- Dona Paula, Goa, India.
- +91-0832- 2450327
- iiosc2020[at]nio[dot]org
| Abstract Submission No. | ABS-2022-06-0021 |
| Title of Abstract | Summer monsoon induced changes in phytoplankton community structure in the central Arabian Sea (2017-2018): After two decades of JGOFS |
| Authors | Mintu Chowdhury*, Haimanti Biswas, Diksha Sharma, Saumya Silori, Veronica Fernandes, Jayu Narvekar, Debasmita Bandyopadhyay, Aziz ur Rahman Shaik |
| Organisation | CSIR-National Institute of Oceanography, Goa |
| Address | Biological Oceanography Division, CSIR-National Institute of Oceanography Panjim, Goa, India Pincode: 403004 Mobile: 7506022427 E-mail: mintuchy90@gmail.com |
| Country | India |
| Presentation | Oral |
| Abstract | The central Arabian Sea is unique for its ⿿open ocean upwelling during the summer monsoon due to the development of a low-level atmospheric jet (Findlater Jet). In the northern part of this jet, the upwelling occurs due to a positive wind stress curl, whereas, the southern part witnesses downwelling induced by negative wind stress curl. After two decades of joint global ocean flux studies (JGOFS), we present here the first report on the phytoplankton community from the central Arabian Sea along 64E (11N⿿21N) during the South West Monsoon (SWM) (August 2017 and 2018). Most of the physicochemical and biological parameters showed significant inter-annual as well as north-south variability which was linked to surface wind forcing. The phytoplankton cell abundance was almost eightfold higher during August 2018 (1.2 x104 L-1) compared to August 2017 (0.14 x104 cells L-1). Statistically significant spatial and inter-annual variability in phytoplankton abundance, diversity, the ratios of diatom: dinoflagellate and centric: pennate diatoms were noticed and were closely coupled with the dissolved inorganic nutrient distribution (bottom-up control). Relatively low phytoplankton cell density in 2017 was coupled with high zooplankton biomass (top-down control). Higher dissolved silicate (DSi) supply in 2018 due to stronger upwelling and the advected nutrients from the Somali coast seemed to promote larger diatoms that are capable of escaping grazing and may lead to higher export production. The large centric diatoms occupied the upwelled regions (21⿿20° N) (e. g. Rhizosolenia imbricata, R. hebetata and Coscinodiscus radiatus) whereas, small pennate diatoms (Pseudo-nitzschia spp., Navicula spp. Nitzschia spp.) and dinoflagellates (Gymnodinium spp.) were pronounced in the south (11⿿15° N). And while comparing the trends with the JGOFS reports, no considerable community shift was noticed. The overall observations indicated that any future change in atmospheric forcing like wind speed related to warming may have a high potential to influence phytoplankton abundance and community structure in this region. This may further impact trophic transfer and carbon export flux in the central Arabian Sea. |