Lake area constraints on past hydroclimate in the western United States: Application to Pleistocene Lake Bonneville

Lake shoreline remnants found in basins of the western United States reflect wetter conditions during Pleistocene glacial periods. The size distribution of paleolakes, such as Lake Bonneville, provide a first-order constraint on the competition between regional precipitation delivery and evaporative demand. In this contribution we downscale previous work using lake mass balance equations and Budyko framework constraints to determine past hydroclimate change for the Bonneville and Provo shoreline extents of Lake Bonneville during the last glacial cycle. For the Bonneville basin we derive new relationships between temperature depression and precipitation factor change relative to modern. These scaling relationships are combined with rebound-corrected estimates of lake area and volume and macrofossil-derived surface temperatures to make quantitative estimates of precipitation and water residence times for the lake. For the Bonneville shoreline (~1552 m) we calculate that, prior to spillover to the Snake River drainage, precipitation rates were ~1.37 times modern, with a water residence time of ~185 years. For the Provo shoreline (1444 m), during the period of steady-state spillover, we calculate that precipitation rates were at least 1.26 times modern, with a residence time of ~102 years. These calculations suggest minimal difference in the hydrologic regime between the Bonneville shoreline highstand and the Provo shoreline stillstand during the last glacial termination. These estimates of hydroclimate scaling relationships differ in sensitivity with previous hydrologic modeling for Lake Bonneville, and are complementary to those recently derived from glacier mass balance modeling from the Wasatch Range. INTRODUCTION AND METHODOLOGY The size of pluvial lakes in terminally draining basins of the western United States indicate a substantially different landscape during Pleistocene glacial periods. Building on the seminal work of G.K. Gilbert (1890) and J.C. Russell (1885), shoreline mapping and compilations of late Pleistocene lake surface areas in the western United States (e.g., Hubbs and Miller, 1948; Mifflin and Wheat, 1979; Williams and Bedinger, 1984; Reheis, 1999a; Orme, 2008; Grayson, 2011) has led to estimates of hydroclimate based on steady-state mass balance assumptions related to observed lake areas (e.g., Mifflin and Wheat, 1979; Hostetler and Benson, 1990; Reheis, 1999b; Broecker, 2010; Matsubara and Howard, 2009; Munroe and Laabs, 2013; Reheis and others, 2014; Ibarra and others, 2014; 2018; Barth and others, 2016). Geologic observations of shorelines or outcrop extent from ancient lake systems thus serve as constraints for quantitative paleoclimate reconstructions for comparison to climate model experiments (e.g., Ibarra and others, 2014; Oster and others, 2015; Barth and others, 2016; Lora and others, 2017). Proceedings Volume:2018 Lake Bonneville Geologic Conference and Short Course One such relationship, derived from the steady-state water balance assumption, is for the area of the lake (AL) to the area of the basin (AB) (Hudson and Quade, 2013; Ibarra and others, 2018):