Archaeomagnetic study of five mounds from Upper Mesopotamia between 2500 and 700 BCE: Further evidence for an extremely strong geomagnetic field ca. 3000 years ago
Highlight
► Paleointensities as high as 100 μT around 1000 BCE. ► Comparable results from microwave and thermal Thellier methods. ► Discussion on geomagnetic intensity versus climate based on new and published results.
Introduction
The recent geomagnetic field is well-known from globally distributed observatories and from satellite observations (Hulot et al., 2002), while for the past few centuries the field has been reconstructed from historical navigational observations (Jackson et al., 2000, Jonkers et al., 2003). Older records of the field can be derived through archaeomagnetism, the study of burnt or fired archeological artifacts. These archaeomagnetic directions and intensities of the field are crucial to furthering our understanding of the behavior of the geodynamo over longer, millennial time scales. A number of global and regional field models have recently been developed based on compilations of archaeomagnetic and lake sediment data like the Continuous Archaeomagnetic and Lake Sediment models CALS3k (Korte and Constable, 2003, Korte et al., 2009) and CALS7k (Korte and Constable, 2005) for the past 3 and 7 kyr, respectively. The most recent model for the past 3000 years CALS3k.4 is based on a recently updated and improved data compilation and considered presently to be the best model for Earth surface studies (Korte and Constable, 2011). The model is available through the online database GEOMAGIA50v2 (Donadini et al., 2006, Korhonen et al., 2008) (http://geomagia.ucsd.edu). While the CALSnK models are based on both archaeomagnetic and lake sediments data, the ARCH3k.1 model is based solely on archaeomagnetic data, and the constrained model ARCH3k_cst.1 additionally uses a set of reliability criteria to minimize uncertainties (Donadini et al., 2009, Korte et al., 2009). The ARCH3k models are certain to be more reliable for the northern hemisphere, especially for Western Europe, since archaeomagnetic data for the southern hemisphere are sparse.
Archaeomagnetic studies in the Levant and Middle East are still scarce (Fig. 1), but recently a number of studies have provided a series of paleointensities from the Levant and Mesopotamia during the past 8000 years. These data come from Syria and Iran (Gallet and Al-Maqdissi, 2010, Gallet et al., 2006, Gallet et al., 2008, Gallet and Le Goff, 2006, Genevey et al., 2003) and from Israel and Jordan (Ben-Yosef et al., 2008, Ben-Yosef et al., 2009, Shaar et al., 2011) (Fig. 1). Some of these results have produced unusually high virtual axial dipole moments (VADM) of up to 14–18×1022 Am2 around 700 and 1000 BCE, twice the present-day value of the field which is already considerably higher than the average of the field during the geological past (Juárez et al., 1998, Selkin and Tauxe, 2000, Valet, 2003, Ziegler et al., 2008).
Periods of rapidly increasing intensities from 3000-0 BCE have been called ‘archaeomagnetic jerks’ (Gallet et al., 2003). The visual correlation of these short peaks to cooling episodes in the North Atlantic (Bond et al., 1997, Bond et al., 2001) led Gallet et al. (2006) to suggest that the geomagnetic field may have had an impact on climate and therefore perhaps even on the history of ancient civilizations: major cultural crises would occur at the end of cooling cycles – cool implying arid conditions – in turn coinciding with the rapid increase of geomagnetic field intensity, both in Mesopotamia and the Levant, and possibly during Mayan history as well (Gallet and Genevey, 2007). On the basis of this temporal coincidence, Gallet et al., 2005, Gallet et al., 2006 argued that there may have been a connection between Earth's magnetic field and climate. A proposed mechanism involves variations in the geometry of the geomagnetic field resulting in enhanced cosmic-ray induced nucleation of clouds. This speculation has led to heated debates on potential mechanisms causing climate change in the past (Bard and Delaygue, 2008, Courtillot et al., 2008). More recently, even higher intensities were found in copper slag deposits from Jordan (Ben-Yosef et al., 2009, Shaar et al., 2011), fitting in a gap of previously published data. The authors found unprecedented high values, ranging by more than a factor of two (11–25×1022 Am2) over a short time interval of some 200 years (∼1040–860 BCE). This interval of high intensity values coincides well with one of the cooling cycles (∼1115–910 BCE) or, alternatively, with one of the colder periods (∼1055–805 BCE) as derived from the North Atlantic drift ice index (Bond et al., 2001; the stack of 4 records in their Fig. 2) and therefore seems to support the relation between the geomagnetic field and climate (Gallet et al., 2005, Gallet et al., 2006). Clearly, there is a need for more reliable palaeointensity records to test these hypotheses and to confirm extremely rapid intensity changes.
