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The manganese cycle in the Southern Ocean: the role of physical supply mechanisms and external sources
Thesis (PhD)--Stellenbosch University, 2025.
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Stellenbosch : Stellenbosch University
2026
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| _version_ | 1867613835328749568 |
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| access_status_str | Open Access |
| author | Ramalepe, Thapelo |
| author2 | Ryan–Keogh, Thomas J. |
| author_browse | Ramalepe, Thapelo Ryan–Keogh, Thomas J. |
| author_facet | Ryan–Keogh, Thomas J. Ramalepe, Thapelo |
| author_sort | Ramalepe, Thapelo |
| collection | Thesis |
| dc_rights_str_mv | Stellenbosch University |
| description | Thesis (PhD)--Stellenbosch University, 2025. |
| format | Thesis |
| id | oai:scholar.sun.ac.za:10019.1/134789 |
| institution | Stellenbosch University (South Africa) |
| last_indexed | 2026-06-10T12:42:26.594Z |
| license_str | Other — see source repository |
| provenance_str_mv | Harvested via OAI-PMH from SUNScholar — Stellenbosch University Repository |
| publishDate | 2026 |
| publishDateRange | 2026 |
| publishDateSort | 2026 |
| publisher | Stellenbosch : Stellenbosch University |
| publisherStr | Stellenbosch : Stellenbosch University |
| record_format | dspace |
| source_str | SUNScholar — Stellenbosch University Repository |
| spelling | oai:scholar.sun.ac.za:10019.1/134789 The manganese cycle in the Southern Ocean: the role of physical supply mechanisms and external sources Ramalepe, Thapelo Ryan–Keogh, Thomas J. Roychoudhury, Alakendra Stellenbosch University. Faculty of Science. Dept. of Earth Science. Phytoplankton -- Effect of metals on Manganese -- Environmental aspects -- Southern Ocean Iron -- Environmental aspects -- Southern Ocean Trace elements in water Biogeochemical cycles -- Seasonal variations Carbon cycle (Biogeochemistry) -- Climatic factors UCTD Thesis (PhD)--Stellenbosch University, 2025. Ramalepe, T. 2025. The Manganese Cycle in the Southern Ocean: The Role of Physical Supply Mechanisms and External Sources. Unpublished doctoral dissertation. Stellenbosch: Stellenbosch University [online]. Available: https://scholar.sun.ac.za/items/3dff5685-3de8-4cef-b770-dc5d14cb2fb4 ENGLISH ABSTRACT: Trace metals play important roles as co-factors in various enzymes for phytoplankton metabolism; however, they are often at subnanomolar concentrations thereby inhibiting phytoplankton growth. Manganese (Mn) is essential for phytoplankton photosynthesis, yet in the iron (Fe) limited Southern Ocean, its supply mechanisms, external sources and links to biological demand remain poorly quantified. First, data from two research cruises conducted in the Atlantic sector of the Southern Ocean, during austral winter and spring 2019, demonstrated that winter entrainment is an important physical process supplying dissolved Mn (dMn) to the mixed layer, contributing over 90% of the total flux, with a smaller but sometimes significant contribution from diapycnal diffusion. These physical supply fluxes when compared to estimates of biological requirements, revealed that in most Southern Ocean hydrographic zones, dMn supply during winter is sufficient to meet biological demand in spring and summer, except in the subtropical zone where additional supply mechanisms may be needed. To place these observations in a broader context, a comprehensive compilation of dMn and dFe data from the GEOTRACES Intermediate Data Product was utilised to examine basin-scale physical fluxes across the Southern Ocean. This synthesis allowed the identification of regional hotspots where strong physical forcing enhances Mn and Fe supply, and regions of potential Fe-Mn co-limitation. Across the Southern Ocean, winter entrainment dominates the total vertical supply, with Mn fluxes ranging from ~13.8 to 23.4 μmol m⁻² yr⁻¹ and Fe fluxes from ~24.6 to 35.0 μmol m⁻² yr⁻¹, supplying up to 8 times more Mn and 16 times more Fe than diapycnal diffusion, the next most important supply mechanism. Spatially, Fe supply generally exceeded Mn south of the Polar Front, whereas Mn dominated to the north, especially in the Atlantic sector. Regions with low Fe:Mn supply ratios were identified along the zero meridian and near the Antarctic Peninsula, indicating potential Fe-Mn co-limitation. Finally, the PISCES-BYONIC biogeochemical model was used to evaluate the role and importance of external Mn sources, including sediments, atmospheric dust and hydrothermal vents, in the Southern Ocean. Model simulations showed that sedimentary input is the primary external source supplying surface dMn, supporting primary production and carbon export, while atmospheric dust and hydrothermal sources had relatively minor impacts. These findings highlight the sensitivity of Southern Ocean biogeochemistry to external Mn sources, particularly the regionally important but poorly quantified sedimentary input. Altogether, this thesis provides the first basin-scale assessment of Mn cycling in the Southern Ocean, offers a new approach to evaluate co-limitation with Fe, and lays the groundwork for improved model projections of trace metal dynamics and carbon export under future climate change scenarios. AFRIKAANSE OPSOMMING: Geen opsomming beskikbaar. Doctoral 2026-01-08T06:15:48Z 2026-01-08T06:15:48Z 2025-12 Thesis https://scholar.sun.ac.za/handle/10019.1/134789 Stellenbosch University xii, 161 pages : illustrations, maps application/pdf Stellenbosch : Stellenbosch University |
| spellingShingle | Phytoplankton -- Effect of metals on Manganese -- Environmental aspects -- Southern Ocean Iron -- Environmental aspects -- Southern Ocean Trace elements in water Biogeochemical cycles -- Seasonal variations Carbon cycle (Biogeochemistry) -- Climatic factors UCTD Ramalepe, Thapelo The manganese cycle in the Southern Ocean: the role of physical supply mechanisms and external sources |
| title | The manganese cycle in the Southern Ocean: the role of physical supply mechanisms and external sources |
| title_full | The manganese cycle in the Southern Ocean: the role of physical supply mechanisms and external sources |
| title_fullStr | The manganese cycle in the Southern Ocean: the role of physical supply mechanisms and external sources |
| title_full_unstemmed | The manganese cycle in the Southern Ocean: the role of physical supply mechanisms and external sources |
| title_short | The manganese cycle in the Southern Ocean: the role of physical supply mechanisms and external sources |
| title_sort | manganese cycle in the southern ocean the role of physical supply mechanisms and external sources |
| topic | Phytoplankton -- Effect of metals on Manganese -- Environmental aspects -- Southern Ocean Iron -- Environmental aspects -- Southern Ocean Trace elements in water Biogeochemical cycles -- Seasonal variations Carbon cycle (Biogeochemistry) -- Climatic factors UCTD |
| url | https://scholar.sun.ac.za/handle/10019.1/134789 |
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