Evidence for Pacific‐modulated precipitation variability during the late Holocene from the southwestern USA

Abstract

The mechanisms driving late Holocene drought cycles in the western United States are not well known due to the general scarcity of long‐term, high‐resolution, absolutely dateable proxies for precipitation in continental interiors. Here we show that late Holocene precipitation variability in the southwestern United States has been caused by changes in the Pacific Ocean. We present a stalagmite‐based, annually resolved moisture record that indicates large shifts from pluvial to drought conditions alternating with periods of dampened, near‐average precipitation over the last 3000 years. Significant spectral peaks at decadal‐scale (∼20–50, 70–80 year) frequencies likely correspond to modern frequencies of the Pacific Decadal Oscillation or a low‐frequency component of the El Niño‐Southern Oscillation, and are dominant during episodes of large precipitation shifts. Overall pluvial conditions punctuated by severe droughts may have challenged the adaptive capacities of emerging agrarian communities of ancestral Americans.

Solar forcing of Holocene climate: New insights from a speleothem record, southwestern United States

“…While the relationship between ENSO and the Asian monsoon is less clear, in the summers following an El Niño event the Asian monsoon is typically weakened and the area is often characterized by droughts (Chan and Zhou, 2005). Comparison of modern rainfall data from China and the southwest shows an opposite relationship (Rasmussen et al, 2006). If this relationship between the two regions holds true for the rest of the Holocene, then it suggests that solar forcing might be steering the PDO-ENSO system on millennial and centennial time scales via changes in the Walker circulation.…”

Quantifying the value of laminated stalagmites for paleoclimate reconstructions

“…We analyzed annual growth rate data from eleven stalagmites; three stalagmites from NW Scotland [ Proctor et al , 2002]; two stalagmites from New Mexico [ Polyak and Asmerom , 2001; Rasmussen et al , 2006]; two from Italy [ Frisia et al , 2003]; one from China [ Tan et al , 2003], one from Ethiopia [ Asrat et al , 2007], one from Norway [ Linge et al , 2009] and one from Oman [ Fleitmann et al , 2004]. All stalagmites have continuous annual lamina sequences of between 200–2500 years before present, with the annual growth rate of the Scotland, China and Italy samples having provided paleoclimate proxies [ Smith et al , 2006].…”

Multidecadal to multicentury scale collapses of Northern Hemisphere monsoons over the past millennium

“…1 A and B, respectively). In moisture-limited regions, such as southwestern North America, the thickness of annual growth bands is positively correlated to moisture amount (9,10). Similarly, the stable isotopic data are interpreted to be relative wetness indicators.…”

“…Southwestern North America receives both winter (dominantly Pacific) and summer (dominantly North American monsoon) precipitation. The winter precipitation is part of a northwestern North America and southwestern North American precipitation dipole (3,9). Therefore, we compared our record with a record from part of the southern dipole that mostly gets its moisture from winter precipitation, to establish whether the megadroughts are due to summer monsoon deficit or winter Pacific-sourced moisture deficit.…”

“…2B (below) is coherent with the tree ring chronology that reflects winter precipitation. (B) Comparison between BC-11 growth-banding data and tree ring chronology from Sierra Nevada, California (Upper Wright Lakes) (21), representing the southern portion of the north-south dipole of winter precipitation response to PDO variability (3,9). The lack of coherency between the two records suggest that precipitation variability in southwestern North America during the coverage time is likely dominated by summer North American monsoon precipitation.…”