Holocene Geomagnetic Field Variations Registered by Historical and Radiocarbon Dated Hawaiian Lavas: A Contribution to the Question of the Pacific Non-dipole Low

Abstract : Since decades, an important amount of research has been concentrated on the palaeomagnetic records obtained from Hawaiian lava flows and often great discussion and debate is focused on the existence and persistence of low geomagnetic secular variation (SV) in the Pacific Ocean. We present here a full geomagnetic SV curve based on historical and radiocarbon dated Hawaiian lavas available for the last 10 000 years. To guarantee the quality of the reference data, selection criteria based on the number of samples studied, measurements' quality and laboratory protocols have been applied. The obtained SV curves have been calculated following the most recent advances on curve building based on the Bayesian statistics and are well constrained for the last five millennia while for older periods their error envelopes are wide due to the scarce number of reference data. The new Bayesian SV curves clearly show high amplitude variations in both direction and intensity of the geomagnetic field during the last five millennia. At least three intensity maxima can be indentified during the last 3000 yrs that correspond to contemporaneous sharp directional changes. Such contemporaneous abrupt intensity and directional changes in Pacific Ocean are not clearly evidenced in the global geomagnetic field models probably because of a possible over-smoothing effect caused by the use of sedimentary records and often non homogeneously calibrated radiocarbon data. Going back in time, the obtained Hawaiian directional curves show several other high amplitude directional changes that however cannot be associated to intensity maxima due to the very few reliable archaeointensity records for the periods before 1000 BC. These results do not confirm the debated Pacific non-dipole low even though more high quality data from well dated prehistoric lava flows are still necessary to investigate the existence of such high amplitude and short-term variations of the geomagnetic field back in time.