The impact of air mass circulation dynamics on Late Holocene paleoclimate in northwestern North America

Paleoclimate records from northern British Columbia, southwestern Yukon, and adjacent Alaska suggest that Late Holocene climate may have been influenced by specific air mass circulation dynamics. The Aleutian low pressure index (ALPI) is a measure of sea level pressure fluctuations in the Pacific Northwest associated with the Aleutian low (AL) pressure system. In this study, we show that the AL has a strong influence on historical climate change in the study area and explore the relationships between ALPI polarity and changes in late Holocene paleoclimate records. Analyses of weather station data in the study area indicate positive correlations (r > 0.63) between mean wintertime (December March) temperature and ALPI values; total wintertime snowfall accumulation and total precipitation show moderate and weak negative correlations, respectively. A Late Holocene increase in exotic western hemlock (Tsuga heterophylla) pollen has been observed in regional paleoclimate studies. A sustained positive ALPI phase during the late Holocene is considered as a causative mechanism. Under such conditions, warm maritime air masses would more frequently penetrate inland, potentially resulting in eastward pollen transfer, enhanced growing conditions at coastal sites, and an increase eastwards in the range limit of these species. This study indicates that apparent conflicts in the timing and magnitude of Late Holocene climate change may be the result of a strong regional climate-forcing mechanism that exhibits both temporal and geographical variation. (C) 2002 Elsevier Science Ltd and INQUA. All rights reserved.