Biological evidence of multiple temporal and spatial scales of hydrological variation in the western interior of Canada

Abstract

Abstract Biological records of past variations in moisture balance are available from a number of sites in the western interior of Canada. Such evidence includes fossil pollen, plant macrofossils, peatland records, paleolimnological indices, and tree rings. From these records, a temporal and spatial hierarchy of changes in moisture balance can be recognized. At the largest temporal and spatial scales there is a late Holocene increase in moisture that is apparent in fossil pollen and peatland initiation records from throughout the western interior. This increase in moisture likely reflects decreasing summer insolation and associated changes in atmospheric circulation. At the subregional scale, asynchronous changes in moisture balance that persist for centuries to millennia can be recognized in a number of fossil pollen and paleolimnological records. The explanation for such changes remains speculative. At the smallest scale, annually resolved tree-ring records and instrumental climate data indicate that annual to multi-year droughts of varying severity and geographic extent have been a regular feature of the western interior climate. Such variations in central North America have been attributed to changes in North Pacific sea surface temperatures, solar-magnetic cycles and lunar nodal tidal cycles. Some of the pre-20th century droughts appear to have been more severe and more extensive than any recorded in the instrumental record.