A late Pleistocene to early Holocene climate, vegetation and fire history record for the Bonneville basin, Utah, USA

The Bonneville basin of northwestern Utah acts as a significant source of paleoenvironmental data due to the sedimentary and geomorphic evidence left behind from the late Pleistocene Lake Bonneville. Macroscopic charcoal and pollen from wetland sediments of North Redden Springs, Utah (40° 00' 47.1" N 113° 41' 59.9" W) were used to reconstruct a record for past environmental and climatic changes during the last 36.8 cal ka BP. Changes in charcoal deposition rates (particles/cm2/yr), peak magnitudes (calculated using Char Analysis), and percentages of total pollen were used to interpret the fire, vegetation, and climate dynamics. Additionally, distinct shifts in the magnetic susceptibility and loss-on-ignition of sediments were used to understand past lacustrine events in the basin. During the late Pleistocene (36.8--29 cal ka BP), a cold/dry adapted sagebrush steppe surrounded Lake Bonneville, with no fire episodes near the study site due to the inundation of the site by Lake Bonneville. A subsequent increase in winter precipitation from the southward shift of the jet stream during the latest Pleistocene (29--16 cal ka BP) resulted in the expansion of a conifer forest and deeper lake levels. One fire episode occurred at 21 cal ka BP and is associated with a wet period followed by warming. Greater fuel loads correspond to increased fire episodes during the middle and early Holocene (16--6.0 cal ka BP). As early as 16 cal ka BP, a xeric shrub steppe composed of halophytic Amaranthaceae and Sarcobataceae vegetation dominated large expanses of playa surrounding the North Redden spring-wetland complex. The late Holocene (6.0 cal ka BP--present) was characterized as a period of increased aridity, interspersed with cool-wet episodes. A xeric shrub steppe expanded its range to become the dominate vegetation type on the landscape. Increases in aquatic plants and other diversified vegetation types occurred in response to heightened amounts of summer moisture. Fires continued to increase in frequency and intensity throughout the historical period. Mechanisms behind fire activity likely included wet climate episodes followed by dry climate episodes. Additionally, anthropogenic burning, fire suppression, and invasive plant species may have contributed to increased fire activity.