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Seasonal dynamics of dissolved iron in the marginal ice zone of South Atlantic and Southern Oceans
Thesis (MSc)--Stellenbosch University, 2024.
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Stellenbosch : Stellenbosch University
2025
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| access_status_str | Open Access |
| author | Jansen van Vuuren, Lide |
| author2 | Roychoudhury, Alakendra N. |
| author_browse | Jansen van Vuuren, Lide Roychoudhury, Alakendra N. |
| author_facet | Roychoudhury, Alakendra N. Jansen van Vuuren, Lide |
| author_sort | Jansen van Vuuren, Lide |
| collection | Thesis |
| dc_rights_str_mv | Stellenbosch University |
| description | Thesis (MSc)--Stellenbosch University, 2024. |
| format | Thesis |
| id | oai:scholar.sun.ac.za:10019.1/131679 |
| institution | Stellenbosch University (South Africa) |
| language | English |
| last_indexed | 2026-06-10T12:40:53.123Z |
| license_str | Other — see source repository |
| provenance_str_mv | Harvested via OAI-PMH from SUNScholar — Stellenbosch University Repository |
| publishDate | 2025 |
| publishDateRange | 2025 |
| publishDateSort | 2025 |
| publisher | Stellenbosch : Stellenbosch University |
| publisherStr | Stellenbosch : Stellenbosch University |
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| source_str | SUNScholar — Stellenbosch University Repository |
| spelling | oai:scholar.sun.ac.za:10019.1/131679 Seasonal dynamics of dissolved iron in the marginal ice zone of South Atlantic and Southern Oceans Jansen van Vuuren, Lide Roychoudhury, Alakendra N. Stellenbosch University. Faculty of Science. Dept. of Earth Sciences. Biogeochemical cycles -- Seasonal variations Carbon cycle (Biogeochemistry) Chemical oceanography -- Southern Ocean Trace elements Iron Biological carbon pump Ocean-atmosphere interaction Seawater -- Carbon dioxide content Phytoplankton -- Geographical distribution Marginal ice zone -- Remote sensing UCTD Thesis (MSc)--Stellenbosch University, 2024. ENGLISH ABSTRACT: The Southern Ocean (SO) plays a central role in connecting various ocean basins while also sequestering ~40-50% of the global anthropogenic carbon uptake by oceans (Terhaar et al., 2021). The dynamic region of the marginal ice zone (MIZ, situated between sea ice and open ocean), is known for being a primary production hotspot while influencing surrounding biogeochemical processes (Tagliabue et al., 2017). Dissolved Fe (dFe), a critical micronutrient for phytoplankton, therefore directly linked to the efficiency primary productivity and therefore of the Biological Carbon Pump (Boyd et al., 2007). Improving our understanding of dFe distribution and the key physical and biological processes can provide a more comprehensive view of the SO's carbon cycle. Therefore, this study aimed to examine the spatial and temporal variability of dFe in the Southern Ocean's MIZ and its relationship to sea ice dynamics and biogeochemical processes. Samples were collected at 21 stations during two oceanographic expeditions (59.5 - 51.4 °S, Southern Ocean Seasonal Experiments, 2019). Samples were analysed using a SeaFAST preconcentration module and ICP-MS analysis method. The dataset covers 348 duplicate samples, which were combined with physical, chemical and biological data to aid in evaluate the processes governing Fe distribution. Sub-nanomolar dFe concentrations (nmol/kg) increased with depth during both seasons. Vertical profiles were characterised as nutrient distributions at most stations, with depleted dFe concentration in surface waters (0.053 - 0.082 nmol/kg in upper ~150 m depth) and variable concentrations in deeper waters (0.374-1.44 nmol/kg at depths of ~1000 to maximum 3750 m). Remineralisation depths ranged from the Mixed Layer Depth (MLD) base to ~200-500 m. MLDs shoaled from winter (115 ± 18 m, n=7) to spring (87.0 ± 38 m, n=17 2019). Spring MLD’s also shoaled northwards below the pack ice (59.5 – 55.0 °S), due to sea ice melt and SML freshening (shoaling from 96.0 ± 30 m to mean 44.0 ± 18 m, n=3). An overall deepening of the MLD was seen when comparing stations under ice to those in the open ocean. Macro-nutrients (NO3-, PO43- and Si(OH)4) and oxygen proxies were utilised for internal water column remineralisation estimates. Integrated remineralised dFe [dFerem] stock ranged from 6.06 - 156 μmol/m2 (n=296), increasing northwards and comparable with previous studies (Tagliabue et al., 2014; Van Horsten, 2022). When looking at some of the internal processes (e.g., remineralisation and scavenging) influencing dFe distribution, a surprising lack of winter replenishment was noted. Demonstrated by higher dFe concentrations in spring compared to winter (dFeSML,Winter = 0.190 ± 0.12 nmol/kg, n=26; dFeSML,Spring =0.340 ± 0.17 nmol/kg, n=53). Early spring sampling thus still showed an end-of-winter signal of winter replenishment before the onset of depleting, semi-consistent phytoplankton blooms during spring and summer. Some phytoplankton blooms were observed in spring (19-22nd October and 6-9th November), with chlorophyll-a (Chl-a) exceeding 2.67 mg/kg (n=101), while moderate dFe concentrations (0.350 ± 0.12 nmol/kg, n=37) prevailed. In combination with low Apparent Oxygen Utilisation (AOU) values, this suggests an additional source of dFe to the region other than internal cycling. This thesis provided some of the first insights into the remote MIZ of the SO. Remineralisation estimates highlight the prominent role of internal cycling in the distribution of dissolved iron within this remote region. While hydrothermal vents, were noted as potential source for dFe to this region, internal cycling, winter entrainment, and upwelling were concluded as main drivers of Fe dynamics within this region. In addition to adding to the existing global dataset, this study improved understanding of dFe distributions within this remote, yet pivotal HNLC region. These findings give new perspectives on potential Fe sources, challenging existing theories and opening new avenues for underexplored processes and their global implications. AFRIKAANSE OPSOMMING: Die Suidelike Oseaan (SO) speel 'n sentrale rol in die verbinding van verskeie oseane, terwyl dit ook ongeveer 40-50% van die wêreldwye mensgemaakte koolstofopname deur oseane stoor (Terhaar et al., 2021). Hierdie dinamiese gebied van die marginale-ys-sone (MIS, geleë tussen see-ys en die oseaan), is bekend daarvoor dat dit 'n primêre produksie brandpunt is wat die omliggende biogeochemiese prosesse beïnvloed (Tagliabue et al., 2017). Opgeloste Fe (dFe), 'n kritieke mikro-nutriënt vir fitoplankton, is daarom gekoppel aan die doeltreffendheid van primêre produktiwiteit en dus van die biologiese koolstof pomp (Boyd and Trull, 2007). Verbetering van ons begrip van dFe-verspreiding en die belangrike fisiese en biologiese prosesse gee ons ‘n omvattende siening van die SO se koolstofsiklus. Daarom het hierdie studie ten doel gehad om die ruimtelike en tydelike verandering van dFe in die Suidelike Oseaan se MIZ te ondersoek en die verband daarvan met see-ys-dinamika en biogeochemiese prosesse. Monsters is versamel by 21 stasies tydens twee oseanografiese ekspedisies (59.5-51.4°S, Southern Ocean Seasonal Experiments, 2019). Monsters is geanaliseer met behulp van 'n SeaFAST-voorafkonsentrasie module en ICP-MS-analise metode. Die datastel dek 348 duplikaat monsters, wat gekombineer is met fisiese, chemiese en biologiese data om die prosesse wat Fe-verspreiding beheer, te evalueer. Sub-nanomolêre dFe-konsentrasies (nmol/kg) het gedurende beide seisoene met diepte toegeneem. Vertikale profiele is gekenmerk as voedingstof verspreidings by meeste stasies, met uitgeputte dFe-konsentrasie in oppervlakwaters (0.053-0.082 nmol/kg in die boonste ~150 m), en veranderende konsentrasies in dieper waters (0.374-1.44 nmol/kg by dieptes van ~1000 tot maksimum 3750 m). Hermineralisering dieptes het gewissel vanaf die Gemengde Laag Diepte (GLD) se basis tot en met ~200-500 m. GLDs het vlakker geword van winter (115±18 m, n=7) tot lente (87.0±38 m, n=17 2019). Lente GLD’s het ook noordwaarts