Thellier-type paleointensity data from multidomain specimens

Identifying and excluding inaccurate paleointensity estimates that can arise from the effects of multidomain (MD) particles remains a key challenge for paleointensity studies. Here we approach this problem by incorporating realistic experimental noise into a phenomenological MD model, systematically exploring the parameter space of paleointensity experiments (the choice of protocol, laboratory field strengths and directions), applying optimization algorithms to the model predictions, and testing these against experimental datasets. The results allow us to conclude that: (1) In some cases, applying the lab field in a direction ≲60° from the NRM direction and with a magnitude ∼2 times larger than the ancient field may help to produce more linear and accurate Arai plots by allowing partial thermoremanent magnetization (pTRM) tails to compensate from excess natural remanent magnetization (NRM) loss, the mechanism behind typical MD Arai plot curvature. (2) The recently proposed FRAC criterion is consistently better at isolating accurate results than the traditionally used f parameter and should ideally have minimum values of 0.65, 0.45, 0.65, and 0.55 for the Thellier, Coe, Aitken, and IZZI protocols, respectively. (3) Newly developed sets of selection criteria (MC-CRIT) should maximize the likelihood of accepting accurate estimates from a suite of specimens influenced by MD behavior. The models, methods, and data presented here provide the means to objectively define data selection and demonstrate the effectiveness of a given set of criteria. Such approaches are vital, if we wish to remove the arbitrariness that hinders the identification of reliable paleointensity data.