- Dona Paula, Goa, India.
- +91-0832- 2450327
- iiosc2020[at]nio[dot]org
| Abstract Submission No. | ABS-2022-05-0096 |
| Title of Abstract | Variability in POC and DOC in the eastern and central Arabian Sea during southwest monsoon 2018 |
| Authors | Saumya Silori*, Haimanti Biswas, Diksha Sharma, Mintu Chowdhury, Damien Cardinal, Magloire Mandeng Yogo |
| Organisation | CSIR-National Institute of Oceanography |
| Address | Biological Oceanography Division, National Institute of Oceanography Panjim, Goa, India Pincode: 430004 Mobile: 9130477012 E-mail: saumyasilori27@gmail.com |
| Country | India |
| Presentation | Oral |
| Abstract | Arabian Sea (AS), one of the highly productive zones in the global oceans, is under the marked influence of the Indian monsoon system. During June-September, the low pressure over the Indian subcontinent gives rise to south-westerly winds, which drive upwelling along the Somalia, Oman, and Indian southwest coast. A low-level jet (Findlater) blows almost perpendicular to the coast of Somalia and results in a broader upwelling, whose signature often propagates to the central AS. The strong physical forcing mediates the nutrient supply and makes this bay highly productive. The biogeochemical variability in relation to physical forcing along the west coast of India and in the central AS was monitored in Aug 2018 (RV Sindhu Sadhna, SSD 55). The physical features along the southwest coast of India indicated upwelling, which supported high nutrients, Chla, particulate organic carbon (POC) (31.5 ± 27.1μmol L -1 ), and nitrogen (PN) (4.1 ± 2.6μmol L -1 ) concentrations within the upper mixed layers. In contrast, the northern sector was characterized by, substantially lower POC (8.3 ± 2.9 μmol L -1 ) and PN (1.2 ± 0.4 μmol L -1 ) with deeper mixed depths (MLDs). Interestingly, despite the presence of upwelling in the southern sector, the total organic carbon (TOC) concentrations along the west coast of India varied between 168⿿266 µmol L -1 (0-20 m) and did not differ significantly between the southern and northern sector. On an average, slightly higher dissolved organic carbon (DOC) concentrations were observed in the northern regions (184± 21μmol L -1 ) than in the south (171± 22μmol L -1 ), and the DOC:POC ratios were significantly lower in the south (2.4⿿16.7) than the north (15⿿38). Higher water temperatures, nutrient limitation and dominance of smaller phytoplankton cells were likely to be responsible for the increased partitioning of organic carbon into the dissolved fraction in the north. The contrast in DOC:POC ratios suggest disparate carbon cycling pathways in the two regions. In the central Arabian along 64° E, diverse environmental conditions were apparent from wind speeds and MLDs. The sampled stations were classified into three regions: i) Northern (19°⿿21°N); ii) Findlater Jet Axis (16°⿿18°N) and iii) Southern Stations (11°⿿15°N). Substantially higher POC concentrations were seen at the northern stations (11.7 ± 5.6 μmol L ⿿1 ) influenced by open ocean upwelling that occurs due to the positive wind stress curl. In contrast, low POC concentrations were measured at the stations impacted by the Findlater Jet axis (7.6 ± 1.8 μmol L ⿿1 ) and the southern stations (7.9 ± 2 μmol L ⿿1 ). Despite the highest POC values in the north, the highest TOC concentrations were observed in the center (218⿿286 μmol L -1 ) of the transect between 15⿿17° N bound by lower values (142⿿173 μmol L -1 ) on the northern and southern end. Accordingly, the highest DOC values were observed in the center (209⿿278 μmol L -1 ), flanked by lower values in the north (130⿿144 μmol L -1 ) and south (137⿿166 μmol L -1 ). Notably, the highest TOC and DOC values observed between 15⿿17° N in conjugation with the highest wind speeds, lowest temperatures, and low salinity values indicate the influence of the Findlater Jet axis and its contribution to the lateral advection of TOC from the western Arabian Sea in addition to the local processes.A substantial amount of TOC can be advected towards the Findlater Jet axis to the central Arabian Sea and may supply organic matter that may support the oxygen minimum zone OMZ, and this observation supports the existing hypothesis. |