Alfred Wegener Institute for Polar and Marine Research
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Holocene and contemporary marine dinoflagellate community patterns predict expansion of generalist dinoflagellate blooms in warming oceans
Get PDFExisting data and models suggest increasing prominence of dinoflagellates and their blooms in future warmer ocean but supporting long-term data are sparse. Here, we used 18S rRNA gene sequencing to investigate sedimentary ancient dinoflagellate communities in northern South China Sea and compared them with contemporary dinoflagellate data from global oceans (TARA Oceans data) and 40 years of dinoflagellate bloom records in China. We found a continuous warming (by ~4.3°C in mean annual sea surface temperature) from 12 to 4.3 kiloyears before present (kyr BP), which caused an initial increase in the relative abundance and diversity of dinoflagellates, followed by a decrease reaching the lowest value, probably due to thermal stress. However, dinoflagellates flourished again after 4.3 kyr BP, coinciding with a rapid increase in human activities. Further analyses indicated that warming and environmental changes during the Holocene favored dinoflagellate generalists over specialists. These generalists have also been abundant throughout contemporary low- and mid-latitude regions, whereas specialists were more abundant at higher latitudes. The predominant generalist genera Noctiluca, Gymnodinium, and Prorocentrum in core sediment corresponded to taxa responsible for most dinoflagellate blooms in the contemporary China Seas over the past 40 years. The success of generalists during warmer periods suggests that dinoflagellate blooms are likely to expand geographically rather than simply shift toward high latitudes under global warming. Moreover, the homogenization of dinoflagellate communities resulting from generalist expansion may significantly reduce the complexity of marine plankton interactions and compromise ecosystem services under global warming
Diversity of Amphidomataceae (Dinophyceae) in the Black Sea, including description of Amphidoma pontica sp. nov.
Get PDFSUMMARYThe dinoflagellate family Amphidomataceae includes the genera Azadinium and Amphidoma, several species of which are known producers of lipophilic toxins known as azaspiracids (AZAs). However, the diversity, abundance, and distribution of this important group of nanoplanktonic dinoflagellates in the Black Sea remain poorly understood. To address this knowledge gap, Amphidomataceae were specifically investigated during a PHYCOB research cruise in the western Black Sea in September 2021. The study employed live microscopy observations on board, electron microscopy of field‐collected samples, quantitative assessments of abundance and distribution in preserved samples, and the establishment of clonal strains. Amphidomataceae species were detected at all stations, with abundances ranging from 1.2 to 13.0 × 103 cells per liter. However, no AZAs were detected in any of the field samples. Light microscopy and subsequent SEM analyses revealed a high diversity of species. Field‐sample‐SEM‐documented records included Azadinium trinitatum, Az. spinosum, Az. luciferelloides, an undescribed Azadinium species, Amphidoma languida, and an undescribed species of Amphidoma. Additionally, two clonal strains were successfully established and are newly described here as Amphidoma pontica. This new species closely resembles Am. languida and Am. fulgens, but is distinguished by the absence of contact between the distalmost apical plate (6′) and the distalmost precingular plate (6″). Molecular phylogenetic analysis based on concatenated ribosomal markers supports its classification as a distinct species. Neither of the Am. pontica strains produced detectable levels of AZAs. This study significantly contributes to a foundational assessment of the species diversity, distribution, and potential toxicity of Amphidomataceae in the Black Sea.</jats:p
Moisture Source Controls on Water Isotopes in Antarctic Precipitation—Insights From Water Tracers in ECHAM6‐Wiso
Get PDFThe interpretation of water isotope records in Antarctic ice cores is crucial for our understanding of past climate changes. Here we use novel water tracers in an ECHAM6‐wiso simulation to investigate moisture source controls on deuterium excess in Antarctic precipitation, particularly the logarithmic variant . The simulation captures the amplitude of seasonal changes in observed and of precipitation. There are, however, some model biases that cannot be resolved through adjustments to kinetic fractionation parameters or the model resolution. These may reflect issues in the hydrological cycle representation or the representation of isotope processes. The simulated in Antarctic precipitation reliably reflects moisture source sea surface temperature (SST): shows a higher correlation than traditionally defined deuterium excess. Ocean surface relative humidity with respect to SST (RHsst) influences during evaporation, however, this influence weakens above the ocean surface. 79% of the variance in of annual precipitation at Dome C is due to changes in moisture source SST. is more sensitive to source SST in inland Antarctica than in coastal regions, making it a robust proxy for reconstructing past SST at the inland ice core sites. The explained variance of by source SST for daily precipitation at Dome C is lower at 28%, which increases to 59% after excluding very low precipitation days (0.02 mm). Finally, we find reversed relationships between source SST and in the vapor above the Southern Ocean, potentially driven by cold air outbreaks or precipitation processes
The Arctic Beaufort Gyre in CMIP6 Models: Present and Future
