Browsing by Subject "Lake sediment"

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    A Holocene record of Pacific Decadal Oscillation (PDO)-related hydrologic variability in Southern California (Lake Elsinore, CA)
    (Springer, 2010-10-01) Kirby, M. E.; Lund, S. P.; Patterson, W. P.; Anderson, M. A.; Bird, Broxton W.; Ivanovici, L.; Monarrez, P.; Nielsen, S.
    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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    Indicators of Euro-American land-use change as geochronologic markers in Midwest floodplain lake sediment archives
    (2024-02) LaRoche, Kierstin Marie; Bird, Broxton W.; Licht, Kathy J.; Gilhooly, William P., III
    In association with predicted rising global average temperatures, spring and winter precipitation in the Midwest is projected to increase by up to 30% by the end of this century. Enhanced by the alteration of natural environments, this increase will likely result in more frequent extreme flood events. To best prepare for these circumstances, interest has risen in reconstructing the dynamics between changing climate, altered landscapes, and fluvial systems with age-depth modeling, often using radiocarbon (14C) and 210Pb dating and multi-proxy evidence from floodplain lake sediment archives. Age- depth modeling over the last 300 years can be difficult, however, due to a large plateau in the radiocarbon calibration curve, and 210Pb dating is not reliable for all sediment records. Here, indicators of land-use change, magnetic susceptibility, Rb/Sr, Pb/Zr, and d15N values, were used to create age-depth control for Shannon Lake, IN, a difficult-to-date 600-year-old oxbow lake of the White River near Indianapolis. Age control for Shannon Lake was completed by correlating the timing in the rise of the same proxies from a previously well-dated lake record from Half Moon Pond, an oxbow lake of the White River near Petersburg, IN. The Shannon and Half Moon records were compared to those of three floodplain lake records of the Ohio River floodplain: Avery Lake, IL, Goose Pond, IN, and Grassy Pond, KY to investigate how these proxies varied in floodplain lake sediment from the lower Ohio River. The land-use indicators provided age-control for Shannon Lake, and the indicators of land-use change for the White River records resembled those of the Ohio River records over the last 600 years, where the onset of Euro-American land-use changes were detected at or around 1750 CE. MS, Rb/Sr, and d15N values displayed the greatest resemblance, while greater variations in Rb/Sr values were observed across the five lake records, potentially due to differences in regional setting or differences in the scale of the White River and Ohio River watersheds.
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    Ocean-atmosphere forcing of centennial hydroclimate variability in the Pacific Northwest
    (AGU, 2014-03-11) Steinman, Byron A.; Abbott, Mark B.; Mann, Michael E.; Ortiz, Joseph D.; Feng, Song; Pompeani, David P.; Stansell, Nathan D.; Anderson, Lesleigh; Finney, Bruce P.; Bird, Broxton W.; Earth Sciences, School of Science
    Reconstructing centennial timescale hydroclimate variability during the late Holocene is critically important for understanding large-scale patterns of drought and their relationship with climate dynamics. We present sediment oxygen isotope records spanning the last two millennia from 10 lakes, as well as climate model simulations, indicating that the Little Ice Age was dry relative to the Medieval Climate Anomaly in much of the Pacific Northwest of North America. This pattern is consistent with observed associations between the El Niño–Southern Oscillation (ENSO), the Northern Annular Mode, and drought as well as with proxy-based reconstructions of Pacific and Atlantic ocean-atmosphere variations over the past 1000 years. The large amplitude of centennial variability indicated by the lake data suggests that regional hydroclimate is characterized by longer-term shifts in ENSO-like dynamics and that an improved understanding of the centennial timescale relationship between external forcing and drought is necessary for projecting future hydroclimatic conditions in western North America.