Alfred Wegener Institute for Polar and Marine Research
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Dissimilarity analysis based on diffusion maps
Get PDFCompositional measurements from species assemblages define a high dimensional dataspace in which the data can form complex structures, termed manifolds. Comparing assemblages in this dataspace is difficult because the data is often sparse relative to its dimensionality and the complex structure of the manifold introduces bias and error in measurements of distance. Here, we apply diffusion maps, a manifold learning method, to find and characterize manifolds in high‐dimensional compositional data. We show that diffusion maps embed the data in reduced dimensions in which the Euclidean distance between data points approximates the distance between them along the manifold. This is especially useful when species turnover is high, as it provides a way to measure meaningful distances between assemblages even when they harbor disjoint sets of species. We anticipate diffusion maps will therefore be particularly useful for characterizing community change over large spatial and temporal scales.</jats:p
Continental-scale drivers of lake drainage in permafrost regions
Get PDFLakes are ubiquitous with high-latitude ecosystems, covering up to 60 percent of the land surface in some regions. Due to their influence on an array of key biogeophysical processes, the recent decline in lake area (via gradual and abrupt) observed across permafrost ecosystems may hold significant implications for shifting carbon and energy dynamics. Since lakes are often highly dynamic, understanding the main drivers of lake area change may ultimately enable the prediction of lake persistence in a warmer climate; key to anticipating future carbon-climate feedbacks from Arctic ecosystems.
Here we conducted a data-driven analysis of >600k lakes across four continental-scale transects (Alaska, E Canada, W Siberia, E Siberia), combining remote sensing-derived lake shape parameters and spatial dynamics with other ecosystem datasets, such as ground temperatures, climate, elevation/geomorphology, and permafrost landscape parameters. We grouped our lake-change dataset into non-drained, partially and completely drained lakes (25-75 %, >75% loss) and used the RandomForest Feature Importance to calculate the relative importance of each parameter. Furthermore we predicted the probability of lake drainage under current environmental conditions and changing permafrost temperatures.
Initial results suggest a strong importance of ground temperatures, lake shape, and local geomorphology on lake drainage. Spatially coarser datasets of permafrost and thermokarst properties did not reveal correlations with the result. Our drainage prediction results show distinct spatial patterns, which are matching regional lake drainage patterns. Our model estimated ground temperature as one of the main impact factors, with an increased drainage likelihood in permafrost regions from -5 to 0 °C.
Going forward, we will further test for short term influences, such as extreme weather events and wildfire on widespread lake drainage. As this analysis is purely data-driven, a comparison or combination with physics-based models and predictions will help to better validate our analysis
Polar Ice and Climate Change - what's in store for the 21st century?
Get PDFPresentation about the disastrous influence of climate change on sea level ris
MARINE RADIOCARBON CALIBRATION IN POLAR REGIONS: A SIMPLE APPROXIMATE APPROACH USING MARINE20
Get PDFThe Marine20 radiocarbon (14C) age calibration curve, and all earlier marine 14C calibration curves from the IntCal group, must be used extremely cautiously for the calibration of marine 14C samples from polar regions (outside ∼40ºS-40ºN) during glacial periods. Calibrating polar 14C marine samples from glacial periods against any Marine calibration curve (Marine20 or any earlier product) using an estimate of, the regional 14C depletion adjustment, that has been obtained from samples in the recent (non-glacial) past is likely to lead to bias and overconfidence in the calibrated age. We propose an approach to calibration that aims to address this by accounting for the possibility of additional, localized, glacial 14C depletion in polar oceans. We suggest, for a specific polar location, bounds on the value of during a glacial period. The lower bound may be based on 14C samples from the recent non-glacial (Holocene) past and corresponds to a low-depletion glacial scenario. The upper bound, representing a high-depletion scenario is found by increasing according to the latitude of the 14C sample to be calibrated. The suggested increases to obtain are based upon simulations of the Hamburg Large Scale Geostrophic Ocean General Circulation Model (LSG OGCM). Calibrating against the Marine20 curve using the upper and lower bounds provide estimates of calibrated ages for glacial 14C samples in high- and low-depletion scenarios which should bracket the true calendar age of the sample. In some circumstances, users may be able to determine which depletion scenario is more appropriate using independent paleoclimatic or proxy evidence
