01-05 December 2025
INCOIS, Hyderabad, India.
| Abstract Submission No. | ABS-06-0095 |
| Title of Abstract | Tracing Nitrogen Cycling and Loss with Nitrate Isotopes in the Bay of Bengal and East Equatorial Indian Ocean |
| Authors | Gesa Schulz*, Kirstin Dähnke, Tina Sanders, Jan Penopp, Hermann W. Bange, Rena Czeschel, Birgit Gaye |
| Organisation | University of Hamburg |
| Address | Bundesstraÿe 55 Hamburg, Hamburg, Germany Pincode: 20146 E-mail: gesa.schulz@uni-hamburg.de |
| Country | Germany |
| Presentation | Oral |
| Abstract | Oxygen minimum zones (OMZ) play a key role in the global marine nitrogen cycle, contributing 20⿿40% of the total loss of bioavailable nitrogen, despite occupying only ~1% of ocean volume. The Bay of Bengal (BoB) hosts one of the most pronounced OMZ with near anoxic conditions. However, it has not yet been recognized as a site with significant nitrate reduction. Here, we present new data on nitrogen cycling from the East Equatorial Indian Ocean (EEIO) and BoB, collected during the SO305 BIOCAT-IIOE2 cruise (April⿿May 2024). Water column profiles of temperature, salinity, oxygen, and nutrients, alongside nitrate isotopic compositions, reveal distinct biogeochemical processes in both regions. Hydrographic data indicate limited exchange between BoB and EEIO intermediate waters at ~5°N. Nitrate isotope depth profiles varied with depth and region, influenced by water mass structure below 300m and biological processes above. In surface waters, phytoplankton uptake led to isotopic enrichment and nitrate deficits. Regenerative nitrification dominated in subsurface layers, primarily recycling nitrogen from previously assimilated organic matter. Within the OMZ of the BoB, we identified a persistent nitrogen deficit and slightly enriched nitrate isotopes, indicating nitrogen loss, which we attributed to anammox as the dominant nitrogen loss pathway in the BoB. |
| Are you part of IIOE-2 endorsed project | yes |
| Endorsed Project Number | IIOE2-EP07, IIOE2-EP52 |
| Keywords | Oxygen Minimum Zone, Bay of Bengal, East Equatorial Indian Ocean, Nitrogen, Nitrate Isotopes, Nitrogen Loss, Nitrate Isotopes |
| For Awards | no |