A recent groundbreaking study analyzing the growth patterns recorded in clam shells has provided fresh insights into the stability of Atlantic Ocean currents, revealing that these vital oceanic systems may be nearing a critical tipping point. The research focuses on the annual growth rings of long-lived bivalves, particularly the quahog clam, scientifically known as Arctica islandica, which can live for over five centuries. These shells serve as natural archives, chronicling records of the ocean’s changing conditions year after year with remarkable continuity, thus enabling scientists to extend climate and oceanographic reconstructions far beyond the reach of modern instrumental data.
Central to the study is an examination of the Atlantic Meridional Overturning Circulation (AMOC) and the subpolar gyre (SPG), two interconnected circulation systems that play a pivotal role in regulating climate patterns across the North Atlantic and beyond. The AMOC, often dubbed the “ocean conveyor belt,” transports warm water northwards in the upper layers of the Atlantic and returns cold water southwards at depth, facilitating heat exchange and impacting weather systems on a global scale. The SPG, a cyclonic current swirling in the subpolar North Atlantic, influences regional climates and modulates the distribution of heat and salinity. Both features are integral to the Earth’s climate balance, and any disruption in their dynamics could precipitate profound and irreversible environmental changes.
In recent scientific discourse, substantial debate has centered on the possibility that the AMOC and SPG could undergo abrupt shifts or collapses, phenomena referred to as tipping points. Such transitions, once crossed, would drastically transform climate regimes, with cascading effects including intensified winters across northwestern Europe and fundamental shifts in global precipitation patterns. Weaker currents can lead to increased frequency and intensity of extreme weather events in the North Atlantic region, exacerbating climate vulnerability for millions of people.
The study, spearheaded by researchers at the University of Exeter’s Global Systems Institute, utilized advanced statistical analyses of growth variations in bivalve shells to detect early-warning signs of destabilization in these ocean currents. Variability in shell growth, influenced by numerous environmental factors such as temperature, salinity, and nutrient availability, serves as a sensitive proxy for changes in the ocean’s physical state. By analyzing these growth bands in a high-resolution, continuous dataset spanning more than 500 years, the team identified patterns indicative of “critical slowing down” — a phenomenon where a system’s recovery from perturbations becomes progressively sluggish as it approaches a tipping point.
This critical slowing down was manifest as an increasing inertia in the system’s response to external disturbances, suggesting a reduction in the resilience of the AMOC and SPG. Specifically, the analysis revealed two distinct episodes of destabilization within the last 150 years. The first episode, which likely involved the subpolar gyre, occurred in the early 20th century and has been tentatively linked to a documented warming phase in the Arctic and North Atlantic regions during the 1920s. This finding aligns with paleoclimatic observations and supports the notion that ocean circulation changes can precipitate regional climate anomalies.
More notably, a second, more pronounced destabilization began around the mid-20th century and persists to the present day. This ongoing trend raises alarming concerns about the proximity of the North Atlantic circulation system to a tipping point. While the study does not definitively identify whether the AMOC, the SPG, or both are responsible for the observed signals of reduced stability, the evidence collectively points toward a substantial loss of resilience in these linked systems. Such a loss increases the risk of abrupt transitions that could irreversibly alter oceanic and atmospheric dynamics, with profound implications for global weather patterns, marine ecosystems, and human societies dependent on stable climate conditions.
Researchers caution that attributing causation remains complex due to the interconnected nature of these oceanic systems. However, one clear driver contributing to this weakening trend is the accelerated melting of polar ice resulting from anthropogenic climate change. The influx of freshwater into the North Atlantic dilutes seawater density, impeding the sinking of cold, salty water that powers the deep limb of the AMOC. This disruption to the thermohaline circulation cycle compounds existing stresses and moves the system closer to collapse.
Given these findings, the study underscores the urgency of aggressive climate mitigation efforts. Rapid reductions in greenhouse gas emissions are paramount to prevent further weakening or potential tipping of these critical ocean currents. Maintaining the integrity of the AMOC and SPG is essential for preserving climate stability, biodiversity, and the livelihoods of populations across the Atlantic basin and beyond.
The use of biogenic proxies, such as the shells of long-lived clams, represents a novel and powerful approach to oceanographic research. These natural time capsules provide invaluable long-term data that complement and extend beyond the relatively short span of direct instrumental measurements, thereby enhancing our understanding of ocean dynamics under changing climatic conditions.
This research advances the frontier in detecting early-warning signs of critical transitions in complex environmental systems, leveraging interdisciplinary expertise across marine biology, climatology, and ocean physics. It highlights the intricate feedback mechanisms within the Earth’s climate system and the precarious balance maintained by oceanic currents in the face of rapid environmental change.
Overall, the study serves as a clarion call for the scientific community and policymakers alike, emphasizing the importance of continuous monitoring and integrated approaches to climate action aimed at safeguarding ocean circulation systems. Their stability is not only a linchpin for regional climates but also a cornerstone for global climate equilibrium.
This pioneering investigation exemplifies how innovative use of paleoenvironmental archives can inform contemporary climate risk assessments and shape adaptive strategies in an era marked by unprecedented environmental challenges.
Subject of Research: Stability and tipping points of Atlantic Ocean currents, specifically the Atlantic Meridional Overturning Circulation (AMOC) and subpolar gyre (SPG), analyzed through bivalve shell growth records.
Article Title: Recent and early twentieth century destabilization of the subpolar North Atlantic recorded in bivalves.
News Publication Date: 3-Oct-2025
Web References:
https://www.science.org/doi/10.1126/sciadv.adw3468
References:
Arellano Nava, B., Halloran, P., et al. (2025). Recent and early twentieth century destabilization of the subpolar North Atlantic recorded in bivalves. Science Advances, DOI: 10.1126/sciadv.adw3468.
Image Credits: Paul Butler
Keywords: Ocean circulation, Climate change, Climatology, Atlantic Meridional Overturning Circulation, Subpolar gyre, Tipping points, Marine paleoarchives, Arctic warming, Ocean physics
