HR: 11:55h
AN: OS32A-07    [Abstracts]
TI: Holocene Rainfall and Productivity Variation in the Gulf of California
AU: * Gonzalez-Yajimovich, O
EM: yajimo@uabc.mx
AF: Ciencias Marinas, Universidad A. de Baja California, Apdo Postal 453, Ensenada, BC 22800, Mexico
AU: Douglas, R
EM: rdouglas@usc,edu
AF: Earth Sciences, University of Southern California, Earth Sciences, LA, CA 90089-0740, United States
AU: Gorsline, D
EM: gorsline@usc.edu
AF: Earth Sciences, University of Southern California, Earth Sciences, LA, CA 90089-0740, United States
AB: Recent data reveals significant Holocene climate and oceanography changes in the Gulf of California (GC). Much of the published data is based on sediment cores from Guaymas basin in the mid GC region. We report on laminated sediment cores data from slope basins in the lower GC. Our history covers about 7700 YBP (cal yrs) in Alfonso basin (west side) and 9500 YBP in eastern Pescadero basin (east side) and is based on an analysis of sediment microfabric, organic carbon, biogenic and lithogenic components and stable isotopes. The broad picture of ocean-climate change in the lower GC is similar to Guaymas basin, with interesting differences. Prior to about 7000 YBP, the mass-accumulation rates (MAR) of terrigenous and biogenic silica on the mainland side are high but variable and suggests high primary productivity (PP) and runoff. Monsoon conditions were established by at least 6000 YBP with higher accumulation of biogenic silica on the east and carbonate on the west, reflective of the strong gradient in PP across the GC. In the early Holocene, biogenic and lithogenic components vary at ca. 900 yr cycles but are out of phase. Between 7000 and 4200 YBP, a general decline in biogenic silica flux rates and an increase in benthic δ¹³C of intermediate waters suggest a period of declining PP. Beginning at about 4200 YBP, the sediment and biogenic records signal a significant change in the lower GC. A major pulse of biogenic sedimentation occurs between 4000 and 3400 YBP across the GC, followed by a cyclic pattern of biogenic silica accumulation and carbonate dissolution with periodicities at 350 and 900 yrs. There are strong peaks of variability in the laminations, biogenic silica and coccolith record at about 150, 200 and 350 yrs, suggestive of solar forcing. The variability in all of the sediment records increases after about 2 ka. Rates of terrigenous accumulation fall in step-like fashion at 3000, 2000 and 1500 YBP and reverse only during the Little Ice Age (LIA). The data suggest sharp contrasts in climate with declining rainfall and intensified winds. After 2000 YBP the west-east gradient in PP appears to intensify. During the last 400 yrs there has been an intensification of these trends, especially since the end of the LIA (130 YBP)
DE: 3002 Continental shelf and slope processes (4219)
DE: 3022 Marine sediments: processes and transport
DE: 3305 Climate change and variability (1616, 1635, 3309, 4215, 4513)
DE: 3339 Ocean/atmosphere interactions (0312, 4504)
DE: 3344 Paleoclimatology (0473, 4900)
SC: Ocean Sciences [OS]
MN: 2007 Joint Assembly