Diagram from the study.
The ratio of protactinium to thorium isotopes in marine sediment is often used as an indicator of past changes in the strength of Atlantic overturning, but this ratio can be affected by a wide range of other processes that also need to be considered. Credit: Scheen et al. [2025], Figure 1
Editors’ Highlights are summaries of recent papers by AGU’s journal editors.
Source: Paleoceanography and Paleoclimatology

Climate models predict that the Atlantic Meridional Overturning Circulation (AMOC) – a major conveyor-like system of ocean currents in the Atlantic – will weaken under global warming scenarios, causing major shifts in climate patterns. To build confidence in these projections, it is valuable to test how capable the models are at capturing past AMOC behavior.

One method used for reconstructing the strength of the AMOC over the past 100,000 years has been the measurement of the ratio of protactinium (231Pa) to thorium (230Th) isotopes preserved in seafloor sediments that have built up, layer-upon-layer, over time. Although often simplistically linked to changes in AMOC strength, the 231Pa/230Th ratio preserved in deep-sea sediments is controlled by a vast array of biogeochemical, sedimentological, and oceanographic factors.

Scheen et al. [2025] take an important step forward by modeling the behavior of these isotopes in an Earth system model of intermediate complexity that includes many of the key environmental processes affecting these isotopes. Their results largely support the traditional interpretation of some of the iconic 231Pa/230Th records, but they also reveal the sometimes-counterintuitive behavior of this proxy system, thus cautioning us to recognize its full complexity. The results are also used to suggest optimal locations for developing new 231Pa/230Th reconstructions. The model presented by the authors should not be treated as the final word, since – necessarily – it is still a simplified representation of a very complex system, yet they are to be commended for advancing our interpretation of a proxy system oft viewed as a key tool for constraining past AMOC behavior. 

Citation: Scheen, J., Lippold, J., Pöppelmeier, F., Süfke, F., & Stocker, T. F. (2025). Promising regions for detecting the overturning circulation in Atlantic 231Pa/230Th: A model-data comparison. Paleoceanography and Paleoclimatology, 40, e2024PA004869. https://doi.org/10.1029/2024PA004869

—David Thornalley, Associate Editor, Paleoceanography and Paleoclimatology

Text © 2024. The authors. CC BY-NC-ND 3.0
Except where otherwise noted, images are subject to copyright. Any reuse without express permission from the copyright owner is prohibited.