Goulven Gildas Laruelle

Dust deposits in ice cores provide a valuable archive of past atmospheric circulation, offering insights into climate dynamics during key climate transitions such as the last glacial termination. Here, we present a novel high-resolution reconstruction of dust provenance in the EPICA Dome C (EDC) ice core from 33.7 to 2.8 kyr BP, based on Rare Earth Element (REE) patterns. Using a statistical unmixing algorithm on 279 samples, we quantify, for the first time, contributions from key Southern Hemisphere dust sources. During the late Marine Isotope Stage 3 (MIS3), the Last Glacial Maximum (LGM) and Heinrich Stadial 1 (HS1), dust at EDC was dominated by Patagonian sources, ∼ 65 %–75 % of total deposition, with secondary inputs from Australia (∼ 9 %–11 %), Southern Africa (∼ 5 %–9 %), New Zealand (∼ 6 %–14 %), and Puna-Altiplano (∼ 2 %–4 %). After ∼ 14.5 kyr BP, and especially during the Holocene, the dust assemblage shifted toward greater contributions from low-latitude sources including Australia (21 %–28 %), Southern Africa (∼ 8 %–9 %), and the Puna-Altiplano (∼ 8 %–9 %) – while the Patagonian contribution decreased to an average of ∼ 43 %–53 %, New Zealand (∼ 4 %–10 %) – and source compositions became more variable. This transition in dust provenance contribution is supported by our modeled Sr-Nd isotope composition of EDC dust, which also aligns with changes observed in other East Antarctic ice cores. Comparison with the EDML ice core provenance record reveals overall agreement in major sources and timing of the shifts but also highlights regional variations in the secondary contributions, with EDC showing more consistent inputs from Australia and EDML from Southern Africa. The coherence of the provenance shift recorded at EDC and EDML ice cores points to a common large-scale control, in line with the influence of eustatic sea-level rise and postglacial reorganization of fluvial sediment routing and availability in southern South America.

Tropical urban estuaries receive year-round nutrient loads, yet their strongest phytoplankton blooms often occur in the dry season. The proximate control on this seasonality remains unresolved in wastewater-impacted tropical systems. Here we apply a transient one-dimensional Carbon Generic Estuarine Model (C-GEM) to the Saigon River Estuary, southern Vietnam, and evaluate it against 24 months of monitoring data (2017–2018). Simulated dry-season chlorophyll-a at the urban station reached 37 μg L^(-1), matching observations and reproducing the observed approximately sevenfold dry-to-wet contrast. Urban residence time increased from approximately 20 days during the monsoon to approximately 53 days during the dry season, and the chlorophyll–residence-time relationship showed an inflection at 32 days. The corresponding Damköhler number shifted from Da≈33 in the dry season to Da≈1 in the wet season, consistent with a transition from bloom-permissive to bloom-suppressive conditions. The hydrodynamics-related predictors explained 60–62% of simulated phytoplankton variability at the upstream bloom-forming stations, whereas nutrient loads contributed 21–27%; near the urban discharge sources, nutrients accounted for up to 40%. The coupled carbonate module showed persistent urban CO_2 supersaturation (pCO_2 > 10,000 μatm) and mean estuarine evasion of 142.9 Gg C yr^(-1). These results show that hydraulic residence time is the dominant proximate control on bloom expression in this hyper-eutrophic estuary. Wastewater reduction remains the durable management solution, whereas flow augmentation may serve only as a constrained near-term complement in regulated tropical systems. Similar growth–flushing behaviour is most likely in tropical megacity estuaries that combine chronic nutrient excess with strong monsoon-driven retention swings.

