HR: 0800h
AN: P31A-0966    [Abstracts]
TI: Layering and Double-Diffusion Style Convection in Europa's Ocean
AU: * Vance, S
EM: svance@ess.washington.edu
AF: Department of Earth and Space Sciences, University of Washington, Box 351310, Seattle, WA 98195 United States
AU: Brown, J
EM: brown@ess.washington.edu
AF: Department of Earth and Space Sciences, University of Washington, Box 351310, Seattle, WA 98195 United States
AB: We assess the effects of fluid composition and depth-dependent hydrostatic pressure on dynamics in Europa's ocean for aqueous Na2SO4 and MgSO4. We observe a salinity- and pressure-dependent check on buoyancy in putative upwellings, which may act as mechanism for storing heat in the ocean's base. For either sodium or magnesium, a small excess in salinity of an initially buoyant parcel of water, even for low average ambient salinity, causes upwellings to lose buoyancy before reaching the base of the overlying ice. The result is a two-layer convecting system with a characteristic lifetime dependent on the properties of Europa's ocean, including the balance of heat flow through the system and details of pressure effects on thermal expansion and volumes of mixing. When volume of mixing is neglected plume rise remains dependent on temperature and pressure effects alone. Stratification develops as bottom water continually acquires heat and salt. The added mass of the salt dominates over the thermal expansion. As the rise in temperature becomes sufficient to overcome the salinity effect, upwellings rise to a terminal height determined by the pressure dependence of thermal expansion of the fluid, and by differences in the fluid's temperature and salinity. This regime is similar to double-diffusive convecting systems observed in the Red Sea and Lake Vanda over the last forty years. In the Red Sea, boundary layers separating convecting zones have been observed to move upward as the lower layer acquires heat and salt. By analogy using reasonable parameters for Europa's ocean, we estimate a time scale on the order of 10 Myr for the upward progress of a lower convecting layer saturated with MgSO4, which could correlate with recently inferred change in surface alteration style over the last 70-80 Myr.
DE: 5418 Heat flow
DE: 5460 Physical properties of materials
DE: 6218 Jovian satellites
SC: Planetary Sciences [P]
MN: 2004 AGU Fall Meeting