turned out to be higher, especially
during periods of winter and summer phytoplankton blooms. The marine
biogeochemistry feedback also affects the amount of precipitation in the
model in particular during the monsoon season. The associated SST
cooling leads to a reduction of the precipitation but affects it in
different ways. In the Arabian Sea, the reduction of the transport of
humidity across the equator leads to a reduction of the large scale
precipitation in the eastern part of the basin, reinforcing reduction of
the convective precipitation. In the Bay of Bengal, the feedback
increases the large scale precipitation, contouring the decrease of
convective precipitation. Thus, the main impacts of including the
biogeochemical coupling in the Indian Ocean include the enhanced
phytoplankton primary production, a shallower thermocline and decreased
SST, with cascading effects upon the model ocean physics which further
translates into altered atmosphere dynamics.