Observed periodicities and the spectrum of field variations in Holocene magnetic records

•No evidence for dominant discrete periodicities in Holocene magnetic records.•Find broadband spectrum of variations explained by power law with a mean exponent of −2.3.•Provides support for chaotic core convection as driver of secular variation.

In order to understand mechanisms that maintain and drive the evolution of the Earthʼs magnetic field, a characterization of its behavior on time scales of centuries to millennia is required. We have conducted a search for periodicities in Holocene sediment magnetic records, by applying three techniques: multitaper spectral estimation, wavelet analysis and empirical mode decomposition. When records are grouped according to their geographical locations, we find encouraging consistency amongst the observed periods, especially in nearby inclination records. No evidence was obtained for discrete, globally observed, periods. Rather we find a continuous broadband spectrum, with a slope corresponding to a power law with exponent of −2.3±0.6 for the period range between 300 and 4000 yr. This is consistent with the hypothesis that chaotic convection in the outer core drives the majority of secular variation.