Quantifying mercury (Hg) release from coastal erosion along the Yukon coast, Canada

Permafrost stores large amounts of mercury (Hg), locking this toxic element in frozen soils across the Arctic. Mercury and its organic form methylmercury, in particular, is a neurotoxin which accumulates along the food chain. With increasing rates of coastal erosion driven by rising air and ground temperatures, Hg is being mobilized and released into the Arctic Ocean. This process does not only threaten local ecosystems but has broader implications, as Hg might be transported over long distances or taken up by marine organisms, posing risks to both wildlife and human health. To better understand such risks, we aim to quantify the amount of Hg that is stored in permafrost and released by coastal erosion along the Yukon Coast, Canada. Samples were taken from various landscape features including permafrost cliffs, active layer, and marine sediments along the Yukon Coast and on Herschel Island-Qikiqtaruk. We analyzed over 70 samples for elemental mercury, organic carbon, nitrogen, and grain-size distribution, and supplemented these results with existing data from previous field campaigns and the literature to create a regional database. Based on these data we will first estimate Hg stocks in the upper permafrost for the Yukon Coast. Combined with coastal erosion rates we will then estimate annual Hg fluxes into the ocean for this region. Together with Hg concentrations in marine sediments our findings will provide a clearer picture of the Hg stocks, fluxes, and its fate along the Yukon Coast. These data are crucial for decision makers and might help to assess Hg exposure to Arctic wildlife and human populations, whose diet largely relies on marine biological resources

On the path to cosmopolitanism: the continuing geographic expansion of Caprella mutica (Crustacea, Amphipoda)

Human activities have been transporting caprellid amphipods (or “skeleton shrimps”) across the oceans for many decades. As a result, some caprellid amphipods now are among the most widespread non-indigenous species in many different coastal regions of the world. The global spread of these species is still ongoing in some cases, such as that of the successful invader Caprella mutica Schurin, 1935. Here, we report on the arrival of C. mutica in South America and modelled its environmental niche based on its current global distribution in order to evaluate future expansion risks. The species distribution model confirmed high occupancy probabilities for already invaded areas of Europe and North America with generally lower probabilities in the southern hemisphere and mean sea surface temperature as best predictor. Further, the model suggested that our discovery of C. mutica in northern Chile was made in a region that is less favorable for this species, while occupancy probabilities increased further south. Given the invasion history of C. mutica in other marine regions of the world and the more favorable oceanographic conditions, a further spread of this invader southwards along the South American Pacific coast seems very likely

Surface processes and drivers of the snow water stable isotopic composition at Dome C, East Antarctica – a multi-dataset and modelling analysis

Water stable isotope records in polar ice cores have been largely used to reconstruct past local temperatures and other climatic information such as evaporative source region conditions of the precipitation reaching the ice core sites. However, recent studies have identified post-depositional processes taking place at the ice sheet’s surface, modifying the original precipitation signal and challenging the traditional interpretation of ice core isotopic records. In this study, we use a combination of existing and new datasets of precipitation, snow surface, and subsurface isotopic compositions (δ18O and deuterium excess (d-excess)); meteorological parameters; ERA5 reanalyses; outputs from the isotope-enabled climate model ECHAM6-wiso; and a simple modelling approach to investigate the transfer function of water stable isotopes from precipitation to the snow surface and subsurface at Dome C in East Antarctica. We first show that water vapour fluxes at the surface of the ice sheet result in a net annual sublimation of snow, from 3.1 to 3.7 mm w.e. yr−1 (water equivalent) between 2018 and 2020, corresponding to 12 % to 15 % of the annual surface mass balance. We find that the precipitation isotopic signal cannot fully explain the mean, nor the variability in the isotopic composition observed in the snow, from annual to intra-monthly timescales. We observe that the mean effect of post-depositional processes over the study period enriches the snow surface in δ18O by 3.0 ‰ to 3.3 ‰ and lowers the snow surface d-excess by 3.4 ‰ to 3.5 ‰ compared to the incoming precipitation isotopic signal. We also show that the mean isotopic composition of the snow subsurface is not statistically different from that of the snow surface, indicating the preservation of the mean isotopic composition of the snow surface in the top centimetres of the snowpack. This study confirms previous findings about the complex interpretation of the water stable isotopic signal in the snow and provides the first quantitative estimation of the impact of post-depositional processes on the snow isotopic composition at Dome C, a crucial step for the accurate interpretation of isotopic records from ice cores

