HR: 15:25h
AN: OS33C-08 [Abstracts]
TI: Basin-Scale Vertical Mixing Coefficients in the Deep Southern Pacific Derived From the Distribution of Mantle He-3
AU: * Schlosser, P
EM: schlosser@ldeo.columbia.edu
AF: Lamont-Doherty Earth Observatory, Columbia University, 61 Route 9W, Palisades, NY
10964, United States
AU: * Schlosser, P
EM: schlosser@ldeo.columbia.edu
AF: Department of Earth and Environmental Sciences, Columbia University, 2960 Broadway,
New York, NY 10027, United States
AU: * Schlosser, P
EM: schlosser@ldeo.columbia.edu
AF: Department of Earth and Environmental Engineering, Columbia University, 2960 Broadway,
New York, NY 10027,
AU: Newton, R
EM: bnewton@ldeo.columbia.edu
AF: Lamont-Doherty Earth Observatory, Columbia University, 61 Route 9W, Palisades, NY
10964, United States
AU: Winckler, G
EM: winckler@ldeo.columbia.edu
AF: Lamont-Doherty Earth Observatory, Columbia University, 61 Route 9W, Palisades, NY
10964, United States
AB:
Most of the oceanic excess 3He above solubility equilibrium with the atmosphere is due to injection of mantle
helium with high 3He/4He ratios at the crests of the global mid-ocean ridge system with the strongest
signal of mid-ocean ridge 3He being found in the South Pacific. The mantle 3He is injected over a fairly
narrow depth interval and is re-distributed vertically on its pathway from the mid-ocean ridges to the boundaries of
the deep ocean basins. Here, we use a comprehensive 3He data set for the South Pacific and document the
vertical spreading of the plume injected at the crest of the Mid-Ocean Ridge System. The diapycnal spreading of
the 3He plume is interpreted as the combined effect of vertical turbulent exchange and isopycnal transport to
and from regions with rough topography and the related enhanced vertical mixing at these sites. Using a simple
1-D advection/diffusion 'Munk' model, we place constraints on the average vertical exchange that can be
interpreted as an apparent vertical mixing coefficient (kz). We performed sensitivity tests of this simple model
to the width over which 3He injection occurs, as well as to kz. Apparent kz values range from ca.
0.5*10-4 m2 sec-1 to 0.9*10-4 m2 sec-1, i.e., they are close to the average values
obtained for the deep ocean by Munk (1966). We discuss the implications of these values for large scale
distributions of properties in the deep ocean.
DE: 4200 OCEANOGRAPHY: GENERAL
DE: 4536 Hydrography and tracers
DE: 4568 Turbulence, diffusion, and mixing processes (4490)
DE: 4820 Gases
SC: Ocean Sciences [OS]
MN: 2007 Fall Meeting