Get PDFThe Beaufort Gyre (BG) is an important feature of the Arctic Ocean. By accumulating or releasing freshwater, it influences ocean properties both within the Arctic and as far as the North Atlantic. Yet, its future remains uncertain: the gyre could strengthen as sea ice declines and allows increased wind stress on the ocean, or weaken along with the Beaufort High (BH) pressure system. Here, we provide a first evaluation of the BG in historical and climate‐change simulations from 27 available global climate models. We find that the vast majority of models overestimate the gyre area, strength, and northward extent. After discarding the models with too inaccurate a gyre and its drivers—namely, the sea ice cover and BH—we quantify changes in the BG under two emission scenarios: the intermediate SSP2‐4.5 and the high‐warming SSP5‐8.5. By the end of the 21st century, most models simulate a significant decline or even disappearance of the BG, especially under SSP5–8.5. We show that this decline is mainly driven by a simulated future weakening of the BH, whose influence on the BG variations is enhanced by the transition to a thin‐ice Arctic. The simulated gyre decline is associated with an expected decrease in freshwater storage, with reduced salinity contrasts between the gyre and both Arctic subsurface waters and freshwater outflow regions. While model biases and unresolved processes remain, such possible stratification changes could shift the Atlantic‐Arctic meridional overturning circulation northward
Stable iron isotope signals indicate a “pseudo-abiotic” process driving deep iron release in methanic sediments
Get PDFThe low δ56Fe values of dissolved iron liberated by microbial iron reduction are characteristic of many shallow subsurface sediments and – if not significantly changed within the oxic sediment layer – the related benthic Fe fluxes into the water column. Here, we decipher whether stable Fe isotope signatures in pore water and the respective solid-phase sediment samples are also useful for unraveling the processes driving Fe liberation in deeper methanic sediments. We investigated the fine-grained deposits of the Helgoland mud area, North Sea, where Fe reduction in the methanic subsurface sediments was previously suggested to be coupled to methanogenic fermentation of organic matter and anaerobic methane oxidation. In the evaluated subsurface sediments, a combination of iron isotope geochemistry with reactive transport modeling for the deeper methanic sediments hints at a combination of processes affecting the stable isotope composition of dissolved iron. However, the dominant process releasing Fe at depth does not seem to lead to notable iron isotope fraction. Under the assumption that iron reducing microbes generally prefer isotopically light iron, the deep Fe reduction in this setting appears to be “pseudo-abiotic”: if fermentation is the main reason for Fe release at depth, the fermenting bacteria transfer electrons directly or indirectly to Fe(III), but our data do not indicate notable related isotopic fractionation. Our findings strongly contribute to the debate on the pathway for deep Fe2+ release by showing that the main underlying process is mechanistically different to the microbial Fe reduction dominating in the shallow sediments and encourages future studies to focus on the fermentative degradation of organic matter as a source of dissolved iron in methanic sediments
Exploring Site‐Specific Carbon Dioxide Removal Options With Storage or Sequestration in the Marine Environment – The 10 Mt CO2 yr−1 Removal Challenge for Germany
Get PDFAbstractMarine carbon dioxide removal (mCDR) and geological carbon storage in the marine environment (mCS) promise to help mitigate global climate change alongside drastic emission reductions. However, the implementable potential of mCDR and mCS depends, apart from technology readiness, also on site‐specific conditions. In this work, we explore different options for mCDR and mCS, using the German context as a case study. We challenge each option to remove 10 Mt CO2 yr−1, accounting for 8%–22% of projected hard‐to‐abate and residual emissions of Germany in 2045. We focus on the environmental, resource, and infrastructure requirements of individual mCDR and mCS options at specific sites, within the German jurisdiction when possible. This serves as an entry point to discuss main uncertainty factors and research needs beyond technology readiness, and, where possible, cost estimates, expected environmental effects, and monitoring approaches. In total, we describe 10 mCDR and mCS options; four aim at enhancing the chemical carbon uptake of the ocean through alkalinity enhancement, four aim at enhancing blue carbon ecosystems' sink capacity, and two employ geological off‐shore storage. Our results indicate that five out of 10 options would potentially be implementable within German jurisdiction, and three of them could potentially meet the challenge. Our exercise serves as an example on how the creation of more tangible and site‐specific CDR options can provide a basis for the assessment of socio‐economic, ethical, political, and legal aspects for such implementations. The approach presented here can easily be applied to other regional or national CDR capacity considerations.</jats:p
Snow accumulation patterns from 2023 Airborne Laser Scanning data in Trail Valley Creek, Western Canadian Arctic
Get PDFTrail Valley Creek, located in the Northwest Territories (NWT), approximately 45km north of Inuvik, Canada, marks the northern boundary of the tundra-taiga transition zone. This region, underlain by continuous permafrost, is experiencing rapid warming and vegetation changes, including shrub expansion. These shifts may lead to increased snow depths, which could in turn affect subsurface temperatures and potentially impact permafrost stability.
