This thesis investigates Late Quaternary palaeoclimate in Patagonia to increase our
understanding of the nature and timing of climate change in the mid-latitude regions of the
Southern Hemisphere. Palaeoenvironmental reconstructions are presented which date
back to the Last Glacial Interglacial Transition (> c. 13.5 cal ka BP) from two lakes in
Chilean Patagonia: Laguna Boal in the Chonos Archipelago (44° 39'S, 73° 39'W) and Laguna
Leta in the Chilean Lake District (41° 33'S, 73° 10'W). The investigation focuses principally
on the analysis of sub-fossil Chironomidae (Insecta: Diptera) to infer palaeoenvironmental
conditions. Combined 14C dating and tephrochronology provide the chronological
framework for the records. As ecological information about the modem Patagonian
Chironomidae fauna is scarce, faunal assemblages at 78 lakes were analysed in conjunction
with potentially controlling environmental variables in order to aid the ecological
interpretation of sub-fossil assemblages.
Analysis of the modem data raised taxonomic issues related to identification of sub-fossil
larval specimens, highlighting the need for more Neotropical taxonomic studies.
Multivariate analysis of relationships between the modern day fauna and environmental
variables indicated that the relationships present were not strong enough to produce a
transfer function for the region. The environmental factors that varied most with the
taxonomic assemblages were the organic content of substrate, lake depth, altitude, latitude
and longitude. Water temperature, which has previously been demonstrated to have a
strong effect on Chironomidae distribution, was not significantly correlated with the
Patagonian faunal assemblages. These results indicate that the fauna encountered in this
study may be more eurytopic than that studied in previous Holarctic investigations.
Although the strength of environmental -
taxonomic relationships was insufficient to
warrant production of a transfer function, the investigation allowed qualitative
interpretations of the down-core record to be made in conjunction with previously
published data on Holarctic midge ecology.
The records from Laguna Leta and Laguna Boal both indicate that climate oscillated during
the transition from glacial to interglacial conditions, as fluctuations in lake depths are
suggested by changes in both the chironomid assemblages and sediment properties.
Results are generally equivocal in terms of determining whether such changes were
precipitation or temperature driven. Nonetheless, such inferred changes add valuable
evidence to the assertion that climatic instability prevailed throughout this time period in
Patagonia - an argument that has been refuted by previous palynological work. Climatic
interpretation of the Laguna Boal Holocene record is somewhat equivocal, but indicates
that local, basin specific changes may have determined the assemblage versus
palaeoclimatic controls. However, at a Laguna Leta a drop in lake levels during the early
Holocene may have been followed by a notable rise in water level at c. 7.8 cal yr BP. This
latter record supports previous palynological work in the region indicative of a
concomitant rise in effective precipitation. The results of this pioneering study suggest that
the use of chironomid analysis as a palaeoclimatic technique for this area is promising, but
that more information on the midges' modern distribution in Patagonia is required to
improve its application in future studies.