Alfred Wegener Institute for Polar and Marine Research
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The Expeditions PS139/1 and PS139/2 of the Research Vessel POLARSTERN to the Atlantic Ocean in 2023
Get PDFIs the Isotopic Composition of Precipitation a Robust Indicator for Reconstructions of Past Tropical Cyclones Frequency? A Case Study on Réunion Island From Rain and Water Vapor Isotopic Observations
Get PDFBased on a 6-year long record (2014–2020) of the isotopic composition of rain (δ18Op) at Réunion Island (55°E, 22°S), in the South-West Indian Ocean, this study shows that the annual isotopic composition of precipitation in this region is strongly controlled by the number of cyclones, the number of best-track days, and the proportion of cyclonic rain during the year. Our results support the use of δ18Op in annual-resolved tropical climate archives as a reliable proxy of past cyclone frequency. The influence of the proportion of cyclonic rain on the annual isotopic composition arises from the systematically more depleted precipitation and water vapor during cyclonic events than during less organized convective systems. The analysis of the daily to hourly isotopic composition of water vapor (δ18Ov) during low-pressure systems and the reproduction of daily δ18Ov observations by AGCMs with a global medium to coarse resolution (LMDZ-iso and ECHAM6-wiso) suggest that during cyclonic periods the stronger depletion mainly arises from both enhanced large-scale precipitation and water vapor-rain interactions under humid conditions
Effects of bottom‐up factors on growth and toxin content of a harmful algae bloom dinoflagellate
No full textThe toxin-producing dinoflagellate Alexandrium pseudogonyaulax has become increasingly abundant in northern European waters, replacing other Alexandrium species. A. pseudogonyaulax produces goniodomins and lytic substances, which can be cytotoxic toward other organisms, including fish, but we still know little about the environmental conditions influencing its growth and toxicity. Here, we investigated the impacts of different nitrogen sources and light intensities, common bottom-up drivers of bloom formation, on the growth and toxin content of three A. pseudogonyaulax strains isolated from the Danish Limfjord. While the growth rates were significantly influenced by nitrogen source and light intensity, the intracellular toxin contents only showed strong differences between the exponential and stationary growth phases. Moreover, the photophysiological response of A. pseudogonyaulax showed little variation across varying light intensities, while light-harvesting pigments were significantly more abundant under low light conditions. This study additionally highlights considerable physiological variability between strains, emphasizing the importance of conducting laboratory experiments with several algal strains. A high physiological plasticity toward changing abiotic parameters points to a long-term establishment of A. pseudogonyaulax in northern European waters
Improving daily-to-seasonal sea ice forecasts of the AWI coupled prediction system with sea-ice and ocean data assimilation and atmospheric large-scale wind nudging.
Get PDFPredictive skills of coupled sea-ice/ocean and atmosphere models are limited by the chaotic nature of the atmosphere. Assimilation of observational information on ocean hydrography and sea ice allows to obtain a coupled-system state that provides a basis for subseasonal-to-seasonal ocean and sea-ice forecast (Mu et al., 2022). However, if the atmosphere is not additionally constrained, the quasi-random atmospheric states within an ensemble forecast lead to a fast divergence of the ocean and sea-ice states, degrading the system’s performance with respect to the sea ice forecasts. As reported previously, imposing an additional constraint by nudging large-scale winds to the ERA5 reanalysis data (Sánchez-Benítez et al., 2021; Athanase et al., 2022) improves predictive skills of the AWI Coupled Prediction System (AWI-CPS, Mu et al. 2022) with regard to sea ice drift (Losa et al., 2023). Here we provide results based on a much more extensive set of ensemble-based data assimilation experiments spanning the time period from 2002 to 2023 and a series of long forecast experiments over 2010 – 2023, initialized in four different seasons. We compare the performance of forecasts initialized from two sets of data assimilation experiments, with and without atmospheric wind nudging. The additional relaxation of the large-scale atmospheric circulation to the ERA5 reanalysis data for the initialization leads to reasonable atmospheric forecast skill on weather timescales: Despite the simple technique, the coarse resolution compared to NWP systems, and the limited optimization efforts, 10-day forecasts of the 500 hPa geopotential height are about as skillful as the best performing NWP forecasts were about 10 –15 years ago. Among other aspects, this leads to significantly improved subseasonal-to-seasonal sea-ice concentration and thickness forecasts.
