The Amplitude and Timescales of 0-15 ka Paleomagnetic Secular Variation in the Northern North Atlantic

We investigate the amplitude and frequency of directional geomagnetic change since 15 ka in the Northern North Atlantic (similar to 67 degrees N) using five "ultra-high" resolution continental shelf sediment cores deposited at rates greater than 1 m/kyr. The ages of these cores are constrained by 103 radiocarbon dates with reservoir ages assessed through tephra correlation to terrestrial archives. Our study aims to address many of the uncertainties that are common in sedimentary paleomagnetic studies, including signal attenuation in low to moderate resolution archives and difficulty to demonstrate reproducibility in higher resolution archives. The "ultra-high" accumulation rates of our cores reduce "lock-in" and smoothing uncertainties associated with magnetic acquisition processes. Abundant radiocarbon dates along with an objective alignment algorithm provide a test of signal reproducibility at sub-millennial timescales. The paleomagnetic secular variation (PSV) signal, evaluated as individual records and as a new stack (GREENICE15k), validates prior results, but provides stronger geochronological constraints, demonstrates a reproducible PSV signal and amplitude, and extends through the abrupt Bolling-Allerod and Younger Dryas climate transitions of the latest Pleistocene. While broadly consistent with time-varying spherical harmonic models and varve dated records from Northern Europe, we demonstrate greater variance and higher amplitudes-particularly at sub-millennial timescales. This robust variability on centennial timescales is rarely observed or discussed, but is likely important to our understanding of some of the most intriguing aspects of the geodynamo. Plain Language Summary Our study used mud from the seafloor to investigate changes in Earth's magnetic field in the Northern North Atlantic region over the past 15 thousand years. Magnetic minerals eroded from rocks and deposited on the seafloor can preserve a record of the geomagnetic field, like little compass needles suspended in mud. We obtained sediment cores from areas near land with very high accumulation rates, which are rare in the modern ocean, that can record short magnetic field variations that occur on the timescale of centuries. We used radiocarbon dating to determine the ages of the sediment samples and a new alignment algorithm to verify the accuracy and consistency of the magnetic signal we observed. Understanding these short geomagnetic field variations is challenging, but it is key to unlocking many mysteries about the past and future of Earth's magnetic field.