Pierre Francus

Hydroclimate variability in western Iberia during the Holocene remains insufficiently resolved despite the high sensitivity of this region to the North Atlantic atmosphere and ocean dynamics. Here, we present the first source‐resolved reconstruction of centennial‐ to millennial‐scale moisture variability over the last 11,000 years using sediments from Lake Peixão (Portugal) based on compound‐specific hydrogen and carbon isotopes of plant wax n ‐alkanes, supported by bulk organic geochemistry and continuous X‐ray fluorescence elemental data. Terrestrial source‐resolved isotope series, obtained using non‐negative matrix factorization, primarily reflect precipitation isotopic composition and plant water use efficiency. The record indicates a wet early Holocene, a progressive mid‐Holocene drying trend that culminated in maximum aridity at approximately 4,000 calibrated years before present, and a transition to generally wetter but more variable late Holocene conditions, partly overprinted by anthropogenic land‐use change. These trends are interpreted as reflecting orbitally driven changes in Northern Hemisphere insolation that modified the latitudinal temperature gradient (LTG) and, in turn, influenced the North Atlantic storm track position and intensity. Enhanced early Holocene moisture reflects a higher LTG and southward‐displaced storm tracks, whereas mid‐Holocene aridity corresponds to a reduced LTG and northward‐shifted westerlies. The late Holocene recovery of wetter conditions agrees with a higher LTG and increased storm‐track influence over Iberia. Superimposed centennial‐scale variability likely reflects changes in North Atlantic Oscillation phases, the position of the Azores Front, and the intensity of the subpolar gyre. These results demonstrate the dominant roles of the LTG and coupled ocean–atmosphere dynamics in shaping the western Iberian hydroclimate throughout the Holocene.

This work employs micro-computed tomography (micro-CT) and laser-ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) to characterize a sample of sixteenth and seventeenth century silica-based beads of heterogeneous composition recovered in Ontario and Québec, Canada. The interiors of these beads are diverse in structure and composition, and it is likely that different methods and materials were employed to produce them. Compositional analysis suggests that at least some beads were produced in France, which is consistent with earlier archaeometric and historical findings. Based on the diversity in composition and production of the beads, we infer that, unlike drawn beads that were produced on an industrial scale for export, these beads may have been produced by small-scale bead makers. Further, the original purpose of these beads may have been as rosary beads, suggesting a different trajectory for their incorporation into archaeological deposits in North America.

Paleomagnetic and rock magnetic analyses were conducted on sediment cores from the northeastern Greenland Shelf and Young Sound along the western edge of Fram Strait. The paleomagnetic signal in all three sediment cores is characterized by a strong and stable single component magnetization carried by low coercivity ferrimagnetic single domain or vortex state grains, attesting to the quality of the recorded relative paleointensity (RPI) and paleomagnetic secular variation (PSV) signals. Comparison with other archives from the northern North Atlantic, northern Greenland, and northern Europe and with geomagnetic field model outputs indicates broad similarities between the records, particularly with Finnish, Swedish and southern Greenland records. Comparison of the new RPI records with global geomagnetic field models and cosmogenic isotope production rates highlights the global character of the geomagnetic variations from the northeastern Greenland Shelf. Virtual geomagnetic pole (VGP) paths for the last 8 kyr compared to geomagnetic field strength maps at the core‐mantle boundary over the same time interval illustrate that, at times of high intensity, geomagnetic flux lobes could have an effect on VGP migration. We suggest that High Arctic PSV is most likely driven by millennial‐scale hemispheric geomagnetic flux lobe geometry changes.

Arctic coastlines underlain by ice-rich permafrost are retreating at accelerating rates due to the compounding effects of rising air and ocean temperatures, longer ice-free seasons, and increasing storm activity. Unlike temperate coasts, erosion of unconsolidated, ice-rich permafrost bluffs is governed by a thermomechanical process in which wave-driven heat transfer induces thawing, and hydrodynamic forcing removes the sediment matrix. Despite its significance for coastal hazard prediction, infrastructure resilience, and climate feedback, this coupled process remains poorly represented in existing models, largely because of limited experimental data, logistical challenges associated with long-term field monitoring, and analytical formulations that rely on simplified or weakly constrained parameterizations, particularly for convective heat transfer at the turbulent water-permafrost interface. Here, we present thermalFOAM, a physics-based numerical framework implemented in OpenFOAM, for simulating the ablative erosion of permafrost bluffs under wave forcing. The solver resolves transient heat conduction with phase change through an enthalpy-porosity formulation, incorporates temperature-dependent thermophysical properties, and drives dynamic mesh evolution through a calibrated erosion law. A key innovation is a wave-aware Robin boundary condition that enables spatially and temporally varying thermal forcing based on instantaneous water surface elevation, allowing the model to capture intermittent wetting that governs heat transfer in the swash and surf zones. Validation against laboratory datasets demonstrated that thermalFOAM successfully reproduced the observed niche geometries and retreat rates across the tested parameter space. This integrated framework bridges laboratory-scale process understanding and field-scale prediction, offering an open-source tool for assessing Arctic coastal dynamics under future climate scenarios.

