Paleomagnetic intensity data: a window on the dynamics of Earth’s fluid core?

We consider paleomagnetic intensity data obtained from sedimentary cores as a time sequence related to fluctuations of the fluid velocity in Earth’s core. Although this is a gross oversimplification of the relationship between the geomagnetic and velocity fields, some aspects of their possible interaction might be obtained through inversion of paleomagnetic intensity data. In particular, a signature for the onset and development of turbulence as seen in laboratory experiments on rotational parametric instabilities in rotating fluids, may be contained in a paleointensity time sequence. Just as in laboratory experiments, changes in flow regimes can be traced using these observations. The paleomagnetic intensity itself is subject to several factors which contribute to uncertainty including the determination of the intensity as well as errors in timing due to offsets in age determination. near inversions of several records from the ODP 983 data set of paleomagnetic amplitudes are presented. Growth and decay with time of paleomagnetic amplitudes are modelled as the sum of an exponential plus two harmonics. This simple model accounts for most of the paleomagnetic amplitude signal, yielding geophysically plausible growth and decay rates for a proposed rotational parametric instability in Earth’s core. This model provides a new interpretation for observed paleomagnetic intensity changes and thus, an improved understanding of the dynamical processes producing the geomagnetic field.