Much of the precipitation delivered to western North America arrives during the cool season via midlatitude Pacific storm tracks, which may experience future shifts in response to climate change. Here, we assess the sensitivity of the hydroclimate and ecosystems of western North America to the latitudinal position of cool‐season Pacific storm tracks. We calculated correlations between storm track variability and three hydroclimatic variables: gridded cool‐season standardized precipitation‐evapotranspiration index, April snow water equivalent, and water year streamflow from a network of
Winter is a critical season for land‐surface feedbacks and ecosystem processes; however, most high‐latitude paleo‐environmental reconstructions are blind to cold season conditions. Here we introduce a winter‐sensitive, paleo‐proxy record that is based on the relative frequency of tangential rows of traumatic resin ducts (TRDs) in the annual growth rings of mountain hemlocks (
- NSF-PAR ID:
- 10448294
- Publisher / Repository:
- DOI PREFIX: 10.1029
- Date Published:
- Journal Name:
- Journal of Geophysical Research: Biogeosciences
- Volume:
- 124
- Issue:
- 7
- ISSN:
- 2169-8953
- Page Range / eLocation ID:
- p. 1923-1938
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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The hydroclimate of the southwestern United States (US) region changed abruptly during the latest Pleistocene as the continental ice sheets over North America retreated from their most southerly extent. To investigate the nature of this change, we present a new record from Lake Elsinore, located 36 km inland from the Pacific Ocean in Southern California and evaluate it in the context of records across the coastal and interior southwest United States, including northwest Mexico. The sediment core recovered from Lake Elsinore provides a continuous sequence with multi-decadal resolution spanning 19e9 ka BP. Sedimentological and geochemical analyses reveal hydrologic variability. In particular, sand and carbonate components indicate abrupt changes at the Oldest Dryas (OD), BøllingeAllerød (BA), and Younger Dryas (YD) transitions, consistent with the timing in Greenland. Hydrogen isotope analyses of the C28 nalkanoic acids from plant leaf waxes (dDwax) reveal a long term trend toward less negative values across 19 9 ka BP. dDwax values during the OD suggest a North Pacific moisture source for precipitation, consistent with the dipping westerlies hypothesis. We find no isotopic evidence for the North American Monsoon reaching as far west as Lake Elsinore; therefore, we infer that wet/dry changes in the coastal southwest were expressed through winter-season precipitation, consistent with modern climatology. Comparing Lake Elsinore to other southwest records (notably Cave of Bells and Fort Stanton) we find coincident timing of the major transitions (OD to BA, BA to YD) and hydrologic responses during the OD and BA. The hydrologic response, however, varied during the YD consistent with a dipole between the coastal and interior southwest. The coherent pattern of hydrologic responses across the interior southwest US and northwest Mexico during the OD (wet), the BA (drier), and YD (wet) follows changes in the Atlantic Meridional Overturning Circulation, presumably via its combined influence on North Pacific winter storm tracks and the extent/magnitude of the North American Monsoon. In contrast, Lake Elsinore and the coastal southwest experiences a deglacial drying trend punctuated by abrupt change at the OD to BA and BA to YD transitions. This trend tracks rising greenhouse gases through the deglacial, with an apparent southward shift in westerly moisture sources adjusting to the retreating ice sheet.more » « less
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