Atlantic Canada experiences frequent major storms, particularly tropical cyclones transitioning into post-tropical storms. Events such as Hurricane Fiona (2022), Dorian (2019), and Juan (2003) have caused significant damage, loss of life, and coastal erosion, exacerbated by sea level rise and warming waters. Despite this, centennial- to millennial-scale storm records in the region remain scarce. Existing studies in North America focus primarily on marine and coastal overwash records, with limited use of aeolian mineral inputs in ombrotrophic peatlands as storm proxies. Here, we address these gaps by analysing grain-size and geochemical data from two peatlands in Quebec, Canada's Magdalen Islands. Our 4000-year peat-based storm reconstructions reveal consistent storm signals with three key intervals of increased activity: 800–550 BCE, 500–750 CE, and 1300–1700 CE. These records align with marine overwash archives from eastern Canada, the US, and the Bahamas, supporting reduced storminess during the Medieval Climate Anomaly and heightened activity during the Little Ice Age. This regional coherence suggests storm variability at higher latitudes is strongly influenced by local climatic drivers, such as sea surface temperature gradients and storm intensification mechanisms, rather than tropical cyclone formation alone. Despite broad similarities, notable discrepancies in geochemical and mineralogical profiles between our two peatlands highlight the influence of site-specific factors, including proximity to sediment sources, bog size, and local geomorphology, on sediment deposition and storm signal strength. These findings underscore the importance of site selection and local context when interpreting peat-based storm records. Furthermore, challenges remain in calibrating peat proxies to historical storm events, limiting direct event attribution over the past 150 years. Our study demonstrates the complementary value of peatland archives alongside marine overwash records in reconstructing paleo-storm activity, enriching understanding of storm dynamics and expanding potential reconstruction sites, particularly in mid-latitude coastal regions. Continued research is needed to refine calibration methods and clarify climatic mechanisms driving storm variability, which is essential for projecting future storm impacts in Atlantic Canada.

Permafrost coastal systems are critical to Arctic environmental processes, and understanding their erosion dynamics is essential for addressing climate change impacts. These coastlines undergo unique thermomechanical erosion, where wave action, rising sea levels, and thermal degradation jointly drive a rapid coastline recession. This study demonstrates advancements in physically modeling coastal permafrost erosion using a laboratory setup that replicates natural Arctic coastal conditions. A wave flume with a representative nearshore slope and reproducible permafrost specimen preparation methodology allowed isolation of the hydrodynamic and thermodynamic effects. Distinct erosion patterns and rates were quantified under varying wave heights, periods, and thermal conditions. Results indicate that wave height is a dominant mechanical driver, with mean erosion rates increasing by over 100% from low to high wave conditions. Even low‐energy waves ( H = 0.02 m) enhanced erosion by more than 50% compared to still‐water conditions. Additionally, a higher ice content reduced niche deepening rates by 38%, which is attributed to latent heat delaying thawing. A new scalable thermomechanical model for erosional niche incision on an Arctic bluff is proposed based on a power‐law relationship that integrates the Froude, Iribarren, and Stefan numbers. This dimensionless approach captures the coupled influence of wave‐induced forces and permafrost thermal properties, exhibiting a strong predictive capability ( R ² = 0.90) and outperforming existing analytical models. The experimental framework and new model offer new insights into Arctic coastal retreat mechanisms and provide a promising foundation for regional‐scale applications in coastal management under changing climatic conditions.

Permafrost coastal systems are critical to Arctic environmental processes and understanding their erosion dynamics is essential for addressing climate change impacts. These coastlines undergo unique thermomechanical erosion, where wave action, rising sea levels, and thermal degradation jointly drive rapid coastline recession. This study demonstrates advancements in physically modeling coastal permafrost erosion using a laboratory setup that replicates natural Arctic coastal conditions. A wave flume with a representative nearshore slope and reproducible permafrost specimen preparation methodology allowed isolation of the hydrodynamic and thermodynamic effects. Distinct erosion patterns and rates were quantified under varying wave heights, periods, and thermal conditions. Results indicate that wave height as a dominant mechanical driver, with mean erosion rates increasing by over 100% from low to high wave conditions, while wave period had minimal influence. Even low-energy waves (H = 0.02 m) enhanced erosion by more than 50% compared to still-water conditions. Additionally, a higher ice content reduced niche deepening rates by 38%, attributed to latent heat delaying thawing. A new scalable thermomechanical model for erosional niche incision on an Arctic bluff is proposed based on a power-law relationship that integrates the Froude, Iribarren, and Stefan numbers. This dimensionless approach captures the coupled influence of wave-induced forces and permafrost thermal properties, exhibiting a strong predictive capability (R² = 0.90) and outperforming existing analytical models. The experimental framework and new model offer new insights into Arctic coastal retreat mechanisms and provide a promising foundation for regional-scale applications in coastal management under changing climatic conditions.

Grand Lake, located in Labrador, at the northeastern margin of North America, is a deep lacustrine basin that contains a well-preserved annual laminations record spanning the interval 493 to 2016 CE (1524 years). The chronology of this new varved sequence is established from layer counting of high-resolution images of thin sections. Radiometric dating (¹³⁷Cs and ¹⁴C) validates the reliability of the varve chronology. Varve thickness is significantly correlated (r = 0.38) with the total precipitation recorded at the nearest weather station Goose A. The varve thickness series reveals high values during the 1050–1225 CE period, which corresponds to the Medieval Climate Anomaly, whereas the 15th–19th centuries, related to the Little Ice Age, shows low values. The teleconnections between several Goose A instrumental data series and some modes of climate variability such as the winter Greenland Blocking (negative North-Atlantic Oscillation) and the significant correlations between our varve thickness record and three other Northern Hemisphere high-resolution proxy records suggest that the Grand Lake record tracks North-Western Atlantic large-scale modes of hydroclimate variability over the past ∼ 1500 years.