Differential response of vegetation to postglacial climate in the Lower Salmon River Canyon, Idaho

摘要

Late Pleistocene to Holocene terrestrial climate and vegetation records in the Lower Salmon River Canyon of Idaho are interpreted from the stable isotopic composition of soil carbonates and from aeolian sedimentation frequencies. Carbonate and sediment samples from six sections were processed and analyzed, with the resulting isotopic and grainsize data organized in relation to a normalized time series developed from an associated radiocarbon chronology. This record is interpreted in regards to changes in aridity, temperature and wind speed during the Late Quaternary and is further compared with regional paleoenvironmental records. Lowered δ~(18)O and δ~(13)C concentrations before 20000 yr BP are interpreted as reflecting Late Wisconsinan cold conditions. After 18000 yr BP, climatic conditions show warmer periods punctuated by sharp returns to colder temperatures and increased C_3 flora by 12000 yr BP. Higher resolution data show very unstable climatic conditions across the Pleistocene-Holocene boundary, reflected in wide variations in δ~(18)O and δ~(13)C and aeolian sand deposition. During the period between 12000 and 9000 yr BP, the Lower Salmon River Canyon is thought to have experienced marked seasonality with summers and winters, respectively, warmer and colder than today. This climatic scenario was accompanied by an initial instability in canyon vegetation. Following the establishment of a low-energy floodplain in the canyon after 10000 yr BP, a pattern of C_3-dominant riparian flora appears. During the middle Holocene, climatic and vegetative variability is much reduced from the preceding period. After 4000 yr BP, soil carbonate isotopes reflect a trend toward cooler climate conditions and more mesic vegetation populations.