The distribution of archaeomagnetic data in eastern Europe and the Near and Middle East shows a remarkable gap in Turkey (Fig. 1), despite the fact that Turkey is extremely rich in archeological sites from Neolithic times onwards. Turkey has been at the ‘cross-roads’ between Asia and Europe, and has seen many civilizations and migrations (Fig. A1). Only two studies are listed in GEOMAGIA50v2 (Bucha and Mellaart, 1967, Sarıbudak and Tarling, 1993), while a more recent but unlisted study (Sayın and Orbay, 2003) provides directional results from mostly central Anatolian sites ranging from 7900 BCE to 1750 CE. This latter study also reports the results (from 400 BCE to 1800 CE) of an unpublished thesis (Ponat, 1995).
Although the existing data around Turkey and the global field models give a first approximation of the ancient field, the use of archaeomagnetism as a dating tool requires a well established palaeosecular variation (PSV) curve for this large region. The lack of Turkish data combined with the lushness of its archeology makes new archaeomagnetic studies very timely and relevant. We have therefore recently began a new (Ph.D.) project of which this study presents the first archaeomagnetic results from southeast Turkey (Fig. 1), the northern part of Mesopotamia.
Section snippets
Archeological background and sampling
The area known as the ‘Fertile Crescent’ consists of the fertile regions of Mesopotamia and the Levant, delimited by the dry climate of the Syrian Desert to the south and the Anatolian highlands to the north (Fig. 1). The area is important as a ‘land bridge’ between Africa and Eurasia, allowing the Fertile Crescent to retain a great amount of biodiversity and to contribute to the modern distribution of Old World flora and fauna, including the spread of humanity. The southeastern fringe of
Rock magnetic properties
For all the sites and for the different materials from each site, we measured thermomagnetic (Curie balance) curves and low field magnetic susceptibilities, and for sites that appeared promising for archaeointensity research we also performed hysteresis loop experiments, including First Order Reversal Curve (FORC) diagrams (Roberts et al., 2000) – the analysis of FORC diagrams may increase the efficiency of paleointensity measurements (Carvallo et al., 2006) – and acquisition of Isothermal
Methods
To determine the characteristic remanent magnetization direction (ChRM), at least 7 (generally more than 10, and occasionally more than 50) specimens per site were demagnetised, both by thermal (TH) and alternating field (AF) demagnetization (Table 2). The demagnetization was performed with small AF or TH increments up to a maximum of 100 mT or 620 °C. The natural remanent magnetization (NRM) was measured on a horizontal 2G Enterprises DC SQUID cryogenic magnetometer (noise level 3×10−12 Am2) for
Arslantepe (AT)
For the furnaces AT-A, AT-C and AT-D, half of the samples were demagnetized thermally and the other half by using alternating fields. AT1 and AT-B were too fragile for thermal treatment, and specimens of these sites were carefully glued into perspex sample holders and demagnetized only by AF. The results are straightforward: a single component decays straight to the origin. Samples from AT1 are completely demagnetized at 100 mT (Fig. 4a) indicating that there is no high coercivity mineral like
Directions
The directional results from this study, corrected for local declination at the time of sampling, are relocated to Kayseri as the approximate center of Turkey (lat: 38.85°N, long: 35.63°E), and plotted against the data from GEOMAGIA50v2 (countries within ∼1600 km radius), the Turkish data (Sarıbudak and Tarling, 1993, Sayın and Orbay, 2003) and the global geomagnetic field models CALS7k.2, CALS3k.4 and ARCH3k_cst.1 at Kayseri (Fig. 7a and b). The Turkish data from the literature are kept ‘as is’
Acknowledgments
We are grateful to the teams of the archeological sites who were at all times very helpful. In particular, we thank Francesca Balossi at Zeytinli Bahçe for her help.
Yves Gallet provided a manuscript with relevant data, while he and an anonymous reviewer provided critical comments that greatly helped to improve the original manuscript. Nuretdin Kaymakci has been an indispensable help in the field, carefully and unrelentingly drilling with expertise the fragile archeological material. The late
References (83)
- et al.
Comment on “Are there connections between the Earth's magnetic field and climate?” by V. Courtillot, Y. Gallet, J.-L. Le Mouël, F. Fluteau, A. Genevey (2007) EPSL 253, 328
Earth Planet. Sci. Lett.
(2008) - et al.
Geomagnetic intensity spike recorded in high resolution slag deposit in Southern Jordan
Earth Planet. Sci. Lett.
(2009) First-order symmetry of weak-field partial thermoremanence in multi-domain (MD) ferromagnetic grains: 2. Implications for Thellier-type palaeointensity determination
Earth Planet. Sci. Lett.
(2006)Are systematic differences between thermal and microwave Thellier-type palaeointensity estimates a consequence of multidomain bias in the thermal results?
Phys. Earth Planet. Inter.
(2010)- et al.
Microwave palaeointensities from a recent Mexican lava flow, baked sediments and reheated pottery
Earth Planet. Sci. Lett.
(2003) - et al.
Paleointensity of the geomagnetic field recovered on archaeomagnetic sites from France
Phys. Earth Planet. Inter.
(2000) - et al.
Are there connections between the Earth's magnetic field and climate?
Earth Planet. Sci. Lett.
(2007) - et al.
