In a groundbreaking study that reshapes our understanding of Earth’s climatic history, an international team of scientists has uncovered compelling evidence indicating that vast expanses of the Northern Hemisphere were almost entirely devoid of permafrost during the late Miocene epoch. This revelation stems from an innovative analysis of Arctic speleothems—secondary mineral deposits such as stalagmites and stalactites found within caves—offering an unprecedented glimpse into conditions that prevailed approximately 11 to 5 million years ago. The research, recently published in Nature Communications, harnesses cutting-edge geochemical techniques, effectively rewriting assumptions about the temperature and environmental dynamics that once shaped much of the planet’s northern latitudes.
At the heart of this study lies the meticulous examination of speleothems collected from Arctic cave systems. Speleothems act as natural climate archives; their layered mineral deposits record changes in temperature and moisture over millennia with remarkable precision. By employing uranium-thorium dating and stable isotope geochemistry, the researchers unlocked temporal and environmental data embedded within these formations. The data crucially suggest that the Northern Hemisphere experienced a climate substantially warmer than previously documented for the late Miocene, with permafrost—which today underlies a significant portion of the Arctic—being largely absent.
This discovery directly challenges long-standing paradigms regarding Miocene climate patterns. Traditionally, paleoclimatologists have considered extensive permafrost a continuous feature of Northern high latitudes since the Pliocene or even earlier, assuming cold polar conditions dominated much of the Neogene period. However, the evidence extracted from speleothem growth intervals and isotopic signatures indicates episodic warmth sufficient to inhibit the formation or persistence of permafrost layers. This finding reframes the late Miocene as a markedly different world, characterized by minimal permafrost coverage and potentially extensive zones of unfrozen ground.
The methodology used in this research represents a significant advance in paleoclimate reconstructions, combining precise chronometric techniques with novel interpretation of isotopic records. Uranium-thorium dating, a radiometric method leveraging the decay of uranium isotopes to thorium, allows for precise age determination of carbonate deposits up to several hundred thousand years old. Coupled with stable isotope analyses of oxygen and carbon, this approach reveals past temperatures and precipitation sources, enabling scientists to correlate speleothem growth phases with geological time scales and climate events.
Isotopic ratios of oxygen (δ¹⁸O) in speleothem calcite provide direct proxies for paleotemperatures and moisture source variations. Lower δ¹⁸O values typically indicate cooler conditions or altered precipitation patterns, while higher values suggest warming and changes in hydrological cycles. In this study, the observed isotopic signatures align with a much warmer Arctic environment than previously reconstructed, supporting the hypothesis of minimal permafrost coverage during the late Miocene.
Furthermore, the physical presence of intact speleothem formations themselves bear testimony to the absence of sustained permafrost. Permafrost dynamics, characterized by freeze-thaw cycles and ground ice presence, generally inhibit the growth and preservation of speleothems. The discovery of well-preserved speleothem deposits thus implies that temperatures remained above freezing in these cave environments for prolonged periods, allowing uninterrupted mineral precipitation over thousands of years.
This revelation has profound implications for understanding the northern terrestrial ecosystem and evolutionary biology during the late Miocene. Without a pervasive permafrost barrier, vegetation zones could have extended much farther north, fostering rich and diverse plant and animal communities. Such environments might have supported early mammalian fauna adapted to more temperate climates, profoundly influencing migration patterns and biological diversification at high latitudes.
Climatic models traditionally struggle to replicate Miocene warmth, often underestimating Arctic temperatures and overemphasizing polar glaciation. The speleothem data presents a valuable calibration tool, providing real-world targets for validating and improving predictive climate models focusing on past greenhouse gas concentrations, ocean-atmosphere circulation, and ice sheet dynamics. This study thereby not only illuminates past climates but also informs projections of future Arctic environmental change under ongoing global warming.
One of the study’s most striking aspects is how it bridges gaps between disparate scientific disciplines. The integration of geochemistry, geology, paleoecology, and climatology yields a coherent narrative that enhances our capacity to interpret Earth’s deep past. This multidisciplinary approach is pivotal in unraveling the complexities of past environments, particularly in extreme polar regions where direct fossil records can be sparse or biased.
Scientists caution, however, that the absence of permafrost in the late Miocene was not uniform across the Arctic. The speleothems analyzed pertain primarily to regions where cave systems could form and be studied; other regions likely retained colder microclimates or variable permafrost extents. Nonetheless, the broad implications signal a much warmer Arctic climate phase lasting hundreds of thousands, if not millions, of years, preceding the widespread glaciations associated with the Pliocene and Quaternary periods.
From a geological perspective, the late Miocene was a time of significant tectonic and oceanographic shifts, including the gradual closure of the Central American Seaway and intensified Antarctic glaciations. These global changes undoubtedly influenced atmospheric CO₂ concentrations and heat distribution, contributing to Arctic climate fluctuations. The speleothem evidences provide constraints on how such global events translated into localized climatic effects at high northern latitudes.
This discovery also revisits hypotheses about the formation and degradation of Arctic permafrost and its feedbacks with global climate systems. Permafrost stores vast reservoirs of organic carbon; its presence or absence strongly impacts greenhouse gas fluxes and climate stability. Understanding when and where permafrost dynamically shifted in geologic history is critical for predicting future feedback loops, especially as contemporary Arctic warming threatens rapid permafrost thaw.
Intriguingly, the speleothem record reveals intervals of alternating warmer and cooler phases within the generally permafrost-free late Miocene epoch. These fluctuations suggest that the Arctic climate was not monotonously warm but experienced complex variability driven by orbital cycles, ice volume changes, and perhaps volcanic or solar forcing. This nuanced understanding challenges assumptions of linear climate trends and highlights the delicate balance governing Earth’s high latitude environments.
As research continues, the team aims to expand the spatial coverage of speleothem sampling, integrating data from diverse Arctic cave systems to build a more comprehensive picture of late Miocene climatic heterogeneity. They are also exploring advancements in microanalytical techniques such as clumped isotope thermometry and trace element profiling to refine paleotemperature reconstructions and elucidate past cave microenvironments.
In sum, the discovery of nearly permafrost-free conditions in the late Miocene Arctic through speleothem evidence not only transforms our conception of past climate dynamics but also lays foundational knowledge vital for contemporary climate science. It accentuates the sensitivity of Arctic environments to global climatic shifts while highlighting the power of geological archives in decoding Earth’s ancient environmental narratives. As humanity faces unprecedented climate change, lessons etched in the silence of speleothems millions of years old provide a poignant reminder of nature’s evolving complexity and resilience.
Subject of Research: Arctic speleothems and late Miocene permafrost conditions in the Northern Hemisphere
Article Title: Arctic speleothems reveal nearly permafrost-free Northern Hemisphere in the late Miocene
Article References:
Vaks, A., Mason, A., Breitenbach, S.F.M. et al. Arctic speleothems reveal nearly permafrost-free Northern Hemisphere in the late Miocene. Nat Commun 16, 5483 (2025). https://doi.org/10.1038/s41467-025-60381-5
Image Credits: AI Generated
