Late Holocene intensification of the westerly winds at the subantarctic Auckland Islands (51° S), New Zealand
Imogen M. Browne1, Christopher M. Moy1, Christina R. Riesselman1,2, Helen L. Neil3, Lorelei G. Curtin1, Andrew R. Gorman1, and Gary S. Wilson1,2,41Department of Geology, University of Otago, Dunedin, 9016, New Zealand 2Department of Marine Science, University of Otago, Dunedin, 9016, New Zealand 3National Institute of Water and Atmospheric Research (NIWA), Wellington, 6021, New Zealand 4New Zealand Antarctic Research Institute (NZARI), Christchurch, 8053, New Zealand
Received: 22 Mar 2017 – Accepted for review: 27 Mar 2017 – Discussion started: 04 Apr 2017
Abstract. The Southern Hemisphere westerly winds (SHWW) play a major role in controlling wind-driven upwelling of Circumpolar Deep Water (CDW) and outgassing of CO2 in the Southern Ocean on interannual to glacial-interglacial timescales. Despite their significance in the global carbon cycle, our understanding of millennial-scale changes in the strength and latitudinal position of the westerlies during the Holocene (especially since 5000 yr BP) is limited by a scarcity of paleoclimate records from comparable latitudes. Here, we reconstruct middle to late Holocene variability in the SHWW using a fjord sediment core collected from the subantarctic Auckland Islands (51° S, 166° E), located in the modern centre of the westerly wind belt. Drainage basin response to variability in the strength of the SHWW at this latitude is reconstructed from downcore variations in magnetic susceptibility (MS) and bulk organic δ13C and atomic C/N, which monitor influxes of lithogenous and terrestrial vs marine organic matter, respectively. The hydrographic response to SHWW variability is reconstructed using benthic foraminifer δ18O and δ13C, both of which are influenced by the isotopic composition of shelf water masses entering the fjord. Using these data, we provide marine and terrestrial-based evidence for increased wind strength from ~ 1600–900 yr BP at subantarctic latitudes that is broadly consistent with previous studies of vegetation response to climate at the Auckland Islands. Comparison with a SHWW reconstruction using similar proxies from Fiordland suggests a northward migration of the SHWW over New Zealand at the beginning of the Little Ice Age (LIA). Comparison with paleoclimate and paleoceanographic records from southern South America and the western Antarctic Peninsula indicates a late Holocene strengthening of the SHWW after ~ 1600 yr BP that appears to be broadly symmetrical across the Pacific basin, although our reconstruction suggests that this symmetry breaks down during the LIA. Contemporaneous increases in SHWW at localities either side of the Pacific in the late Holocene are likely controlled atmospheric teleconnections between the low and high latitudes and by variability in the Southern Annular Mode (SAM) and El Niño Southern Oscillation (ENSO).
Browne, I. M., Moy, C. M., Riesselman, C. R., Neil, H. L., Curtin, L. G., Gorman, A. R., and Wilson, G. S.: Late Holocene intensification of the westerly winds at the subantarctic Auckland Islands (51° S), New Zealand, Clim. Past Discuss., doi:10.5194/cp-2017-52, in review, 2017.