Late-Quaternary climatic change on the American North Pacific Coast

Abstract

Temporal changes in solar radiation caused by variations in the Earth's orbit figure prominently in current Quaternary climate theory^1–4. Experimental design of atmospheric circulation models emphasizes the importance of solar radiation in the heating of interglacial land and ocean surfaces at different seasons of the year, whereby monsoon-type circulation—seasonal shifting of regional cyclonic and anticyclonic centres—develops, while during glacial ages, seasonality is greatly modified by the influence of ice sheets^5–7. We investigated the late-Quaternary climate of the North Pacific, where according to modelling, solar radiation in the early Holocene at the time of the summer solstice is high and in the late Holocene is relatively low. We compared quantitative temperature and precipitation estimates from southern Alaska, obtained by application of transfer functions to fossil pollen records, with estimates from western Washington⁸ and southern British Columbia⁹. Data extending over > 10,000 years show a broadly consistent pattern of climatic change in general agreement with predicted variations in solar radiation and their effect on atmospheric circulation and seasonal duration of pressure systems over the North Pacific Ocean. In the early Holocene, as monsoon-type circulation became established with melting of glaciers, the subtropical North Pacific anticyclone annually regulated climate for a longer period at higher latitudes than at present, so that warmth and dryness (high summer radiation) increased in southern Alaska. The Aleutian low-pressure centre, locus of cyclonic storm activity, intensified during the late Holocene, resulting in colder and more humid coastal climate (low summer radiation) over much of the year and increased frequency of glacier growth in the cordillera.