A 9170-year record of decadal-to-multi-centennial scale pluvial episodes from the coastal Southwest United States: a role for atmospheric rivers?

Abstract

A well-dated, 9170 calendar year before present (cal yr BP) paleohydrologic reconstruction is presented from Lower Bear Lake in the San Bernardino Mountains of the coastal southwest United States. This new multi-proxy record is characterized by alternating organic-rich/carbonate-rich sediment units, interpreted to reflect hydrologically-forced changes in the lake's depositional environment. Our interpretation of the proxy data indicates nine decadal-to-multi-centennial pluvial episodes (PE) over the past 9170 cal yr BP. Of these nine inferred pluvials, five are interpreted as more pronounced based on their combined proxy interpretations: (PE-V) 9170?–8250, (PE-IV) 7000–6400, (PE-III) 3350–3000, (PE-II) 850–700, and (PE-I) 500–476 (top of core) cal yr BP. The Lower Bear Lake record indicates that the San Bernardino Mountains, source region for the Mojave River and its terminal playa, was wet during the same periods (within dating errors), to several of the major pluvials proposed from the lakes in the sink of the Mojave River. Our comparison extends north also to Tulare Lake, which drains the southcentral-western Sierra Nevada Mountains. This temporally and spatially coherent signal indicates that a similar climate forcing acted to increase regional wetness at various times during the past 9170 cal yr BP. As originally proposed by Enzel, Ely, and colleagues (e.g., Enzel et al., 1989; Enzel, 1992; Ely et al., 1994; Enzel and Wells, 1997), we too contend that Holocene pluvial episodes are associated with changing the frequency of large winter storms that track across a broad region at decadal-to-multi-centennial timescales. We build upon their hypothesis through the addition of new and better-dated site comparisons, recent advances in the understanding of atmospheric rivers, and improved knowledge of the ocean–atmosphere dynamics that caused the early 20th century western United States pluvial.