NOAA/WDS Paleoclimatology - California Margin ODP1018 600KYr Multiproxy Data

STUDY NOTES: Multiproxy data from ODP Site 1018 off the central California coast. Data include stable isotopes, alkenone SST, carbon, biogenic silica, and terrestrial pollen data. Total organic carbon and carbonate data were measured from 0 to 114.6 mbsf (2.8 to 614 ka). Age model is from oxygen isotope stratigraphy using a spline age model developed using Analyseries software (see Lyle et al. 2010). Sediments were freeze-dried, a split was analyzed for total carbon, and a second split was acidified and analyzed for organic carbon. The difference between total carbon and organic carbon was assigned to be inorganic carbon in CaCO3. CaCO3 was estimated by multiplying the inorganic carbon by 8.33, the CaCO3/C weight ratio. Alkenone sea surface temperature data were measured from 0 to 31.9 mbsf (2.7 to 160 ka). Age model is from oxygen isotope stratigraphy using a spline age model developed using Analyseries software (see Lyle et al. 2010). Alkenones were extracted from sediments using methylene chloride-methanol, analyzed via gas chromatography, and reported as SST using the Muller et al (1998) calibration equation. Oxygen isotopes for Site 1018 are reported in Andreasen et al., [2000]. The >250-um-size fraction was sampled for benthic foraminiferal species Cibicidoides wuellerstorfi, Cibicidoides pachyderma, and Uvigerina spp. Most analyses were conducted using one or two C. wuellerstorfi or three or four Uvigerina spp. tests. However, the number of tests of C. wuellerstorfi analyzed ranged from shell fragments to four specimens. Occasional analyses were done using species C. pachyderma when C.wuellerstorfi were scarce. All values reported here are relative to VPDB. Pollen data were obtained using standard processing procedures. KOH and HF digestion and acetolysis were preceded and succeeded by sieving through 7-mm nylon screening [Heusser and Stock, 1984]. An exotic tracer (Lycopodium) was added prior to sieving to determine pollen concentration per gram of sediment. Taxonomic identification of pollen was based on comparison with modern pollen reference collections from western North America, and pollen counts were continued until at least 300 pollen grains were identified from each sample. Biogenic silica was measured by the method described in Anderson and Ravelo [2001]. Samples were freeze-dried, lightly ground, and sieved. Splits were extracted for biogenic Si by the Mortlock and Froelich [1989] extraction technique using Na2CO3 and analyzed via an automated spectrophotometric flow injection analysis system [Lachat QuickChem 8000].
ABSTRACT SUPPLIED BY ORIGINATOR: Coastal marine sediments contain mixtures of terrestrial and marine paleoclimate proxies that record how the coastal water cycle has behaved over long time frames. We explore a 600-kyr marine record from ODP Site 1018, located due west of Santa Cruz, California, to identify coastal wet and dry periods, and to associate them with oceanographic processes. Wet periods in central California, identified by increased tree pollen relative to pollen from grasslands and scrublands, are found on every major deglaciation in the last 600 kyr. Sea surface temperature (SST) data were collected for the last 2 deglaciation. Wet periods are associated with a rapid rise in SST off central California. SST gradients along the California margin and changes in biogenic deposition show that wet periods in central California are associated with a weakening of the California Current and weakened coastal upwelling. High carbonate production suggests that there was significant curl-of-windstress upwelling offshore. We propose that wet periods in Central California are associated with a meteorological connection to the tropical Pacific and weakened southward flow in the California Current that shunted temperate Pacific water northward into the Alaska gyre. We do not observe evidence for a south-shifted westerly storm track at the last glacial maximum but find that wet periods are diachronous along the California margin. The wettest period around the Santa Barbara Basin peaked at 16 ka, preceding the wet peak in central and northern California by 4 kyr.