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Our understanding of the past behavior of the geomagnetic field arises from magnetic signals stored in geological materials, e.g., (volcanic) rocks. Bulk rock samples, however, often contain magnetic grains that differ in chemistry, size, and shape; some of them record the Earth's magnetic field well, others are unreliable. The presence of a small amount of adverse behaved magnetic grains in a sample may already obscure important information on the past state of the geomagnetic field. Recently it was shown that it is possible to determine magnetizations of individual grains in a sample by combining X-ray computed tomography and magnetic surface scanning measurements. Here we establish this new Micromagnetic Tomography (MMT) technique and make it suitable for use with different magnetic scanning techniques, and for both synthetic and natural samples. We acquired reliable magnetic directions by selecting subsets of grains in a synthetic sample, and we obtained rock-magnetic information of individual grains in a volcanic sample. This illustrates that MMT opens up entirely new venues of paleomagnetic and rock-magnetic research. MMT's unique ability to determine the magnetization of individual grains in a nondestructive way allows for a systematic analysis of how geological materials record and retain information on the past state of the Earth's magnetic field. Moreover, by interpreting only the contributions of known magnetically well-behaved grains in a sample, MMT has the potential to unlock paleomagnetic information from even the most complex, crucial, or valuable recorders that current methods are unable to recover.

For archeomagnetic dating, high-quality directional and intensity paleosecular variation curves are needed. The Azores Archipelago in the mid-Atlantic Ocean provides a wealth of volcanic products erupted during the Holocene, making it an ideal location to (1) gather paleomagnetic data from well dated lava flows and (2) construct a paleosecular variation (PSV) curve that enables paleomagnetic dating of volcanic products with unknown age. Here, we present new full-vector paleomagnetic data from Pico Island, and combine the new data with existing data from neighboring islands to construct a new full-vector PSV curve for the Azores Archipelago. An extensive rock-magnetic study underpins the quality of our paleomagnetic carriers. From Pico Island, we obtained 21 new mean site directions; and 15 paleointensity estimates with the multimethod paleointensity approach from 12 sites, the age was known for 14 and 10 sites, respectively. By bootstrapping the non-Gaussian uncertainty estimates of the radiocarbon age calibrations and the confidence intervals associated with the direction and paleointensity estimates, we produce the first full-vector PSV curve with confidence intervals for the Azores covering the past 2 kyr. The PSV curve reveals a period of low inclination between ∼900 and 1560 AD, with minimum values of 32°. The potential of our new full-vector PSV curve is demonstrated by successfully dating five lava flows from Pico Island.

Paleointensity.org is an online, open source, application to analyze paleointensity data produced by the most common paleointensity techniques. Our application currently supports four different methods: thermal Thellier (all variations), microwave Thellier, pseudo-Thellier, and the multispecimen protocol. Data can be imported using a variety of input file formats such as ThellierTool files, the generic PmagPy file format, and a number of lab-specific formats. The data for the individual paleointensity methods are visualized by the relevant graphs and parameters, which are updated dynamically while interpreting the data. Beyond manual interpretation, Paleointensity.org features an autointerpreter for specimen level Thellier-type data. Interpretations and data can be exported to csv and MagIC files. Moreover, it is possible to export the local storage containing all data, saved interpretations, and settings. This file can be shared among researchers or attached to a paper as supporting information. Because of its many features and ease of use, Paleointensity.org is a major step forward in enhancing an open paleomagnetic community in which data can be shared, checked, and reused in line with the findable, accessible, interoperable, and reusable data principles.