Mathematics – Logic
Scientific paper
Dec 2001
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2001agufm.u12b..07t&link_type=abstract
American Geophysical Union, Fall Meeting 2001, abstract #U12B-07
Mathematics
Logic
3035 Midocean Ridge Processes, 5770 Tidal Forces, 6218 Jovian Satellites
Scientific paper
Chaos-type features on the surface of Europa are interpreted as melt-through structures formed by rotationally confined, steady and/or episodic oceanic plumes that rise to the base of the ice shell from magmatically heated hydrothermal venting regions on the seafloor. The ocean is assumed to be weakly stratified due to turbulent convection generated by heating from below and cooling from above. Seafloor heating, maintained by tidal dissipation in the rocky interior, generates an estimated global heat flux of 8.7x 1012 W and limits the mean ice thickness to 2 to 5 km. For seafloor heat sources with radii, r, that are less than the ocean's deformation radius ND/f (where N is the buoyancy frequency, D is the water depth, and f is the magnitude of the Coriolis parameter), the diameters of chaos-type regions are expected to diminish from O(100 km) within equatorial regions to O(10 km) at high latitudes. Provided there is sufficient time before refreezing, ice rafts in large melt-through regions are imbedded in episodes of preferentially anticyclonic circulation, corresponding to clockwise motions in the northern hemisphere. Although the Coriolis effect may be unimportant for short-lived ice-raft displacements characteristic of most melt-through regions, rotation is of fundamental importance in determining the formation and physical dimensions of the melt regions. Roughly 1021 j were required to melt the ice in the 100 km diameter Conamara Chaos region. For a steady, localized heat flux of 10^11 W ( ~ 1% of the global heat flux), it would take about 1000 years for the initial melt-through to occur, an acceptable time-scale for steady state venting systems on earth. As on Earth, the Europan ocean may also switch between weak and strong stratification modes over geological time scales. At times of strong stratification, most convective plumes would not penetrate to the base of the ice and heat would be trapped in the lower portion of the water column. Continued bottom heating and surface cooling would eventually weaken the upper ocean stratification, allowing thermal plumes to again penetrate to the base of the ice cover. The stratification-destratification cycle would be completed by the formation of low salinity, upper ocean melt-water during times of increased under-ice melting.
Delaney John R.
Thomson Richard E.
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