SANTA BARBARA BASIN SEDIMENT RECORD OF VOLCANIC WINTERS TRIGGERED BY TWO YELLOWSTONE SUPERVOLCANO ERUPTIONS AT 639 KA

A 4,000-year-duration sedimentary paleoclimatic record from Santa Barbara Basin, California provides an unprecedented high resolution climatic history of the glacial to interglacial transition that occurred about 630,000 years ago (Glacial Termination VII between Marine Isotopic Stages 16 and 15). The Lava Creek B tephra, with its unique geochemical fingerprint and well dated radiometric age of 639 +/- 2 kyr, occurs as two thin tephra layers, distinct in sediment composition and particle size, in this and a nearby core following the onset of warming into an interglacial stage. This ash fall deposit, widely distributed over western North America, records the massive explosive volcanic episode that formed the present vast Yellowstone volcanic caldera, one of the largest of the last 23 million years. For the first time, this tephra has been directly compared with a climatic record with decadal resolution that demonstrates that the volcanism was precisely coincident with and therefore likely the cause of two episodes of abrupt sea-surface cooling of ~3 degrees C in Santa Barbara Basin, a site well known for recording near-global climatic history during the late Quaternary. Each of these volcanic winters lasted at least ~80 yrs based on counts of annual laminations (varves) in another part of the core, assuming constant sedimentation rates over the deglacial episode. Volcanic winters of this duration are significantly longer than most models predict based on atmospheric dust and sulfur loads, and suggest involvement of positive climatic feedbacks including oceanographic effects. These cool episodes also suggest that the global climate system was highly sensitive in response to such perturbations during deglacial transitions.