Home > Formation and maintenance of high-nitrate, low pH layers in the Eastern Indian Ocean and the role of nitrogen fixation
Formation and maintenance of high-nitrate, low pH layers in the Eastern Indian Ocean and the role of nitrogen fixation
| Title | Formation and maintenance of high-nitrate, low pH layers in the Eastern Indian Ocean and the role of nitrogen fixation |
| Publication Type | Journal Article |
| Year of Publication | 2013 |
| Authors | Waite, AM, Rossi V, Roughan M, Tilbrook B, Akl J, Thompson PA, Feng M, Wyatt ASJ, Raes EJ |
| Journal | Biogeosciences Discussions |
| Volume | 10 |
| Issue | 3 |
| Pagination | 3951 - 3976 |
| Date Published | 2013 |
| Keywords | biogeochemistry, Ningaloo Reef, nirtogen fixation, sea water pH |
| Abstract | We investigate the biogeochemistry of Low Dissolved Oxygen High Nitrate layers form-ing against the backdrop of several interleaving regional water masses in the EasternIndian Ocean, off northwest Australia adjacent to Ningaloo Reef. These water masses, including the forming Leeuwin Current, have been shown directly to impact the ecological function of Ningaloo Reef and other iconic coastal habitats downstream. Our results indicate that LODHN layers are formed from multiple subduction events of the Eastern Gyral Current beneath the Leeuwin Current (LC); the LC originates from both the Indonesian Throughflow and tropical Indian Ocean. Density differences of up to 0.025kgm between the Eastern Gyral Current and the Leeuwin Current produce sharp gradients that can trap high concentrations of particles (measured as low transmission) along the density interfaces. The oxidation of the trapped particulate matter results in local depletion of dissolved oxygen and regeneration of dissolved nitrate (nitrification). We document an associated increase in total dissolved carbon dioxide, which lowers the seawater pH by 0.04 units. Based on isotopic measurements (δ15N)and (δ18O) of dissolved nitrate, we determine that∼ 40–100% of the nitrate found in LODHN layers is likely to originate from nitrogen fixation, and that regionally, the importance of N fixation in contributing to LODHN layers is likely be highest at the surface and offshore. |
| URL | http://biogeosciences-discuss.net/10/3951/2013/bgd-10-3951-2013.pdf |
| DOI | 10.5194/bgd-10-3951-2013 |
| Short Title | Biogeosciences Discuss. |
