NOAA/WDS Paleoclimatology - Holocene multidecadal and multicentennial droughts affecting Northern California and Nevada

Continuous, high-resolution d18O records from cored sediments of Pyramid Lake, Nevada, indicate that oscillations in the hydrologic balance occurred, on average, about every 150 years (yr) during the past 7630 calendar years (calyr). The records are not stationary; during the past 2740 yr, drought durations ranged from 20 to 100yr and intervals between droughts ranged from 80 to 230yr. Comparison of tree-ring-based reconstructions of climate change for the past 1200 yr from the Sierra Nevada and the El Malpais region of northwest New Mexico indicates that severe droughts associated with Anasazi withdrawal from Chaco Canyon at 820 calyrBP (calendar years before present) and final abandonment of Chaco Canyon, Mesa Verde, and the Kayenta area at 650 calyrBP may have impacted much of the western United States. During the middle Holocene (informally defined in this paper as extending from 8000 to 3000 calyrBP), magnetic susceptibility values of sediments deposited in Pyramid Lake's deep basin were much larger than late-Holocene (3000-0 calyrBP) values, indicating the presence of a shallow lake. In addition, the mean d18O value of CaCO3 precipitated between 6500 and 3430calyrBP was 1.6 less than the mean value of CaCO3 precipitated after 2740 calyrBP. Numerical calculations indicate that the shift in the d18O baseline probably resulted from a transition to a wetter (>30%) and cooler (3-5°C) climate. The existence of a relatively dry and warm middle-Holocene climate in the Truckee River-Pyramid Lake system is generally consistent with archeological, sedimentological, chemical, physical, and biological records from various sites within the Great Basin of the western United States. Two high-resolution Holocene-climate records are now available from the Pyramid and Owens lake basins which suggest that the Holocene was characterized by five climatic intervals. TIC and d18O records from Owens Lake indicate that the first interval in the early Holocene (11,600-10,000 calyrBP) was characterized by a drying trend that was interrupted by a brief (200 yr) wet oscillation centered at 10,300 calyrBP. This was followed by a second early-Holocene interval (10,000-8000 calyrBP) during which relatively wet conditions prevailed. During the early part of the middle Holocene (8000-6500 calyrBP), high-amplitude oscillations in TIC in Owens Lake and d18O in Pyramid Lake indicate the presence of shallow lakes in both basins. During the latter part of the middle Holocene (6500-3800 calyrBP), drought conditions dominated, Owens Lake desiccated, and Lake Tahoe ceased spilling to the Truckee River, causing Pyramid Lake to decline. At the beginning of the late Holocene (~3000 calyrBP), Lake Tahoe rose to its sill level and Pyramid Lake increased in volume.