01-05 December 2025
INCOIS, Hyderabad, India.
| Abstract Submission No. | ABS-03-0200 |
| Title of Abstract | Diatom-Diazotroph Associaions (DDAs): A Potential Source Of New Nitrogen In The Arabian Sea During The Southwest Monsoon |
| Authors | Vishal C.R*, Manguesh U. Gauns, Anil K. Pratihary |
| Organisation | CSIR-National Institute of Oceanography |
| Address | CSIR-National Institute of Oceanography, Goa Panaji, Goa, India Pincode: 403004 E-mail: vishalrajan22@gmail.com |
| Country | India |
| Presentation | Poster |
| Abstract | Diatom-diazotroph associations (DDAs) are ubiquitous in the tropical and subtropical oceans. Although the mixed layer of the open ocean generally remains nitrogen-limited year-round, DDAs are predominantly found during the summer monsoon (SM) in the Eastern Arabian Sea (EAS). Globally, DDAs peak between June and September, though the drivers behind this seasonal pattern are not well established. Our observations indicated that during this period, sea surface temperatures (SSTs) rise in the Pacific and Atlantic but slightly decline in the Arabian Sea (AS). Nevertheless, SSTs across all these regions converge to ~25⿿28°C, creating a uniform thermal environment that likely supports the global occurrence of DDAs between June-September. During this period, we studied the variability of DDAs in the euphotic zone (0⿿80 m) along the eastern Arabian Sea (68°E, 8°N⿿21°N) over two consecutive summer monsoons (July 2020 and July 2021). Our results revealed that the Arabian Sea⿿s mixed layers remain oligotrophic and serve as a hotspot for DDAs. During the SM-2020, DDAs were mostly found in moribund stages of Richelia-Rhizosolenia (R-R) and Climacodium-Crocosphaera (C-C), associated with elevated temperatures (>28°C). In contrast, the SM-2021 observed healthier DDAs R-R, Hemiaulus-Richelia (H-R), and C-C associations occurring at lower temperatures (<28°C). The higher abundance of DDA in the EAS, particularly in the NEAS is likely driven by excess phosphate and high silicate concentrations, increased aeolian dust deposition and availability of iron, and relatively lower temperatures compared southeastern AS. Climacodium-Crocosphaera, found across all latitudes, suggests that iron availability may play a key role in DDAs distribution in the EAS. Our estimated N⿿ fixation rates, based on heterocyst abundance, ranged from 6 to 103µmolNm⁻²d⁻¹ in the EAS, suggesting a substantial input of new nitrogen which is previously unaccounted in the regional N⿿ fixation budgets in the EAS. |
| Are you part of IIOE-2 endorsed project | no |
| Keywords | Diatom-diazotrophs, Global oceans, N2 fixation, summer monsoon, Eastern Arabian Sea |
| For Awards | yes |
| Date Of Birth | 10-12-1992 |
| ECSN Registration Number | IIOE2-ECSN-0139 |