HR: 0800h
AN: GC51A-0157    [Abstracts]
TI: Constraining the shallow subtropical overturning circulation with archived radiocarbon records
AU: * Rosenheim, B E
EM: brosenheim@whoi.edu
AU: Swart, P K
EM: pswart@rsmas.miami.edu
AF: Rosenstiel School of Marine and Atmospheric Sciences, University of Miami MGG 4600 Rickenbacker Causeway, Miami, FL 33149, United States
AU: Thorrold, S R
EM: sthorrold@whoi.edu
AF: Woods Hole Oceanographic Institution, Biology Department MS #35, Woods Hole, MA 02543, United States
AU: Roberts, M L
EM: mroberts@whoi.edu
AF: Woods Hole Oceanographic Institution, Department of Geology and Geophysics MS #8, Woods Hole, MA 02543, United States
AB: Archived radiocarbon records in accretionary skeletons can be used to constrain the shallow overturning subtropical cells (STC's) that transport significant amounts of tropical heat poleward in the world's oceans. Radiocarbon values of DIC in the world's oceans reflect a continuum between waters residing on the surface over long periods (high Δ¹⁴C due to equilibration with "modern" atmosphere) and waters decoupled from the atmosphere in the abyss (low Δ¹⁴C due to radioisotope decay), as well as mixtures between water masses of different ages. Thus, measurements of radiocarbon have demonstrated utility in assessing convective heat tranport such as the Meridional Overturning Circulation that is central to global climate. A prominent radiocarbon gradient is also present between the subsiding subtropical surface waters and the upwelling equatorial surface waters in the world's oceans due to the presence of STC's. These convection cells transport a major proportion of tropical heat in the Pacific and a significant proportion of tropical heat in the Atlantic towards the poles. Archived radiocarbon records in surface corals and subsurface sclerosponges constrain the N. Atlantic STC's on a centennial time scale. Published short records from Cape Verde corals indicate significant changes in radiocarbon content; this is potentially related to migration of the front between upwelled tropical waters and downwelled subtropical waters. An approach is outlined to estimate the proportion of tropical to subtropical waters at Cape Verde using as endmembers high-resolution sclerosponge radiocarbon records from Bahamas subsurface waters and coral radiocarbon records from São Tome and Principe in the Gulf of Guinea. Preliminary data from Bahamas sclerosponges indicate the need for high-resolution subsampling of the skeletons. Initial novel AMS measurements from fine scale laser-decomposition of the skeletons are presented.
DE: 1616 Climate variability (1635, 3305, 3309, 4215, 4513)
DE: 3344 Paleoclimatology (0473, 4900)
DE: 4231 Equatorial oceanography
DE: 4572 Upper ocean and mixed layer processes
DE: 4924 Geochemical tracers
SC: Global Environmental Change [GC]
MN: 2007 Fall Meeting