A POTENTIAL 700,000 YEAR HISTORY OF CATACLYSMIC STORM AND FLOOD EVENTS, SANTA BARBARA BASIN, COASTAL CALIFORNIA: PRELIMINARY RESULTS

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-sized deposits that punctuate typical olive hemipelagic sediment. Thirty-two piston cores recovered from a breached anticline in the SBB provide an ultra-high resolution climate record, possibly as old as Oxygen Isotope Stage 16. Precipitation, and therefore sedimentation, in the SBB is affected by both the Pacific Decadal Oscillation and El Niño Southern Oscillation (ENSO); however, many of the gray layers have larger magnitude and lower frequencies (> 60 years) than can be explained by typical variation associated with these phenomena.

Three cores were examined using NIH Image J software to determine variations in the magnitude and frequency of gray layer events. Each core represents a different climatic regime – glacial, intermediate and interglacial. Based on these preliminary analyses, the largest storm events (>4 mm thick gray layers, ~160-year events and rarer) were only present in the interglacial core. The frequencies for smaller events were similar for all three cores – approximately 15 and 25 years for >0.5 mm and >1 mm events, respectively. Larger events were absent during the glacial period. Frequencies of 3-7 years (ENSO) have been recognized within the annual varves (<1 mm) of the SBB. The greater thickness and lower frequency of the gray layers suggest they are much larger events than those witnessed during modern ENSO storms in southern California. As found at ODP Site 893 over the last 160 ky, the sedimentation rate at this location in the SBB remains remarkably constant, between 0.53 and 0.63 mm/yr, for cores tentatively dated back to 480 ka. Sedimentation rates were obtained by counting laminations within minimally disturbed intervals using the grayscale contrast of the annual couplets (assuming them to be varves). These preliminary results span much of the sampled stratigraphic sequence, however, quantification of the magnitude and frequency of gray layers during all climatic regimes will be needed to confirm trends reported above. Variations of sedimentation rate with changing climate will also become more apparent as a more detailed record is acquired.