Pliocene-Pleistocene evolution of Benguela upwelling and Agulhas Leakage in the SE Atlantic

PhD ThesisUnderstanding the impacts of the transition from the warmth of the middle Pliocene to the large amplitude, 100 ka glacial-interglacial cycles of the late Pleistocene helps us to better interpret both the local forcings and global impacts of possible future climate changes. In this thesis, changes in ocean circulation over the last 3.5 million years (Ma) are investigated using a marine sediment core recovered from the SE Atlantic Ocean, a region often described as an ocean gateway because it includes the transfer of heat and salt from the Indian to the Atlantic Ocean between Antarctica and South Africa (the “Agulhas Leakage”). However, the response of this region to Pliocene-Pleistocene climate evolution remains unclear. This thesis analyses the climate information recorded at Ocean Drilling Program (ODP) Site 1087 (31º28’S, 15º19’E, 1374m water depth) to investigate the history of Agulhas Leakage and associated ocean circulation changes including the Antarctic Circumpolar Current to the south, and the productive Benguela upwelling system to the north.. This thesis presents the results generated using several organic geochemistry proxies and foraminiferal analyses to reconstruct the climate history at ODP 1087. These include the UK37’ index (for sea surface temperatures, SSTs), the TEX86 index (for ocean temperatures and an upwelling indicator), pigment analysis (for productivity changes), foraminifera assemblages (as water mass indicators), and dinoflagellate assemblages (for SSTs and water mass indicators). During the Pliocene and early Pleistocene, ODP 1087 was dominated by the Benguela Upwelling system, which had shifted south relative to today, and three prominent cold periods punctuate the overall warmth (during the M2 and KM2 stages, and at 2.8 Ma). From 2.2 Ma a longer term cooling trend begins, and further cooling occurs at 1.6 Ma, both of which are interpreted to represent periods of intensification of the Benguela Upwelling. The start of modern Agulhas Leakage occurs at ~0.9 Ma, marked by the start of early warming at the site ahead of the terminations. Finally, from 0.6 Ma there is an intensification of Agulhas Leakage which has led to an overall warming of SSTs which span both glacial and interglacial stages. Overall, the ODP 1087 record shows that this region is more reactive to southern hemisphere and local forcings such as changes in the southern wind field and ice expansion around Antarctica, rather than to northern hemisphere forcing.School of Geography, Politics and Sociology, Newcastle University: NERC

Montana Kaimin, October 19, 1977

Student newspaper of the University of Montana, Missoula.https://scholarworks.umt.edu/studentnewspaper/7702/thumbnail.jp

Annual reports of the selectmen, treasurer, road agents and board of education of the town of Lee, for the year ending February 15, 1898.

This is an annual report containing vital statistics for a town/city in the state of New Hampshire

Variation in methanotroph-related proxies in peat deposits from Misten Bog, Hautes-Fagnes, Belgium

Methane emissions from peat bogs are strongly reduced by aerobic methane oxidising bacteria (methanotrophs) living in association with Sphagnum spp. Field studies and laboratory experiments have revealed that, with increasing water level and temperature, methanotrophic activity increases. To gain a better understanding of how longer term changes in methanotrophic activity are reflected in methanotroph biomarkers, a peat record (0–100 cm) from the Hautes-Fagnes (Belgium) encompassing the past 1500 years, was analysed for methanotroph-specific intact bacteriohopanepolyols (BHPs) and the carbon isotopic composition of diploptene. A predominance of aminobacteriohopanetetrol (aminotetrol) over aminobacteriohopanepentol (aminopentol) indicated the prevalence of type II methanotrophs. Relatively high methanotrophic activity was indicated by all methanotroph markers between 20 and 45 cm depth, around the present oxic–anoxic boundary, most likely representing the currently active methanotrophic community. Comparing methanotrophic markers in the deeper part of the peat profile with environmental variables afforded, however, no clear correlation between change in water level and methanotrophic activity. This is potentially caused by a predominance of type II methanotrophs, a combination of sources for methanotrophic biomarkers or insufficient variation in climatic changes. A proposed way forward would include a study of a core covering a longer timescale, thereby involving greater variability

Financial Report, 1921-1922

University of Montana annual financial report for fiscal year ending June 30, 1922.https://scholarworks.umt.edu/annual_financial_reports/1003/thumbnail.jp

Montana Kaimin, November 1, 1979

Student newspaper of the University of Montana, Missoula.https://scholarworks.umt.edu/studentnewspaper/7937/thumbnail.jp

The Hilltop 8-29-1986

This document created through a generous donation of Mr. Paul Cottonhttps://dh.howard.edu/hilltop_198090/1151/thumbnail.jp

An integrated palaeoenvironmental investigation of a 6200 year old peat sequence from Ile de la Possession, Iles Crozet, sub-Antarctica

International audienceA 6200 year old peat sequence, cored in a volcanic crater on the sub-Antarctic Ile de la Possession (Iles Crozet), has been investigated, based on a multi-proxy approach. The methods applied are macrobotanical (mosses, seeds and fruits) and diatom analyses, complemented by geochemical (Rock-Eval6) and rock magnetic measurements. The chronology of the core is based on 5 radiocarbon dates. When combining all the proxy data the following changes could be inferred. From the onset of the peat formation (6200 cal yr BP) until ca. 5550 cal yr BP, biological production was high and climatic conditions must have been relatively warm. At ca. 5550 cal yr BP a shift to low biological production occurred, lasting until ca. 4600 cal yr BP. During this period the organic matter is well preserved, pointing to a cold and/or wet environment. At ca. 4600 cal yr BP, biological production increased again. From ca. 4600 cal yr BP until ca. 4100 cal yr BP a “hollow and hummock” micro topography developed at the peat surface, resulting in the presence of a mixture of wetter and drier species in the macrobotanical record. After ca. 4100 cal yr BP, the wet species disappear and a generally drier, acidic bog came into existence. A major shift in all the proxy data is observed at ca. 2800 cal yr BP, pointing to wetter and especially windier climatic conditions on the island probably caused by an intensification and/or latitudinal shift of the southern westerly belt. Caused by a stronger wind regime, erosion of the peat surface occurred at that time and a lake was formed in the peat deposits of the crater, which is still present today