Alfred Wegener Institute for Polar and Marine Research
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Future Arctic Climate Change in CMIP6 Strikingly Intensified by NEMO‐Family Climate Models
Get PDFClimate change in the Arctic has substantial impacts on human life and ecosystems both within and beyond the Arctic. Our analysis of CMIP6 simulations shows that some climate models project much larger Arctic climate change than other models, including changes in sea ice, ocean mixed layer, air-sea heat flux, and surface air temperature in wintertime. In particular, dramatic enhancement of Arctic Ocean convection down to a few hundred meters is projected in these models but not in others. Interestingly, these models employ the same ocean model family (NEMO) while the choice of models for the atmosphere and sea ice varies. The magnitude of Arctic climate change is proportional to the strength of the increase in poleward ocean heat transport, which is considerably higher in this group of models. Establishing the plausibility of this group of models with high Arctic climate sensitivity to anthropogenic forcing is imperative given the implied ramifications
Distribution and origin of organic matter in marine surface sediments on the Canadian Beaufort Shelf
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Aerosol and dynamical contributions to cloud droplet formation in Arctic low-level clouds
Get PDFThe Arctic is one of the most rapidly warming regions of the globe. Low-level clouds and fog modify the energy transfer from and to space and play a key role in the observed strong Arctic surface warming, a phenomenon commonly termed "Arctic amplification". The response of low-level clouds to changing aerosol characteristics throughout the year is therefore an important driver of Arctic change that currently lacks sufficient constraints. As such, during the NASCENT campaign (Ny-Ålesund AeroSol Cloud ExperimeNT) extending over a full year from October 2019 to October 2020, microphysical properties of aerosols and clouds were studied at the Zeppelin station (475 m a.s.l.), Ny-Ålesund, Svalbard, Norway. Particle number size distributions obtained from differential mobility particle sizers as well as chemical composition derived from filter samples and an aerosol chemical speciation monitor were analyzed together with meteorological data, in particular vertical wind velocity. The results were used as input to a state-of-the-art cloud droplet formation parameterization to investigate the particle sizes that can activate to cloud droplets, the levels of supersaturation that can develop, the droplet susceptibility to aerosol and the role of vertical velocity. We evaluate the parameterization and the droplet numbers calculated through a droplet closure with in-cloud in situ measurements taken during nine flights over 4 d. A remarkable finding is that, for the clouds sampled in situ, closure is successful in mixed-phase cloud conditions regardless of the cloud glaciation fraction. This suggests that ice production through ice-ice collisions or droplet shattering may have explained the high ice fraction, as opposed to rime splintering that would have significantly reduced the cloud droplet number below levels predicted by warm-cloud activation theory. We also show that pristine-like conditions during fall led to clouds that formed over an aerosol-limited regime, with high levels of supersaturation (generally around 1 %, although highly variable) that activate particles smaller than 20 nm in diameter. Clouds formed in the same regime in late spring and summer, but aerosol activation diameters were much larger due to lower cloud supersaturations (ca. 0.5 %) that develop because of higher aerosol concentrations and lower vertical velocities. The contribution of new particle formation to cloud formation was therefore strongly limited, at least until these newly formed particles started growing. However, clouds forming during the Arctic haze period (winter and early spring) can be limited by updraft velocity, although rarely, with supersaturation levels dropping below 0.1 % and generally activating larger particles (20 to 200 nm), including pollution transported over a long range. The relationship between updraft velocity and the limiting cloud droplet number agrees with previous observations of various types of clouds worldwide, which supports the universality of this relationship
Climate-controlled submarine landslides on the Antarctic continental margin
Get PDFAntarctica’s continental margins pose an unknown submarine landslide-generated tsunami risk to Southern Hemisphere populations and infrastructure. Understanding the factors driving slope failure is essential to assessing future geohazards. Here, we present a multidisciplinary study of a major submarine landslide complex along the eastern Ross Sea continental slope (Antarctica) that identifies preconditioning factors and failure mechanisms. Weak layers, identified beneath three submarine landslides, consist of distinct packages of interbedded Miocene- to Pliocene-age diatom oozes and glaciomarine diamicts. The observed lithological differences, which arise from glacial to interglacial variations in biological productivity, ice proximity, and ocean circulation, caused changes in sediment deposition that inherently preconditioned slope failure. These recurrent Antarctic submarine landslides were likely triggered by seismicity associated with glacioisostatic readjustment, leading to failure within the preconditioned weak layers. Ongoing climate warming and ice retreat may increase regional glacioisostatic seismicity, triggering Antarctic submarine landslides
Landforms and degradation pattern of the Batagay thaw slump, Northeastern Siberia
Get PDFThaw slumps are clear indicators of rapid permafrost degradation. They form preferentially in near-surface ice-rich permafrost of northern high latitudes after initial thermal disturbance by the subsequent interplay of thermal (thawing of frozen deposits and melting of ice) and mechanical (slumping and erosion) processes. The largest known thaw slump on Earth – the Batagay megaslump – has been identified in sloping terrain on the Yana Upland in northern Yakutia. Its initiation began in the 1980s, with a current area of >0.8 km2. It continues to grow and has headwall retreat rates of up to 15 m per year. While various satellite remote sensing studies of the Batagay thaw slump have been undertaken, on-site studies characterizing internal landforms, terrain changes, and geomorphic processes have not yet been conducted. To fill this knowledge gap and to enhance our understanding of the dynamics of very large thaw slumps, our study employs on-site observations and detailed permafrost sampling combined with unoccupied aerial vehicle data from 2019. The latter were used to generate an orthomosaic, a digital surface model, hypsometric slope profiles and a map of relief types in the thaw slump. Within the Batagay thaw slump, the dynamic relationship between headwall morphology and slump floor is largely determined by the cryolithological structure of the permafrost horizons exposed across the headwall rising up to 55 m above the slump floor. Factors include the thickness and overall high volumetric ground-ice content (up to 87 %) of the cryostratigraphic horizons. Furthermore, the diurnal and seasonal insolation exposure of the headwall perimeter superimposes both thermal denudation activity and meltwater transport of eroded material. Thus, recent degradation patterns are linked to permafrost properties. Therefore, the Batagay thaw slump is not only a window into Earth's past as it reveals ancient permafrost, but its modern dynamics highlight that ongoing rapid permafrost thaw under present Arctic warming is directly influenced by its Quaternary geological and permafrost history
Does Large Herbivore Activity influence Mercury levels in Arctic Soils?
