Alfred Wegener Institute for Polar and Marine Research
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Unexpected Delayed Incursion of Highly Pathogenic Avian Influenza H5N1 (Clade 2.3.4.4b) Into the Antarctic Region
Get PDFThe current highly pathogenic avian influenza H5N1 panzootic is having substantial impacts on wild birds and marine mammals. Following major and widespread outbreaks in South America, an incursion to Antarctica occurred late in the austral summer of 2023/2024 and was confined to the region of the Antarctic Peninsula. To infer potential underlying processes, we compiled H5N1 surveillance data from Antarctica and sub-Antarctic Islands prior to the first confirmed cases
A Model‐Data Comparison of the Hydrological Response to Miocene Warmth: Leveraging the MioMIP1 Opportunistic Multi‐Model Ensemble
Get PDFThe Miocene (23.03–5.33 Ma) is recognized as a period with close to modern-day paleogeography, yet a much warmer climate. With large uncertainties in future hydroclimate projections, Miocene conditions illustrate a potential future analog for the Earth system. A recent opportunistic Miocene Model Intercomparison Project 1 (MioMIP1) focused on synthesizing published Miocene climate simulations and comparing them with available temperature reconstructions. Here, we build on this effort by analyzing the hydrological cycle response to Miocene forcings across early-to-middle (E2MMIO; 20.03–11.6 Ma) and middle-to-late Miocene (M2LMIO; 11.5–5.33 Ma) simulations with CO2 concentrations ranging from 200 to 850 ppm and providing a model-data comparison against available precipitation reconstructions. We find global precipitation increases by ∼2.1 and 2.3% per degree of warming for E2MMIO and M2LMIO simulations, respectively. Models generally agree on a wetter than modern-day tropics; mid and high-latitude, however, do not agree on the sign of subtropical precipitation changes with warming. Global monsoon analysis suggests most monsoon regions, except the North American Monsoon, experience higher precipitation rates under warmer conditions. Model-data comparison shows that mean annual precipitation is underestimated by the models regardless of CO2 concentration, particularly in the mid- to high-latitudes. This suggests that the models may not be (a) resolving key processes driving the hydrological cycle response to Miocene boundary conditions and/or (b) other boundary conditions or processes not considered here are critical to reproducing Miocene hydroclimate. This study highlights the challenges in modeling and reconstructing the Miocene hydrological cycle and serves as a baseline for future coordinated MioMIP efforts
Scale Dependence of Subsurface Density Gradients
Get PDFHorizontal sampling of the ocean has been sparse for decades because of technical limitations. This can contribute to an incomplete depiction and misleading understanding of the hydrography. This is a particular concern for complex sub- mesoscale and smaller scale flow structures that influence stratification and vertical transport of properties.
We used high resolution observations from a Triaxus towed undulating vehicle and developed a statistical subsampling routine in order to present the first multi-scale investigation of subsurface horizontal density variability in a global context. Hydrographic transects were performed between 2018 and 2022 in the oceanographically distinct regimes of the Arctic marginal ice zone, of a coastal up- welling area, of the equatorial Atlantic, and of the Antarctic Circumpolar Current. The main objectives of this thesis are to determine the scaling properties of density fronts and to identify oceanic regimes that are susceptible to an underestimation of their thermohaline variability.
We find that the amplitude of horizontal density gradients increases non-linearly as the horizontal resolution is increased. This relation is applicable throughout all study regions allowing for a potential prediction of the gradient distribution for scales not resolved by measurements. Submesoscale density gradients are of higher amplitude along the base of shallow mixed layers, and in the presence of frontal systems, eddies, and subsurface currents. Furthermore, the gradient fields are primarily driven by salinity variability at high northern latitudes and by temperature variability in regions closer to the equator; in the Southern Ocean temperature and salinity largely compensate. The decay rate of the estimated gradients with increasing horizontal distance is related to fractal properties and a scale-dependent compensation of the density field.
