New insights into Late Miocene Arctic climate dynamics have emerged from a detailed study of speleothems collected from eastern North Greenland. These mineral deposits, formed over millions of years in subterranean environments, have undergone state-of-the-art isotopic and elemental analyses, unveiling unprecedented records of past terrestrial climate and sea-ice variability. The research, led by Moseley and colleagues, paints a complex picture of Arctic climate behavior during the Late Miocene epoch, challenging prevailing assumptions and providing crucial data to understand polar climate evolution within the context of global climate shifts.
The foundation of this groundbreaking study lies in the careful correction of speleothem oxygen isotope (δ^18O) records to account for prior calcite precipitation (PCP). PCP can bias the δ^18O values, enriching them independently of climate signals. By quantifying and correcting for this effect, the researchers restored the original, climate-driven isotope signal of groundwater bicarbonate to between measured and PCP-corrected limits. This robust approach enabled the identification of higher amplitude isotopic shifts and oscillations, previously obscured in uncorrected data, which serve as reliable proxies of regional climate variability.
Crucially, the researchers ruled out tectonic elevation changes as a confounding factor influencing δ^18O signals, as regional uplift had ceased prior to speleothem deposition. Instead, the δ^18O variability was confidently interpreted as primarily driven by climate fluctuations. In parallel, the study tackled the challenge of reconstructing past sea-ice conditions through trace elemental analyses. Sodium (Na) was examined as a proxy for sea-salt aerosol input, with normalization against siliciclastic elements, aluminum (Al) and titanium (Ti), to isolate a marine aerosol signature representing the sea-ice extent in the surrounding Arctic Ocean.
Intriguingly, this Na-based marine aerosol record aligns remarkably with biomarker data from the Late Miocene Arctic Ocean, which indicates an irregular pattern of spring sea ice and largely ice-free summer conditions. The speleothem data thus appears to capture the transient nature and oscillatory behavior of sea ice during this period, revealing a far more dynamic Arctic cryosphere than previously appreciated. These findings fundamentally reshape our understanding of Late Miocene Arctic marine-terrestrial interactions.
The timing and pacing of climate variability recorded in the speleothems were calibrated using radiometric dating and Bayesian age modeling, despite inherent age uncertainties. This rigorous chronological framework permitted analysis of orbital influences on Arctic climate dynamics. Consistent with broader Late Miocene patterns, the data reveals a dominant role for obliquity forcing in modulating speleothem δ^18O variability. However, a striking anomaly emerged between approximately 9.6 and 9.3 million years ago, when δ^18O values inversely correlated with eccentricity-tilt orbital cycles, deviating from later phases where alignment is more straightforward.
This anomalous interval corresponds to a period of diminished orbital eccentricity and tilt forcing, yet paradoxically exhibits elevated δ^18O values suggestive of warmer temperatures amid expanded Antarctic ice volume, as indexed by global benthic δ^18O stacks. Meanwhile, the Arctic’s Na signal remained generally low, punctuated by episodic increases that coincided with temperature downturns. This hemispheric anti-phasing—Antarctic ice advancing during Arctic warmth and retreat during Arctic cooling—implies complex heat transport and feedback mechanisms governed regional climate.
Supporting this interpretation, the 9.6–9.3 million-year timeframe also encompasses evidence for enhanced North Atlantic poleward heat transport and a collapsed meridional temperature gradient, conditions that subsequently reversed to restore more typical latitudinal temperature contrasts by later growth phases. The implications of this hemispheric seesaw extend deeply into the marine and terrestrial climate systems, suggesting that Late Miocene Arctic warmth was influenced by interhemispheric energy redistribution and dynamic oceanic circulation.
The study highlights the potential role of evolving vegetation feedbacks in modulating these climatic states. Palynological records indicate that Arctic forest canopy density peaked around 9.7 million years ago before transitioning to more open shrub and herb-dominated landscapes. These shifts in vegetation cover would have altered surface albedo, latent heat flux, and evapotranspiration, thereby amplifying or dampening regional temperature responses. It appears that during low eccentricity-tilt phases, longer warm seasons interacted with denser vegetation to sustain elevated Arctic temperatures despite weaker orbital forcing.
