Synoptic scale controls on the δ 18 O in precipitation across Beringia

Oxygen isotope records of precipitation (δ 18 O precip ) from Beringia are thought to reflect synoptic‐scale circulation changes associated with the Aleutian Low. To delineate the spatial pattern of δ 18 O precip associated with the two dominant modes of Aleutian Low circulation, we combine modern δ 18 O precip and deuterium excess data with climate reanalysis and back trajectory modeling. Aleutian Low strength and position are revealed to systematically affect regional moisture source and δ 18 O precip ; whereby a strengthened Aleutian Low causes lower (higher) δ 18 O precip in western (eastern) Beringia. We compare a new 100 year long δ 18 O record from the Aleutian Islands with the North Pacific Index, the primary indicator of Aleutian Low strength, and find a significant positive relationship ( r  = 0.43, P  < 0.02, n  = 28) that tracks late twentieth century change. This study demonstrates synoptic‐scale circulation controls on our isotope record and provides a coherent framework for interpreting existing and emerging paleoisotope data from the region.