Alfred Wegener Institute for Polar and Marine Research
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Quantifying mercury (Hg) release from coastal erosion along the Yukon coast, Canada
Full text linkPermafrost 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
Age–depth distribution in western Dronning Maud Land, East Antarctica, and Antarctic-wide comparisons of internal reflection horizons
Full text linkRadio-echo sounding provides the opportunity to study the internal architecture of ice sheets through imaging stratified englacial reflections, known as internal reflection horizons (IRHs). They represent consistent time horizons formed at the former ice-sheet surface and buried over time, thus reflecting the ice sheet's age–depth architecture. Their analysis allows crucial insights into past and present glaciological conditions, e.g. bed topography, surface and basal mass balance, and physical properties and ice dynamics. This study presents a comprehensive data set of IRHs and insight into the age–depth distribution in western Dronning Maud Land (DML), East Antarctica, spanning the Holocene to the Last Glacial Period (4.8–91.0 ka). Using data from various radar systems deployed by the Alfred Wegener Institute between 1996 and 2023, we traced and dated nine IRHs over an area of 450 000 km2. A precise age could be assigned to the IRHs by two-way travel time to depth conversion and employing radar forward modelling based on conductivity peaks of the EPICA DML ice core. Six IRHs correlate with the timing of past volcanic eruptions, and our findings suggest that most IRHs correspond to IRHs of similar age in other regions of East and West Antarctica, thus likely originating from the same physical reflectors at depth, although some could not be physically connected. This work enhances understanding of the englacial architecture and relationships with snow accumulation and ice-dynamic processes of this sector of the Antarctic ice sheet and provides boundary conditions for numerical ice flow models and paleoclimatic studies
Nansen and Amundsen basins: Gradients of physico-chemical properties and biota composition with implications for future resource management of the central Arctic Ocean
Full text linkThe projected transition of the central Arctic Ocean (CAO) into a warmer, seasonally ice-free ocean requires more knowledge of this environment to predict changes in the structure and dynamics of its ecosystems. We aimed to compare the state and underlying processes of Nansen Basin and Amundsen Basin ecosystems observed in August–September 2021 and assess impacts of Atlantic Water inflow and fresher Transpolar Drift waters, respectively, on these ecosystems. The basins differed in features of sea ice, hydrography, and chemical and biological compositions. The near-slope open water in western Nansen Basin showed a clear fingerprint of warm, saline Atlantic Water, with larger vertical turbulent fluxes facilitating nutrient transport across the pycnocline and supporting larger standing stocks of bacteria, protists, and zooplankton. Pelagic primary production and microbial and faunal stocks decreased northward and into Amundsen Basin, likely due to lower nutrient concentrations, stronger stratification, and reduced light through the more continuous and thicker ice and snow cover in Amundsen Basin, possibly also impacted by seasonally declining light levels. Transpolar Drift signals included lower salinity, stronger stratification, and higher silicate concentrations in Amundsen Basin surface waters. Similarities to earlier observations included the increase in small-sized algae from Nansen Basin into Amundsen Basin and overall low faunal abundances in the CAO, suggesting that overarching patterns remained unchanged over past decades. Examples of species range extensions and notable taxon absences relative to earlier studies, however, could be due to borealization and changes in sea-ice conditions, respectively. Higher density ecosystem sampling and consistent time series are recommended to confirm such conclusions. The distinct basin differences call for a regional approach to future management of the CAO. We especially caution against using the area of strong Atlantic Water inflow in southern Nansen Basin as representative of the entire basin, let alone Amundsen Basin or the CAO.</jats:p
Improved Method for the Retrieval of Extinction Coefficient Profile by Regularization Techniques
Full text linkIn this work, we revise the retrieval of extinction coefficient profiles from Raman
Lidar. This is an ill-posed problem, and we show that methods like Levenberg–Marquardt
or Tikhonov–Phillips can be applied. We test these methods for a synthetic Lidar profile
(known solution) with different noise realizations. Further, we apply these methods to
three different cases of data from the Arctic: under daylight (Arctic Haze), under daylight
with a high and vertically extended aerosol layer, and at nighttime with high extinction.
