Rapid oscillations in western North America vegetation and climate during oxygen isotope stage 5 inferred from pollen data from Santa Barbara Basin (Hole 893A)

Chronologically-controlled, high-resolution (∼200 yr average sampling interval) pollen data from a core in the Santa Barbara Basin (SBB) provide evidence of millennial-scale climate variability on the southern California coast from ∼70 to 140 ka B.P. The first climate event, inferred from a brief reversal in the glacial/interglacial shift from montane conifer to lowland oak assemblages, occurred during the oxygen isotope stage (OIS) 6/5 transition. In OIS 5e, oak-dominated assemblages imply conditions similar to or slightly warmer than present. Cooler conditions that gradually replaced the relatively stable warm Mediterranean climate that continued across the OIS 5e/5d transition ended abruptly just before the end of OIS 5d. Warming, inferred from oak expansion, continued in OIS 5c. This lengthy cyclic sequence of high amplitude warming events, which peaked below interglacial values, extended into the first part of OIS 5b. Similar oscillations occurred in OIS 5a. These pollen data, that are directly correlated with isotopic data from the same sediment samples from Hole 893A, support previous observations that the last interglacial (sensu stricto) on the west coast of North America was correlative with oxygen isotope substage 5e. In addition, pollen data show that significant warming events reflected in terrestrial vegetation also occurred in different background states of the climate system — during processes of ice growth as well as ice decay.