HR: 17:30h
AN: PP34B-07    [Abstracts]
TI: Southern California Hydrographic Shifts During the Medieval Climate Anomaly and the Little Ice Age.
AU: * Hendy, I L
EM: ihendy@umich.edu
AF: University of Michigan, 1100 North University Ave, Ann Arbor, MI 48109-1005, United States
AU: Pak, D K
EM: pak@geol.ucsb.edu
AF: University of California, Santa Barbara, Department of Earth Science University of California, Santa Barbara, CA 93106-9630, United States
AU: Barron, J A
EM: jbarron@usgs.gov
AF: U.S. Geological Survey, 345 Middlefield Rd., MS 915, Menlo Park, CA 94025, United States
AU: David, L w
EM: lea@geol.ucsb.edu
AF: University of California, Santa Barbara, Department of Earth Science University of California, Santa Barbara, CA 93106-9630, United States
AB: We present records of the marine environmental change that occurred as regional climate shifted from the Medieval Climate Anomaly (MCA) into the Little Ice Age (LIA) based on planktonic foraminiferal and diatom assemblages alongside geochemical evidence of surface water temperature and salinity change from Santa Barbara Basin (SBB). The present climate reconstructions available in SBB clearly demonstrate that ocean and atmospheric circulation changes are occurring during the MCA and LIA. Records of sinistral Neogloboquadrina pachyderma absolute and relative abundance from ODP Site 893 suggest that surface waters cooled at ~600 years BP (varve chronology) or ~800 years BP (radiocarbon chronology). SSTs must have dropped below 8-10°C during winter through these intervals to provide favorable environmental conditions as sinistral N. pachyderma does not inhabit the modern SBB where annual SSTs range from 13-17°C. These results conflict with assemblage records of planktonic diatoms from the same core where increased relative abundance of Fragilariopsis doliolus occurred during the LIA. F. doliolus is a subtropical diatom associated with warm gyral waters that has been used extensively on the northern California Margin as an indicator of surface water warming and weak California Current (CC) flow. However, 20^th century records suggest a close relationship of F. doliolus relative abundance to spring SSTs in the basin. Preliminary planktonic foraminiferal Mg/Ca results ( Globigerina bulloides) from core MV0508-32TC indicate that during the MCA, SBB surface waters were between 15 and 16°C, similar to modern warm season temperatures in the region, and cooled to 14°C during the LIA. This is consistent with the planktonic foraminiferal and radiolarian assemblage records from the region, which suggest a warm CC during the MCA, but stands in contrast with the δ¹⁸O and diatom assemblage records. δ¹⁸O records from ODP Site 893 indicate a cooling of surface waters during the MCA and warming during the LIA (demonstrated by a δ¹⁸O decrease during the LIA of ~0.4‰). Mg/Ca and δ¹⁸O records can only be reconciled if surface salinity decreased dramatically during the LIA. The following scenario may explain the record. As upwelling cools surface waters, warming of surface waters indicated by the presence of F. doliolus suggests reduced spring upwelling during the LIA. The presence of sinistral N. pachyderma suggests that during a portion of the year during the LIA surface waters in the basin were extremely cool perhaps cooled by the advection of subpolar water into the region via the CC. Reduced salinity during the LIA may be the result of either increased upwelling of low salinity water (although this conflicts with the diatom evidence), or advection of subpolar water from the NE Pacific. In contrast the MCA appeared to be associated with more saline, warmer surface waters and spring upwelling. These surface water shifts maybe related to ocean and atmospheric circulation changes associated with the PDO.
DE: 4922 El Nino (4522)
DE: 4944 Micropaleontology (0459, 3030)
DE: 4954 Sea surface temperature
DE: 4964 Upwelling (4279)
SC: Paleoceanography and Paleoclimatology [PP]
MN: 2007 Fall Meeting