The Late Quaternary evolution of subsurface water masses in the Gulf of Guinea: High-latitude versus monsoonal control
The area of this study has been under the influence of a monsoon-driven tropical climate and has experienced variable contributions from river systems in a near shelf area characterized by a complex hydrography. The goal of this study is to improve the understanding of the coupling mechanisms betwee...
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| Other Authors: | , |
| Format: | Doctoral or Postdoctoral Thesis |
| Language: | English |
| Published: |
2013
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| Online Access: | https://nbn-resolving.org/urn:nbn:de:gbv:8-diss-136188 https://macau.uni-kiel.de/receive/diss_mods_00013618 https://macau.uni-kiel.de/servlets/MCRFileNodeServlet/dissertation_derivate_00005184/Kraft_Steffanie_2013_Dissertation.pdf |
| Summary: | The area of this study has been under the influence of a monsoon-driven tropical climate and has experienced variable contributions from river systems in a near shelf area characterized by a complex hydrography. The goal of this study is to improve the understanding of the coupling mechanisms between high latitudes and the tropics via atmospheric and oceanic circulation. The study investigates subsurface tropical water masses and their role in hydrographic changes in response to bipolar climatic oscillations and in modulating the inter-hemispheric heat exchange, focussing on glacial-interglacial cycles and shorter term millennial scale variability, in particular during Marine Isotope Stage 3 (MIS 3). MIS 3 was characterized by millennial-scale temperature oscillations, which were essentially in opposite phase in the northern and southern hemisphere. Various geochemical proxies are investigated and tested for their reliability for distinct applications, such as reconstructing past riverine input, water mass mixing and boundary exchange. The radiogenic neodymium (Nd) isotope composition is a widely used proxy to investigate past changes in sources and mixing of water masses, in particular that extracted from foraminiferal shells. However, the extracted seawater Nd isotope ratios can be biased by con-taminant phases such as organic matter, detrital silicates, and early diagenetic ferromanganese coatings. We tested different cleaning methods (Flow Through and batch cleaning) of planktonic foraminifera in order to obtain seawater εNd signatures to distinguish surface water mass mixing from riverine inputs and deep water signatures. Both methods reveal indistinguishable levels of cleaning efficiency and identical Nd isotope compositions. Element/calcium ratios and rare earth element (REE) concentration patterns, as well as similar εNd ratios for cleaned and uncleaned foraminiferal samples, suggest that the planktonic foraminiferal Nd isotope signatures reflect bottom water or sedimentary pore water signa-tures. The ... |
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