Southern high-latitude vegetation and climate change during the Holocene (South Georgia) and Oligocene (Wilkes Land, Antarctica)

Strother, Stephanie (2016) Southern high-latitude vegetation and climate change during the Holocene (South Georgia) and Oligocene (Wilkes Land, Antarctica). Doctoral thesis, Northumbria University.

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Abstract

Significant climate and vegetation changes have occurred during the Cenozoic era (66 Ma - present), particularly in the southern-high latitudes. The terrestrial record in Antarctica is fragmentary and available successions are limited due to remoteness and thick ice cover. The aim of this study is to provide new insights into what changes
occurred during available successions in two epochs of the Cenozoic, the Holocene (11.7 ka - present) and the Oligocene (33.9 - 23.03 Ma) in the sub- Antarctic and East Antarctic region. This thesis begins on South Georgia Island in the sub-Antarctic region, where a 5.8-m long high-resolution pollen record covering the last 7000 years was taken from Fan Lake on Annenkov Island. Palynological and sedimentological analyses indicated warm late Holocene conditions between 3790 and 2750 cal. yr BP transitioning to a cooler and wetter environment. Increases in long-distance pollen grains from South America between c. 2210 and 1670 cal. yr BP and after 710 cal. yr BP suggested strong Southern Hemisphere Westerly Winds over South Georgia during the late Holocene. These results question previous studies which proposed highest wind intensity during the warmer mid-Holocene climate optimum.

Little is known about how Antarctic vegetation changed from the subtropical and temperate rainforests of the warm Eocene to the cold tundra shrubs which dominated
during the Miocene. Oligocene assemblages from site U1356 Wilkes Land, East Antarctica (IODP 318) covering ~33-30 and ~25-23 Ma are characterised by lowland fragmented cool forests and tundra/shrubland. Temperature reconstructions derived from the fossil pollen assemblages using the Coexistence Approach suggest mean
annual temperatures between 5.8-13.7°C during the Oligocene. A decline in warmer taxa (e.g. Dacrydium praecupressinoides and Phyllocladidites mawsonii) and high abundance of reworked sporomorphs and Leiosphaeridia sp. indicate the progression towards cooler/glaciated conditions between ~25-23 Ma. The Wilkes Land assemblage shows a warmer palaeoflora compared to previous Antarctic palaeorecords and the regional vegetation differences may be explained by the palaeotopography of Wilkes Land which has a lower altitude and reduced glacial influence in contrast to other sites.

After the formation of the cryosphere at the Eocene-Oligocene transition glacial reworking is a major component in Antarctic marine and terrestrial sedimentary
deposits. Uncertainty as to whether Cenozoic sporomorphs were reworked or in situ has previously restricted palaeoenvironmental reconstructions. This thesis presents a new red fluorescence approach to differentiate reworked and in situ sporomorphs over relatively short geologic timescale (e.g. Paleogene and Neogene). The establishment of an in situ palaeoflora assemblage from Wilkes Land enables a robust interpretation of Oligocene environments without the influence of reworking.

Item Type:	Thesis (Doctoral)
Uncontrolled Keywords:	palaeoclimate, palynology, palaeoenvironmental reconstructions, palynomorphs, pollen and spores
Subjects:	F800 Physical and Terrestrial Geographical and Environmental Sciences
Department:	Faculties > Engineering and Environment > Geography and Environmental Sciences University Services > Graduate School > Doctor of Philosophy
Depositing User:	Ay Okpokam
Date Deposited:	18 Jul 2016 15:37
Last Modified:	25 Oct 2019 16:19
URI:	https://nrl.northumbria.ac.uk/id/eprint/27303

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