Geomagnetic secular variation of Bransfield Strait (Western Antarctica) from analysis of marine crossover data.

Tracking the secular variation of the geomagnetic field in the past is severely limited in some cases by factors relating to the remoteness of the sites. This is maximal in the Antarctic where the remote location and severe climate lead to logistic limitations that make it difficult to keep a continuous record of magnetic field variations. From the magnetic information available from historical marine expeditions, it is possible to infer this time-varying component from the comparison of readings at crossovers. This study focuses on this technique, discusses the impact of the different error sources and proposes a simple mathematical procedure to infer average secular variation rates. The result is validated by comparing it with local data from the Arctowski and Livingston magnetic observatories, sited in the area. Additionally, using a high-quality data set from a local area in the neighbourhood of Deception Island, we have detected a systematic distribution in its secular variation. This dichotomy has been interpreted in terms of a volcano-magnetic signal. This fact and the nature of its principal mechanisms are analysed and discussed. [ABSTRACT FROM AUTHOR]