Relative Paleointensity: a Proxy for Fluctuating Fluid Velocity in Earth's Core
Abstract
Observations of relative paleointensity obtained from oceanic sediments are interpreted as measures of fluid velocity in Earth's fluid core. As long as ohmic dissipation rates and fluid velocities remain low, it has been established that the spectra of fluctuating magnetic fields and fluid velocities are derivable from one another. Accordingly, in order to assess models of core velocity fields, we have derived an algorithm which searches records of relative paleointensity for expected characteristics of fluid velocity in Earth's core. Here we report on the application of our algorithm to single records and composite stacks of relative paleointensity obtained from oceanic cores. Our model for the fluid velocity field in Earth's core is based on parametric instability produced externally through gradients of the gravitational field. It is well known that these gradients can lead to instability of the core fluid through both elliptical and shear straining of fluid streamlines. Such an instability will exist as long as the externally produced strain-rate exceeds the dissipation rate in Earth's fluid core. From both theoretical models and experimental observations it is known that a sequence of alternately growing and decaying velocities will develop in a strained, rotating fluid. Accordingly, our algorithm has searched the records and stacks of relative paleointensity for exponential growths and decays. Since a balance may exist between strain and decay rates described above, our algorithm includes the possibility for a segment of relative paleointensity that neither grows nor decays. Such segments do indeed occur in relative paleointensity sequences and are expected by the model of parametric instability. Results of the application of our algorithm including comparison of both spatial and temporal averaging of six records spanning up to 2 Ma will be presented.
- Publication:
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AGU Spring Meeting Abstracts
- Pub Date:
- May 2009
- Bibcode:
- 2009AGUSMGP11C..06A
- Keywords:
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- 1521 Paleointensity;
- 1560 Time variations: secular and longer