Journal Article

Paleointensity Estimates From the Pleistocene of Northern Israel: Implications for Hemispheric Asymmetry in the Time‐Averaged Field

Shaar, R., Tauxe, L., Koppers, A. A. P., Asefaw, H., Behar, N.

2022

Overview

Twenty‐two sites, subjected to an IZZI‐modified Thellier‐Thellier experiment and strict selection criteria, recover a paleomagnetic axial dipole moment (PADM) of 62.2 ± 30.6 ZAm2 in Northern Israel over the Pleistocene (0.012–2.58 Ma). Pleistocene data from comparable studies from Antarctica, Iceland, and Hawaii, re‐analyzed using the same criteria and age range, show that the Northern Israeli data are on average slightly higher than those from Iceland (PADM = 53.8 ± 23 ZAm2, n = 51 sites) and even higher than the Antarctica average (PADM = 40.3 ± 17.3 ZAm2, n = 42 sites). Also, the data from the Hawaiian drill core, HSDP2, spanning the last half million years (PADM = 76.7 ± 21.3 ZAm2, n = 59 sites) are higher than those from Northern Israel. These results, when compared to Pleistocene results filtered from the PINT database (www.pintdb.org) suggest that data from the Northern hemisphere mid‐latitudes are on average higher than those from the southern hemisphere and than those from latitudes higher than 60°N. The weaker intensities found at high (northern and southern) latitudes therefore, cannot be attributed to inadequate spatiotemporal sampling of a time‐varying dipole moment or low quality data. The high fields in mid‐latitude northern hemisphere could result from long‐lived non‐axial dipole terms in the geomagnetic field with episodes of high field intensities occurring at different times in different longitudes. This hypothesis is supported by an asymmetry predicted from the Holocene, 100 kyr, and 5 million year time‐averaged geomagnetic field models. Plain Language Summary According to the Geocentric Axial Dipole hypothesis, the geomagnetic field may be approximated by a dipole that is aligned with the spin axis and positioned in the center of Earth. Such a field would produce field strengths that vary with respect to latitude with high latitudes associated with high intensities, or, converted to equivalent “virtual” dipole moments, would be essentially independent of latitude. It has long been suggested that high latitudes have had lower field strengths than predicted by such a model, when compared to data from mid‐latitudes, but these claims have always been accompanied by caveats regarding differences in temporal coverage or methodological approaches. Here, we present new data from Pleistocene aged rapidly cooled cinder cones and lava flow tops from Israel. We compare these data to other recent data sets obtained from rapidly cooled materials collected in Hawaii, Iceland, and Antarctica. These confirm that virtual dipole moments from mid northern hemisphere latitudes are higher than those from high latitudes and from the southern hemisphere. Global compilations spanning the Pleistocene, when filtered for quality also shows this behavior as do time averaged field models. Therefore, field strengths over even millions of years can have persistent non‐dipole field contributions. Key Points We present 26 40Ar/39Ar ages from volcanic rocks from Northern Israel (90 ka to 3.3 Ma) Twenty‐two Pleistocene intensity estimates have a mean paleomagnetic dipole moment of 62.2 ± 30.6 ZAm2 The northern hemisphere had persistently higher fields than the southern during the Pleistocene

• Publisher: John Wiley & Sons, Inc,Wiley
• Subject: Geomagnetic field / Geomagnetic field models / Holocene / Hypotheses / Latitude / Lava / Lava flows / Magnetism / Palaeomagnetism / paleointensity / paleointensity methods / Paleomagnetism / Pleistocene / spatial variations