SEA-LEVEL PRESSURE VARIABILITY AROUND ANTARCTICA SINCE AD 1750 INFERRED FROM SUB-ANTARCTIC TREE-RING RECORDS

A tree-ring chronology network recently developed from the subantarcti c forests provides an opportunity to study long-term climatic variabil ity at higher latitudes in the Southern Hemisphere. Fifty long (1911-1 985), homogeneous records of monthly mean sealevel pressure (MSLP) fro m the southern latitudes (15-65 degrees S) were intercorrelated on a s easonal basis to establish the most consistent, long-term Trans-Polar teleconnections during this century. Variations in summer MSLP between the South America-Antarctic Peninsula and the New Zealand sectors of the Southern Ocean are significantly correlated in a negative sense (r = -0.53, P < 0.001). Climatically sensitive chronologies from Tierra del Fuego (54-55 degrees) and New Zealand (39-47 degrees) were used to develop verifiable reconstructions of summer (November to February) M SLP for both sectors of the Southern Ocean. These reconstructions, whi ch explain between 37 and 43% of the instrumentally recorded pressure variance, indicate that inverse trends in MSLP from diametrically oppo site sides of Antarctica have prevailed during the past two centuries. However, the strength of this relationship varies over time. Differen ces in normalized MSLP between the New Zealand and the South America-A ntarctic Peninsula sectors were used to develop a Summer Trans-Polar I ndex (STPI), which represents an index of sea-level pressure wavenumbe r one in the Southern Hemisphere higher latitudes. Tree-ring based rec onstructions of STPI show significant differences in large-scale atmos pheric circulation between the nineteenth and the twentieth centuries. Predominantly-negative STPI values during the nineteenth century are consistent with more cyclonic activity and lower summer temperatures i n the New Zealand sector during the 1800s. In contrast, cyclonic activ ity appears to have been stronger in the mid-twentieth than previously for the South American sector of the Southern Ocean. Recent variation s in MSLP in both regions are seen as part of the long-term dynamics o f the atmosphere connecting opposite sides of Antarctica. A detailed a nalysis of the MSLP and STPI reconstructions in the time and frequency domains indicates that much of the interannual variability is princip ally confined to frequency bands with a period around 3.3-3.6 y. Cross spectral analysis between the STPI reconstruction and the Southern Os cillation Index suggests that teleconnections between the tropical oce an and extra-tropical MSLP variations may be influencing climate fluct uations at southern latitudes.