Evolution of magnetic declination in South America since the 17th century

Abstract

Magnetic declination, the first measurable angular component of the magnetic field was longtime considered as an essential element to facilitate the navigation. Direct, historical measurements of the Earth Magnetic Field's components were commonly carried out during maritime exploration campaigns. Therefore, this invaluable source of information provides an almost unique tool to reveal the ‘geomagnetic past’ of our planet. Thanks to the development (and continuous updating) of historical and global geomagnetic databases, it is now possible to access a numerous geomagnetic field measurement. In particular, 400 years of continuous declination data are available for South America. The primary objective of this study is to estimate the temporal and spatial variation of historical declination values and try to define some fine characteristics of the geomagnetic field. A database of 12,462 well-distributed declination measurements across South America including the margins of Atlantic and Pacific Oceans, was compiled. The whole area was divided into six sub-regions in Brazil (2), Peru (1), Chile (1), Argentina (1) and Uruguay (1) in order to obtain local paleosecular variation curves and meet the mandatory requirement of relocation error procedure. These curves were generated using the Bootstrap algorithm and the penalized cubic spline method. The paleosecular variation curves were compared with currently available global geomagnetic models. Three local curves showed significant differences from the models due to the relatively uneven distribution of the geomagnetic data. First and second temporal derivative of paleosecular variation curves revealed the most significant fluctuations while the global data analysis confirms the existence of the so-called westward drift.