This highlights that there is a certain arbitrariness regarding the strengths of density gradients in the present literature. We recommend that the employed hori- zontal resolution always be quoted alongside values of the horizontal density gradient. The developed statistical method provides a novel approach for handling high-resolution data; its full potential has yet to be explored
Wasser in einer aufgeheizten Welt
Get PDFIn einer klimatisch und geopolitisch aufgeheizten Welt verschärfen sich die Herausforderungen um Wasser substanziell. Unsicherheit wird Normalität, Grenzen der Beherrschbarkeit könnten überschritten werden. Notwendig ist ein klimaresilientes Wassermanagement mit langfristigem Blick, das blaues und grünes Wasser zusammendenkt und flexibel auf Veränderungen reagieren kann. Es muss vorhandene selbstorganisierte Strukturen einbeziehen und benötigt eine begleitende Wissenschaft. Eine Internationale Wasserstrategie mit regionalen Plattformen sollte entwickelt werden
Marine Big Data-driven Machine Learning Based Monitoring of Phytoplankton Functional Types in the Arctic Ocean
Get PDFThe Arctic Ocean is experiencing rapid and significant changes due to climate warming, profoundly impacting its physical and biological systems. Phytoplankton, as primary producers, play a crucial role in marine ecosystems and biogeochemical cycles. Monitoring their distribution and abundance is essential for understanding the health of the Arctic marine environment. This study focuses on developing an ensemble machine learning model to predict concentrations of Chl-a of various Phytoplankton Functional Types (PFTs) and Total Chlorophyll-a (TChl-a) in the Arctic Ocean, leveraging data from satellite observations, simulation model outputs and in-situ measurements.
The ensemble model combines Gradient Boosting Machine (GBM), Fully Connected Neural Network (FCNN), Random Forest Regression (RFR), and Support Vector Machine (SVM) through a Ridge Regression Ensemble approach. The model was trained by using satellite data and model simulations outputs from Copernicus Marine Service (CMEMS) that were matched with in situ data collected during 1997-2020 and validated using in-situ measurements from the PS131 expedition. The model demonstrates strong predictive capabilities, particularly for diatoms and TChl-a, which are crucial for understanding primary production and nutrient dynamics in the Arctic. Results indicate that the ensemble model performs well in capturing the spatial and temporal distribution of TChl-a and PFTs. The model’s robust performance during the training phase and its ability to generalise to the validation dataset, regardless of its higher variability respect to the training dataset, underscore its potential for large-scale ecological monitoring.
The creation of Arctic maps for PFTs and TChl-a provided valuable insights into the spatial distribution of these variables. In the maps created, higher concentrations of diatoms were observed near coastal areas, aligning with known nutrient-rich environments such as river outflows and upwelling zones, particularly along the coasts of northern Europe and northern Asia. Green algae showed a patchy distribution influenced by localised environmental factors, such as variations in light availability and nutrient inputs from specific sources like the Barents Sea and Laptev Sea. Haptophytes exhibited specialised niches in cooler waters, reflecting their ecological roles in regions like the Kara Sea, where lower temperatures and nutrient availability favor their growth. Dinoflagellates were distributed along various coastal regions in northern Europe and northern
Asia without a specific area of high concentration, suggesting their adaptability to a range of environmental conditions. In general, the model effectively identified areas of high phytoplankton activity, which are essential for understanding the Arctic marine food web and biogeochemical cycles. Hence, this study demonstrates the potential of using machine learning models for predicting phytoplankton dynamics in the Arctic, offering a robust tool for monitoring and managing marine ecosystems
Analyses of sea surface chlorophyll a trends and variability from 1998 to 2020 in the German Bight (North Sea)
