High resolution lacustrine records of Late Holocene climate change from southern New Zealand
New Zealand freshwater ecosystems are directly impacted by temperature and precipitation variations controlled by the strength and position of the Southern Hemisphere Westerly Winds. Understanding westerly wind controls on hydroclimate is essential for predicting ecosystem response to future warming projections. However, New Zealand lacks this context due to short duration of our instrumental records and poorly resolved paleoclimate records that span the last 1000 years. Sedimentary paleoclimate records developed from remote alpine lakes are sensitive recorders of temperature and precipitation change and offer an opportunity to provide highly resolved records of present and past climate. This study presents two highly resolved (centennial-scale) sedimentary records from southern New Zealand alpine lakes that can be used to evaluate the last ~13,600 years of hydrologic change associated with Southern Hemisphere Westerly Winds. Highly resolved proxy records obtained from non-destructive scanning are assessed together with biogenic silica concentration, δ13C and δ15N isotope data, bulk organic carbon and nitrogen concentrations, and 14C and 210Pb dates, to reveal temporal trends linked to temperature and precipitation change. High-resolution non-destructive μX-ray fluorescence core scanning and hyperspectral imaging produce continuous, sub-millimetre elemental and pigment profiles, respectively. Principal component analysis of elemental data indicates elements that track lithogenic change (Ti, K, Fe, Ca, Si, = PC1) are leading contributors of geochemical variance in both records. Elemental proxies that track lithogenic variation (PC1) and biosiliceous sediment (Si/Ti) are assessed with hyperspectral imagingindices that track productivity (Chl a; RABD660-670) and minerogenic (R570/R630) change. Early Holocene evidence for enhanced productivity with limited lithogenic contribution indicate lower lake level and warm, dry conditions. Consistent with previous studies, these observations are attributed to southward-shifted and/or weaker westerly winds. Results of Early Holocene millennial-scale trends inform assessment of Late Holocene hydroclimate. A long-term cooling trend, linked to strengthening of the westerly winds, is overprinted by centennial-scale trends. These records provide insight into how Late Holocene climate mechanisms influence westerly wind in southern New Zealand. Present trends toward increasing temperature and increased aquatic productivity suggest these mechanisms are critical to the understanding and prediction of how forecasted future climate will affect southern New Zealand lakes.
Advisor: Moy, Christopher
Degree Name: Master of Science
Degree Discipline: Geology
Publisher: University of Otago
Keywords: New Zealand; Late Holocene; climate change; Itrax; XRF; Hyperspectral Imaging; lake sediment; Southern Annular Mode; ENSO; Southern Hemisphere Westerly Winds; SHWW; stable isotopes; PCA
Research Type: Thesis