A 16,000 year Record of Paleoclimate Variability from Lake Von, Southern Central Otago, New Zealand.

Anderson, Harris

The Southern Hemisphere westerly winds (SHWW) control the amount and distribution of precipitation in the southern mid latitudes and is a key component in the global climate system, yet little is known about how the SHWW has varied in the past. Understanding past variability is crucial to evaluating present and future general circulation models forecasting Southern Hemisphere climate change. Lake Von is a topographically closed lake in southern central Otago situated in the rainshadow of the Southern Alps and is ideally located for reconstructing late Pleistocene and Holocene variability in hydrologic change. A multi-­‐proxy approach incorporating bulk sedimentary organic carbon and nitrogen stable isotopes and concentrations, terrestrial and lacustrine derived biomarkers, and sediment physical properties were measured on multiple sediment cores obtained from the lake. A radiocarbon chronology consisting of 10 dates was applied to the Lake Von composite stratigraphy and produced an age model spanning the last 17,600 years. The age model and down-­‐core geochemical and physical properties were combined to define four hydrologically distinct periods. A deglacial period from 17,600 to 14,500 cal yr BP is characterised by high δ13C and magnetic susceptibility, as sediment transitions from grey inorganic silts to brown organic rich sediments. Relatively low δ13C, δD and the low abundance of green algae biomarkers were observed from 14,500 to 8,500 cal yr BP and is inferred to be a period of low productivity and increased precipitation caused by an intensification and/or equator-­‐ward shift of the SHWW. At 8,500 cal yr Bp an abrupt shift to relatively higher δ13C, δD, and higher abundance of aquatic algae biomarkers occurs, which continues to 4,000 cal yr BP inferring a more productive system driven by warmer summer temperatures that were perhaps driven by increasing summer insolation. From ~4,000 cal yr BP to present, enhanced hydrologic variability is interpreted from all proxies is likely related to increased El-­‐Niño Southern Oscillation variability in the eastern equatorial Pacific. These results are broadly similar to other New Zealand and southern South American paleoclimate records, suggesting a common response to SHWW forcing along similar latitudes during the Holocene and Late Glacial.

iii, 83 pages, maps and illustrations A4

2013Anderson

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