A palaeoenvironmental study of a peat sequence from Iles Kerguelen (49°S, Indian Ocean) for the Last Deglaciation based on pollen analysis

Detta är en Master-uppsats från Lunds universitet/Geologiska institutionen

Författare: Victor Henao; [2015]

Nyckelord: Earth and Environmental Sciences;

Sammanfattning: In recent years, the Southern Hemisphere (SH) and the vast Southern Ocean (SO) have gained awareness and importance within the scientific community in relation to global climate change and the global CO2 cycle, par-ticularly since the Last Glacial Maximum (LGM) and into the Holocene. It is believed that the Southern Hemi-sphere Westerlies (SHW) play a key role in regulating climate change in the mid-to-high latitudes of the SH, thus reconstructing the SHW latitudinal positioning since the LGM has been crucial. However, terrestrial records of the mid-to-high latitudes are sparse. Most of the evidence is generally constrained to southern South America and New Zealand, and at times reveals contradictory results. Scientists have been trying to obtain a clearer picture of shifts in the SHW in the mid-to-high latitudes through analyzing terrestrial records from the island groups that make up the sub-Antarctic region. Here, a c.14000 cal yr BP terrestrial record from Port Douzieme (P12) at Iles Kerguelen (49°S) is analyzed using a multi-proxy approach (lithostratigraphy, magnetic susceptibility, loss on ignition, and pollen). The P12 record reveals clear changes since c.14000 cal yr BP, at which time a sparsely vegetated environ-ment existed, dominated by grasses (Poaceae). Then, the wind tolerant, cushion plant Azorella selago became a much more influential species by c.13600, coinciding with the presence of lacustrine-type-sediments, suggesting windier and wetter conditions. By c.12900 cal yr BP the lowland species Acaena magellanica suddenly expanded, becoming the dominant species and coinciding with the end of the Antarctic Cold Reversal (ACR). Finally, at c.11200 cal yr BP the species Uncinia compacta and Blechnum penna-marina appear in the pollen record, suggest-ing much warmer conditions on the Kerguelen archipelago. The record from P12 was compared with a previous study done by Van der Putten et al. (submitted) at the Estacade site in the Kerguelen archipelago, approximately 50 km northeast of the P12 site. The pollen record from the Estacade site shows a similar vegetation history as the rec-ord from P12 for the Kerguelen archipelago. At the Estacade site, Poaceae is prominent between c.16000-13650 cal yr BP, followed by a period of dominance by the wind tolerant species Azorella selago and Lyallia kerguelensis at 13650 cal yr BP. At around 11200 cal yr BP the lowland species Acaena magellanica and Uncinia compacta ex-panded. Additionally, the pollen record from P12 reveals a higher influence of the SHW at about 13600 cal yr BP, when a great diversity in long distance pollen grains is recorded, coinciding with the expansion of the wind tolerant species Azorella selago, as well as the presence of lacustrine-type-sediments at both the Estacade site and P12.

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