HR: 17:00h
AN: DI14A-05 INVITED    [Abstracts]
TI: Global Mantle Flow Models Constrained by Observations of Long Term Sea Level Change
AU: * Conrad, C P
EM: conrad@jhu.edu
AF: Johns Hopkins University, Department of Earth and Planetary Sciences, Baltimore, MD 21218, United States
AU: Husson, L
EM: laurent.husson@univ-rennes1.fr
AF: Universite de Rennes 1, Geosciences Rennes, UMR CNRS 6118, Rennes, 35042, France
AU: Robinson, A
EM: arobin22@jhu.edu
AF: Johns Hopkins University, Department of Earth and Planetary Sciences, Baltimore, MD 21218, United States
AB: Geological and sedimentological observations of continental transgressions show that sea level has fallen 100- 200 meters during the past 65 Myr. ~60 m can be attributed to climatic cooling (ocean water contraction and ice sheet formation), and at least ~120 m is caused by an increase in basin volume associated with a shortening of the Pacific ridge system. Thus, between ~20 m of fall and ~80 m of rise were accomodated by other processes that affect sea level. We use this constraint to test the possibility that long- wavelength topography dynamically supported by viscous flow in the mantle can change the volume of the ocean basins, thus changing sea level. Using a global mantle flow model driven by tomographically-inferred mantle density heterogeneity, we produced a global map of dynamic topography that reproduces patterns of observed dynamic topography in some locations. In this model, the ocean basins, on average, are elevated ~150 m while the continents are depressed ~340 m. This dichotomy occurs because mantle slabs generate downwellings that produce negative surface topography and form preferentially beneath continental regions. When isostatically compensated, the elevated seafloor produces a sea level that is 105 m higher than it would be on a non-convecting Earth. We investigate the possibility that this dynamically-elevated sea level has changed with time to cause Cenozoic sea level change. Using the first time-derivative of our instantaneous mantle flow models, we show that changes in the dynamic topography field probably do produce sea level rise (at rates of 0.3-0.5 m/Myr), but that the motion of continents over this dynamic topography field also produces between -0.3 to +0.3 m/Myr of sea level change, depending on the plate motion reference frame. Thus, dynamic topography should produce 0 to 50 m of sea level rise during the Cenozoic, and could possibly be a significant contributor to eustatic variations, comparable in magnitude to the effects of continental fragmentation and climate change.
DE: 0473 Paleoclimatology and paleoceanography (3344, 4900)
DE: 3045 Seafloor morphology, geology, and geophysics
DE: 4556 Sea level: variations and mean (1222, 1225, 1641)
DE: 8121 Dynamics: convection currents, and mantle plumes
DE: 8166 Stresses: deep-seated
SC: Study of the Earth's Deep Interior [DI]
MN: 2007 Fall Meeting