A high-resolution record of pollen, charcoal, diatom, and lithologic data from Dailey Lake in southwestern Montana describes postglacial terrestrial and limnologic development from ice retreat ca. 16,000. cal. yr BP through the early Holocene. Following deglaciation, the landscape surrounding Dailey Lake was sparsely vegetated, and erosional input into the lake was high. As summer insolation increased and ice recessional processes subsided, Picea parkland developed and diatoms established in the lake at 13,300. cal. yr BP. Closed subalpine forests of Picea, Abies, and Pinus established at 12,300. cal. yr BP followed by the development of open Pinus and Pseudotsuga forests at 10,200. cal. yr BP. Increased planktic diatom abundance indicates a step-like warming at 13,100. cal. yr BP, and alternations between planktic and tychoplankic taxa suggest changes in lake thermal structure between 12,400 and 11,400. cal. yr BP. An increasingly open forest, in combination with increased benthic diatoms, indicates warm dry summers during the early Holocene after 11,400. cal. yr BP, in contrast to nearby records in northern Yellowstone that register prolonged summer-wet conditions until ca. 8000. cal. yr BP. Because of its low elevation, Dailey Lake was apparently sensitive to the direct effects of increased summer insolation on temperature and effective moisture, registering dry summers. In contrast, higher elevations in northern Yellowstone responded to the indirect effects of an amplified seasonal insolation cycle on atmospheric circulation, including elevated winter snowpack and/or increased summer convective storms as a result of enhanced monsoonal circulation.
Bibliographical noteFunding Information:
This research was supported by National Science Foundation grants, including EAR-0801467 to Whitlock and Fritz and OISE-0966472 to Whitlock. Support in the field came from D. McWethy and V. Nagashima. We thank V. Nagashima, J. Giskaas, M. Spendel, and A. Peery for lab assistance, and two anonymous reviewers for their helpful comments.
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- Early holocene