Trans-Tasman Sea climate variability since AD 1740 inferred from middle tohigh latitude tree-ring data

The limited length and spatial coverage of instrumental climate data for ma ny areas of the Southern Hemisphere impedes the study of atmosphere-ocean d ynamics prior to the past century. Such analyses are important for understa nding interannual to decadal variation of the Southern Hemisphere circulati on and whether recent changes are related to anthropogenic effects rather t han natural variability. We use a middle- to high-latitude tree-ring width data set (from Tasmania, New Zealand and Tierra del Fuego) to reconstruct s ealevel pressure (SLP) variability spanning the Tasman Sea and vicinity sin ce AD 1740. The variables reconstructed are austral summer (November-March) SLP for Hobart, Tasmania (43 degrees S, 147 degrees E) and the Chatham Isl ands, New Zealand (44 degrees S, 177 degrees E), as well as a meridional ci rculation index (Hobart-Chatham Islands index) which measures the pressure gradient between these two stations. The three reconstructions are well ver ified statistically and capture between 40 and 48% of the variance in the S LP data. The instrumental and estimated SLP show similar spatial patterns o f correlation with the sea surface temperature (SST) field for the Pacific. Statistically significant (above 95% level) 3-3.5 year spectral peaks are identified in the three reconstructions using multitaper spectral analysis, and a significant 4-5 year peak is found in both the Chatham Islands and H obart-Chatham Islands SLP reconstructions. These two modes are within the b andwidth of the El Nino-Southern Oscillation. Although very speculative, th ey may also correspond to a proposed Antarctic circumpolar wave of SLP, SST , wind and sea-ice extent, believed to play a key role in atmosphere-ocean circulation for the Southern Hemisphere.