gestyg onder die pakys (59.5–55.0 °S), as gevolg van see-ys smelting en SML verfrissing (van 96.0±30 m tot gemiddeld 44.0±18 m, n=3). ’n Algehele verdieping van die MLD is gesien wanneer 3- stasies onder ys vergelyk is met dié in die oop-oseaan. Makro voedingstowwe (NO³⁻, PO4 en Si(OH)4) en suurstof proksies was gebruik vir interne waterkolom hermineralisering berekeninge. Geïntegreerde hermineralisering dFe [dFerem] voorraad het gewissel van 6.06- 156 µmol/m² (n=296), toenemend noordwaarts en vergelykbaar was met vorige studies (Tagliabue et al., 2014; Van Horsten, 2022). Sommige interne prosesse (bv. hermineralisering en afskerming) wat dFe-verspreiding beïnvloed was ondersoek en het 'n verrassende gebrek aan winter aanvulling gewys. Dit is aangedui deur hoër dFe-konsentrasies in lente in vergelyking met dies gedurende winter (dFeSML,Winter = 0.190±0.12 nmol/kg, n=26; dFeSML,Spring =0.340±0.17 nmol/kg, n=53). Vroeë lente monsters wys dus 'n einde-van-winter sein van winter aanvulling voor die aanvang van uitputtende, semi-konsekwente fitoplankton bloeisels gedurende lente en somer. Fitoplankton bloeisels is in die lente waargeneem (19-22 Oktober en 6-9 November), met chlorofil-a (Chl-a) wat 2.67 mg/kg oorskry het (n=101), terwyl matige dFe-konsentrasies (0.350±0.12 nmol/kg, n=37) nogsteeds opgemerk was. In kombinasie met lae Skynbare Suurstofverbruik (AOU) waardes, dui dit op 'n addisionele bron van dFe vir die gebied buiten interne sirkulasie. Hierdie tesis verskaf van die eerste insigte in die afgeleë MIZ van die SO verskaf. Hermineralisasie estimasies beklemtoon die prominente rol van interne sirkulasie in die dFe verspreiding in hierdie afgeleë gebied. Terwyl hidrotermiese vents as potensiële dFe bron aangeteken is, het interne sirkulasie, winterinvloed en opwelling as hoofdrywers van Fe-dinamika beskou. Benewens die toevoeging tot die bestaande globale datastel, het hierdie studie die begrip van dFe-verspreidings binne hierdie afgeleë, maar deurslaggewende HNLC-gebied verbeter. Hierdie bevindings gee nuwe perspektiewe oor potensiële Fe-bronne, wat bestaande teorieë uitdaag en nuwe weë open vir onontginde prosesse en hul wêreldwye implikasies. Masters 2025-02-05T10:40:02Z 2025-02-05T10:40:02Z 2024-12 Thesis https://scholar.sun.ac.za/handle/10019.1/131679 en Stellenbosch University 124 pages : illustrations, maps application/pdf Stellenbosch : Stellenbosch University |
| spellingShingle | Biogeochemical cycles -- Seasonal variations Carbon cycle (Biogeochemistry) Chemical oceanography -- Southern Ocean Trace elements Iron Biological carbon pump Ocean-atmosphere interaction Seawater -- Carbon dioxide content Phytoplankton -- Geographical distribution Marginal ice zone -- Remote sensing UCTD Jansen van Vuuren, Lide Seasonal dynamics of dissolved iron in the marginal ice zone of South Atlantic and Southern Oceans |
| title | Seasonal dynamics of dissolved iron in the marginal ice zone of South Atlantic and Southern Oceans |
| title_full | Seasonal dynamics of dissolved iron in the marginal ice zone of South Atlantic and Southern Oceans |
| title_fullStr | Seasonal dynamics of dissolved iron in the marginal ice zone of South Atlantic and Southern Oceans |
| title_full_unstemmed | Seasonal dynamics of dissolved iron in the marginal ice zone of South Atlantic and Southern Oceans |
| title_short | Seasonal dynamics of dissolved iron in the marginal ice zone of South Atlantic and Southern Oceans |
| title_sort | seasonal dynamics of dissolved iron in the marginal ice zone of south atlantic and southern oceans |
| topic | Biogeochemical cycles -- Seasonal variations Carbon cycle (Biogeochemistry) Chemical oceanography -- Southern Ocean Trace elements Iron Biological carbon pump Ocean-atmosphere interaction Seawater -- Carbon dioxide content Phytoplankton -- Geographical distribution Marginal ice zone -- Remote sensing UCTD |
| url | https://scholar.sun.ac.za/handle/10019.1/131679 |
| work_keys_str_mv | AT jansenvanvuurenlide seasonaldynamicsofdissolvedironinthemarginalicezoneofsouthatlanticandsouthernoceans |