Alfred Wegener Institute for Polar and Marine Research
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Transient climate simulation of the past 4.5 million years based on the coupled intermediate complexity model iLOVECLIM
Get PDFThe Earth experienced dramatic climate changes during the past million years, including a long-term gradual cooling from the Pliocene (5.3-2.6 million years ago; Ma) to the Pleistocene (2.6-0.011 Ma) and an abrupt transition from 41-kyr to 100-kyr glacial-interglacial cycles at ca. 1.2-0.8 Ma (i.e., the Mid-Pleistocene transition). Investigating the mechanisms that triggered these climatic responses requires long-term transient climate simulations which can be used to quantify the sensitivity of the Earth&#8217;s climate to different external and internal forcings. However, few such simulations exist and therefore, key questions regarding the long-term evolution of the earth system remain unanswered.Here, we used iLOVECLIM, a coupled Earth system numerical climate model of intermediate complexity, to generate a 4.5 Ma transient climate simulation, the longest to date. iLOVECLIM is ideally suited for this task as it requires substantially less computational resources and time to perform transient climate simulations compared to fully coupled general circulation models. We performed the simulations with interactive atmosphere, ocean and vegetation components and used the methodology of previous long-term transient simulations. Briefly, we applied an acceleration factor of five to the external forcings (orbital parameters, greenhouse gases concentration and ice-sheets) and split the 4.5 Ma simulation into 44 chunks run in parallel to reduce the computing time from several years to a couple of months. Each chunk was initialized from an interglacial period, covers at least one glacial-interglacial cycle and has an overlap period of 20,000 years in order to compensate for issues related to spin-up effects and initial conditions. The complete simulation is a composite of all the individual chunks and time-sliding linear interpolation performed on the overlap intervals.While the simulations are still ongoing, preliminary results demonstrate that our new model set-up and experimental design are able to produce reasonable outputs. When it is completed, the final simulation will be evaluated against available paleoclimate data and existing transient climate simulations. Apart from running a simulation with all the external forcings combined, we also plan to run subsequent simulations with each individual forcing alone to evaluate the climate responses associated with each. This unique long transient simulation will provide a better mechanistic understanding of the major climate reorganizations that occurred during the Plio-Pleistocene and will be useful for future data-model comparisons and data assimilation endeavours.</jats:p
Seismic Surveys in the Arctic: Visualization on maps and link to data archive at the Alfred Wegener Institute
Get PDFSeismic reflection experiments are carried out to image the structure of the subsurface and reconstruct geological or geophysical events such as erosion, modifications in depositional conditions or tectonic. The findings provide constraints on the development of ocean basins, gateways, ridge- and rifts-systems, and how they influenced paleoceanography and natural climate variability on long timescales.
The contribution presents the way in which the Alfred Wegener Institute makes its seismic data visible and accessible, and the difficulties that arise. Aim is to visualize the marine seismic profiles measured to date on maps via track lines and to make the corresponding data accessible to the geoscientific community via the digital library system "PANGAEA" as part of the "Open Access Agreement".
For a first overview the online portal https://marine-data.de presents the location of the acquired seismic reflection lines. By clicking on the profile, it displays meta data as expedition data, contact persons, descriptions of the surveys, and link to the cruise report. JPG-Images are provided for some significant seismic profiles. These maps can be quickly updated after new expeditions to keep the community informed about where data has been collected and where there are still gaps.
