Insights from a synthesis of old and new climate-proxy data from the Pyramid and Winnemucca lake basins for the period 48 to 11.5 cal ka
A synthesis of old and new paleoclimatic data from the Pyramid and Winnemucca lake basins indicates that, between 48.0 and 11.5·10 3 calibrated years BP (hereafter ka), the climate of the western Great Basin was, to a degree, linked with the climate of the North Atlantic. Paleomagnetic secular variation (PSV) records from Pyramid Lake core PLC08-1 were tied to the GISP2 ice-core record via PSV matches to North Atlantic sediment cores whose isotopic and(or) carbonate records could be linked to the GISP2 δ 18 O record. Relatively dry intervals in the western Great Basin were associated with cold Heinrich events and relatively wet intervals were associated with warm Dansgaard-Oeschger (DO) oscillations. The association of western Great Basin dry events with North Atlantic cold events (and vice versa) switched sometime after the Laurentide Ice Sheet (LIS) reached its maximum extent. For example, the Lahontan highstand, which culminated at 15.5 ka, and a period of elevated lake level between 13.1 and 11.7 ka were associated with cold North Atlantic conditions, the latter period with the Youngest Dryas event. Relatively dry periods were associated with the Bølling and Allerød warm events. A large percentage of the LIS may have been lost to the North Atlantic during Heinrich events 1 and 2 and may have resulted in the repositioning of the Polar Jet Stream over North America. The Trego Hot Springs, Wono, Carson Sink, and Marble Bluff tephras found in core PLC08-1 have been assigned GISP2 calendar ages of respectively, 29.9, 33.7, 34.1, and 43.2 ka. Given its unique trace-element chemistry, the Carson Sink Bed is the same as Wilson Creek Ash 15 in the Mono Lake Basin. This implies that the Mono Lake magnetic excursion occurred at approximately 34 ka and it is not the Laschamp magnetic excursion. The entrance of the First Americans into the northern Great Basin is dated to approximately 14.4 ka, a time when the climate was relatively dry. Evidence for human occupation of the Great Basin is lacking for the next 1100 years (y); i.e., the oldest western stemmed point site in the Great Basin dates to 13.3 ka. Two hypotheses are suggested for this cultural hiatus: (1) the climate had deteriorated to the point that people vacated the Great Basin, or (2) people moved to basin-bottom wetlands that persisted during the dry period, and then the subsequent Younger Dryas wet event erased the archaeological evidence deposited around the low-elevation wetland sites.