HR: 1330h
AN: PP12A-0228    [PDF]
TI: Eastern Equatorial Pacific $^{14}$C Reservoir Age Variability During the Last Deglaciation
AU: * Miller, M A
EM: mrkmiller@ucdavis.edu
AF: Dept. of Geology, University of California, Davis, One Shields Ave., Davis, CA 95616 United States
AU: Guilderson, T P
EM: tguilderson@llnl.gov
AF: CAMS - Lawrence Livermore National Laboratory, 7000 East Ave., Livermore, CA 94551 United States
AU: Spero, H J
EM: spero@geology.ucdavis.edu
AF: Dept. of Geology, University of California, Davis, One Shields Ave., Davis, CA 95616 United States
AB: Radiocarbon and stable carbon isotope data from the thermocline dwelling planktonic foraminifera, {\it Neogloboquadrina dutertrei}, in Eastern Equatorial Pacific (EEP) core TR-163-22 (92.24$\deg$ W, 0.31$\deg$ N, 2830 m depth, mean sedimentation rate of 10 cm/kyr) reveal a sustained pulse of relatively young, low-$\delta^{13}$C water into the tropical Pacific thermocline during the last deglacial carbon isotope minimum event (CIME) between $\sim$20 and 16 cal kybp. $^{14}$C ages show the CIME is coeval with a sharp decrease in the apparent $^{14}$C age of intermediate waters at the same time Mg/Ca-derived sea surface temperatures (SST) in the EEP begin to rise. At the initiation of the CIME (189 cm core depth), {\it N. dutertrei} records an age of 18,920 $\pm$ 70 $^{14}$C years, followed by an abrupt decrease to 14,695 $\pm$ 45 $^{14}$C years (172 cm core depth). {\it N. dutertrei} ages remain fairly constant at $\sim$13.7 to 14.7 $^{14}$C ky for the duration of the CIME, while $\delta^{13}$C values continue to decline until the $\delta^{13}$C minimum is reached at 124 cm. {\it N. dutertrei} returns an age of 13,695 $\pm$ 45 $^{14}$C years in the 124 cm interval. None of these $^{14}$C ages have been reservoir corrected. Comparison of {\it N. dutertrei} $^{14}$C data with $^{14}$C analyses of mixed benthic foraminifera and of the surface-dwelling foraminifera {\it Globogerinoides ruber} from the same samples show that the event is absent from the deep and surface ocean, supporting previous hypotheses that the CIME is confined to intermediate waters. Atlantic records from intermediate depths show a similar CIME with similar $^{14}$C-derived water mass ages. Potential sources of young water during the CIME are the resurgence of upwelled Circumpolar Deep Water (CPDW) as the sea ice margin retreated southward, or meltwater from marine or terrestrial sources. This Southern Ocean signal would then be transmitted via subducted intermediate water masses to low latitudes. Because sea ice is formed from existing surface waters, it is an unlikely source for a unique isotopic signal. Terrestrial meltwater is also an unlikely candidate because it may not have enough volume to significantly change the isotopic composition of intermediate waters throughout the southern hemisphere. Thus the most plausible explanation for the $^{14}$C age plateau in the EEP thermocline during the CIME is resumed upwelling of a low-$\delta^{13}$C Southern Ocean water mass with subsequent advection of this low-reservoir age water mass into the source regions of low-latitude thermocline waters.
DE: 3344 Paleoclimatology
DE: 4267 Paleoceanography
SC: Paleoceanography and Paleoclimatology [PP]
MN: 2003 Fall Meeting