01-05 December 2025
INCOIS, Hyderabad, India.
| Abstract Submission No. | ABS-03-0035 |
| Title of Abstract | Variability in the secondary nitrite maxima in the central Arabian Sea: Summer (2017 -2018) Vs. Winter monsoon (2019) |
| Authors | Haimanti Biswas*, Saumya Silori, Diksha Sharma, Medhavi Pandey |
| Organisation | CSIR-National Institute of Oceanography, Dona Paula, Goa |
| Address | CSIR-National Institute of Oceanography Dona Paula, Goa, India Pincode: 403004 E-mail: haimanti.biswas.nio@gmail.com |
| Country | India |
| Presentation | Oral |
| Abstract | The secondary nitrite maxima (SNM), expanding up to several hundred meters, are a typical feature that develops in the subsurface waters of most of the Oxygen Deficient Zones (ODZs) in the global oceans. SNM indicates nitrogen loss that occurs under severe oxygen deficiency, when the denitrifying microbes utilize oxygen via a dissimilatory nitrate reduction pathway by reducing nitrate (NO3-) to nitrite (NO2-). Hence, within the core ODZs where denitrification occurs, oxygen levels vary inversely with nitrite concentrations and linearly with nitrate levels. Monitoring the formation of SNM is important to understand nitrogen loss, which may impact primary productivity. In the Arabian Sea, one of the intense and persistent ODZs is found on its eastern side, which is spatially decoupled from the high-productivity regions. In this basin, monsoon strength is a key factor affecting primary productivity, ODZs, as well as associated features like the distribution of SNM. Here we present the variability in SNM along the central Arabian Sea (64°E, 11 °N -21°N) during two consecutive summer monsoon (Aug 2017 and Aug 2018) and winter monsoon (Dec 2019) seasons. Significant difference in monsoon onset and intensity was reflected in most of the physicochemical and biological processes, including the SNM. During summer monsoon, the SNM was expanded between 200-400 m, and the core was mostly present between 13 -17 °N, with the highest nitrite level (>5 µM) seen in 2018 (200 m; 14 °N). Within the two summer monsoons, the highest nitrite concentration was observed in 2018. Contrarily, during winter, the SNM was shrunken and the maximum nitrite value was lower (3 µM; 300 m; 16 °N) compared to summer (4-5 µM). These variabilities were correlated in terms of space, nitrate, and oxygen levels with monsoon intensity and onset, which largely impacts organic matter transport to sustain the ODZs. |
| Are you part of IIOE-2 endorsed project | no |
| Keywords | Monsoon, Oxygen, Indian ocean, Nitrite, Nitrate, Organic matter |
| For Awards | no |