Constraining the suitability of barium as an indicator of paleoproductivity in different environments

Stavreva, Raya (2020-12)

Thesis (MSc)--Stellenbosch University, 2020.

Thesis

ENGLISH ABSTRACT: Primary productivity is a vital factor in the global carbon cycle, as it regulates atmospheric carbon dioxide through sequestration. Therefore, climate change is largely dependent on the fluctuations in productivity. To develop effective climate models, past productivity must be reconstructed. There are a variety of established paleoreconstruction methods applied to aquatic environments, one of which is based on total organic carbon (TOC). TOC is a traditionally utilized proxy has been applied to modern and past aquatic environments, as it is the dominant component of biological material. However, its preservation is strongly influenced by oxidation and consequently degradation. Barium, especially in the form of barite, has become a promising tool, due to its refractory nature and positive linear relationship to organic matter. Its application to productivity reconstruction is primarily constrained to open ocean settings, with only rare utilization in coastal shelf or lacustrine environments. This study investigates the efficiency of barium or barium-bearing compounds as a paleoproductivity proxy in various aquatic environments (freshwater lake, peatland, coastal upwelling and Open Ocean). Barium concentration profiles were constructed in different sedimentary records by ICP-MS and XRF analysis. These barium profiles were compared to primary productivity proxies (TOC and chlorophyll degradation products), elemental proxies (C/N), isotopic proxies (δ13C) and Al concentration as an indicator for lithogenic input. Statistical analysis was applied to the datasets to comment on the relationship between barium and the productivity proxies. Scanning Electron Microscope (SEM) analysis was used to further assess whether barium has an affinity to biological cell structures or mineral precipitates. Our study showed that barium exhibited no significant positive relationship with any paleoproductivity proxy in the continental settings (lacustrine and peatland). However, in core 2 (North Namibian Cell, 20°30 S) of the coastal upwelling environment, barium exhibited a strong and positive relationship with productivity. Therefore this study concludes that barium was not a suitable proxy for paleoproductivity in continental settings (lacustrine and peatland) and only exhibited potential suitability in one sediment core in the shallow marine (coastal upwelling cell) setting, which should be further explored. For future research, higher resolution is required for the application of statistical analysis, in order to better define the suitability of barium in different study locations.

AFRIKAANSE OPSOMMING: Primêre produktiwiteit is 'n belangrike faktor in die globale koolstofsiklus, aangesien dit reguleer atmosferiese koolstofdioksied deur sekwestrasie. Daarom, klimaatsverandering is grootliks afhanklik van die skommelinge van produktiwiteit. Ten einde effektiewe klimaatmodelle te ontwikkel, moet vorige produktiwiteit herbou word. Daar is 'n verskeidenheid van gevestigde paleoreconstruction metodes toegepas op water omgewings, waarvan een is gebaseer op totale organiese koolstof (TOC). Die TOC as tradisioneel gebruik gevolmagtigde is toegepas op moderne en verlede akwatiese omgewings, want dit is die dominante komponent van biologiese materiaal. Die bewaring daarvan word egter sterk beïnvloed deur oksidasie en gevolglik agteruitgang. Barium, veral in die vorm van barite, het 'n belowende instrument geword, as gevolg van sy vrolike aard en oënskynlike verhouding tot organiese materiaal. Die toepassing van produktiwiteit rekonstruksie is hoofsaaklik beperk tot oop oseaan instellings, met slegs skaars benutting in die kus rak of lacustrine en. Hierdie studie ondersoek die doeltreffendheid van barium- of bariumdraende verbindings as 'n paleoproductivity gevolmagtigde in verskeie wateromgewings (varswater meer, peatland, kusopwelling en Oop Oseaan). Barium konsentrasie profiele is gebou in verskillende sedimentêre rekords deur ICP-MS en XRF analise. Hierdie bariumprofiele is vergelyk met primêre produktiwiteitsgevolmagtigdes (TOC- en chlorofilaglegende agteruitgangsprodukte), elementêre gevolmagtigdes (C/N), isotoopgevolmagtigdes (113C) en Al-konsentrasie as 'n aanwyser vir lithogeniese insette. Regressie en statistiese analise is toegepas op die datastelle om kommentaar te lewer op die verhouding tussen barium en die produktiwiteitsgevolmagtigdes. Skandering elektronmikroskoop (SEM) analise is gebruik om verder te bepaal of barium 'n affiniteit vir biologiese selstrukture of minerale neerslag het. Ons analise het getoon dat barium geen beduidende positiewe verhouding met enige paleoproductivity gevolmagtigde in die kontinentale instellings (lacustrine en peatland) uitgestal het nie. In kern 2 (Noord-Namibiese Sel, 20 ° 30 S) van die kus-opwellingsomgewing het barium egter 'n sterk en positiewe verhouding met produktiwiteit uitgestal. Daarom kom hierdie studie tot die gevolgtrekking dat barium nie 'n geskikte gevolmagtigde vir paleoproduktiwiteit in kontinentale instellings (melkeen en peatland) was nie en slegs potensiële geskiktheid in een sedimentkern in die vlak mariene (kusopwellingsel) omgewing uitgestal moet word, wat verder ondersoek moet word. Vir toekomstige navorsing word hoër resolusie vereis vir die toepassing van statistiese analise om die geskiktheid van barium in verskillende studieplekke beter te definieer.

Please refer to this item in SUNScholar by using the following persistent URL: http://hdl.handle.net/10019.1/109374
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