The aim of this thesis is to model climate change in the Bolivian Andes through the last glacial-interglacial cycle, using glaciers and palaeolakes. This is important because the extent and timing of glacier and palaeolake fluctuations in this area are poorly understood. Furthermore, determining the synchrony of glaciers and palaeolakes has direct implications for understanding the nature of palaeoclimatic change in this high altitude sub-tropical region during the last glacial-interglacial transition. The results of this study are directly applicable to general circulation models (GCMs) attempting to simulate past and future global climate change. Glacier-fed delta depositional systems on massifs at the margin of the southern Altiplano, Bolivia, suggest a broadly coeval expansion of glaciers and palaeolake Tauca during the Late-glacial. This is shown by the succession of hummocky moraine, ice-contact fan sediment-landform associations that extend from within lateral moraines and connect with Hjulstrom and Gilbert-type deltas at Cerro Azanaques, Cerro Tunupa and Cerro Condor Iquina between altitudes of 3770 and 3720 m. Radiocarbon ages on peat underlying glacigenic debris flow and glacifluvial deposits reveal glaciers reached their maximum extent soon after 13,300-12,850 14C yr B.P. The delta-plain/delta-front contacts of the glacier-fed deltas confirm that this glacier advance broadly coincided with palaeolake Tauca radiometrically dated to the interval 13,500-11,500 14C yr B.P. Therefore these climatically sensitive systems in the Bolivian Andes attained their greatest extent during the Late-glacial and not during the Last Glacial Maximum (LGM). Independent modelling of the climatic controls required to produce the simultaneous lowering of Late-glacial glacier equilibrium line altitudes (ELAs) and volumetric changes in palaeolake water balance suggest the primary forcing mechanism was increased summer (wet season) precipitation, while overflow from the northern basin was also necessary to raise the level of palaeolake Tauca in the southern Altiplano. Palaeoclimatic simulations show that an increase in precipitation of 330-425 mm/yr above modern values, combined with greater cloud cover (10%) that depressed local temperatures (2-3 °C) and reduced evaporation rates (10%) could have generated the Stage 3 glaciers and a 3760 m palaeolake highstand in the southern Altiplano. The ELA of former glaciers rose towards the south and west, like the gradient of modem precipitation, which suggest that increased moisture during the Late-glacial was probably brought to the Altiplano by tropical circulation systems similar to those at present, but atmospheric conditions were cooler-and-cloudier than present.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:592257 |
| Date | January 1998 |
| Creators | Clayton, James Dominic |
| Publisher | University of Aberdeen |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Source | http://digitool.abdn.ac.uk:80/webclient/DeliveryManager?pid=217036 |
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