01-05 December 2025
INCOIS, Hyderabad, India.
| Abstract Submission No. | ABS-08-0287 |
| Title of Abstract | Biological⿿Physical Interactions Regulating Nutrient Dynamics in the Lakshadweep Sea during the Winter Monsoon |
| Authors | Harikrishna Prasad Mamidala*, Ganguly D, Purvaja R, R.S. Robin, Hariharan G, Subbareddy B, Ramesh R |
| Organisation | National Centre for Sustainable Coastal Management |
| Address | H. No. 8-57, Pedabrahmadevam Kakinada, Andhra Pradesh, India Pincode: 533434 E-mail: dattuhari@gmail.com |
| Country | India |
| Presentation | Oral |
| Abstract | Hydrographic profiles (up to 500m) from the open-ocean region of the Arabian Sea near the Lakshadweep Islands (8°N - 12°N) were examined during the winter monsoon (November) of 2019, to understand biogeochemical dynamics in this region. The temperature profile from 25 locations, exhibited strong stratification, with surface waters exceeding 30°C and gradually decreasing to ~17°C at 300 m depth. Salinity ranged from 38.6 to 40.4, with the highest values occurring in the upper 100 m between 10 and 10.5°N along the transect, indicating high evaporation and limited freshwater input during the northeast monsoon. Below 100 m, salinity gradually decreased to less than 39 at 300m. Chlorophyll concentrations ranged from 0.06 to 0.36 µg l⁻¹, with higher values mainly in the upper 50⿿100 m, coinciding with the chlorophyll maximum zone. Three distinct high-chlorophyll patches (>0.33 µg l⁻¹) were observed (around 50 m depth), suggesting localized biological enhancement. Below 150 m, concentrations declined sharply (<0.15 µg l⁻¹), reflecting reduced light availability and weaker primary productivity. Dissolved oxygen ranged from 1.75 to 5.85 mg l⁻¹, exhibiting strong vertical and spatial gradients. Surface waters (0⿿50 m) were well-oxygenated (>5.5 mg l⁻¹), while concentrations decreased to as low as 1.75 mg l⁻¹ between 150 and 300 m, indicating intense subsurface respiration and limited ventilation. During the study, the surface water was mostly limited in dissolved inorganic nitrogen and oxygen depleted waters, coinciding with the nitrite maximum in the mid-section, at ~100⿿150 m depth. Lateral variability revealed localized low-oxygen intrusions in the mid-water column (9 - 10.5°N), possibly associated with mesoscale eddies and advective processes transporting low-oxygen waters from the central Arabian Sea. The observed oxygen structure highlights the interplay between physical circulation and biological productivity, providing important baseline information on biogeochemical dynamics in the Lakshadweep open waters during the winter monsoon. |
| Are you part of IIOE-2 endorsed project | no |
| Keywords | Thermocline; stratification; biogeochemistry; Nutrients; Lakshadweep Sea; Winter Monsoon. |
| For Awards | yes |
| Date Of Birth | 20-04-1983 |
| ECSN Registration Number | IIOE2-ECSN-0169 |