HR: 09:30h
AN: PP31B-07    [Abstracts]
TI: A $^{231}$Pa/$^{230}$Th record of Atlantic Ocean circulation rate during MIS3
AU: * Major, C O
EM: cmajor@whoi.edu
AF: WHOI, Dep't of Geology and Geophysics, Woods Hole, MA 02458 United States
AU: McManus, J F
EM: jmcmanus@whoi.edu
AF: WHOI, Dep't of Geology and Geophysics, Woods Hole, MA 02458 United States
AU: Francois, R
EM: rfrancois@whoi.edu
AF: WHOI, Dep't of Marine Chemistry and Geochemistry, Woods Hole, MA 02458 United States
AU: Keigwin, L
EM: lkeigwin@whoi.edu
AF: WHOI, Dep't of Geology and Geophysics, Woods Hole, MA 02458 United States
AU: Brown-Leger, S
EM: sbrownleger@whoi.edu
AF: WHOI, Dep't of Marine Chemistry and Geochemistry, Woods Hole, MA 02458 United States
AU: Hoffmann, S
EM: shoffmann@whoi.edu
AF: WHOI, Dep't of Geology and Geophysics, Woods Hole, MA 02458 United States
AB: $^{231}$Pa/$^{230}$Th has been shown to be a useful kinematic proxy for ocean circulation rate and a valuable complement to nutrient proxies which record 'snapshots' of past water mass configurations. Recent work using $^{231}$Pa/$^{230}$Th indicates stagnation of abyssal waters in the subtropical north Atlantic Ocean between ~17.5 and 15 ka BP, time equivalent to the most recent Heinrich event (McManus et al., 2004). Modeling results indicate a last glacial maximum deep ventilation rate of about 70 percent the modern circulation (Marchal et al., 2000). Questions remain about whether such shifts are typical, and whether changes in circulation rates and deep ocean ventilation are associated with the large-amplitude stadial-interstadial climate variability of the more distant past. A $^{231}$Pa/$^{230}$Th record from the MIS3 interval (~30 to 60 ka BP) on the Blake Outer Ridge (~3400 m core depth) suggests low-amplitude variations in circulation rate related to Dansgaard-Oeschger cycles (defined by correlation of $\delta$$^{18}$O with the GISP2 ice core record). Preliminary data suggest increased circulation vigor during interstadial events relative to stadial events. Heinrich events during this time do not appear to be associated with the dramatic drops in circulation rate seen in the H1 interval on the Bermuda Rise. These new results indicate that there was ventilation of the deep basin through most if not all of MIS3. In contrast to the deeper basin records, an intermediate depth (~1980 m) $^{231}$Pa/$^{230}$Th record from the Carolina Slope indicates greater circulation rates during the LGM than late Holocene; in fact, core-top values from the Carolina Slope are very close to the highest (i.e., lowest rate) values recorded at the deeper Blake Outer Ridge site during MIS3. This depth relationship may indicate more intense intermediate water circulation during glacial times.
DE: 4860 Radioactivity and radioisotopes
DE: 4215 Climate and interannual variability (3309)
DE: 4267 Paleoceanography
DE: 1050 Marine geochemistry (4835, 4850)
SC: Paleoceanography and Paleoclimatology [PP]
MN: 2004 AGU Fall Meeting