Spatial and temporal variability of the acoustic repertoire of Antarctic minke whales (Balaenoptera bonaerensis) in the Weddell Sea
Get PDFSince the attribution of the bio-duck call to Antarctic minke whales (AMW Balaenoptera bonaerensis), different studies have retrospectively identified several bio-duck call types at various sites throughout the Southern Hemisphere. The function of their vocal behavior however, remains largely unknown. Further insights into their repertoire usage may help to reveal the function of their calls. Here, we use passive acoustic monitoring (PAM) data collected across six locations throughout the Weddell Sea (WS) in 2013 and from PALAOA Station (Ekström Ice Shelf, eastern WS) in 2015, 2016 and 2017. In 2013, we detected 11 bio-duck call types throughout the WS between May and December, with additional acoustic activity in February on the western recorder AMW calls fell into four general call clusters. Seasonal patterns of calls showed variability between locations and years. Furthermore, this is the first study to show that similar to other baleen whale species, AMWs also produce songs
Response of harbor porpoises (Phocoena phocoena) to different types of acoustic harassment devices and subsequent piling during the construction of offshore wind farms
Get PDFBefore piling of offshore wind farm foundations, acoustic harassment devices (AHDs) are used to drive harbor porpoises out of the area where they could suffer injuries. Until 2017, a combination of pingers and seal scarer devices (usually SPL = 174-193 dB re 1 μPa (rms) @ 1m at 1 to 20 kHz depending on the device) was prescribed for mitigation purposes in Germany. However, seal scarers led to decreased porpoise detection rates in much larger distances than intended, when 750 m is usually rendered sufficient to avoid injuries. Therefore, devices specifically designed for mitigation purposes were developed and are prescribed since then. These acoustic porpoise deterrents (APDs; e.g. FaunaGuard Porpoise Module; SPL = 172 dB re 1 μPa (rms) @ 1m at 60 to 150 kHz) aim to keep the animals away from offshore construction sites but should not lead to large-scale disturbance as caused by a seal scarer. Although project-specific evaluations indicated that APDs are effective, a cross-project analysis and a comparison with data from previous piling procedures employing seal scarers were still pending. The present study aimed to fill this gap. Between March 2018 and April 2019, harbor porpoise detection rates were monitored acoustically in four offshore wind farm projects using CPODs before, during and after piling at different distances up to 10 km from piling. APD operation led to a significant decrease in detection rates in the vicinity of the device, indicating the displacement of the animals from a small-scale area. Depending on the wind farm, detection rates during APD operation decreased by 30 to 100% at 750 m distance compared to 6 hours before APD operation. Furthermore, reduced detection rates during APD operation were only observed up to about 2.5 km distance even when the APD was switched on for over 40 minutes. Given that the extent of disturbance to harbor porpoises is lower when using an acoustic porpoise deterrent compared to the seal scarer, we consider that preferential use of an acoustic porpoise deterrent is an improvement to mitigation strategies and an important step forward to a less harmful piling procedure
Vergleich zweier aus Fernerkundungsdaten abgeleiteter globaler Gewässerdatensätze in arktischen Permafrostgebieten
Get PDFGlobal climate change is a current problem that is discussed in many publications. The data provides only limited possibilities for the detection of future consequences. Surface water dynamics are described with some examples, but these give only a small insight into the complexity of this system. Using remote sensing methods, past and present dynamics can be analyzed. Nevertheless, the number of data sets with global data series is very small. Due to modifications of the "System Earth" caused by climate change, the global surface water dynamics is also changing. In high latitudes this is still poorly understood and an analysis of the data can provide an important insight into future consequences. Therefore, it is important to monitor Arctic surface water dynamics.