Topography and vegetation are key drivers of spatial variation in snow depth, with wind redistribution leading to snow accumulation in topographic lows, leeward slopes, and densely vegetated areas. However, landscape complexity also affects snow measurement accuracy, adding variability to depth estimates. Understanding these relationships is essential but often limited by the scarcity of high-resolution, large-scale data that can capture landscape heterogeneity. In this study, I investigated snow depth patterns across different topographic features (landforms, slopes, and aspects) and vegetation types (height ranges and cover classes) within an area of 127 km². To achieve this, I used LiDAR (Light Detection and Ranging) data collected over the snow-covered surface (April 2, 2023) and the snow-free terrain (July 10, 2023) of Trail Valley Creek to create a 1-meter resolution snow depth map. I then compared the LiDAR data with two reference sources: 9569 coordinate reference points along the Inuvik-Tuktoyaktuk Highway (ITH), which intersects the area and is maintained at minimal snow depth throughout winter, and snow depth measurements from 4615 field survey points. Field surveys recorded deeper snow depths than LiDAR estimates, with an overall bias of 0.18 m. The discrepancy between LiDAR and field measurements varied significantly, with the largest biases over trees (0.30 m) and on steep east-facing slopes (0.37 m). However, LiDAR measurements closely aligned with the ITH reference points, showing a median depth deviation of just 0.017 m. The analysis showed that, with regard to topography, snow depth was highest over footslopes and valleys, with median depths of 0.38m and 0.44 m, respectively, and lowest on ridges (0.20 m). Snow depth also increased with slope steepness and was consistently greater on east-facing slopes, in response to predominant winds from the west and northwest. In terms of vegetation, snow depth increased with vegetation height, with medians ranging from 0.29m over vegetation shorter than 0.50m to 0.54m in areas where vegetation height exceeded 1.5 m. These findings align with results by vegetation class, where single and riparian shrubs exhibited the highest accumulations, with snow depth medians reaching 0.49 m
Warmer Sphagnum moss, less soil carbon loss: Anaerobic respiration and temperature response along a boreal forest-peatland ecotone
Get PDFClimate warming is predicted to rapidly change the local environmental conditions in peatland systems at high latitudes. This study explored soil respiration rates with microbial community compositions along a transect from well-drained upland forest to a Sphagnum moss peatland in boreal Finland. We found that soils from the upland forest and intermediate habitats incubated at 20°C generally produced more anaerobic CO2 than the cooler incubation temperature groups (0, 4°C) and that the initial soil carbon content was the strongest geochemical and physical parameter correlated with cumulative CO2 produced over the course of this 140 day incubation. Interestingly, bog samples were the exception to this, and were more productive at cooler temperatures. This implies that the controls on anaerobic CO2 production in bogs differ from those in the soils of the surrounding habitats. This finding, along other parameters, such as soil carbon content, could give greater insights into potential carbon production in high-latitude soils
Addressing grand ecological challenges in aquatic ecosystems: how can mesocosms be used to advance solutions?
Get PDFRapid and drastic anthropogenic impacts are affecting global biogeochemical processes and driving biodiversity loss across Earth's ecosystems. In aquatic ecosystems, species distributions are shifting, abundances of many species have declined dramatically, and many are threatened with extinction. In addition to loss of diversity, the ecosystem functions, processes and services on which humans depend are also being heavily impacted. Addressing these challenges not only requires direct action to mitigate environmental impacts but also innovative approaches to identify, quantify and treat their effects in the environment. Mesocosms are valuable tools for achieving these goals as they provide controlled environments for evaluating effects of stressors and testing novel mitigation measures at multiple levels of biological organisation. Here, we summarise discussions from a survey of marine and freshwater researchers who use mesocosm systems to synthesise their opportunities and limitations for advancing solutions to grand ecological challenges in aquatic ecosystems. While most research utilising mesocosm systems in aquatic ecology has focused on quantifying the effects of environmental threats, there is a largely unexplored potential for using them to test solutions. To overcome spatio-temporal constraints, there are opportunities to scale up the size and time-scales of mesocosm studies, or alternatively, test the outcomes of habitat-scale restoration at a smaller scale. Enhancing connectivity in future studies can help to overcome the limitation of isolation and test an important aspect of ecological recovery. Conducting ‘metacosm' studies: coordinated, distributed mesocosm experiments spanning wide climatic and environmental gradients and utilising more regression-based experimental designs can help to tackle the challenge of context dependent results. Finally, collaboration of theoretical, experimental and applied ecologists and biogeochemists with environmental engineers and technological developers will be necessary to develop and test the tools required to advance solutions to the impacts of human activities on Earth's vulnerable aquatic ecosystems
Surface processes and drivers of the snow water stable isotopic composition at Dome C, East Antarctica – a multi-dataset and modelling analysis
Get PDFWater 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