CHEMTAX determination of Southern Ocean phytoplankton distribution and adaption: An observational and experimental study assessing the co-limitation of Light, Iron and other Trace Metals on phytoplankton productivity and community composition.

Viljoen, Johannes Jacobus (2018-12)

Thesis (MSc)--Stellenbosch University, 2018.

Thesis

ENGLISH ABSTRACT: This multi-manuscript study reports an elucidated understanding of the consequences key environmental changes has on phytoplankton community structure, productivity and their acclimation abilities for the Atlantic Sector of the Southern Ocean. All three manuscripts are based on data gathered on board the RV SA Agulhas II on a north-south transect along the Good Hope monitoring between Cape Town and the Antarctic Fimbul ice shelf (0° longitude). This transect crossed multiple oceanic fronts and zones from which a multi-parameter in-situ observational study of the links between trace metals and phytoplankton dynamics could be carried out. In addition, two stations were used to conduct bulk-community bottle incubation experiments to assess the response of phytoplankton in growth, photophysiology and community structure to iron and light variability in the Polar Frontal Zone and Antarctic waters. The results from the incubation studies revealed that the response of phytoplankton to changes in iron and light availability are very region-specific. In the Polar Frontal Zone irradiance is limiting significant phytoplankton growth and in the Antarctic Zone, iron addition resulted in growth stimulation even at low light levels. By combining data from the surface and the un-amended incubation bottles sampled from the respective depth of fluorescence maximum an assessment of how representative the surface and chla-max communities are of their region and, considering logistical constraints, if we can only use one to understand phytoplankton dynamics. Due to additional changes in irradiance and availability of iron with vertical depth, which is region specific, the acclimation of phytoplankton, which affects their photochemical efficiency (Fv/Fm) and productivity, can vary with depth which is exemplified by regional differences in water column structure and dynamics. The possibility of sampling a niche community when only one depth is sampled, which could lead to results of a very depth-specific acclimated phytoplankton community and not that of a regional representative one, was also investigated. The multi-parameter in-situ observational study that includes parallel trace metal and phytoplankton community structure data showed that there are certain changes in phytoplankton community structure that can only be explained by the addition of a suite of trace metals as additional variables. This led to the observation that when these essential micronutrients are incorporated into studies, the timing of phytoplankton sampling relative to the time of an event like the release of trace metals from hydrothermal vents or melting ice can be very important. For the Atlantic Southern Ocean, it can be shown that the present and future state of phytoplankton dynamics greatly depends on key environmental changes such as irradiance, varying degrees of iron-light co-limitation and the proven strong influence of trace metal availability. Keywords: pigments; acclimation; multi-parameter; incubation; GEOTRACES

AFRIKAANSE OPSOMMING: Hierdie studie bestaan uit veelvoudige manuskripte wat lig werp op die gevolge wat kern omgewingsveranderinge het op fitoplankton se gemeenskapstrukture, produktiwiteit en hul vermoë om te akklimatiseer in die Atlantiese Sektor van die Suidelike Oseaan. Al drie manuskripte wat hierin vervat is, is gebaseer op data wat ingesamel is aan boord die RV SA Agulhas II op ʼn noord-suid transek, al langs die Goeie Hoop moniteringslyn tussen Kaapstad en die Antarktiese Fimbul-ysbank (0° lengtegraad). Aangesien hierdie transek verskeie oseanies fronte en sones gekruis het, was dit moontlik om ʼn multi-parameter, in situ waarnemingstudie uit te voer wat die verhouding tussen spoormetale en fitoplankton dinamika ondersoek. Daarbenewens is daar by twee monsternemingstasies inkubasiebottel eksperimente uitgevoer op omvangryke fitoplankton gemeenskappe om hul reaksie in groei, fotofisiologie en gemeenskapstrukture tot die veranderlikheid van yster en lig in die Polêre Frontsone en die Antarktiese seegebied te bepaal. Die uitslae van die inkubasiestudies het onthul dat die reaksie van fitoplankton tot veranderinge in die beskikbaarheid van yster en lig baie streekspesifiek is. In die Polêre Frontsone beperk uitstraling opmerklike fitoplankton groei en in die Antarktiese sone het die toevoeging van yster die groei van fitoplankton gestimuleer ten spyte van die lae ligvlakke. Deur die data te kombineer van die watermonsters wat op die oppervlak geneem is en die ongewysigde inkubasiebottels wat op die respektiewe dieptes van die maksimum fluoressensie geneem is, kan ‘n waardebepaling gedoen word van hoe verteenwoordigend die fitoplanktongemeenskappe op die oppervlakte en die gemeenskappe by die chlorofil maksimum van die streek is. Dit kan ook ‘n aanduiding gee van die moontlikheid om net een datastel (oppervlak/diepte) te gebruik, veral wanneer logistieke uitdagings in ag geneem moet word. Die akklimatisering van fitoplankton, wat hul fotochemiese doeltreffendheid (Fv/Fm) en produktiwiteit beïnvloed, kan verskil met diepte as gevolg van die bykomende veranderinge in uitstraling en beskikbaarheid van yster. Hierdie veranderinge is streekspesifiek en kan verduidelik word deur streeksverskille in die waterkolomstruktuur en –dinamika. Daar is ook ondersoek ingestel na die moontlikheid om ʼn nisgemeenskap te toets wanneer monsters slegs op een diepte geneem word. Dit kan daarna toe lei dat resultate slegs verteenwoordigend is van ʼn baie spesifieke fitoplankton gemeenskap wat op ʼn spesifieke diepte geakklimatiseer het en dus nie ʼn streeksvoorstelling is nie. Die multi-parameter, in situ waarnemingstudie, wat parallelle spoormetaaldata en fitoplankton gemeenskapstruktuurdata insluit, het getoon dat daar sekere veranderinge in die fitoplanktongemeenskapstruktuur is wat slegs deur die toevoeging van ‘n spoormetaaldatastel as addisionele veranderlikes verduidelik kan word. Wanneer hierdie noodsaaklike mikrovoedingstowwe in ‘n studie ingesluit word, speel tydsberekening ‘n baie belangerike rol. Die inagneming van die vrystelling van spoormetale deur hidrotermiese openinge of smeltende ys ten tye van fitoplankton-monsterneming is baie belangrik. Die huidige en toekomstige toestand van fitoplankton dinamika in die Atlantiese Suidelike Oseaan is grootliks onderhewig aan kern omgewingsveranderinge soos uitstraling, wisselende vlakke van die gelyktydige beperkinge van yster en lig en die bevestigde sterk invloed van die beskikbaarheid van spoormetale. Sleutelwoorde: pigmente; akklimatisering; multi-parameter; inkubasie; GEOTRACES

Please refer to this item in SUNScholar by using the following persistent URL: http://hdl.handle.net/10019.1/104834
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