Alfred Wegener Institute for Polar and Marine Research
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Greenhouse gas production potential of drained lake basin sediments from the Yukon Coastal Plain
Get PDFGlobal biogeographic regions for ants have complex relationships with those for plants and tetrapods
Get PDFOn a global scale, biodiversity is geographically structured into regions of biotic similarity. Delineating these regions has been mostly targeted for tetrapods and plants, but those for hyperdiverse groups such as insects are relatively unknown. Insects may have higher biogeographic congruence with plants than tetrapods due to their tight ecological and evolutionary links with the former, but it remains untested. Here, we develop a global regionalization for a major and widespread insect group, ants, based on the most comprehensive distributional and phylogenetic information to date, and examine its similarity to regionalizations for tetrapods and vascular plants. Our ant regionalization supports the newly proposed Madagascan and Sino-Japanese realms based on tetrapod delineations, and it recovers clusters observed in plants but not in tetrapods, such as the Holarctic and Indo-Pacific realms. Quantitative comparison suggests strong associations among different groups—plants showed a higher congruence with ants than with tetrapods. These results underscore the wide congruence of diverse distribution patterns across the tree of life and the similarities shared by insects and plants that are not captured by tetrapod groups. Our analysis highlights the importance of developing global biogeographic maps for insect groups to obtain a more comprehensive geographic picture of life on Earth
Brain structure and function: a multidisciplinary pipeline to study hominoid brain evolution
Get PDFTo decipher the evolution of the hominoid brain and its functions, it is essential to conduct comparative studies in primates, including our closest living relatives. However, strong ethical concerns preclude in vivo neuroimaging of great apes. We propose a responsible and multidisciplinary alternative approach that links behavior to brain anatomy in non-human primates from diverse ecological backgrounds. The brains of primates observed in the wild or in captivity are extracted and fixed shortly after natural death, and then studied using advanced MRI neuroimaging and histology to reveal macro- and microstructures. By linking detailed neuroanatomy with observed behavior within and across primate species, our approach provides new perspectives on brain evolution. Combined with endocranial brain imprints extracted from computed tomographic scans of the skulls these data provide a framework for decoding evolutionary changes in hominin fossils. This approach is poised to become a key resource for investigating the evolution and functional differentiation of hominoid brains.</jats:p
Variability of Eddy Kinetic Energy in the Eurasian Basin of the Arctic Ocean Inferred From a Model Simulation at 1‐km Resolution
No full textMesoscale eddies play an important role in driving the dynamics of the Arctic Ocean. Understanding their behavior is crucial for comprehending the ongoing changes in the region. In this study, by using a novel decade-long simulation at 1 km resolution with the unstructured-mesh Finite volumE Sea ice-Ocean Model, we evaluate the spatial and temporal variability of eddy kinetic energy in the Eurasian Basin. We find that monthly, annual, and interannual variability of EKE near the surface is predominantly influenced by changes in sea ice cover, while the eddy activity at deeper depth, being shielded from the surface by ocean stratification, is more strongly influenced by local baroclinic energy conversion. Moreover, our research demonstrates that eddies in the Eurasian Basin can transport ocean heat from the Atlantic Water layer toward sea ice and cause local basal melting in the order of about 20 cm per month even in wintertime. Our study suggests that eddy activity in the Arctic Ocean will strengthen along with future sea ice decline, and that the impact of ocean heat of the Atlantic Water layer on sea ice retreat may become prominent
A microstructure-based parameterization of the effective anisotropic elasticity tensor of snow, firn, and bubbly ice
Get PDFQuantifying the link between microstructure and effective elastic properties of snow, firn, and bubbly ice is essential for many applications in cryospheric sciences. The microstructure of snow and ice can be characterized by different types of fabrics (crystallographic and geometrical), which give rise to macroscopically anisotropic elastic behavior. While the impact of the crystallographic fabric has been extensively studied in deep firn, the present work investigates the influence of the geometrical fabric over the entire range of possible volume fractions. To this end, we have computed the effective elasticity tensor of snow, firn, and ice by finite-element simulations based on 391 X-ray tomography images comprising samples from the laboratory, the Alps, Greenland, and Antarctica. We employed a variant of Eshelby's tensor that has been previously utilized for the parameterization of thermal and dielectric properties of snow and utilized Hashin-Shtrikman bounds to capture the nonlinear interplay between density and geometrical anisotropy. From that we derive a closed-form parameterization for all components of the (transverse isotropic) elasticity tensor for all volume fractions using two fit parameters per tensor component. Finally, we used the Thomsen parameter to compare the geometrical anisotropy to the maximal theoretical crystallographic anisotropy in bubbly ice. While the geometrical anisotropy clearly dominates up to ice volume fractions of φ≈0.7, a thorough understanding of elasticity in bubbly ice may require a coupled elastic theory that includes geometrical and crystallographic anisotropy
Microstructure-based simulations of the viscous densification of snow and firn