Athanase, M., Schwager, M., Streffing, J., Andrés-Martínez, M., Loza, S., and Goessling, H.: Impact of the atmospheric circulation on the Arctic snow cover and ice thickness variability , EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-5836, https://doi.org/10.5194/egusphere-egu22-5836, 2022.
Losa, S. N., Mu, L., Athanase, M., Streffing, J., Andrés-Martínez, M., Nerger, L., Semmler, T., Sidorenko, D., and Goessling, H. F.: Combining sea-ice and ocean data assimilation with nudging atmospheric circulation in the AWI Coupled Prediction System, EGU General Assembly 2023, Vienna, Austria, 24–28 Apr 2023, EGU23-14227, https://doi.org/10.5194/egusphere-egu23-14227, 2023.
Mu, L. , Nerger, L. , Streffing, J. , Tang, Q. , Niraula, B. , Zampieri, L., Loza, S. N. and Goessling, H. F. (2022): Sea‐Ice Forecasts With an Upgraded AWI Coupled Prediction System , Journal of Advances in Modeling Earth Systems, 14 (12) . doi: 10.1029/2022ms003176
Sánchez-Benítez, A. , Goessling, H. , Pithan, F. , Semmler, T. and Jung, T. (2022): The July 2019 European Heat Wave in a Warmer Climate: Storyline Scenarios with a Coupled Model Using Spectral Nudging , Journal of Climate, 35 (8), pp. 2373-2390 . doi: 10.1175/JCLI-D-21-0573.
Aerosol Transport from the Asian Summer Monsoon into the Arctic Lower Stratosphere
Get PDFThe Asian summer monsoon is linked to deep convection over the Indian subcontinent and to an anticyclonic flow that extends from the upper troposphere into the lower stratosphere region. This allows both gas-phase aerosol precursors and aerosol particles from surface sources to reach the stratosphere. The horizontal transport out of the Asian monsoon anticyclone towards the extratropical lower stratosphere of the Northern Hemisphere is the focus of this study.
We present an annual record of Lidar observations at AWIPEV in Ny-Ålesund. The data record is free from obvious layers like polar stratospheric clouds, volcanic eruptions or forest fires. Nevertheless, the lower stratosphere reveals an annual cycle with lower backscatter values in winter and spring and higher backscatter values in summer and autumn. The Lidar measurements have been linked to backward trajectory calculations and simulations of artificial surface origin tracers with the three-dimensional Chemical Lagrangian Model of the Stratosphere (CLaMS). The simulations show that air masses observed above Ny-Ålesund have been transported from surface sources in Asia into the Arctic lower stratosphere. Thus, the increased backscatter values during summer and autumn can be explained by transport of aerosol particles from the Asian summer monsoon into the Arctic lower stratosphere
Ancient Permafrost, Yedoma, and all its Organic Matter: Contribution of the D-A-CH Permafrost Union to the Upcoming Encyclopaedia of Quaternary Science
Get PDFThis contribution provides a short summary of three permafrost-related contributions to the upcoming 3rd volume of the Encyclopaedia of Quaternary Science. There are 24 chapters on ‘Permafrost and Periglacial Features’, and three of those are led by authors from the D-A-CH Permafrost Community. Specifically, these are ‘Ancient and past permafrost’, ‘Yedoma: Late Pleistocene ice-rich syngenetic permafrost of Beringia’ and ‘Organic matter storage and vulnerability in the permafrost domain’. With this presentation, we aim to give you a short introduction and show the key figures out of these three encyclopaedia chapters already now.
In more detail, the broader perspective on ancient permafrost dynamics examines its formation, stability, and degradation in response to climate variations over the Quaternary. This encyclopaedia contribution distinguishes between ancient permafrost persisting since the Pleistocene and past permafrost, no longer existing at a specific locality. Recent research challenges traditional associations between permafrost and glacial periods, highlighting the complexity of permafrost responses to climate change.
The Yedoma segment delves into the unique depositional processes of late Pleistocene Beringia, where a cold, dry climate fostered Yedoma formation due to periglacial weathering and syngenetic ice wedge growth. Yedoma hills in Siberia and foothill regions in Alaska, as well as valley fillings in mountain regions in Siberia and Alaska and in the Yukon Territory of western Canada are remnants of this feature, offering insight into paleoenvironmental, cryolithological, sedimentological and large carbon stock characteristics.
