Department of Earth Sciences

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Browsing Department of Earth Sciences by Subject "Aquaculture -- Effect of climatic changes on"

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    Testing potential drivers for carbon isotopic signature of particulate organic carbon in the Southern Ocean
    (Stellenbosch : Stellenbosch University, 2020-12) Jordaan, Zandria; Fietz, Susanne; Joubert, Warren R.; Stellenbosch University. Faculty of Science. Dept. of Earth Sciences.
    ENGLISH ABSTRACT: The carbon cycle in the Southern Ocean (SO) plays a very important role for all life on earth as it regulates carbon fluxes, transport nutrients to marine organisms and it is linked to the amount of available oxygen in the atmosphere. The conditions driving the carbon cycle dramatically changed over the past few decades which directly effects marine phytoplankton. Phytoplankton are key role players in the marine food web as they utilize atmospheric carbon dioxide transported into the surface ocean through different chemical exchanges. Fractionation of stable carbon isotopes occurs during the biological uptake of inorganic carbon, although all the influential forces behind the fractionation are not yet fully understood. Here we examine the potential physical- and chemical driving factors for carbon isotopic signature of particulate organic carbon (δ13CPOC) in the surface water of the SO. Winter and summer results are compared along the Bonus Good Hope line as well as a section in the Indian Ocean. The aim is to determine potential influences of the physical- and chemical driving factors on phytoplankton δ13CPOC, because it is possible to measure δ13CPOC directly from underlying sediments. Understanding the driving factors of δ13CPOC, will help the interpretation of sedimentary δ13CPOC in paleo-reconstruction studies, such as reconstructing past atmospheric partial pressure of carbon dioxide (pCO2 concentrations). Our results indicate that silicic acid and nitrate concentrations (μM), cyanobacteria and diatoms contributions to total chl-a (%) and temperature (ºC) could potentially be primary driving factors of δ13CPOC during the summer along the Bonus Good Hope line, as all these factors are significantly correlated to δ13CPOC. Winter results in the Atlantic sector of the SO (Winter Cruise 2015) did not show any potential driving factor. This is in contrast with results found in the Indian sector of the SO (Winter Cruise 2017), where all four investigated macronutrients (silicic acid, nitrate, nitrite and phosphate), chl-a, seven phytoplankton groups’ contributions to total chl-a (%), temperature and salinity could potentially drive the carbon isotopic signature. In addition, available pCO2 data was used to determine whether pCO2 is related to δ13CPOC in the upper layer of the Southern Ocean. The pCO2 results obtained during the Winter Cruise 2017, in the Indian sector of the Southern Ocean, were the only cruise where pCO2 had a significant (negative) correlation with δ13CPOC, indicating increased fractionation related to increasing pCO2 concentrations. In conclusion, for both the Atlantic and Indian sector of the SO, possible drivers of δ13CPOC were identified. It is important to take note of the different biological- and environmental factors co-influencing those potential driving factors. Correlations may have been identified where similar distributions of two studied parameters have been driven by a third, common factor. Hence, further studies should be made to confirm which parameter or parameters definitely drives δ13CPOC.