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Beyond the Holocene Geomagnetic field resolution

Periodic Reporting for period 3 - GeoArchMag (Beyond the Holocene Geomagnetic field resolution)

Reporting period: 2021-11-01 to 2023-04-30

Earth magnetic field is constantly changing with time in a chaotic and unpredictable fashion. Direct measurements of the geomagnetic field from the past several centuries have provided useful, but limited, information on the time-varying geomagnetic field. However, recent data obtained from well-dated archaeological materials that recorded the field during their manufacturing have revealed that the geomagnetic field has been anything but stable during the past several millennia – presenting puzzling intervals of extreme decadal-scale fluctuations and unexpected departures from a simple dipolar geomagnetic field structure. This new information introduced an entirely new paradigm to the study of the geomagnetic field and to a wide range of research areas relying on paleomagnetic data, such as geochronology, climate research, and geodynamo exploration.
This aim of this research is providing a continuous time series of the geomagnetic field vector throughout the past ten millennia – the Holocene geological epoch - at decadal resolution and unprecedented accuracy. This is accomplished by using an innovative assemblage of data sources, jointly unique to the Levant region: rare archaeological finds, annual laminated stalagmites, varved sediments, and arid marine sediments. Together, these sources provide unprecedented resolution.
The new geomagnetic data will define an innovative geomagnetic chronology that will be used to re-date and synchronize an extensive body of paleo-climatic indicators from geological sources. All together, the data will be used to address four ground-breaking problems:
I) Chronology: Developing dating technique for resolving critical controversies in Levantine archaeology and Quaternary geology.
II) Geophysics: Exploring fine-scale geodynamo features in Earth’s core from new generations of global geomagnetic models.
III) Cosmogenics: Correlating fast geomagnetic variations with cosmogenic isotope production rate.
IV) Climate: Testing one of the most challenging controversial questions in geomagnetism: “Does the Earth's magnetic field play a role in climate changes?”
This main goal of this ERC project is delivering geomagnetic curves of the Holocene (the past 10,000 years), which include high-resolution description of the direction and the intensity of the geomagnetic field, from a combination of several state-of-the-art archives. So far, we focused on developing the following archives:

1. Archaeomagnetic records:
Being one of the most extensively studied archaeological zones worldwide, our study area provides immediate access to vast collection of well-dated archaeological materials. Two PhD student (Yoav Vaknin, Erez Hassul), with the help of several dtidents and per-hour employees, collected and measured hundreds of archaeological artifacts for paleomagnetic analyses. The results of this on-going-study have been summarized in the following articles:

Vaknin, Y., Shaar, R., Gadot, Y., Shalev, Y., Lipschits, O. and Ben-Yosef, E., (2020). The Earth’s magnetic field in Jerusalem during the Babylonian destruction: A unique reference for field behavior and an anchor for archaeomagnetic dating. PloS one, 15(8), p.e0237029.

Shaar, R., Bechar, S., Finkelstein, I., Gallet, Y., Martin, M.A. Ebert, Y., Keinan, J. and Gonen, L. (2020). Synchronizing geomagnetic field intensity records in the Levant between the 23rd and 15th centuries BCE: chronological and methodological implications. Geochemistry, Geophysics, Geosystems, 21(12), p.e2020GC009251.

Shaar, R., Gallet, Y., Vaknin, Y., Gonen, L., Martin, M. A., Adams, M. J., and I. Finkelstein, I. (2022). Archaeomagnetism in the Levant and Mesopotamia reveals the largest changes in the geomagnetic field. Journal of Geophysical Research: Solid Earth, 127(12), e2022JB024962.

Application of the archaeomagnetic data as a new tool for dating archaeological materials was developed by PhD student Yoav Vaknin:

Vaknin, Y., Shaar, R., Lipschits, O., Mazar, A., Maeir, A.M. Garfinkel, Y., Freud, L., Faust, A., Tappy, R.E. Kreimerman, I. and Ganor, S. (2022). Reconstructing biblical military campaigns using geomagnetic field data. Proceedings of the National Academy of Sciences, 119(44), p.e2209117119.

2. Sedimentary magnetism – The Dead Sea
The varved sediments of the Dead Sea consist of annual sequences of layers that enable extraordinary temporal resolution. A PhD student (Yael Ebert) has been developing this unique archive. Two articles summarizing her results were published.

Ebert, Y., Shaar, R., Levy, E. J., Zhao, X., Roberts, A. P., and Stein, M. (2020). Magnetic properties of late holocene dead sea sediments as a monitor of regional hydroclimate. Geochemistry, Geophysics, Geosystems, 21(11), e2020GC009176.

Ebert, Y., Shaar, R., and Stein, M. (2021). Decadal geomagnetic secular variations from greigite bearing Dead Sea sediments. Geochemistry, Geophysics, Geosystems, 22(4), e2021GC009665.

3. The marine sediments of the Mediterranean sea offer a continuous record spanning the entire Holocene. Two students - Konstantin Khrizman and Yakar Zemach – have been working on this material and a first article summarizing their work has been published. A second is in preperation

Amiel, N., Shaar, R. and Sivan, O., (2020). The effect of early diagenesis in methanic sediments on sedimentary magnetic properties: Case study from the SE Mediterranean continental shelf. Frontiers in Earth Science, 8, p.283.

Speleothem magnetism:
4. Laminated stalagmites are potentially ideal magnetic recorders. Recent advances in the sensitivity of magnetic instrumentation, available in my new lab now realize the full potential of speleothem magnetism and a manuscript describing our progress was published:

Burstyn, Y., Shaar, R., Keinan, J., Ebert, Y., Ayalon, A., Bar-Matthews, M., & Feinberg, J. M. (2022). Holocene wet episodes recorded by magnetic minerals in stalagmites from Soreq Cave, Israel. Geology, 50(3), 284-288.