Benthic Foraminiferal Responses to Seasonal and Spatial Changes in Organic Input Within the Southern California Bight

HR: 1340h
AN: PP23B-1438 [Abstracts]
TI: Benthic Foraminiferal Responses to Seasonal and Spatial Changes in Organic Input Within the Southern California Bight
AU: * Bahls, A S
EM: amandabahls@yahoo.com
AF: Indiana State University, Geology Program, Science 159, Terre Haute, IN 47809 United States
AU: Rathburn, A E
EM: gerathbu@isugw.indstate.edu
AF: Indiana State University, Geology Program, Science 159, Terre Haute, IN 47809 United States
AU: PＳez, M E
EM: geperez@isugw.indstate.edu
AF: Indiana State University, Geology Program, Science 159, Terre Haute, IN 47809 United States
AB: One of the primary means to determine ancient changes in productivity is through the use of microfossils. Although abundance changes in fossil benthic foraminiferal assemblages are used to assess paleoproductivity, questions remain about the use of this method in areas with high organic carbon input. This study examined intra-annual (Oct. 1995 to Oct. 1996) and spatial changes in living (Rose Bengal stained) foraminifera from the $>$150 micron and $>$63 micron fractions collected at two sites along a sea-surface productivity gradient within the Southern California Bight. Foraminiferal density increases of the 63-150 micron and $>$63 micron fractions were positively related to surface productivity in this region. In contrast, abundances of the $>$150 micron fraction appeared negatively correlated with surface productivity. Comparisons of vertical profiles showing changes in abundances within the sediments revealed appreciable differences in patterns for the $>$150 micron and the $>$63 micron fractions. Vertical profiles of foraminiferal densities from the $>$63 micron fraction showed surface maxima (0-1 cm interval) for all seasons at both sites, except in May at the southern (lower surface productivity) site. Vertical profile patterns for the $>$150 micron fraction were more variable. At the southern site, total foraminiferal abundances in May reached a subsurface maximum at the 1-1.5 cm interval, and abundance patterns were similar for both the $>$150 micron and the $>$63 micron fractions. Based on these modern analog results, examination of the $>$63 micron fraction is a viable, necessary means for benthic foraminiferal assessments of paleoproductivity in organic rich environments.
DE: 4267 Paleoceanography
SC: Paleoceanography and Paleoclimatology [PP]
MN: 2004 AGU Fall Meeting