A 154 year-long, tree-ring based stable oxygen isotope time series (δ 18 O TRC ) of the evergreen southern beech ( Nothofagus betuloides ) was established for the southernmost part of Patagonia. The trees grew on the terminal moraine system of the Schiaparelli Glacier (54.4°S) within the windward and hyper-humid zone of the Austral Andes. The annually resolved δ 18 O TRC record spans the common period 1861–2015 and is based on the analysis of five individually analyzed tree individuals showing a significant mean interseries correlation ( r = 0.69). To date, this time series represents the worldwide southernmost chronology of tree-ring δ 18 O TRC . Variations of the δ 18 O TRC values are significantly correlated with hydroclimatic conditions, as derived from ERA-Interim reanalysis gridded data. Negative relationships between the δ 18 O TRC -series and relative humidity (r Oct-Feb = −0.62, p < 0.0001) or the amount of precipitation (r Jan-Feb = −0.52, p < 0.0001) can be observed for the austral spring and summer seasons. In contrast, a drier environment will increase the δ 18 O TRC as revealed by a positive influence of evaporation (r Sep-Feb = 0.44, p < 0.01), sea level pressure (r Oct-Feb = 0.56, p < 0.0001) or maximum temperature (r Oct-Feb = 0.43, p < 0.01). Spatial correlation maps indicate a strong supra-regional influence of climate variables on the chronology. The annular pressure seesaw, termed as Antarctic Oscillation (AAO), mostly influences climate variability within the Southern Hemisphere and is positively correlated with the δ 18 O TRC -chronology (r JF = 0.61, p < 0.0001). Since our chronology, as well as a neighboring δ 18 O TRC -chronology from the Perito Moreno Glacier (50°S), are showing a high correspondence in their sensitivities to climate variabilities and towards the AAO, we merged both time series into a mean chronology. This new regional mean δ 18 O TRC -chronology is highly sensitive to variations of the AAO ( r = 0.79, p < 0.0001)) and is tested for the suitability to reconstruct the AAO for the last 150 years. The reconstructed time series of the AAO reveals an increasing trend towards more positive index values, which is associated with an amplification in the amount of precipitation and wind speed in southernmost South America. • Southernmost existing tree-ring cellulose (δ 18 O TRC ) time series from the hyper-humid Austral Andes, Tierra del Fuego. • Highly significant hydroclimate imprints on δ 18 O TRC of the evergreen southern beech ( Nothofagus betuloides ). • Strong fingerprints of the Antarctic Oscillation (AAO) are reflected in δ 18 O TRC from Southern Patagonia. • Annual reconstruction of the Antarctic Oscillation based on tree-ring δ 18 O TRC since 1860.