Get PDFMercury (Hg), a neurotoxic pollutant of global significance, is stored in high amounts in Arctic grounds, while its deposition in the Arctic further increases. With climate change inducing accelerated permafrost thaw as well as shortened freezing seasons in seasonal frozen ground, this could lead to the rerelease of Hg into the environment. For this reason, this study addressed the question of whether differences in activity by large herbivores might correlate with differences in soil mercury content in Arctic ground, due to the ground-cooling effects attributed to the animals. Therefore, soil cores from north-eastern Siberia (permafrost soil) and northern Finland (seasonally frozen soil) from sites with different grazing intensities were analyzed and compared for their mercury concentration. Additionally, depth trends of the cores regarding their mercury content, as well as possible correlations with other variables (total organic carbon, absolute water content and mean grain size) were examined. For a merged data set, grazing intensity did not show a significant correlation with mercury content in the soil, while a decrease with depth was detectable for most cores, which was attributed to decreasing surface influence and the associated input of mercury through the atmosphere, vegetation, animal dung and flooding. Total organic carbon showed the most relevant and highest correlation on the mercury content, due to the adsorbing property of organic matter. A separate consideration of the permafrost ground in Siberia and the seasonally frozen ground in Finland showed clear differences in regard to the influence of herbivore activity. While the animals did not show an effect on the concentration of mercury in seasonally frozen ground, the Siberian permafrost sites showed a clear variation in their mercury concentration between grazed and ungrazed sites. In contrast, a difference between sites with existing grazing but of varying intensity was less pronounced. A cause of this phenomenon was presumed in insufficiently diverse animal density, insufficient sample size, prevailing vegetation, as well as occasional flooding. Nevertheless, the samples from Siberia showed a positive correlation between grazing intensity and mercury, indicating that with higher herbivore activity mercury levels increase and suggesting a more effective fixation of the pollutant in permafrost soil
Feasibility of ice sheet conservation using seabed anchored curtains
Get PDFSea level rise is expected to be rapid and extremely damaging to coastal communities and infrastructure, with unavoidable losses and coastal protection costs in the tens of billions per year. Retreat of the Thwaites and Pine Island Glaciers is likely already in an unstable regime as their oceanic fronts are ablated by deep intruding layers of relatively warm seawater. Warm water can be blocked from reaching the grounding line by thin flexible buoyant curtains anchored to the seabed. The consequent reduction in ice shelf melting could result in increased ice sheet buttressing as the shelf makes contact with seabed highs. Flexible curtains are less costly than solid artificial barriers, more robust against iceberg collisions, and easier to repair or remove in the event of unforeseen side effects. We illustrate the technical viability of this approach by considering curtain design concepts that should withstand oceanographic forces, and feasible methods of installation. Suitable materials are commonly available. Installation of a seabed curtain in temperate ocean waters would be entirely within the capabilities of existing offshore and deep ocean construction techniques. Installing in polar waters presents severe challenges from icebergs, harsh weather, and brief working seasons, which can however, be overcome with present-day technology. An 80 km long curtain installed in 600 m deep waters on alluvial sediments could help stabilize Pine Island and Thwaites glaciers over the next few centuries at much lower cost (1-2 billion/yr maintenance) than the global coastline protection (∼$40 billion/yr) needed due to their collapse
Limited diversity of epibiont bdelloid rotifers and no pattern of codiversification with the highly diverse endemic amphipods of a coastal zone of Lake Baikal
Get PDFAn extreme radiation of hundreds of species of different groups of animals occurred in Lake Baikal, Siberia, Russia; among them, amphipods represent one of the most remarkable groups of invertebrates with about 350 endemic species. Amphipods host associated epibiont rotifers, and the aim of the study is to explore the possibility that bdelloid rotifers living as epibionts on amphipods in Lake Baikal coevolved with their hosts and diversified with species-specific host–epibiont associations. We sampled 148 individual amphipods belonging to 16 species and isolated all epibiont bdelloids from them, discovering that only one bdelloid species, Embata parasitica, lives associated with at least six amphipod species belonging to three different families. Similar to what is known in most other bdelloid species, the morphospecies Embata parasitica from Lake Baikal is likely to be a complex of cryptic species, as suggested by the high genetic diversity we found in one mitochondrial marker sequenced from several animals. Yet none of the divergent genetic lineages seemed to be associated to only one or a few amphipod species. In addition, nine bdelloid species were found living in the lake, increasing the known diversity of the area to 12 bdelloid species