A high-resolution record of climate, vegetation, and fire in the mixed conifer forest of northern Colorado, USA

Abstract

High-resolution pollen, charcoal, δ13C, total organic carbon (TOC), and magnetic susceptibility data from sediment cores from a montane lake in northern Colorado record variations in vegetation, fire history, and sedimentation since 14.5 ka (1 ka = 1000 cal yr B.P.). This record shows warm conditions during the Bolling-Allerod and the coldest conditions in this area during the Younger Dryas event. Warming occurred throughout the early and middle Holocene, lasting until ca. 5 ka, when the warmest and wettest summer conditions were recorded. Progressive climate cooling and enhanced winter precipitation are then observed until present day. These long-term climatic trends correlate to changes in summer insolation. Charcoal accumulation rates (CHAR) increased along with the arboreal vegetation, from minima in the Late Glacial period to maxima during the early and middle Holocene, suggesting that charcoal influx was also controlled by climate and vegetation. TOC and δ13C show a progressive increase and a decrease trend during the late Pleistocene and Holocene, respectively, related to changes in vegetation and productivity in the lake. Major peaks in the CHAR record correspond with peaks in magnetic susceptibility, indicating enhanced fire-induced erosion and sedimentation. Millennial- and centennial-scale changes are also observed throughout the different proxy records. They exhibit strong correlations with climate records from distant regions, including Greenland and the North Atlantic, providing evidence for global teleconnections among regional climates. A solar-climate connection is suggested by prominent ca. 225 and 390 yr cycles, which may correlate with the 208 yr (Suess) and 400 yr solar cycles.