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Palaeolimnological reconstruction of Holocene climate and relative sea-level change in Lützow Holm Bay (East Antarctica) = Paleolimnologische reconstructie van Holocene klimaat- en relatieve zeespiegelveranderingen in Lützow Holm Bay (Oost-Antarctica)
Tavernier, I. (2014). Palaeolimnological reconstruction of Holocene climate and relative sea-level change in Lützow Holm Bay (East Antarctica) = Paleolimnologische reconstructie van Holocene klimaat- en relatieve zeespiegelveranderingen in Lützow Holm Bay (Oost-Antarctica). PhD Thesis. Faculty of Sciences, Biology Department, Research group Protistology : Gent. 282 pp.
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Documenttype: Doctoraat/Thesis/Eindwerk
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| Abstract |
Despite the fact that both Antarctica and the Southern Ocean play a major role in controlling the global climate system (Turner et al. 2009), still relatively few highresolution climate proxy records have been obtained from the Southern Hemisphere (SH) high latitudes (Mann et al. 2009). Moreover, several vast areas, including Lützow Holm Bay (Hall 2009; Verleyen et al. 2011 in Appendix 2) remain largely understudied. A better knowledge of past climate and ice-sheet fluctuations in East Antarctica (EA) will enable us to understand the mechanisms behind Holocene climate changes and allow us to place recent climate anomalies in a longer-term context. In this thesis, we analysed biological, geochemical and sedimentological proxies in radiocarbon-dated sediment cores from three glacial and four isolation lakes to infer past climate changes and ice-sheet dynamics in Lützow Holm Bay (EA), between 69 - 70°S and 35 - 40°E. We also developed a regional diatom-based transfer function to reconstruct past changes in lake water specific conductance. Our multi-proxy evidence suggests that both West Ongul Island and Skarvsnes deglaciated during the Holocene, although not simultaneously. Radiocarbon dates indicate that West Ongul Island deglaciated around 11.2 cal. ka BP. These findings contradict with previous studies which suggested that the islands were ice-free during the Last Glacial Maximum (LGM; Miura et al. 1998). However it is possible that the Ongul Islands were covered by extensive blankets of snow during and after the LGM, leading to a delay in the onset of biogenic sedimentation. Radiocarbon dates from Skarvsnes indicate that the region deglaciated around 7.4 cal. ka BP, which is in agreement with dates from raised beaches (Miura et al. 1998) and cosmogenic isotope dating (Yamane et al. 2011) but slightly later than most other East Antarctic regions (Hall 2009). Evidence for the occurrence of an Early-Holocene Climate Optimum (EHCO) is lacking from these regions, as they were still snow- or ice-covered. In Skarvsnes, low primary productivity was inferred from marine sediments between 7.4 and 4.6 cal. ka BP. This was followed by a period with increased primary production between c. 4.6 and 3.7 cal. ka BP. Initially, the site was possibly a shallow marine lagoon, only suitable for a limited number of diatom species, after which a more diverse community and seasonally open-water conditions were inferred. Near West Ongul Island, the marine environment was characterised by the presence of diatoms thriving in sea-ice and under seasonally stratified conditions between 6.5 and 5.0 cal. ka BP. Between 4.2 and 0.9 cal. ka BP, a climate optimum could be inferred, both on West Ongul Island and on Skarvsnes, which culminated between 2230 and 2090 cal. yr BP. In the lakes from West Ongul Island, this was observed as increased primary production and changes in the moisture balance of the lakes, indicating increased snow melt, whereas in Skarvsnes, sedimentological changes could be potentially linked to the disappearance of multi-year snow banks, similarly indicating warmer conditions. The presence of a Mid- to Late-Holocene warm period is in accordance with other East Antarctic terrestrial records, in which a climate optimum was roughly identified between 4.7 and 1 ka BP (Verleyen et al. 2011 in Appendix 2). It is likely that Neoglacial cooling occurred from c. 1.2 cal. ka BP onwards, as indicated by decreased primary productivity and stabilised or increased specific conductance in the closed lakes, indicating a lower amount of meltwater entering the lakes, both on Skarvsnes and West Ongul Island. Also in other East Antarctic regions, a similar cooling was observed. We found no evidence for an event coeval with the Northern Hemisphere (NH) Medieval Climate Anomaly (MCA), Little Ice Age (LIA) or Twentieth-Century Warming (TCW), which is consistent with other lake records (Verleyen et al. 2011 in Appendix 2) and ice cores from Antarctica (Goosse et al. in press). We extended an existing relative sea-level (RSL) curve, which was solely based on marine terraces from Nakada et al. (2000), with published (Takano et al. 2012) and new data from isolation lakes . A complex RSL history for Lützow Holm Bay was obtained, with regional differences in the uplift rate and maximum sea-level high stand, which is likely related to the interplay between glacial isostatic adjustment (GIA) and local neotectonic faulting on Skarvsnes. This RSL curve is furthermore different from RSL curves from other East Antarctic regions, where maximum sea-level was reached between c. 8 and 6 cal. ka BP (Zwartz et al. 1998; Verleyen et al. 2005), after which RSL fall occurred due to outpacing of the eustatic component by isostatic uplift. Moreover, in Skarvsnes, RSL remained at its maximum until at least 4.8 cal. ka BP. These findings suggest a more extended ice-sheet prior to deglaciation and/or a relatively recent disintegration of the ice mass. |
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