The winds of change: evaluating New Zealand’s hydrologic response to changing Southern Hemisphere westerly winds

Air-sea CO2 flux in the Southern Ocean is controlled by the strength and latitudinal position of the Southern Hemisphere westerly winds. Today, southward-shifting and intensifying winds are thought to reduce the efficiency of the Southern Ocean carbon sink, with direct implications for the rate at which anthropogenic CO2 accumulates in the atmosphere. However, Holocene westerly wind variability is poorly constrained at present, inhibiting our ability to place these modern changes in any long-term context. We therefore propose to reconstruct past variations in the westerly winds by examining cores obtained from well-positioned lakes and wetlands in southern New Zealand. We have identified a network of sites within the northern margin of the wind field where the precipitation regime is well-coupled to westerly wind intensity. We will apply multiple stable isotope proxy methods to modern water and sediment trap samples, lake sediment cores, and peat cores to evaluate Holocene changes in hydrologic balance, temperature, and lake/vegetation dynamics that are directly attributed to the westerly winds. Comparing our network of sites with high latitude records across the Pacific will identify hemisphere-scale westerly shifts. Results from this research will be used to evaluate current theories on how the westerlies influence the global carbon cycle.