The Land–Ocean Aquatic Continuum (LOAC) is a critical and complex component of the global carbon cycle, regulating the transfer, transformation, and evasion of carbon from terrestrial ecosystems to the coastal ocean. Last layer of this continuum before the coastal ocean, estuaries play a dual role: 1) as reactors that process organic and inorganic carbon and 2) as sometimes significant sources of CO₂ emissions to the atmosphere compared to their modest surface areas. These processes are tightly controlled by a wide array of external factors including upstream land-based emissions (influenced by lithological context, land use, etc.), riverine transport and in-stream biogeochemical transformations, as well as internal estuarine morphology, hydrodynamics and metabolism. With over 50 000 estuaries worldwide and a wide heterogeneity between systems, performing an exhaustive carbon budget analysis, even regionally is a major but necessary challenge to better constrain the carbon land-ocean exchange and the contribution of estuaries to CO2 budgets.To investigate the coupling between lateral carbon fluxes and atmospheric CO₂ exchanges over a continuous stretch of coast, batch simulations of the 1D depth integrated generic estuarine hydrological/biogeochemistry C-GEM has emerged as a suitable solution because of its design build on limited data and computing demand. In an application on the Atlantic French coast, estuarine dynamics were explicitly represented in time and space for 35 selected macro-tidal estuaries. This regional application quantifies the cascading fluxes of Organic Carbon (OC), Dissolved Inorganic Carbon (DIC), from the upstream influence of tides to the estuarine outlets, while simulating air–water CO₂ exchanges within estuaries. This exercise is based on a structured database that compile an exhaustive inventory of all aquatic measurements at the upstream boundary of the estuarine modelling domain (for all watersheds larger than 300 km²), as well as along the estuarine longitudinal profiles themselves for model validation.Our integrated approach allows the establishment of a consistent regional carbon budgets that account for terrestrial inputs and estuarine processing, coastal exports, and CO₂ evasion to the atmosphere. Our simulations indicate that estuaries along the French Atlantic coast act predominantly as net sources of CO₂, with strong spatial variability driven by size, watershed characteristics, riverine carbon loads, and estuarine residence times. The fraction of riverine carbon loads that is outgassed towards the atmosphere as CO2 within the estuary ranges from a few percents to 20% from the smaller systems to the largest. By detailing the nature and intensity of carbon fluxes in the LOAC estuarine compartment, this work highlights the importance of proposing integrated land-sea modelling approaches that explicitly include estuarine interfaces in order to constrain regional carbon budgets and national and continental greenhouse gas inventories. Moreover, it opens to door to longer time scale simulations to disentangle the natural component of the global estuarine carbon budget from its anthropic perturbation, partitioning that is currently virtually unknown.

Dust deposits in ice cores provides a valuable archive of past atmospheric circulation, offering insights into climate dynamics during key climate transitions such as the last glacial termination. Here, we present a novel continuous, high-resolution reconstruction of dust provenance in the EPICA Dome C (EDC) ice core from 33.7 to 2.9 kyr BP, based on Rare Earth Element (REE) patterns. Using a statistical unmixing algorithm on 241 samples, we quantify for the first-time contributions from key Southern Hemisphere dust sources. During the Marine isotope 3 (MIS3), the Last Glacial Maximum (LGM) and Heinrich Stadial 1 (HS1), dust at EDC was dominated by Patagonia sources (~65–75 %), with secondary inputs from Australia, Southern Africa, New Zealand, and Puna-Altiplano. After ~14.5 kyr BP, the dust assemblage shifted toward greater inputs from low-latitude sources – Australia, Southern Africa, and the Puna-Altiplano – culminating during the Holocene with more variable compositions and reduced Patagonian input (~49 % on average). This transition is supported by Sr-Nd isotopic calculations and aligns with changes observed in other East Antarctic ice cores. Comparison with the EDML ice core reveals overall agreement in major sources and timing of the shifts but also highlights regional variations in the secondary contributions, with EDC showing more consistent inputs from Australia and EDML from Southern Africa. We attribute the shift in provenance to long-lasting hydrological changes in Patagonian river systems and a rapid submersion of the Patagonian shelf around 14.5 kyr BP, linking dust composition to eustatic sea-level rise.

Dust deposits in ice cores provides a valuable archive of past atmospheric circulation, offering insights into climate dynamics during key climate transitions such as the last glacial termination. Here, we present a novel continuous, high-resolution reconstruction of dust provenance in the EPICA Dome C (EDC) ice core from 33.7 to 2.9 kyr BP, based on Rare Earth Element (REE) patterns. Using a statistical unmixing algorithm on 241 samples, we quantify for the first-time contributions from key Southern Hemisphere dust sources. During the Marine isotope 3 (MIS3), the Last Glacial Maximum (LGM) and Heinrich Stadial 1 (HS1), dust at EDC was dominated by Patagonia sources (~65–75 %), with secondary inputs from Australia, Southern Africa, New Zealand, and Puna-Altiplano. After ~14.5 kyr BP, the dust assemblage shifted toward greater inputs from low-latitude sources – Australia, Southern Africa, and the Puna-Altiplano – culminating during the Holocene with more variable compositions and reduced Patagonian input (~49 % on average). This transition is supported by Sr-Nd isotopic calculations and aligns with changes observed in other East Antarctic ice cores. Comparison with the EDML ice core reveals overall agreement in major sources and timing of the shifts but also highlights regional variations in the secondary contributions, with EDC showing more consistent inputs from Australia and EDML from Southern Africa. We attribute the shift in provenance to long-lasting hydrological changes in Patagonian river systems and a rapid submersion of the Patagonian shelf around 14.5 kyr BP, linking dust composition to eustatic sea-level rise.

