Late Glacial and Holocene Palaeoecology of the Lake St Clair Region, Tasmania
Date
2018
Authors
Hopf, Felicitas Viktoria Luise
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Abstract
This thesis presents a history of regional and local changes in
vegetation in the Lake St Clair region, supported by modern
vegetation and pollen analyses. The records span into oxygen
isotope stage 3, with a focus on the last Glacial Holocene
transition and fill a gap in the poorly studied region of Central
Tasmania.
The vegetation during the last glaciation prior to the Last
Glacial Maximum was characterised by widespread Pherosphaera
hookeriana dominated alpine coniferous heath growing together
with a mosaic of alpine grasslands, herbfields, heathland and
sedgeland. The lakes at Clarence Lagoon and Excalibur Bog are
inferred to have dried up under the cold and dry climate during
the Last Glacial Maximum. The legacy of Pherosphaera hookeriana
dominated vegetation extends to the early deglacial sediments in
Lake St Clair, declining to only trace representation through the
remainder of the late Glacial and Holocene in the wider Lake St
Clair region.
Deglaciation of Lake St Clair was complete by c. 18.3 cal kyr BP
and subsequent replacement of an early mosaic of alpine
vegetation types, by subalpine Athrotaxis cupressoides and
Diselma archeri dominated rainforest and/or woodland in response
to rapidly rising temperatures and precipitation, is in sync with
postglacial Antarctic warming and rising sea surface
temperatures. A 900-year period of renewed grassland expansion is
inferred to represent slightly cooler/drier conditions leading
into the Antarctic Cold Reversal, abruptly ended by strong
increases in rainforest mid-way through the Antarctic Cold
Reversal suggesting a shift to a wetter and warmer climate
leading to the establishment of Phyllocladus
aspleniifolius-Nothofagus cunninghamii rainforest. The abrupt
decline in Phyllocladus aspleniifolius at c. 12.4 cal kyr BP
marks the expansion of Nothofagus cunninghamii-Atherosperma
moschatum callidendrous rainforest growing under optimal
conditions during the Early Holocene, which becomes more complex
between c. 10-8 cal kyr when Phyllocladus aspleniifolius returns
to high values, together with a secondary peak of
Athrotaxis/Diselma under an inferred wetter and warm climate. At
c. 8 cal kyr BP, the rainforest taxon Anodopetalum/Eucryphia
becomes important and the remainder of the Holocene sees an
overall decline in rainforest taxa and increase in sclerophyll
and herbaceous taxa and fire activity, which intensifies during
the late Holocene. The observed changes in the record are
consistent with the onset of ENSO and a more variable climate
from c. 8 cal kyr BP and an intensification and cooling
temperatures from c. 5 cal kyr BP.
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Keywords
pollen, vegetation, Holocene, charcoal, history, palaeoecology
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Thesis (PhD)
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DOI
10.25911/5d51476295497