PSVM: A global database for the Miocene indicating elevated paleosecular
variation relative to the last 10 Myrs.
Statistical studies of paleosecular variation (PSV) are used to infer
the structure and behavior of the geomagnetic field. This study presents
a new database, PSVM, of high-quality directional data from the Miocene
era (5.3 – 23 Ma), compiled from 1,454 sites from 44 different
localities. This database is used to model the latitude dependence of
paleosecular variation with varying selection criteria using a quadratic
form after Model G. Our fitted model parameter for latitude-invariant
PSV (Model G a) is 15.7° and the latitude dependent PSV term (Model G b)
is 0.23. The latitude invariant term is substantially higher than
previously observed for the past 10 Myrs or any other studied era. We
also present a new stochastic model of the time-average field, BB-M22,
using a covariant giant Gaussian process (GGP) which is constrained
using data from PSVM and Earth-like geodynamo numerical simulations.
BB-M22 improves the fit to PSVM data relative to prior GGP models, as it
reproduces the higher VGP dispersion observed during the Miocene. Our
findings suggest a more variable magnetic field and more active
geodynamo in the Miocene era than the past 10 Myrs, perhaps linked to
stronger driving by elevated core-mantle heat flow. Although our results
support that the average axial dipole dominance of the
time-instantaneous field was lower than in more recent times, we note
that based on inclination anomaly estimates cannot rule out that the
Miocene time averaged field resembles a geocentric axial dipole.