Precession Controls on Climate and Water Isotope Signals in Northern Africa

Precessional forcing is a key driver of quaternary climate change. Based on 24 experiments covering a full precession cycle, this study explores spatio‐temporal variations of both climate and isotope signals in Northern Africa. We find a synchronous phasing of precipitation variations with solar radiation levels and an asynchronous timing of surface air temperature changes across different sub‐regions of Northern Africa. Based on daily precipitation, our results reveal earlier onset and withdrawal, as well as a shorter duration of the West Africa summer monsoon (WASM) at minimum precession compared to maximum precession. The onset of the WASM is controlled by the intensity of the Sahara Heat Low, while the monsoon termination is linked to subtropical solar radiation and interhemispheric thermo contrast. Using a novel scale‐flux tracing technique, we find that, precipitation during minimum precession is more influenced by evaporation from warmer and more humid regions compared to maximum precession. Additionally, certain inland areas of Northern Africa exhibit positive temporal isotope‐precipitation gradients, violating the “amount effect.” This phenomenon mainly occurs during precession phases associated with Green Sahara periods. The isotope composition changes in such places primarily reflect changes in upstream rainfall quantity, rather than changes in local precipitation as is inferred from present day analogs. Conversely, the “amount effect” remains applicable during dry periods in Africa when the Sahara desert is present. This suggests that isotope‐based reconstruction of past precipitation variations during Green Sahara periods over Northern Africa needs to be taken with caution

Long-term changes of wildfire regimes in eastern Siberia: an evaluation based on lake sediment indicators and individual-based modeling

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Justification for high-ascent attainment for balloon radiosonde soundings at GRUAN and other sites

We assess and illustrate the benefits of high altitude attainment of balloon-borne radiosonde soundings, up to and beyond 10 hPa level compared to, for example, 30 hPa, at operational stations and at sites of the Global Climate Observing System (GCOS) Reference Upper Air Network (GRUAN). We first discuss technical challenges and the possible solutions for balloon soundings at these higher altitudes. Then, we assess the role of high-ascent radiosonde measurements in climate monitoring and various process studies, contributions to satellite calibration and validation, and impacts on numerical weather prediction systems. The analysis herein shows that the extra costs and technical challenges involved in consistent attainment of high ascents are more than outweighed by the benefits for a broad variety of real-time and delayed-mode applications. Consistent attainment of high ascents should therefore be pursued across the GRUAN network and the broader observational network

Strengthening policy action to tackle social acceptability issues in European aquaculture

Despite the rapid development of aquaculture worldwide, production has stagnated in Europe and North America, notwithstanding the public policies that support the sector. This stagnation may stem from the insufficient integration of social dimensions into aquaculture governance, often characterized by top-down policies and technology-driven approaches. While environmental, economic and social factors significantly influence the social acceptability of aquaculture, environmental impacts, such as habitat degradation and the spread of disease, have historically dominated regulatory frameworks. Today, low social acceptability appears to be the major obstacle to the sector’s growth, highlighting shortcomings in terms of stakeholder engagement, transparency and fairness in the distribution of the benefits generated by the sector. This paper reflects the collective insights from the ICES Working Group on Social and Economic Dimensions of Aquaculture, emphasizing that challenges to social acceptability of aquaculture are widespread but context-dependent and remain insufficiently addressed in public policies related to aquaculture development. This paper recommends broadening governance beyond environmental concerns to include social and economic dimensions from the outset, strengthening public participation in decision-making processes and adopting holistic, socially informed marine spatial planning. In addition, it highlights the importance of recognizing the role of informal governance mechanisms and the production of meaningful social data as essential aspects to foster community acceptance and the sustainable development of aquaculture. Adapting aquaculture policies to local contexts through inclusive and adaptive governance is therefore essential to the sustainable growth of the sector

Closing the Plio-Pleistocene 13C cycle in the 405 kyr periodicity by isotopic signatures of geological sources

The 13C cycle of the Plio-Pleistocene, as recorded in δ13C of benthic foraminifera, has power in periodicities related to the long eccentricity cycle of 405 kyr that is missing in corresponding climate records (e.g. δ18O). Using a global carbon cycle model, I show in an inverse approach that the long eccentricity in δ13C might have been caused by variations in the isotopic signature of geological sources, namely of the weathered carbonate rock (δ13Crock) or of volcanically released CO2 (δ13Cv). This closure of the 13C cycle in these periodicities also explains the offset in atmospheric δ13CO2 seen between the Penultimate Glacial Maximum (PGM) and the Last Glacial Maximum (LGM). The necessary isotopic signatures in δ13Crock or δ13Cv, which align my simulations with reconstructions of the 13C cycle on orbital timescales, have the most power in the obliquity band (41 kyr), suggesting that land ice dynamics are the ultimate cause for these suggested variations. Since the Asian monsoon as reconstructed from speleothems also has an obliquity-related component and since precipitation (or runoff) is one main driver for local weathering rates, it is possible that these proposed changes in weathering are indeed, at least partly, connected to the monsoon as previously suggested. Alternatively, the suggested impact of land ice or sea level on volcanic activity might also be influential for the 13C cycle. This indirect influence of ice sheets on the long eccentricity cycle in δ13C implies that these processes might not have been responsible for the 405 kyr periodicity found in times of the pre-Pliocene parts of the Cenozoic that have been largely ice-free in the Northern Hemisphere