Mathematics – Logic
Scientific paper
May 2007
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2007agusmpp43b..02e&link_type=abstract
American Geophysical Union, Spring Meeting 2007, abstract #PP43B-02
Mathematics
Logic
1616 Climate Variability (1635, 3305, 3309, 4215, 4513), 1635 Oceans (1616, 3305, 4215, 4513), 3022 Marine Sediments: Processes And Transport, 4900 Paleoceanography (0473, 3344)
Scientific paper
Terrestrial runoff from major storm and flood events in southern California is captured in the Santa Barbara Basin (SBB) as distinct gray layers of well-sorted clay to silt that punctuate typical olive hemipelagic mud. Thirty-two partially overlapping piston cores recovered from a breached anticline provide ultra-high resolution windows into an approx. 700,000-year climate record. We document the magnitude, frequency, mass accumulation rate, grain size and mineralogy of these deposits to gain insight into climatically related variations and trends. In addition to investigating chronological trends, we also compare glacial, interglacial and intermediate climate regimes. Bulk and clay mineralogy (determined by X-ray diffraction) of the gray layers has remained remarkably constant throughout the entire record indicating a consistent source for terrigenous input despite fluctuating sea level. Relative abundance of smectite:illite may reflect changes in weathering, vegetation and/or humidity. Mean grain size shows little variation (10.43-14.01 micrometers) through time, with no apparent relationship to the thickness of event deposits. Therefore, gray layer thickness likely reflects the intensity and transport efficiency of the erosional event rather than a change in proximity or energy of depositional currents. Gray layers often occur in amalgamated beds or clusters, possibly representing pulses of runoff during storm fronts or reworking of major deposits over extended time. Bulk mass accumulation rates (MARs) were calculated for each core using varve-counted time and bulk density. MARs show little variation (0.06-0.12 gcm-2yr-1), lacking a definite climatic trend. Average MARs are slightly higher during interglacial (0.097 gcm-2yr-1) than glacial (0.089gcm-2yr-1) intervals and show significant variation within similar climatic regimes. Where not bioturbated, gray layers account for a significant percentage of overall sedimentation (8-17%). Mass percent gray is slightly greater (11.4%) during interglacial intervals than during glacial (10.5%) or intermediate (8.5%) climatic intervals. Gray-layer contribution to overall sedimentation peaked near the OIS 8/9 transition (16%) and the Holocene (17%). Small events (<0.3 gcm-2) are by far the most frequent. Based on comparison of frequency and magnitude of historic precipitation events, the majority of events we measured occurs less frequently and match or exceed the magnitude of moderate to strong El Niño events. Large events (>0.6 gcm-2) are most frequent during the intermediate climate regimes (avg. 470 years) and least frequent during glacial MIS 8 (approx. 1000 yrs) indicating either smaller storms during this glacial or more vegetation to restrict erosion. Glacial MIS 12, MIS 6 and the Holocene have the greatest frequency of large events (approx. 250 yr). Large events occur every 450-550 years during interglacials and 500-650 years during intermediate intervals. The gray layers recorded in these cores are up to ten times larger by mass than the largest historic flood deposit in the SBB. The SBB provides a record of major precipitation and erosional events, changes in local climate and an opportunity to link coastal southern California climate to global and nonmarine climate archives.
Behl R. J.
Escobedo D. K.
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