|Collaborative Research: Testing the Conveyor Belt Hypothesis|
Maureen Raymo (Boston University)
Jerry McManus (WHOI)
Our recent work (Raymo et al., 2004) suggests that over much of the Pleistocene, low carbon isotope values characterized mid-depth North Atlantic drift sites. As these sites are bathed by waters that flow over sills from the Nordic Seas, it is possible that overflow waters were characterized by low carbon isotope values in the past. If true, this would confound reconstructions of past deep water mass geometry, which relies on the assumption that deep waters derived from the North Atlantic have high values and deep waters derived from the Southern Ocean have low values. It would also have implications for the mechanisms of deep water formation. Low values characterize the mid-depths during both interglacials and glacials of the "40-kyr world", and during all but the strongest "100-k" glacials and interglacials.
This projects reexamines the evidence for low carbon isotope values at mid-depths by generating more detailed records from the same sites. In addition, we are generating grain-size records that will help us assess whether the low carbon isotope waters represent rapidly moving overflow waters or pooly ventilated waters with a more distant origin. As part of this project, we are generating paired carbon isotope-grain size records for the last 20,000 years, the previous glacial-interglacial transition (stage 6/5) and several earlier time slices.
Most Closely Related Publications:
Raymo, M.E., D.W. Oppo, B.P. Flower, D.A. Hodell, J. F. McManus, K.A. Venz, K.F. Kleiven, K. McIntyre, Stability of North Atlantic water masses in face of pronounced natural climate variability, Paleoceanography, 19, doi:10.1029/2003PA000921, 2004.
Curry, W. B. and Oppo, D. W., Glacial water mass geometry and the distribution of d13C of SCO2 in the Western Atlantic Ocean, Paleoceanography, 20, PA1017, doi:10.1029/2004PA001021, 2005.
Oppo, D. W., L. D. Keigwin, J. F. McManus, and J. L. Cullen, Evidence for millennial scale variability during Marine Isotope Stage 5 and Termination II, Paleoceanography, 16, 280-292, 2001.
Flower, B.P., D.W. Oppo, J.F. McManus, K.A. Venz, D.A. Hodell, and J. Cullen, North Atlantic intermediate to deep water circulation and chemical stratification during the past 1 Myr., Paleoceanography, 1, 388-403, 2000.
Marchitto, T. M., W. B. Curry, and D. W., Oppo, Zinc concentrations in benthic foraminifera reflect seawater chemistry, Paleoceanography, 15, 299-306, 2000.
Oppo, D.W. and S. J. Lehman, Mid-depth circulation of the subpolar North Atlantic during the Last Glacial Maximum, Science 259, 1148-1152, 1993.
Raymo, M. E., W. F. Ruddiman, N. J. Shackleton, and D. W. Oppo, The evolution of Atlantic-Pacific d13C gradients over the last 2.5 myrs: Evidence for decoupling of deep ocean circulation and global ice volume changes. Earth and Planet. Sci. Letts., 97, 353-368, 1990.
Oppo, D. W., and R. G. Fairbanks, Variability in the deep and intermediate water circulation of the Atlantic Ocean: Northern Hemisphere modulation of the southern ocean. Earth and Planet. Sci. Letts., 86, 1-15, 1987.