As the Late Miocene progressed, the Arctic underwent a fundamental transition marked by progressive cooling, vegetation openness, and a reinvigorated meridional temperature gradient in the North Atlantic. These changes coincided with the strengthening of the Atlantic Meridional Overturning Circulation and North Atlantic Current, mechanisms that facilitated more direct hemispheric synchronization of glacial-interglacial cycles. Speleothem δ^18O data from this period exhibit more conventional in-phase relationships with global benthic δ^18O and orbital parameters, reflecting a climate regime dominated by stronger seasonal contrasts and transient glacial advances.
The culmination of these trends is evident in the latest speleothem growth phase beginning around 5.57 million years ago, which captures the maximum recorded Arctic sea-ice extent during the Late Miocene. This interval followed a prolonged depositional hiatus coincident with the pronounced TG20 glacial event. Although subsequent glacial cycles exhibited diminished intensity, Arctic sea ice persisted even during interglacial intervals, supported by elevated Na_ss concentrations. This persistence aligns with proxy reconstructions suggesting perennial summer sea ice under moderately elevated CO_2 concentrations.
Rapid fluctuations in sea-ice extent characterized the final growth phase, with abrupt expansions and retreats synchronous with obliquity-driven insolation cycles and deep-sea δ^18O variability. Notably, the TG12 deglacial event featured a swift disappearance of sea ice, an episode followed by a transient re-expansion corresponding with TG10. Between 5.49 and 5.38 million years ago, the Arctic experienced sustained low sea-ice conditions with minor oscillations, paralleling limited deep-sea δ^18O variability and rapid Antarctic deglaciation events such as TG9.
Collectively, the dual record of δ^18O and marine aerosol proxies from eastern North Greenland speleothems offers a window into the dynamic and transient climate system of the Late Miocene Arctic. Contrary to previous assumptions of relative climatic stability, these results demonstrate that the Arctic cryosphere and climate were highly sensitive to orbital forcing, ocean circulation changes, and terrestrial ecosystem feedbacks. This nuanced understanding helps reconcile marine and terrestrial paleoclimate records and refines models of polar climate evolution.
The complexity unearthed in this study underscores the limitations of existing climate models that often focus on discrete time slices or fixed CO_2 boundary conditions. The revealed variability and responsiveness of Late Miocene Arctic climate suggest that transient processes and feedbacks operated over multiple timescales, driving climate states far from equilibrium. Future modeling efforts will need to incorporate these spatially and temporally resolved proxy datasets to capture the true nature of past Arctic climate dynamics.
Beyond regional implications, the study contributes intricately detailed evidence toward understanding hemispheric climate interactions during key intervals of Earth’s climate history. The identification of hemispheric anti-phasing controlled by oceanic and biospheric feedbacks reveals how the Arctic did not evolve in isolation but was electrically wired into global climate systems. Such insights are crucial for predicting future polar climate trajectories under anthropogenic forcing.
In summary, the speleothems from eastern North Greenland have emerged as a unique and invaluable paleoclimate archive, preserving records of Late Miocene temperature variability, sea-ice fluctuations, and coupled biospheric processes. By integrating geochemical proxies, radiometric dating, and orbital tuning, this study pioneers a comprehensive reconstruction of Arctic terrestrial climate dynamics and their connection with global ice sheet behavior and ocean circulation. The findings challenge conventional narratives and open new avenues for multidisciplinary climate research at the polar frontiers.
Continued investigation and refinement of speleothem-based and complementary marine-terrestrial proxies will be essential for disentangling complex climatic feedbacks and improving chronological frameworks. As these archives grow in number and resolution, they will increasingly contribute to a holistic understanding of how Arctic climate systems respond to natural forcings, providing critical context for predicting their sensitivity in an era of rapid anthropogenic change.
Subject of Research:
Late Miocene Arctic terrestrial climate and sea-ice variability as recorded by speleothems from eastern North Greenland.
Article Title:
Late Miocene Arctic warmth and terrestrial climate recorded by North Greenland speleothems.
Article References:
Moseley, G.E., Koltai, G., Baker, J.L. et al. Late Miocene Arctic warmth and terrestrial climate recorded by North Greenland speleothems. Nat. Geosci. (2025). https://doi.org/10.1038/s41561-025-01822-0
Image Credits: AI Generated
