Volume 128, Issue 6 e2023JB026891
Research Article

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

Brendan T. Reilly

Corresponding Author

Brendan T. Reilly

Lamont-Doherty Earth Observatory, Columbia University, Palisades, NY, USA

Correspondence to:

B. T. Reilly,

[email protected]

Contribution: Conceptualization, Methodology, Formal analysis, ​Investigation, Data curation, Writing - original draft, Writing - review & editing, Funding acquisition

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Joseph S. Stoner

Joseph S. Stoner

College of Earth, Ocean, and Atmospheric Sciences, Oregon State University, Corvallis, OR, USA

Contribution: Conceptualization, Formal analysis, ​Investigation, Resources, Data curation, Writing - review & editing, Supervision, Project administration, Funding acquisition

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Sædís Ólafsdóttir

Sædís Ólafsdóttir

Reykjavík Energy, Reykjavík, Iceland

Contribution: ​Investigation, Writing - review & editing

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Anne Jennings

Anne Jennings

INSTAAR, University of Colorado, Boulder, CO, USA

Contribution: ​Investigation, Writing - review & editing

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Robert Hatfield

Robert Hatfield

Department of Geological Sciences, University of Florida, Gainesville, FL, USA

Contribution: Formal analysis, ​Investigation, Writing - review & editing

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Gréta Björk Kristjánsdóttir

Gréta Björk Kristjánsdóttir

School of Engineering and Natural Sciences, University of Iceland, Reykjavík, Iceland

Contribution: Writing - review & editing

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Áslaug Geirsdóttir

Áslaug Geirsdóttir

Faculty of Earth Sciences, University of Iceland, Reykjavík, Iceland

Contribution: ​Investigation, Writing - review & editing

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First published: 14 June 2023
Citations: 1

Abstract

We investigate the amplitude and frequency of directional geomagnetic change since 15 ka in the Northern North Atlantic (∼67°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 Bølling–Allerød 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.

Key Points

  • Sediment cores with ultra-high accumulation rates are used to study directional changes in the Northern North Atlantic's geomagnetic field

  • Study addresses uncertainties in sedimentary paleomagnetic research, such as signal attenuation, chronology, and reproducibility

  • Study reveals robust variability on centennial timescales with greater variance than generally observed over the last 15,000 years

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.

Data Availability Statement

Data are available in MagIC (doi: 10.7288/V4/MAGIC/19300 and 10.7288/V4/MAGIC/19360) and Zenodo (doi: 10.5281/zenodo.7734229). PSV Dynamic Time Warping code is available through GitHub (https://github.com/CedricHagen/PSV-dynamic-time-warping).