Get PDFAccurate models for the viscous densification of snow (understood here as a density below 550 kg m−3) and firn (a density above 550 kg m−3) under mechanical stress are of primary importance for various applications, including avalanche prediction and the interpretation of ice cores. Formulations of snow and firn compaction in models are still largely empirical instead of using microstructures from micro-computed tomography to numerically compute the mechanical behavior directly from the physics at the microscale. The main difficulty of the latter approach is the choice of the correct rheology/constitutive law governing the deformation of the ice matrix, which is still controversially discussed. Being aware of these uncertainties, we conducted a first systematic attempt of microstructure-based modeling of snow and firn compaction. We employed the finite element suite Elmer FEM using snow and firn microstructures from different sites in the Alps and Antarctica to explore which ice rheologies are able to reproduce observations. We thereby extended the ParStokes solver in Elmer FEM to facilitate parallel computing of transverse isotropic material laws for monocrystalline ice. We found that firn densification can be reasonably well simulated across different sites assuming a polycrystalline rheology (Glen’s law) that is traditionally used in glacier or ice sheet modeling. In contrast, for snow, the observations are in contradiction with this rheology. To further comprehend this finding, we conducted a sensitivity study on different ice rheologies. None of the material models is able to explain the observed high compactive viscosity of depth hoar compared to rounded grains having the same density. While, on one hand, our results re-emphasize the limitations of our current mechanical understanding of the ice in snow, they constitute, on the other hand, a confirmation of the common picture of firn as a foam of polycrystalline ice through microstructure-based simulations
Ecological genomics in the Northern krill uncovers loci for local adaptation across ocean basins
Get PDFKrill are vital as food for many marine animals but also impacted by global warming. To learn how they and other zooplankton may adapt to a warmer world we studied local adaptation in the widespread Northern krill (Meganyctiphanes norvegica). We assemble and characterize its large genome and compare genome-scale variation among 74 specimens from the colder Atlantic Ocean and warmer Mediterranean Sea. The 19 Gb genome likely evolved through proliferation of retrotransposons, now targeted for inactivation by extensive DNA methylation, and contains many duplicated genes associated with molting and vision. Analysis of 760 million SNPs indicates extensive homogenizing gene-flow among populations. Nevertheless, we detect signatures of adaptive divergence across hundreds of genes, implicated in photoreception, circadian regulation, reproduction and thermal tolerance, indicating polygenic adaptation to light and temperature. The top gene candidate for ecological adaptation was nrf-6, a lipid transporter with a Mediterranean variant that may contribute to early spring reproduction. Such variation could become increasingly important for fitness in Atlantic stocks. Our study underscores the widespread but uneven distribution of adaptive variation, necessitating characterization of genetic variation among natural zooplankton populations to understand their adaptive potential, predict risks and support ocean conservation in the face of climate change
A new Activity Monitor for Aquatic Zooplankter (AMAZE) allows the recording of swimming activity in wild-caught Antarctic krill (Euphausia superba)
Get PDFAntarctic krill (Euphausia superba, hereafter krill) is a pelagic living crustacean and a key species in the Southern Ocean ecosystem. Krill builds up a huge biomass and its synchronized behavioral patterns, such as diel vertical migration (DVM), substantially impact ecosystem structure and carbon sequestration. However, the mechanistic basis of krill DVM is unknown and previous studies of krill behavior in the laboratory were challenged by complex behavior and large variability. Using a new
experimental set-up, we recorded the swimming activity of individual wild-caught krill under light– dark cycles. Krill individuals exhibited differential phototactic responses to the light regime provided. However, using a new activity metric, we showed for the first time a consistent nocturnal increase in krill swimming activity in a controlled environment. Krill swimming activity in the new set-up was
strongly synchronized with the light–dark cycle, similar to the diel vertical migration pattern of krill in the field when the krill were sampled for the experiment, demonstrated by hydroacoustic recordings. The new set-up presents a promising tool for investigating the mechanisms underlying krill behavioral patterns, which will increase our understanding of ecological interactions, the spatial distribution of populations, and their effects on biogeochemical cycles in the future
Kelp forest community structure and demography in Kongsfjorden (Svalbard) across 25 years of Arctic warming
No full textThe Arctic archipelago of Svalbard is a hotspot of global warming and many fjords experience
a continuous increase in seawater temperature and glacial melt while sea-ice
cover declines. In 1996/1998, 2012–2014, and 2021 macroalgal biomass and species
diversity were quantified at the study site Hansneset, Kongsfjorden (W-Spitsbergen)
in order to identify potential changes over time. In 2021, we repeated the earlier studies
by stratified random sampling (1 × 1 m2, n = 3) along a sublittoral depth transect (0,
2.5, 5, 10, and 15 m) and investigated the lower depth limits of dominant brown algae
between 3 and 19 m. The maximum fresh weight (FW) of all seaweeds was 11.5 kg m−2
at 2.5 m and to 99.9% constituted of kelp. Although biomass distribution along the
depth transect in 2021 was not significantly different compared to 2012/2013, the
digitate kelp community (Laminaria digitata/Hedophyllum nigripes) had transformed
into an Alaria esculenta-dominated
kelp forest. Consequently, a pronounced shift
in kelp forest structure occurred over time as we demonstrate that biomass allocation
to thallus parts is kelp species-specific.
