Floods and Fires: Decadal-scale terrestrial data from Santa Barbara Basin during the Common Era

High-resolution studies of pollen and charcoal from annually-deposited laminae of Santa Barbara Basin (SBB) reflect the regional dynamics of southern coastal California vegetation from 700- to 1900 C.E. through the Medieval Climate Anomaly, the Little Ice Age to the arrival of Europeans. Kasten core SPR0901-02KC (34°16.8' N, 120°02.3' W; 588 m water depth) was analyzed for pollen at consecutive 0.5 cm depth intervals that correspond with an average deposition of five years from 150 cm to core top. During the Medieval Climate Anomaly (MCA; 800 to 1270 C.E.) SBB sediments were dominated by xeric vegetation types (drought-resistant coastal sagebrush and chaparral) implying reduced precipitation in the southern California region. Subsequent, pulsating increases in mesic arboreal vegetation, notably oak assemblages, increase from a minima at 1200 C.E., stabilizing between 1450-1550 C.E. before gradually decreasing toward the 20th century. Prior to the late 14th century, fire events (inferred from microcharcoal fragments deposited in SBB), are rare and often associated with low lithogenic input into SBB. Notable charcoal peaks normalized to pollen abundance occur at 1110, 1200, 1410-1440, 1530, and 1764, with only the 1530 event associated with a flood layer. Fires do not appear to drive significant sediment input into the basin. Increased charcoal deposition follows the settlement of California rose to peak values in the mid 19th century. Decadal-scale fluctuations in relative abundance of mesic vegetation generally correspond with variations in sea-surface temperatures inferred from foraminiferal assemblages in SBB, and are consistent with changes in northern hemisphere circulation, indicating weakened Arctic Lows and extended La Niña-like conditions during the MCA and strengthened Aleutian Lows and extended El Niño-like atmospheric conditions during the LIA. Minimal abundance of oak and pine beginning in the 18th century corresponds with the historical period in Santa Barbara and clearing of land for ranching and agriculture.