13 Sep 2021

13 Sep 2021

Review status: this preprint is currently under review for the journal ESD.

Indian ocean marine biogeochemical variability and its feedback on simulated South Asia climate

Dmitry V. Sein1,2, Anton Y. Dvornikov1, Stanislav D. Martyanov1, William Cabos3, Vladimir A. Ryabchenko1, Matthias Gröger4, Daniela Jacob5, Alok Kumar Mishra6, and Pankaj Kumar6 Dmitry V. Sein et al.
  • 1Shirshov Institute of Oceanology, Russian Academy of Sciences; Moscow, Russia
  • 2Alfred Wegener Institute, Helmholtz Centre for Polar and Marine Research; Bremerhaven, Germany
  • 3University of Alcala; Alcala, Spain
  • 4Leibniz Institute for Baltic Sea Research, Warnemünde, Rostock 18119, Germany
  • 5Climate Service Center Germany (GERICS); Hamburg, Germany
  • 6Department of Earth and Environmental Sciences, Indian Institute of Science Education and Research Bhopal, India

Abstract. We investigate the effect of variable marine biogeochemical light absorption on Indian Ocean sea surface temperature (SST) and how this affects the South Asian climate. In twin experiments with a regional Earth System Model, we found that the average SST is lower over most of the domain when variable marine biogeochemical light absorption is taken into account, compared to the reference experiment with a constant light attenuation coefficient equal to 0.06 m-1. The most significant deviations (more than 1 °C) in SST are observed in the summer period. A considerable cooling of subsurface layers occurs, and the thermocline shifts upward in the experiment with the activated biogeochemical impact. Also, the phytoplankton primary production becomes higher, especially during periods of winter and summer phytoplankton blooms. The effect of altered SST variability on climate was investigated by coupling the ocean models to a regional atmosphere model. We find the largest effects on the amount of precipitation, particularly during the monsoon season. 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 the reduction of the convective precipitation. In the Bay of Bengal, it increases the large-scale precipitation, countering convective precipitation decline. Thus, the key impacts of including the full biogeochemical coupling with corresponding light attenuation, which in turn depends on variable chlorophyll-a concentration, include the enhanced phytoplankton primary production, a shallower thermocline, decreased SST and water temperature in subsurface layers, with cascading effects upon the model ocean physics which further translates into altered atmosphere dynamics.

Dmitry V. Sein et al.

Status: final response (author comments only)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on esd-2021-64', Anonymous Referee #1, 19 Oct 2021
  • RC2: 'Comment on esd-2021-64', Anonymous Referee #2, 03 Nov 2021

Dmitry V. Sein et al.

Dmitry V. Sein et al.


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Short summary
The effect of the marine biogeochemical variability upon the South Asian regional climate has been investigated. In the experiment where its full impact is activated, the average sea surface temperature is lower over most of the ocean. Including the biogeochemical coupling, the main impacts include the enhanced phytoplankton primary production, a shallower thermocline, decreased SST and water temperature in subsurface layers.