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.
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A Holocene record of Pacific Decadal Oscillation (PDO)-related hydrologic variability in Southern California (Lake Elsinore, CA)
High-resolution terrestrial records of Holocene climate from Southern California are scarce. Moreover, there are no records of Pacific Decadal Oscillation (PDO) variability, a major driver of decadal to multi-decadal climate variability for the region, older than 1,000 years. Recent research on Lake Elsinore, however, has shown that the lake’s sediments hold excellent potential for paleoenvironmental analysis and reconstruction. New 1-cm contiguous grain size data reveal a more complex Holocene climate history for Southern California than previously recognized at the site. A modern comparison between the twentieth century PDO index, lake level change, San Jacinto River discharge, and percent sand suggests that sand content is a reasonable, qualitative proxy for PDO-related, hydrologic variability at both multi-decadal-to-centennial as well as event (i.e. storm) timescales. A depositional model is proposed to explain the sand-hydrologic proxy. The sand-hydrologic proxy data reveal nine centennial-scale intervals of wet and dry climate throughout the Holocene. Percent total sand values >1.5 standard deviation above the 150–9,700 cal year BP average are frequent between 9,700 and 3,200 cal year BP (n = 41), but they are rare from 3,200 to 150 cal year BP (n = 6). This disparity is interpreted as a change in the frequency of exceptionally wet (high discharge) years and/or changes in large storm activity. A comparison to other regional hydrologic proxies (10 sites) shows more then occasional similarities across the region (i.e. 6 of 9 Elsinore wet intervals are present at >50% of the comparison sites). Only the early Holocene and the Little Ice Age intervals, however, are interpreted consistently across the region as uniformly wet (≥80% of the comparison sites). A comparison to two ENSO reconstructions indicates little, if any, correlation to the Elsinore data, suggesting that ENSO variability is not the predominant forcing of Holocene climate in Southern California.
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- Award ID(s):
- 0602269
- NSF-PAR ID:
- 10469671
- Publisher / Repository:
- Springer
- Date Published:
- Journal Name:
- Journal of Paleolimnology
- Volume:
- 44
- Issue:
- 3
- ISSN:
- 0921-2728
- Page Range / eLocation ID:
- 819 to 839
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1007/s10933-010-9454-0