Over the past decade, kelp demography
changed and in 2021 a balanced age structure of kelps (juveniles plus many older kelp
individuals) was only apparent at 2.5 m. In addition, the abundances and lower depth
limits of all dominant brown algae declined noticeably over the last 25 years while the
red algal flora abundance remained unchanged at depth. We propose that the major
factor driving the observed changes in the macroalgal community are alterations in
underwater light climate, as in situ data showed increasing turbidity and decreasing irradiance
since 2012 and 2017, respectively. As a consequence, the interplay between
kelp forest retreat to lower depth levels caused by coastal darkening and potential
macroalgal biomass gain with increasing temperatures will possibly intensify in the
future with unforeseen consequences for melting Arctic coasts and fjord ecosystem
services. The Arctic archipelago of Svalbard is a hotspot of global warming and many fjords experience
a continuous increase in seawater temperature and glacial melt while sea-ice
cover declines. In 1996/1998, 2012–2014, and 2021 macroalgal biomass and species
diversity were quantified at the study site Hansneset, Kongsfjorden (W-Spitsbergen)
in order to identify potential changes over time. In 2021, we repeated the earlier studies
by stratified random sampling (1 × 1 m2, n = 3) along a sublittoral depth transect (0,
2.5, 5, 10, and 15 m) and investigated the lower depth limits of dominant brown algae
between 3 and 19 m. The maximum fresh weight (FW) of all seaweeds was 11.5 kg m−2
at 2.5 m and to 99.9% constituted of kelp. Although biomass distribution along the
depth transect in 2021 was not significantly different compared to 2012/2013, the
digitate kelp community (Laminaria digitata/Hedophyllum nigripes) had transformed
into an Alaria esculenta-dominated
kelp forest. Consequently, a pronounced shift
in kelp forest structure occurred over time as we demonstrate that biomass allocation
to thallus parts is kelp species-specific.
Over the past decade, kelp demography
changed and in 2021 a balanced age structure of kelps (juveniles plus many older kelp
individuals) was only apparent at 2.5 m. In addition, the abundances and lower depth
limits of all dominant brown algae declined noticeably over the last 25 years while the
red algal flora abundance remained unchanged at depth. We propose that the major
factor driving the observed changes in the macroalgal community are alterations in
underwater light climate, as in situ data showed increasing turbidity and decreasing irradiance
since 2012 and 2017, respectively. As a consequence, the interplay between
kelp forest retreat to lower depth levels caused by coastal darkening and potential
macroalgal biomass gain with increasing temperatures will possibly intensify in the
future with unforeseen consequences for melting Arctic coasts and fjord ecosystem
services
Temporal Variability of the Overturning Circulation in the Arctic Ocean and the Associated Heat and Freshwater Transports during 2004–10
Get PDFThis study quantifies the overturning circulation in the Arctic Ocean and associated heat transport (HT) and freshwater transport (FWT) from October 2004 to May 2010 based on hydrographic and current observations. Our main data source consists of 1165 moored instrument records in the four Arctic main gateways: Davis Strait, Fram Strait, Bering Strait, and the Barents Sea Opening. We employ a box inverse model to obtain mass and salt balanced velocity fields, which are then used to quantify the overturning circulation as well as HT and FWT. Atlantic Water is transformed into two different water masses in the Arctic Ocean at a rate of 4.3 Sv (1 Sv ≡ 106 m3 s21). Combined with 0.7 Sv of Bering Strait inflow and 0.15 Sv of surface freshwater flux, 2.2 Sv flows back to the south through Davis Strait and western Fram Strait as the upper limb of the overturning circulation, and 2.9 Sv returns southward through Fram Strait as the lower limb of the overturning. The Arctic Ocean imports heat of 180 ± 57 TW (long-term mean ± standard deviation of monthly means) with a methodological uncertainty of 20 TW and exports FW of 156 ± 91 mSv with an uncertainty of 61 mSv over the 6 years with a potential offset of ~30 mSv. The HT and FWT have large seasonalities ranging between 110 and 260 TW (maximum in winter) and between 40 and 260 mSv (maximum in winter), respectively. The obtained overturning circulation and associated HT and FWT presented here are vital information to better understand the northern extent of the Atlantic meridional overturning circulation