Get PDFSatellite remote sensing of ocean colour properties allows observation of the ocean with high temporal and spatial coverage, facilitating the better assessment of changes in marine primary production. Ocean productivity is often assessed using satellite-derived chlorophyll a concentrations, a commonly used proxy for phytoplankton concentration. We used the Copernicus GlobColour remote sensing chlorophyll a surface concentration to investigate seasonal and nonseasonal variability, temporal trends, and changes in spring bloom chlorophyll a magnitude. Complementary, we analysed the chlorophyll a relationship with sea surface temperature and mixed-layer depth in the German Bight from 1998 to 2020. Empirical orthogonal functions were employed in order to investigate dominant spatial and temporal patterns (modes) related to the main processes of chlorophyll a variability. Multi covariance analysis was used to extract the dominant structures that maximize the covariance between chlorophyll a and sea surface temperature mixed-layer depth fields. High levels of chlorophyll a were found near the coast, showing a decreasing gradient towards offshore waters. A significant chlorophyll a positive trend was observed close to the Elbe estuary and adjacent area, while 55 % of the German Bight was characterized by a significant chlorophyll a negative trend. The chlorophyll a non-seasonal variability showed that the first four modes explained around 45 %, with the first and second modes related to inter- and intra-annual variability, respectively, observed in the temporal principal components spectral analyses. Monthly chlorophyll a concentration anomalies co-varied by 45 % with sea surface temperature anomalies and 23 % with mixed-layer depth anomalies. The monthly averages of chlorophyll a anomaly fields were suitable to investigate long-term trends and variability. The rising water temperature, combined with its indirect effects on other variables, can partially explain the observed trends in chlorophyll a
Circumpolar and Regional Seascape Drivers of Genomic Variation in a Southern Ocean Octopus
Get PDFUnderstanding how ecological, environmental and geographic features influence population genetic patterns provides crucial insights into a species' evolutionary history, as well as their vulnerability or resilience under climate change. In the Southern Ocean, population genetic variation is influenced across multiple spatial scales ranging from circum-Antarctic, which encompasses the entire continent, to regional, with varying levels of geographic separation. However, comprehensive analyses testing the relative importance of different environmental and geographic variables on genomic variation across these scales are generally lacking in the Southern Ocean. Here, we examine genome-wide single nucleotide polymorphisms of the Southern Ocean octopus Pareledone turqueti across the Scotia Sea and the Antarctic continental shelf, at depths between 102 and 1342 m, throughout most of this species' range. The circumpolar distribution of P. turqueti is biogeographically structured with a clear signature of isolation-by-geographical distance, but with long-distance genetic connectivity also detected between East and West Antarctica. Genomic variation of P. turqueti was also associated with bottom water temperature at a circumpolar scale, driven by a genotype-temperature association with the warmer sub-Antarctic Shag Rocks and South Georgia. Within the Scotia Sea, geographic distance, oxygen and fine-scale isolation-by-water depth were apparent drivers of genomic variation at regional scales. Putative positive selection of haemocyanin (oxygen transport protein), calcium ion transport and genes linked to RNA modification, detected within the Scotia Sea, suggest physiological adaptation to the regional sharp temperature gradient (~0–+2°C). Overall, we identified seascape drivers of genomic variation in the Southern Ocean at circumpolar and regional scales in P. turqueti and contextualised the role of environmental adaptations in the Southern Ocean
Observations of the Antarctic Slope Current in the Southeastern Weddell Sea: A Bottom‐Enhanced Current and Its Seasonal Variability
Get PDFThe Antarctic Slope Front and the associated Antarctic Slope Current dynamically regulate the exchanges of heat across the continental shelf break around Antarctica. Where the front is weak, relatively warm deep waters reach the ice shelf cavities, contributing to basal melting and ultimately affecting sea level rise. Here, we present new 2017–2021 records from two moorings deployed on the upper continental slope (530 and 738 m depth) just upstream of the Filchner Trough in the southeastern Weddell Sea. The structure and seasonal variability of the frontal system in this region, central to the inflow of warm water toward the large Filchner-Ronne Ice Shelf, is previously undescribed. We use the records to describe the mean state and the seasonal variability of the regional hydrography and the southern part of the Antarctic Slope Current. We find that (a) the current is, contrary to previous assumptions, bottom-enhanced, (b) the isotherms slope upwards toward the shelf break, and more so for warmer isotherms, and (c) the monthly mean thermocline depth is shallowest in February-March and deepest in May-June while (d) the current is strongest in April-June. On monthly timescales, we show that (e) positive temperature anomalies of the de-seasoned records are associated with weaker-than-average currents. We propose that the upward-sloping isotherms are linked to the local topography and conservation of potential vorticity. Our results contribute to the understanding of how warm ocean waters propagate southward and potentially affect basal melt rates at the Filchner-Ronne Ice Shelf