The permafrost regions soil organic matter chapter synthesizes recent data and shows that this warming-susceptible region holds a staggering ~1500 Gt of organic carbon on land, with an additional ~2800 Gt in subsea permafrost. As permafrost degrades, it releases carbon, affecting ecosystems and greenhouse gas emissions. Projections indicate that the Arctic might release between 55 and 232 Gt of CO2-equivalent by 2100, emphasizing the region’s potential as a significant carbon source.
The abovementioned chapters in the upcoming Encyclopaedia of Quaternary Science contribute valuable insights into ancient permafrost, Yedoma, and organic matter dynamics in the permafrost domain. Understanding and communicating their complexities and also broader relevance to a wider readership advances not only the knowledge about Earth’s largest terrestrial carbon pool but is vital for climate mitigation considerations
Community dynamics, genetic capacities, and polysaccharide degradation of marine bacteria over geographic, seasonal, and microdiversity scales.
Get PDFMicrobes are the fundamental drivers of Earth’s biogeochemical cycles. Their enormous taxonomic, functional and metabolic diversity are of essential importance for ecosystem functioning − from cellular to community scales, over time and space. Among the multitude of microbial metabolisms in the oceans, polysaccharide degradation is one key process, featuring distinct substrate niches and bacteria-algae interactions. Nonetheless, many aspects regarding the distribution of polysaccharide-degrading taxa and their genetic regulation remain open. One central question is how hydrolytic abilities, and the diversity of metabolic functions in general, affect microbiome assembly over time. Studying temporal variability is especially important in vulnerable and changing systems such as the polar oceans, where the climate crisis exerts substantial pressure on biological communities.
This Habilitation summarizes my research on bacterial polysaccharide degradation, intraspecific diversity, and microbiome seasonality in the Arctic Ocean. The enclosed studies present interdisciplinary insights into the biogeography, identity, genetic repertoire, and regulatory dynamics of polysaccharide degraders on cellular, microhabitat and ocean-wide scales. Experimental incubations revealed distinct “hydrolytic community fingerprints” in the Atlantic, Pacific, and Southern Oceans. Furthermore, studying the genetic machinery and cellular regulation under both simple and complex substrate conditions, including dissolved and particulate polysaccharides, illuminated the microscale underpinnings of larger community dynamics. This integrated molecular and culture-based evidence contributes to a conceptual perspective on polysaccharide utilization in contrasting marine systems.
The establishment of model organisms was essential for studying genetic regulation and intraspecific diversity; addressing hydrolytic capacities and other traits including siderophore production, aromatics degradation, and metabolite secretion – mediators of central element cycles and chemical ecology. Connecting genotypes to niches furthermore contributed to broader eco-evolutionary concepts on species delineation and population assembly.
Finally, my research characterized microbial communities over seasonal and environmental gradients in the Arctic Ocean. Time-series observations via autonomous devices revealed community dynamics over polar day and night, and across different sea-ice and polar water regimes. This microbial inventory in the environmental context establishes a baseline of Arctic microbial ecology, and allows benchmarking future ecosystem shifts.