In a second step the Marine Data Portal is linked to the data archive “PANGAEA”. The data itself can be accessed there within the scope of the “Open Access Agreement”. This is what we are still working on. Some of the expedition data are already archived in Pangaea, but as this step is very time-consuming, it will take us some additional time to enter all available seismic data. The Pangaea archive provides the basis for the data to be permanently visible to the scientific community and to be digitally available for future projects. Another major advantage is that the data is assigned a DOI, which is becoming increasingly important for the submission of publications, research proposals and other applications
Seismic soundscape of the Arctic Ocean: seasonal effects of Sea Ice and Swell on Deep-Sea Ocean Bottom seismometer records
Get PDFSUMMARY
The global oceans are a noisy environment with characteristic acoustic and seismic soundscapes. The enclosed, sea ice-covered Arctic Ocean constitutes a particular noise environment that is rapidly changing. Here, we present a first, comprehensive description of the seismic soundscape of the Arctic Ocean recorded by ocean bottom seismometers especially equipped for the operation in sea ice. They were deployed at 4 km water depth in the Laptev Sea near the sea ice edge in September 2018 and recovered one year later. Analysis of the spectral power between 20 s and 60 Hz demonstrates that ambient noise levels are generally very low compared to other ocean bottom seismic records. Distinct noise bands at high frequencies (&gt;6 Hz) characterize the winter time and are likely caused by the deformation of sea ice emitting seismic signals recordable at the ocean bottom over tens of kilometers. Sea ice noise decays suddenly in May while sea ice concentration is still 100 per cent, but freezing stops and compressional stresses decrease. It only gradually develops in autumn as sea ice becomes thicker, brittle and internally stressed. Microseisms with frequencies of 0.2–2 Hz appear with open water on the Laptev Shelf. Swell events in autumn cause large microseisms and high-frequency noise although ice-noise is not yet present in this season. Ice concentration decreases following the swell events, showing the impact of swell on the sea ice. Ocean bottom seismic records thus represent a powerful tool to monitor the interplay between wave action in the emerging Arctic Ocean and the physical state of its sea ice cover.</jats:p
Demand‐Resource Mismatch Explains Body Shrinkage in a Migratory Shorebird
Get PDFRecent observations of body size declines in animal populations have given rise to discussions of whether or not this is related to climate change-induced temperature increases, with which the body size changes would follow Bergmann's rule. Although the debate is ongoing, the limited thermal benefits of currently observed size reductions make it unlikely that temperature increase shapes a direct selection pressure. Food constraints during early-life development, which could be caused by mismatches between available resources and energetic demands, could cause smaller body sizes too. Here we investigate whether a decrease in body size, observed in a migratory shorebird, the red knot (Calidris canutus canutus) at their West-African nonbreeding grounds over two decades, is linked to developmental plasticity during chick growth in the High Arctic. To do so, we combined datasets from both the wintering and breeding grounds on body size measurements (during chick growth and in fully grown juveniles), food availability, and diet inferred from stable isotopes deposited in feathers grown as chicks. From 2003 to 2021, stable-isotope ratios revealed a decline in the dietary contribution of crane flies (Tipulidae, Diptera), the key food of growing chicks in the Arctic. On the breeding grounds, we observed that while the emergence of adult crane flies advanced along with earlier snowmelt dates, red knots did not adjust the timing of breeding, and this resulted in an increasing mismatch with the demands of growing chicks. As a result, chicks grew slower and, as observed on the wintering grounds, reached smaller final body sizes. Our results imply that increasing resource-demand mismatches may lead to body shrinkage via plasticity during development. In this study, the increasing mismatch was linked with climate warming; the presented causal chain may explain other recent examples of body size reductions as well
Topographic Effect Creates Non‐climatic Variations in Ice‐Core Based Temperature Records of the Last Millennium in Dronning Maud Land, Antarctica
No full textPast temperature reconstructions from polar ice sheets are commonly based on stable water isotope records in ice-cores. However, despite major efforts in the understanding of the ice-core signal formation, the temperature reconstructions of the last millennium in Antarctica remain uncertain. Here, using a 100 km scale representative surface water isotope dataset, we show that the spatial variability of local surface topography and accumulation rate anomalies influences the isotopic composition of the upper-meter snowpack. The magnitude of this non-temperature effect on water isotopes is comparable to the changes observed over the last millennium. We demonstrate that these spatial anomalies are advected into the deeper firn and ice column, and can explain the diverging millennial water isotope trends observed in two ice-cores near the EPICA Dronning Maud Land drilling site. Furthermore, we provide an estimation of areas where this topographic effect could impact temperature reconstructions over the last millenia
Strengthening policy action to tackle social acceptability issues in European aquaculture
Get PDFDespite the rapid development of aquaculture worldwide, production has stagnated in Europe and North America, notwithstanding the public policies that support the sector. This stagnation may stem from the insufficient integration of social dimensions into aquaculture governance, often characterized by top-down policies and technology-driven approaches. While environmental, economic and social factors significantly influence the social acceptability of aquaculture, environmental impacts, such as habitat degradation and the spread of disease, have historically dominated regulatory frameworks. Today, low social acceptability appears to be the major obstacle to the sector’s growth, highlighting shortcomings in terms of stakeholder engagement, transparency and fairness in the distribution of the benefits generated by the sector. This paper reflects the collective insights from the ICES Working Group on Social and Economic Dimensions of Aquaculture, emphasizing that challenges to social acceptability of aquaculture are widespread but context-dependent and remain insufficiently addressed in public policies related to aquaculture development. This paper recommends broadening governance beyond environmental concerns to include social and economic dimensions from the outset, strengthening public participation in decision-making processes and adopting holistic, socially informed marine spatial planning. In addition, it highlights the importance of recognizing the role of informal governance mechanisms and the production of meaningful social data as essential aspects to foster community acceptance and the sustainable development of aquaculture. Adapting aquaculture policies to local contexts through inclusive and adaptive governance is therefore essential to the sustainable growth of the sector
