Abstract
The geomagnetic field variations on the continent of Africa are still largely undeciphered for the past two millennia. In spite of archaeological artefacts being reliable recorders of the ancient geomagnetic field strength, only few data have been reported for this continent so far. Here we use the Thellier-Coe and calibrated pseudo-Thellier methods to recover archaeointensity data from Burkina Faso and Ivory Coast (West Africa) from well-dated archaeological artefacts. By combining our 18 new data with previously published data from West Africa, we construct a reference curve for West Africa for the past 2000 years. To obtain a reliable curve of the archaeointensity variation, we evaluate a penalized smoothing spline fit and a stochastic modelling method, both combined with a bootstrap approach. Both intensity curves agree well, supporting the confidence in our proposed intensity variation during this time span, and small differences arise from the different methodologies of treating data and uncertainties. Two prominent peaks at around 740 AD and 1050 AD appear to be common in ours and several reference curves from other locations, indicating a general westward movement from China to Hawaii of a rather stable feature of the geomagnetic field. However, independent smaller peaks that do not correlate in different locations may hint to localized expressions of the geomagnetic field as a result of temporarily varying non-dipole sources.
| Original language | English |
|---|---|
| Article number | 1121 |
| Number of pages | 15 |
| Journal | Scientific Reports |
| Volume | 10 |
| DOIs | |
| Publication status | Published - 24 Jan 2020 |
Funding
We thank Dr. F. Donadini for his useful comments on the draft. Sampling took place during the archaeological excavation campaigns (2012, 2013 and 2015) organized in the frame of the research project "Origine et Développement de la métallurgie du fer au Burkina Faso et en Côte d’Ivoires" funded by the Swiss-Liechtenstein Foundation for Archaeological Research Abroad (SLFA). The project was co-directed by Prof. V. Serneels (University of Fribourg, Switzerland), Dr. L. Koté and Dr. L. Simporé (University of Ouagadougou, Burkina Faso) and Dr. H.T. Kiénon-Kaboré (University of Abidjan, Ivory Coast). The archaeological excavations were performed with the help of the archaeolgy students of Abidjan and Ouagadougou, supported by a few Swiss volunteer archaeologists. We thank them all for suitable help on the field. Dr. F. Donadini was responsible for sampling at Korsimoro. V. Serneels did the sampling at Siola and Doumbala. All samples were exported for scientific studies with the permission of the relevant responsible persons in both countries. Initial funding for the archaeomagnetic study was provided by the Swiss National Science Foundation (SNSF), project 105211_144102 "Establishing paleomagnetic reference curve for W-Africa: archaeological and geophysical inference". A. Gogichaishvili acknowledges the partial financial support given by CONACYT No. 252149.