Abstract
The latitudinal position and strength of the Southern Hemisphere westerly winds (SHWW) influence mid-latitude precipitation patterns and air-sea gas exchange in the Southern Ocean. Fiordland is ideally located to constrain past variability in the westerlies because latitudinal shifts control precipitation amount and the strength of the overturning fjord circulation. Terrestrial organic carbon burial in Fiordland is also influenced by the SHWW; however the sensitivity of carbon accumulation rates in Fiordland to shifts in the SHWW remains unclear. Few high- resolution records of the SHWW exist from locations sensitive to changes in the strongest winds; however well-constrained paleoclimate records from across the Pacific basin and across >10° of latitude are needed to evaluate the full dynamics of westerly change. In addition, calculated carbon burial rates in the literature only exist for the late Holocene in Fiordland, which do not reflect the entire range of climate conditions projected for our future.
This thesis analyzes sediment cores from multiple basins in Long Sound, Fiordland to evaluate past SHWW change and its influence on carbon burial rates from the Late Glacial to the late Holocene. Bulk organic carbon and nitrogen isotopes, elemental data, physical properties and radiocarbon dates are used to evaluate past change. The results show that late Holocene centennial-scale changes in redox conditions and precipitation-driven erosion coincide with known southward excursions in the SHWW that are recorded in paleoclimate records from Tasmania and southern South America, particularly when the frequency of El Niño occurrence is low. Calculated late Holocene carbon burial rates are similar in magnitude to carbon burial rates obtained from similar basins in other New Zealand fjords, with the exception of the back basin in Long Sound where sediments appear to be trapped by Lake Widgeon. However, Late Glacial carbon accumulation rates are two to three times higher in the fjord lake setting, possibly due to warm temperatures, stratification within the lake, and proximity of the core site to a point source of fluvial discharge. Because future climate is projected to be characterized by a more poleward position of the SHWW, these results provide constraints on fjord process and sediment transport mechanisms that occur during these southward excursions of the wind field. The extremely high rates of carbon burial in fjord lakes during the Late Glacial suggest that these basins need to be considered in in carbon cycle budgets for the deglacial time period.