Thesis (MSc)--Stellenbosch University, 2015. / ENGLISH ABSTRACT: The Southern Ocean (SO) is of significant interest in the understanding of the global carbon
cycle and therefore many studies have been conducted to determine the limiting factors
controlling the biological pump within the region. During photosynthesis phytoplankton require
various nutrients such as NO3, PO4, inorganic carbon and the micronutrient Fe. The SO is a
High-Nutrient Low-Chlorophyll region, therefore no macronutrient limitation is experienced by
resident phytoplankton but instead the micronutrient Fe is a significant limiting factor within
these waters due to limited inputs. Due to deep mixed layer depths, ice cover, low sun angles
and cloud cover throughout parts of the year, light is also considered a limiting factor in the
SO. Fe and light limitation cause a decrease in photosynthetic efficiency and therefore a
decrease in carbon fixation capabilities. During this study we conducted five bioassay
shipboard incubation experiments during two cruises along the Greenwich meridian between
South Africa and the ice edge, SOSCEx during March and SAFePool during January to
February, in which we varied Fe concentrations and light levels to determine the effects of Fe
and light limitation or co-limitation within resident phytoplankton. Spatial and temporal
variations in phytoplankton response were studied to determine varying effects of limitation
across water masses and different stages of bloom decline within the study area. The
combined addition of Fe and light gave the largest increase in biomass, photosynthetic
capacity and nutrient uptake. In support of the hypotheses tested changes in the
photosynthetic apparatus led to changes in the photosynthetic efficiency and growth of the SO
phytoplankton, as a result of variations in Fe and light availability. Variability was also observed
in the response of phytoplankton to Fe and light amendments due to spatial and temporal
variation in resident phytoplankton communities. It was therefore concluded that both Fe and
light are significant controls in the resident phytoplankton photosynthetic apparatus,
photosynthetic capabilities, organic carbon fixation and therefore the biogeochemical cycles
within the Atlantic sector of the SO. / AFRIKAANSE OPSOMMING: Die Suidelike Oseaan (SO) is van beduidende belang in die begrip van die globale
koolstofsiklus en dus is baie studies gedoen om die beperkende faktore te bepaal wat die
biologiese pomp in die streek beheer. Tydens fotosintese benodig fitoplankton verskillende
voedingstowwe soos NO3, PO4, anorganiese koolstof en die mikrovoedingstof Fe. Die SO is
'n High-Nutrient Lae-Chlorofil streek, dus word geen makrovoedingstof beperking ervaar deur
inwoner fitoplankton maar in plaas daarvan is die mikrovoedingstof Fe 'n beduidende
beperkende faktor binne hierdie waters weens beperkte insette. As gevolg van diep gemengde
laag dieptes, ysbedekking, lae son hoeke en wolkbedekking deur dele van die jaar, word lig
ook beskou as 'n beperkende faktor in die SO. Fe en lig beperking veroorsaak 'n afname in
die fotosintetiese doeltreffendheid en dus 'n afname in koolstof binding vermoëns. Tydens
hierdie studie het ons vyf biotoets inkubasie eksperimente aan boord die skeep gedoen tydens
twee vaarte langs die Greenwich meridiaan tussen Suid-Afrika en die ys rand, SOSCEx
gedurende Maart en SAFePool gedurende Januarie tot Februarie, waarin ons Fe
konsentrasies en lig vlakke gewissel het om die gevolge van Fe en lig beperking, of medebeperking,
binne inwoner fitoplankton te bepaal. Ruimtelike en temporale variasies in
fitoplankton reaksie was bestudeer om wisselende gevolge van die beperking oor
watermassas en verskillende stadiums van bloei afname in die studie area te bepaal. Die
gekombineerde byvoeging van Fe en lig het die grootste toename in biomassa, fotosintetiese
kapasiteit en voedingsopname gegee. Ter ondersteuning van die getoetste hipoteses,
veranderinge in die fotosintetiese apparaat het gelei tot veranderinge in die fotosintetiese
doeltreffendheid en groei van die SO fitoplankton, as 'n gevolg van variasies in Fe en lig
beskikbaarheid. Veranderlikheid is ook waargeneem in die reaksie van fitoplankton om Fe en
lig wysigings weens die ruimtelike en tydelike variasie in inwoner fitoplankton gemeenskappe.
Dus was dit by die gevolgtrekking gekom dat beide Fe en lig beduidende kontrole in die
inwoner fitoplankton fotosintetiese apparaat, fotosintetiese vermoëns, organiese koolstof
binding en daarom die biogeochemiese siklusse binne die Atlantiese sektor van die SO.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:sun/oai:scholar.sun.ac.za:10019.1/97861 |
| Date | 12 1900 |
| Creators | Van Horsten, Natasha |
| Contributors | Fietz, Susanne, Mtshali, Thato, Roychoudhury, Alakendra, Stellenbosch University. Faculty of Science. Dept. of Earth Sciences. |
| Publisher | Stellenbosch : Stellenbosch University |
| Source Sets | South African National ETD Portal |
| Language | en_ZA |
| Detected Language | Unknown |
| Type | Thesis |
| Format | 142 pages : illustrations, maps |
| Rights | Stellenbosch University |
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