We show that our methods work and allow a trustful derivation of extinction up to clearly
higher altitudes (at about half a signal-to-noise ratio) compared with the traditional, non-
regularized Ansmann solution. However, these new methods are not trivial and require
a choice of parameters, which depend on the noise of the data. As the Lidar signal
quality quickly decreases with range, a separation of the profile into several sub-intervals
seems beneficial
Silicic acid leakage during Last Glacial Maximum and glacial termination
Full text linkChanges in the marine biological carbon pump during glacial times have been supposed to contribute to the glacial CO2 drawdown. One particular hypothesis that received attention during last two decades is the Silicic Acid Leakage Hypothesis (SALH), which proposed the Si leakage during glacial times from the Southern Ocean (SO) was transported towards lower latitudes and then contributed to enhanced biological productivity there and thus to global cooling by lowering atmospheric pCO2.Thanks to the flexible stoichiometry (C:N:Si:Chl ratios) implemented in the biogeochemistry model REcoM (used with AWIESM2), we are able to study Si leakage based on changes in diatom physiology and its effect on nutrient supply to low-latitude surface waters. Our simulations show a significant increase of Si:N ratios in surface seawater in the SO and southern-sourced mode waters at Last Glacial Maximum (LGM) when compared to pre-industrial, confirming the first part of SALH. However, due to stronger stratification and weaker upwelling during LGM, these Si-enriched waters cannot be transported to the low-latitude surface to induce higher diatom growth, arguing against the second part of SALH but in agreement with reconstructions of marine opal accumulation rates. Instead, the simulation of the beginning of the glacial termination reveals that Si leakage during deglaciation drives a low-latitude productivity increase, supporting the more recent Silicic Acid Ventilation Hypothesis (SAVH). The effect of increased biological carbon uptake is more than compensated by intense CO2 outgassing through stronger ventilation, resulting in a rapid CO2 rise during deglaciation.</jats:p
Diatom shifts and limnological changes in a Siberian boreal lake: a multiproxy perspective on climate warming and anthropogenic air pollution
Full text linkLake ecosystems are affected globally by climate warming and anthropogenic influences. However, impacts on boreal lake ecosystems in eastern Siberia remain underexplored. Our aim is to determine if shifts in diatom assemblages in a remote lake in eastern Siberia are related to climate warming, similar to observations in temperate regions, while also exploring how the ecosystem might be influenced by hydroclimate and human-induced air pollution. We analysed continuous sediment samples from a 210Pb–137Cs-dated short core from Lake Khamra (59.99° N, 112.98° E), covering ∼220 years (ca. 1790–2015 CE), following a multiproxy approach on the same sample material to provide a comprehensive record of environmental changes. Biogeochemical proxies include total organic carbon (TOC) and total nitrogen (TN) concentrations and corresponding stable isotopes of bulk sediment samples (δ13C, δ15N), as well as diatom silicon isotopes (δ30Sidiatom), alongside light microscope diatom species analysis. The diatom assemblage at Lake Khamra is dominated by few planktonic species, primarily Aulacoseira subarctica and Aulacoseira ambigua. At ca. 1970 CE, we observe a major shift in diatom assemblages, characterised by a marked increase in the planktonic species Discostella stelligera and a decrease in both Aulacoseira taxa. We attribute these changes to recent global warming, which is likely associated with earlier ice-out and enhanced summer thermal stratification, consistent with similar observations in temperate lake ecosystems. A rapid increase in chrysophyte scales (Mallomonas) from the 1990s onward further supports an increasing thermal stratification of the lake driven by rising temperatures. Biogeochemical proxies indicate substantial limnological changes around 1950 CE, preceding the major shift in diatom communities, likely driven by hydroclimatic variability. Increased precipitation and weathering are further discussed in order to explain changing silica sources leading to decreasing δ30Sidiatom after ∼1970 CE. Nevertheless, the interpretation of δ30Sidiatom in lacustrine systems is complex, likely influenced by both in-lake biogeochemical processes and catchment dynamics. Indications of anthropogenic influences on Lake Khamra include a δ13C depletion, likely linked to fossil fuel combustion and emissions, coinciding with industrial growth in Asia and Russia. Nonetheless, we find no evidence for atmospheric nitrogen deposition. We conclude that the Lake Khamra ecosystem is severely affected by climate warming and shows indications of human influence. This emphasises the urgent need for comprehensive research to mitigate these impacts on remote lake ecosystems in order to secure natural water resources
Coupling framework (1.0) for the Úa (2023b) ice sheet model and the FESOM-1.4 z-coordinate ocean model in an Antarctic domain
Full text linkThe rate at which the Antarctic ice sheet loses mass is to a large degree controlled by ice–ocean interactions underneath small ice shelves, with the most sensitive regions concentrated in even smaller areas near grounding lines and local pinning points. Sufficient horizontal resolution is key to resolving critical ice–ocean processes in these regions but difficult to afford in large-scale models used to predict the coupled response of the entire Antarctic ice sheet and the global ocean to climate change. In this study we describe the implementation of a framework that couples the ice sheet flow model Úa with the Finite Element Sea Ice Ocean Model (FESOM-1.4) in a configuration using depth-dependent vertical coordinates. The novelty of this approach is the use of horizontally unstructured grids in both model components, allowing us to resolve critical processes directly, while keeping computational demands within the range of feasibility. We use the Marine Ice Sheet Ocean Model Intercomparison Project (MISOMIP) framework to verify that ice retreat and readvance are reliably simulated, and inaccuracies in mass, heat and salt conservation are small compared to the forcing signal. Further, we demonstrate the capabilities of our approach for a global ocean–Antarctic ice sheet domain. In a 39-year hindcast simulation (1979–2018) we resolve retreat behaviour of Pine Island Glacier, a known challenge for coarser-resolution models. We conclude that Úa–FESOM is well suited to improve predictions of the Antarctic ice sheet evolution over centennial timescales
Origin and intra-annual variability of vertical microplastic fluxes in Fram Strait, Arctic Ocean
Full text linkMicroplastic (MP) pollution has reached the remotest areas of the globe, including the polar regions. In the Arctic Ocean, MPs have been detected in ice, snow, water, sediment, and biota, but their temporal dynamics remain poorly understood. To better understand the transport pathways and drivers of MP pollution in this fragile environment, this study aims to assess MPs (≥ 11 μm) in sediment trap samples collected at the HAUSGARTEN observatory (Fram Strait) from September 2019 to July 2021. MP fluxes determined by μ-Fourier transform infrared (FTIR) imaging ranged from 0 to 2.9 MP m−2 d−1, peaking in April 2020 and April 2021, with all detected MPs being <300 μm in size. There was no strong correlation between MPs and any of the recorded biogeochemical and physical variables, as each MP flux event was associated with different variables such as biogenic matter, sea ice concentration, or origin. By providing time series data over 21 months, this study provides a baseline for future MP flux assessments in Fram Strait, Arctic
