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| Abstract Submission No. | ABS-2022-06-0435 |
| Title of Abstract | Long-term trend in high biomass algal bloom in the northern Arabian Sea |
| Authors | Sanjiba Kumar Baliarsingh* |
| Organisation | Indian National Centre for Ocean Information Services |
| Address | Indian National Centre for Ocean Information Services (INCOIS),, "Ocean Valley", Hyderabad, Telangana, India Pincode: 500090 Mobile: 8121448650 E-mail: baliarsingh.s@incois.gov.in |
| Country | India |
| Presentation | Poster |
| Abstract | The open ocean region of the Northern Arabian Sea (NAS) experiences intense high biomass algal bloom during the winter monsoon. This study uses a satellite-based (MODISA) approach to determine the long-term distribution of diatom and green Noctiluca scintillans (GNS) bloom over NAS from 2002 to 2019. The distribution indicates a higher chlorophyll-a (chl-a) concentration in association with GNS and diatom abundance in December as a pre-conditioning for GNS. The distribution of chl-a showed a consistent pattern over the last 17 years with a peak in February-March and a subsequent decline towards April. The Sea Surface Temperature (SST) also showed a similar trend over the years by starting to decrease from December to February and subsequent increase from March until May. Chl-a was observed with a significant inverse relationship with SST. Response of chl-a with elevated levels following a decline in SST signified the utilization of growth-promoting nutrients introduced to the euphotic zone through convective mixing. Daily climatology of chl-a and SST revealed gradual lowering of SST signifying progression of convective mixing and subsequent elevation in the concentration of chl-a indicating initiation of bloom during the initial phase of December. GNS spread area started to increase towards the end of January and surpassed diatom during the initial phase of March. The evolution of GNS within diatom-dominated regions indicated substantial grazing by mixotrophic GNS on its preferred diet diatom as a prerequisite condition in preparing a conducive bed for GNS proliferation. Long-term analysis (2002-2019) of SST during the peak bloom months (February-March) confirmed a stable trend over the years. In contrast, the trend of chl-a was observed with a marginal increasing pattern over the years. The spread area of diatom and GNS for the peak bloom period (February-March) during 2002-2019 discerned stable trends for diatom while GNS with a marginal increasing trend over the years. |