The polar ice sheets, their surrounding land fringes and oceans (68 × 10 ⁶ km ² ; 13% of Earth's surface) are hot spots for carbon cycle perturbation under future climate change due to glacier retreat, rising meltwater fluxes, reduced sea ice, thawing permafrost, warming land‐surfaces and increased precipitation. Here we assess carbon stored and exchanged with the atmosphere (as carbon dioxide and methane) across an expansive bipolar ice‐to‐ocean domain. We show that the polar regions harbor large reserves of carbon stored in sediments, rocks and the ocean, which differ in their reactivity and turnover times: 5,300–22,200 PgC of organic carbon and 5,600–8,600 PgC of inorganic carbon. These carbon reservoirs include potential reserves of marine and subglacial methane hydrate (80–570 PgC), which could become destabilized under future warming scenarios. Oceans (270–360 PgC) and ice sheets (14–96 PgC Greenland, 5,000–21,000 PgC Antarctica) dominate organic carbon stores, with smaller (but regionally important) stocks found in ice sheet land fringes (13–58 PgC). Estimates of natural CO ₂ and CH ₄ fluxes from these polar regions to the atmosphere present high uncertainty but highlight oceanic CO ₂ sinks in Greenland (−110 to −49 TgC‐CO ₂ a ⁻¹ ) and in the ICE and SPSS biomes of the Southern Ocean (−480 to 55 TgC‐CO ₂ a ⁻¹ ), with potential CH ₄ sources associated with the Greenland Ice Sheet. Such high uncertainty in polar carbon reservoirs and fluxes is important to resolve if future feedbacks between the polar regions, Earth's carbon cycle and climate are to be conclusively determined.

Dust deposits in ice cores provides a valuable archive of past atmospheric circulation, offering insights into climate dynamics during key climate transitions such as the last glacial termination. Here, we present a novel continuous, high-resolution reconstruction of dust provenance in the EPICA Dome C (EDC) ice core from 33.7 to 2.9 kyr BP, based on Rare Earth Element (REE) patterns. Using a statistical unmixing algorithm on 241 samples, we quantify for the first-time contributions from key Southern Hemisphere dust sources. During the Marine isotope 3 (MIS3), the Last Glacial Maximum (LGM) and Heinrich Stadial 1 (HS1), dust at EDC was dominated by Patagonia sources (~65–75 %), with secondary inputs from Australia, Southern Africa, New Zealand, and Puna-Altiplano. After ~14.5 kyr BP, the dust assemblage shifted toward greater inputs from low-latitude sources – Australia, Southern Africa, and the Puna-Altiplano – culminating during the Holocene with more variable compositions and reduced Patagonian input (~49 % on average). This transition is supported by Sr-Nd isotopic calculations and aligns with changes observed in other East Antarctic ice cores. Comparison with the EDML ice core reveals overall agreement in major sources and timing of the shifts but also highlights regional variations in the secondary contributions, with EDC showing more consistent inputs from Australia and EDML from Southern Africa. We attribute the shift in provenance to long-lasting hydrological changes in Patagonian river systems and a rapid submersion of the Patagonian shelf around 14.5 kyr BP, linking dust composition to eustatic sea-level rise.

This study presents a new physical-biogeochemical modelling framework for simulating lake methane (CH₄) emissions at regional scales. The new model, FLaMe-v1.0 (Fluxes of Lake Methane), rests on an innovative, computationally efficient lake clustering approach that enables the simulation of CH₄ emissions across a large number of lakes. Building on the Canadian Small Lake Model (CSLM) that simulates the lake physics, we develop a suite of biogeochemical modules to simulate transient dynamics of organic Carbon (C), Oxygen (O₂), and CH₄. We first test the performance of FLaMe-v1.0 by analyzing physical and biogeochemical processes in two theoretical lakes with characteristics that can be considered representative for many lakes (an oligotrophic, deep lake driven by cold climate versus a eutrophic, shallow lake driven by warm climate). Next, we evaluate the model by comparing simulated and observed timeseries of CH₄ emissions in four well-surveyed lakes. We then apply FLaMe-v1.0 at the European scale to evaluate simulated diffusive and ebullitive lake CH₄ fluxes against in-situ measurements in both boreal and central European regions. Finally, we provide a first assessment of the spatio-temporal variability in CH₄ emissions from European lakes with a surface area comprised between 0.1–1000 km² (n= 108 407, total area = 1.33 × 10⁵ km²), indicating a total emission of 0.97 ± 0.23 Tg CH₄ yr⁻¹, with the uncertainty constrained by combining FLaMe-v1.0 and machine learning techniques. Moreover, 30 % and 70 % of these CH₄ emissions are through diffusive and ebullitive pathways, respectively. Annually averaged CH₄ emission rates per unit lake area during 2010–2016 have a South-to-North decreasing gradient, resulting in a mean over the European domain as 7.39 g CH₄ m⁻² yr⁻¹. Our simulations reveal a strong seasonality (with ice-blocking effects accounted for) in European lake CH₄ emissions, with nearly ten times higher emissions during late summer than during winter. This pronounced seasonal variation highlights the importance of accounting for the sub-annual variability in CH₄ emissions to accurately constrain regional CH₄ budgets. In the future, FLaMe-v1.0 could be embedded into Earth System Models to investigate the feedback between climate warming and global lake CH₄ emissions.