On the release and renewal of freshwater in the Beaufort Gyre of the Arctic Ocean
Get PDFThe Arctic Beaufort Gyre plays a critical role in climate and marine ecosystems. This study investigates the response of the liquid freshwater in the Beaufort Gyre to various wind perturbations using numerical simulations. A new diagnostic called “freshwater renewal” is introduced, which quantifies the amount of freshwater that has entered the Beaufort Gyre since a specific point in time. The findings reveal that the process of freshwater renewal is persistently efficient in the Beaufort Gyre region, occurring irrespective of the gyre’s status. The spatial distribution of freshwater renewal varies, influenced by factors such as wind forcing and gyre circulation patterns. Cyclonic wind perturbation associated with a negative Beaufort high sea level pressure anomaly triggers freshwater release from the Beaufort Gyre, with freshwater export and renewal dependent on wind-perturbation locations and time scales. While some released Beaufort Gyre freshwater exits the Arctic Ocean through the Davis and Fram Straits, a considerable portion could remain within the Arctic Ocean for many years under specific conditions. Wind perturbation associated with the positive Arctic Oscillation enhances the Arctic export of Beaufort Gyre freshwater, mainly through the Fram Strait. The Arctic export of total freshwater and the Arctic export of the portion originating from the Beaufort Gyre have different time scales and magnitudes. Hence, it is essential to collectively examine different freshwater components in order to assess the role of Arctic export in the climate system
Chromosome-level genome assemblies and genetic maps reveal heterochiasmy and macrosynteny in endangered Atlantic Acropora
Get PDFBackground: Over their evolutionary history, corals have adapted to sea level rise and increasing ocean temperatures, however, it is unclear how quickly they may respond to rapid change. Genome structure and genetic diversity contained within may highlight their adaptive potential. Results: We present chromosome-scale genome assemblies and linkage maps of the critically endangered Atlantic acroporids, Acropora palmata and A. cervicornis. Both assemblies and linkage maps were resolved into 14 chromosomes with their gene content and colinearity. Repeats and chromosome arrangements were largely preserved between the species. The family Acroporidae and the genus Acropora exhibited many phylogenetically significant gene family expansions. Macrosynteny decreased with phylogenetic distance. Nevertheless, scleractinians shared six of the 21 cnidarian ancestral linkage groups as well as numerous fission and fusion events compared to other distantly related cnidarians. Genetic linkage maps were constructed from one A. palmata family and 16 A. cervicornis families using a genotyping array. The consensus maps span 1,013.42 cM and 927.36 cM for A. palmata and A. cervicornis, respectively. Both species exhibited high genome-wide recombination rates (3.04 to 3.53 cM/Mb) and pronounced sex-based differences, known as heterochiasmy, with 2 to 2.5X higher recombination rates estimated in the female maps. Conclusions: Together, the chromosome-scale assemblies and genetic maps we present here are the first detailed look at the genomic landscapes of the critically endangered Atlantic acroporids. These data sets revealed that adaptive capacity of Atlantic acroporids is not limited by their recombination rates. The sister species maintain macrosynteny with few genes with high sequence divergence that may act as reproductive barriers between them. In the Atlantic Acropora, hybridization between the two sister species yields an F1 hybrid with limited fertility despite the high levels of macrosynteny and gene colinearity of their genomes. Together, these resources now enable genome-wide association studies and discovery of quantitative trait loci, two tools that can aid in the conservation of these species