Response to comment on “Are there connections between Earth's magnetic field and climate?
Earth Planet. Sci. Lett.
(2008) - et al.
On the possible occurrence of ‘archaeomagnetic jerks’ in the geomagnetic field over the past three millennia
Earth Planet. Sci. Lett.
(2003) - et al.
Does Earth's magnetic field secular variation control centennial climate change?
Earth Planet. Sci. Lett.
(2005)
Possible impact of the Earth's magnetic field on the history of ancient civilizations
Earth Planet. Sci. Lett.
On the use of archeology in geomagnetism, and vice-versa: recent developments in archeomagnetism
C. R. Phys.
High-temperature archeointensity measurements from Mesopotamia
Earth Planet. Sci. Lett.
Palaeomagnetic investigation of Tertiary lava from Barrington Tops, NSW, Australia, using thermal and microwave techniques
Earth Planet. Sci. Lett.
Continuous global geomagnetic field models for the past 3000 years
Phys. Earth Planet. Inter.
Improving geomagnetic field reconstructions for 0–3 ka
Phys. Earth Planet. Inter.
Geomagnetic field intensity: how high can it get? How fast can it change? Constraints from Iron Age copper slag
Earth Planet. Sci. Lett.
Paleointensities
Application of ferrimagnetic resonance heating to paleointensity determinations
Phys. Earth Planet. Inter.
Large sample theory of the Langevin distribution
J. Stat. Plann. Infer.
Archaeomagnetic secular variation in the UK during the past 4000 years and its application to archaeomagnetic dating
Phys. Earth Planet. Inter.
Testing the robustness and limitations of 0–1 Ma absolute paleointensity data
Phys. Earth Planet. Inter.
Archaeomagnetic determination of the past geomagnetic intensity using ancient ceramics—allowance for anisotropy
Archaeometry
Determination of the intensity of the Earth's magnetic field during archeological times: reliability of the Thellier technique
Rev. Geophys.
Application of copper slag in geomagnetic archaeointensity research
J. Geophys. Res.—Solid Earth
A method to reduce the curvature of Arai plots produced during Thellier palaeointensity experiments performed on multidomain grains
Geophys. J. Int.
Persistent solar influence on North Atlantic climate during the Holocene
Science
A pervasive millenial-scale cycle in North Atlantic Holocene and glacial climates
Science
Archaeomagnetic intensity measurements on some Neolithic samples from Çatal Hüyük (Anatolia)
Archaeometry
Increasing the efficiency of paleointensity analyses by selection of samples using first-order reversal curve diagrams
J. Geophys. Res.—Solid Earth
Geomagnetic paleointensities from radiocarbon-dated lava flows on Hawaii and the question of the Pacific nondipole low
J. Geophys. Res.
Hysteresis properties of titanomagnetites: grain-size and compositional dependence
Phys. Earth Planet. Inter.
Geomagnetic secular variation and the statistics of palaeomagnetic directions
Geophys. J. Int.
Magnetic behavior of natural goethite during thermal demagnetization
Geophys. Res. Lett.
Magnetic blocking temperatures of single-domain grains during slow cooling
J. Geophys. Res.
Database for Holocene geomagnetic intensity information
EOS Trans. AGU
Geomagnetic field for 0–3 ka: 1. New data sets for global modeling
Geochem. Geophys. Geosyst.
Rock Magnetism: Fundamentals and Frontiers
Cited by (62)
Possible evidence for geomagnetic intensity anomaly around 5500 BP from archaeomagnetic analyses of San Jacinto pottery, Caribbean Colombia
2023, Physics of the Earth and Planetary InteriorsGeomagnetic field variations and low success rate of archaeointensity determination experiments for Iron Age sites in Bulgaria
2021, Physics of the Earth and Planetary InteriorsArcheomagnetic intensity variations during the era of geomagnetic spikes in the Levant
2021, Physics of the Earth and Planetary InteriorsThe directional occurrence of the Levantine geomagnetic field anomaly: New data from Cyprus and abrupt directional changes
2021, Earth and Planetary Science LettersCitation Excerpt :The most prominent feature of these data is the high declination and inclination values observed at the beginning of the first millennium BCE while they also show other periods with fast secular variation rates. Apart from Israel, more directional data are available from countries neighboring Cyprus such as Turkey (Ertepinar et al., 2012, 2016, 2020) and Syria (Speranza et al., 2006). More recently, Ertepinar et al. (2020) published new archaeomagnetic data from the Eastern Mediterranean, including directional results from four archaeological sites in Turkey with ages ranging from 3300 BCE to 672 BCE, and with intensity data from both Turkey and Cyprus that further support extreme field variations in the region.
Geomagnetic field intensity changes in the Central Mediterranean between 1500 BCE and 150 CE: Implications for the Levantine Iron Age Anomaly evolution
2021, Earth and Planetary Science LettersAnalysis of geomagnetic field intensity variations in Mesopotamia during the third millennium BC with archeological implications
2020, Earth and Planetary Science Letters