Overall, the presented research contributes important conclusions for the understanding of microbial diversity and biogeochemical functions in cellular, spatial and temporal dimensions, underlining the relevance of microbes for ecosystem functioning in the current and future ocean
Dynamic species distribution models of Antarctic blue whales in the Weddell Sea using visual sighting and passive acoustic monitoring data
No full textAim: Species distribution models (SDMs) are essential tools in ecology and conservation. However, the scarcity of visual sightings of marine mammals in remote polar areas hinders the effective application of SDMs there. Passive acoustic monitoring (PAM) data provide year-round information and overcome foul weather limitations faced by visual surveys. However, the use of PAM data in SDMs has been sparse so far. Here, we use PAM-based SDMs to investigate the spatiotemporal distribution of the critically endangered Antarctic blue whale in the Weddell Sea. Location: The Weddell Sea. Methods: We used presence-only dynamic SDMs employing visual sightings and PAM detections in independent models. We compared the two independent models with a third combined model that integrated both visual and PAM data, aiming at leveraging the advantages of each data type: the extensive spatial extent of visual data and the broader temporal/environmental range of PAM data. Results: Visual and PAM data prove complementary, as indicated by a low spatial overlap between daily predictions and the low predictability of each model at detections of other data types. Combined data models reproduced suitable habitats as given by both independent models. Visual data models indicate areas close to the sea ice edge (SIE) and with low-to-moderate sea ice concentrations (SIC) as suitable, while PAM data models identified suitable habitats at a broader range of distances to SIE and relatively higher SIC. Main Conclusions: The results demonstrate the potential of PAM data to predict year-round marine mammal habitat suitability at large spatial scales. We provide reasons for discrepancies between SDMs based on either data type and give methodological recommendations on using PAM data in SDMs. Combining visual and PAM data in future SDMs is promising for studying vocalized animals, particularly when using recent advances in integrated distribution modelling methods
Permafrost Carbon: Progress on Understanding Stocks and Fluxes Across Northern Terrestrial Ecosystems
Get PDFSignificant progress in permafrost carbon science made over the past decades include the identification of vast permafrost carbon stocks, the development of new pan‐Arctic permafrost maps, an increase in terrestrial measurement sites for CO2 and methane fluxes, and important factors affecting carbon cycling, including vegetation changes, periods of soil freezing and thawing, wildfire, and other disturbance events. Process‐based modeling studies now include key elements of permafrost carbon cycling and advances in statistical modeling and inverse modeling enhance understanding of permafrost region C budgets. By combining existing data syntheses and model outputs, the permafrost region is likely a wetland methane source and small terrestrial ecosystem CO2 sink with lower net CO2 uptake toward higher latitudes, excluding wildfire emissions. For 2002–2014, the strongest CO2 sink was located in western Canada (median: −52 g C m−2 y−1) and smallest sinks in Alaska, Canadian tundra, and Siberian tundra (medians: −5 to −9 g C m−2 y−1). Eurasian regions had the largest median wetland methane fluxes (16–18 g CH4 m−2 y−1). Quantifying the regional scale carbon balance remains challenging because of high spatial and temporal variability and relatively low density of observations. More accurate permafrost region carbon fluxes require: (a) the development of better maps characterizing wetlands and dynamics of vegetation and disturbances, including abrupt permafrost thaw; (b) the establishment of new year‐round CO2 and methane flux sites in underrepresented areas; and (c) improved models that better represent important permafrost carbon cycle dynamics, including non‐growing season emissions and disturbance effects.</jats:p
Simulating long-term wildfire impacts on boreal forest structure in Central Yakutia, Siberia, since the Last Glacial Maximum
Get PDFBackground: Wildfires are recognized as an important ecological component of larch-dominated boreal forests in eastern Siberia. However, long-term fire-vegetation dynamics in this unique environment are poorly understood. Recent paleoecological research suggests that intensifying fire regimes may induce millennial-scale shifts in forest structure and composition. This may, in turn, result in positive feedback on intensifying wildfires and permafrost degradation, apart from threatening human livelihoods. Most common fire-vegetation models do not explicitly include detailed individual-based tree population dynamics, but a focus on patterns of forest structure emerging from interactions among individual trees may provide a beneficial perspective on the impacts of changing fire regimes in eastern Siberia. To simulate these impacts on forest structure at millennial timescales, we apply the individual-based, spatially explicit vegetation model LAVESI-FIRE, expanded with a new fire module. Satellite-based fire observations along with fieldwork data were used to inform the implementation of wildfire occurrence and adjust model parameters. Results: Simulations of annual forest development and wildfire activity at a study site in the Republic of Sakha (Yakutia) since the Last Glacial Maximum (c. 20,000 years BP) highlight the variable impacts of fire regimes on forest structure throughout time. Modeled annual fire probability and subsequent burned area in the Holocene compare well with a local reconstruction of charcoal influx in lake sediments. Wildfires can be followed by different forest regeneration pathways, depending on fire frequency and intensity and the pre-fire forest conditions. We find that medium-intensity wildfires at fire return intervals of 50 years or more benefit the dominance of fire-resisting Dahurian larch (Larix gmelinii (Rupr.) Rupr.), while stand-replacing fires tend to enable the establishment of evergreen conifers. Apart from post-fire mortality, wildfires modulate forest development mainly through competition effects and a reduction of the model’s litter layer. Conclusion: With its fine-scale population dynamics, LAVESI-FIRE can serve as a highly localized, spatially explicit tool to understand the long-term impacts of boreal wildfires on forest structure and to better constrain interpretations of paleoecological reconstructions of fire activity