High-resolution studies of pollen in laminated sediments deposited in Santa Barbara Basin (SBB) core SPR0901-02KC reflect decadal-scale fluctuations in precipitation spanning the interval from AD 800-1600. From AD 800-1090 during the Medieval Climate Anomaly (MCA) SBB sediments were dominated by xeric vegetation types (drought-resistant coastal sagebrush and chaparral) implying reduced precipitation in the southern California region. Drought-adapted vegetation abruptly decreased at AD 1090 and was rapidly replaced by mesic oak (Quercus) woodlands associated with an increased pollen flux into the basin. After a mesic interval lasting ~100 years, pollen flux and the relative abundance of Quercus pollen dropped abruptly at AD 1200 when the rapid rise of chaparral suggests a significant drought similar to that of the MCA (~AD 800-1090). This brief resurgence of drought-adapted vegetation between AD 1200-1270 marked the end of the MCA droughts. A gradual increase in mesic vegetation followed, characterizing cool hydroclimates of the Little Ice Age (LIA) in coastal southern California.The presence of xeric vegetation in SBB coincides with major drought events recorded in tree rings and low lake levels elsewhere in California except for the brief drought between AD 1130-1160. Correlative diatom and terrigenous sediment input proxy records from SBB are largely supportive of the pollen record predominantly linking the MCA with drought and La Niña-like conditions and the LIA with wetter (more El Niño-like) conditions. Differences between paleoclimate proxies (pollen, diatoms, and terrigenous sediment) in SBB exist, however, possibly reflecting the temporal and spatial differences in the generation of each proxy record, as well as their individual sensitivity to climate change.
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During the interval from 1130 to 1200, arboreal pollen dominated by Quercus indicates continued high soil moisture agreeing with coeval diatom data suggesting a relatively weak CC, which is consistent with wetter conditions onshore ( Barron et al., 2015 ). However, elemental composition of the sediment deposited in our SBB core argues for reduced river runoff between 1130 and 1170, in agreement with the southern California PDSI calculated from tree rings ( Fig. 5 E; Cook et al., 2010 ). Strong upwelling during the early part of this interval is supported by high numbers of Rhizosolenia spp. During the later part of the MCA-LIA transition, severe drought conditions from 1200 to 1270 indicated by the high chaparral pollen abundance in the SBB agree with the southern California PDSI and the diatom-based proxy for strong CC flow. However, the XRF PC1 river runoff proxy suggests relatively wet conditions ( Fig. 5 C).
We would like to acknowledge Robert Thunell for providing sediment trap material, the crew of the R/V Robert Gordon Sproul for assistance in collecting core material, and the Climate and Land Use, Research & Development Program, USGS. We appreciate the time and thoughtfulness of our editors (Norm Catto, Jeannine St. Jacques, and Scott Starratt) and two anonymous reviewers for Quaternary International. This research was funded by NSF grants OCE-0752093 to ILH and by Lamont Doherty Earth Observatory Climate Center grant 4-30802 to LEH. This is Lamont Doherty Earth Observatory Contribution 7832.
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- Little Ice Age
- Medieval warm
- Santa Barbara Basin