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A comparative study of nitrogen uptake and nitrification rates in sub-tropical, polar and upwelling waters
Includes bibliographical references
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| Main Author: | |
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| Other Authors: | |
| Format: | Thesis |
| Language: | English |
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Department of Oceanography
2016
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| _version_ | 1867613481682862080 |
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| access_status_str | Open Access |
| author | Philibert, Marie Catherine Raïssa |
| author2 | Waldron, Howard |
| author_browse | Philibert, Marie Catherine Raïssa Waldron, Howard |
| author_facet | Waldron, Howard Philibert, Marie Catherine Raïssa |
| author_sort | Philibert, Marie Catherine Raïssa |
| collection | Thesis |
| description | Includes bibliographical references |
| format | Thesis |
| id | oai:open.uct.ac.za:11427/16794 |
| institution | University of Cape Town (South Africa) |
| language | eng |
| last_indexed | 2026-06-10T12:36:50.455Z |
| license_str | Not specified — see source repository |
| provenance_str_mv | Harvested via OAI-PMH from UCTD — University of Cape Town Open Access Repository |
| publishDate | 2016 |
| publishDateRange | 2016 |
| publishDateSort | 2016 |
| publisher | Department of Oceanography |
| publisherStr | Department of Oceanography |
| record_format | dspace |
| source_str | UCTD — University of Cape Town Open Access Repository |
| spelling | oai:open.uct.ac.za:11427/16794 A comparative study of nitrogen uptake and nitrification rates in sub-tropical, polar and upwelling waters Philibert, Marie Catherine Raïssa Waldron, Howard Clark, Darren Oceanography Includes bibliographical references Nitrification is the oxidation of ammonium to nitrate through a two step biological process. Nitrification in the euphotic zone has, in the past, been considered negligible even though quantifying this process correctly is important when linking carbon export to nitrate uptake by phytoplankton. However, studies of both nitrogen uptake and nitrification rates in surface waters are rare. This thesis presents such data for the Southern Ocean and St-Helena Bay, located in the Southern Benguela upwelling system. Using 15N tracers, Nitrogen uptake and regeneration rates were measured in the Southern Ocean (during a winter cruise in July 2012 and a summer cruise in February-March 2013) and St-Helena Bay (during three studies in November 2011, March 2012 and March 2013). In St-Helena Bay, the upwelling (bloom) cycle was one of the main drivers of the nitrogen cycle. As the bloom cycle started, nitrate uptake rates (5:47 ± 670:48nmol∙L⁻¹∙h⁻¹) and nitrite regeneration (4:36 - 1:28 ± 22:83 - 1:63nmol∙L⁻¹∙h⁻¹) were high but the contribution of nitrification to the nitrate demand was low. Nitrite regeneration at this time could have been driven by phytoplankton excretion. In contrast, at the end of the bloom cycle, nitrate uptake rates were low and was exceeded by nitrate regeneration rates (25:34 - 6:16 ± 82:74 - 34:41nmol∙L⁻¹∙h⁻¹). Nitrite regeneration decreased and was most likely due to ammonium oxidation at this stage of the upwelling cycle. Nitrification in the Southern Ocean was more variable than in St-Helena Bay. It was only detected at five stations out of fifteen and the accuracy of the high nitrite oxidation rates (37:21 - 9:13 ± 217 - 88nmol∙L⁻¹∙h⁻¹) observed can only be assessed with repeat measurements. Nitrate uptake rates ranged from 0.07 to 57:00nmol∙L⁻¹∙h⁻¹ while ammonium uptake rates ranged from 0.81 - 160:94nmol∙L⁻¹∙h⁻¹. The nitrogen uptake rates were similar for both seasons. Using multivariate statistical approach, it was found that during winter, in the Southern Ocean, light and ammonium availability were the most important factors regulating nitrogen uptake while in the late summer, changes in the mixed layer depth had a larger effect. This study provides new observational data for two undersampled regions and contributes to further the mechanistic understanding of the factors regulating nitrogen uptake and nitrification in the Southern Ocean and St-Helena Bay. 2016-02-05T07:26:59Z 2016-02-05T07:26:59Z 2015 Doctoral Thesis Doctoral PhD http://hdl.handle.net/11427/16794 eng application/pdf Department of Oceanography Faculty of Science University of Cape Town |
| spellingShingle | Oceanography Philibert, Marie Catherine Raïssa A comparative study of nitrogen uptake and nitrification rates in sub-tropical, polar and upwelling waters |
| thesis_degree_str | Doctoral |
| title | A comparative study of nitrogen uptake and nitrification rates in sub-tropical, polar and upwelling waters |
| title_full | A comparative study of nitrogen uptake and nitrification rates in sub-tropical, polar and upwelling waters |
| title_fullStr | A comparative study of nitrogen uptake and nitrification rates in sub-tropical, polar and upwelling waters |
| title_full_unstemmed | A comparative study of nitrogen uptake and nitrification rates in sub-tropical, polar and upwelling waters |
| title_short | A comparative study of nitrogen uptake and nitrification rates in sub-tropical, polar and upwelling waters |
| title_sort | comparative study of nitrogen uptake and nitrification rates in sub tropical polar and upwelling waters |
| topic | Oceanography |
| url | http://hdl.handle.net/11427/16794 |
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