In this master's thesis, the datasets of PICKENS et al. (2020) and PEKEL et al. (2016) are compared with respect to their results in surface water dynamics for Arctic permafrost areas from 2000 to 2020. In regards to this, both datasets were homogenized using the program "Google Earth Engine" and examined in an accuracy analysis. Any areas where both datasets show different results are detected and checked for possible causes. For this purpose, different reference datasets were used, which visually cover the topography, vegetation cover, landscape classification and permafrost content as indicators. Subsequently, in the program "Microsoft Excel", the data from the accuracy analysis were processed for each study area and analyzed in regards to the results.
This shows that permanent water body areas in each study area were classified almost identically between the data sets. The largest differences between the results of PICKENS et al. (2020) and PEKEL et al. (2016) were found for seasonal water areas. The "Producer and Consumer Accuracy" calculations even yielded accuracy values below 65% in one study area. In these scenic areas, the problem of mixed pixels exists where, depending on pixel size and current water level, accurate classification becomes difficult. Also other factors, like seasonal events, cloud formations or technical errors cannot be excluded and have a share in the differences between the results of the data sets. Based on topography, the forest cover, the landscape classes and the permafrost content, differences between the data sets were recognized and distinctive shapes determined
MOSAiC airborne laser scanning of the sea-ice surface: data product overview and insights to seasonal roughness evolution
Get PDFOral presentation at the 2nd MOSAiC science conference showing the MOSAiC airborne laser scanner product overview and first results of seasonal surface roughnes
Umweltbildung – Aus der Forschung in die Gesellschaft Wissenstransfer am Beispiel der Plastikmüllproblematik in Flüssen und Meeren
Get PDFPlastik in der Umwelt ist eines der prominentesten Themen der aktuellen Forschung und stellt die Menschheit vor eines der grundlegenden Herausforderungen des 21. Jahrhunderts: die Eindämmung der Ressourcenverschwendung und die Verminderung weltweiter Umweltzerstörung. Diese Lerneinheit thematisiert diese Probleme durch praxisnahe Experimente und den direkten Zusammenhang zur Alltagswelt der Schüler/innen und leistet dadurch einen wertvollen Beitrag zur Bildung für nachhaltige Entwicklung
Carbon dynamics following permafrost thaw gradient in a high latitude peatland environment
No full textNorthern peatlands store a considerable proportion of global soil carbon in perennially frozen soil areas in Arctic and Sub-Arctic regions. Recent warming causes permafrost areas to thaw and expose formerly frozen carbon-rich soil to potential accelerated microbial decomposition. The goal of this study is to describe Holocene peatland development and quantify carbon dynamics along a thaw gradient of a rapidly thawing palsa in the sporadic‐discontinuous permafrost zone of Northern Finland (68°52´40´´N 21°04´45´´E). Peat cores until mineral soil were collected along a thaw chronosequence, from intact permafrost site (FRO), through partly thawed intermediate site (INT) and recently (~25 years since thaw) thawed area (THA). Macrofossil and 14C analyses showed a synchronicity of peatland development until recent thaw, with the initiation of peatland formation ~9200 cal. yr. BP, followed by a succession of peatland stages prior to permafrost aggradation ~4200 cal. yr. BP. However, the thawed area indicates a much younger onset of permafrost accumulation, which in turn suggests different permafrost dynamics. Analysis of soil carbon stocks indicated 15.2 kg m-2 (14.7 %) of carbon accumulated prior to thaw was lost in ~20 years post‐thaw. While this is the case for the comparison between the palsa and thawed area carbon stocks, the intermediate site has a higher calculated C stock compared to the most intact site. Based on C:N ratios, visual descriptions, and stable carbon isotope data, no significant increase in peat humification has been observed. Rapid peat accumulation post-thaw (159.4 g C m−2 yr−1) might offset potential losses. However, differences in the peat properties across the individual cores and different thawing features indicate a high degree of spatial heterogeneity, which ultimately casts doubt on a direct comparison of C stocks. Although this approach cannot conclusively determine if thermokarst wetlands in the sporadic permafrost zone of Fennoscandia are long-term carbon sinks or sources post-thaw, it emphasizes the importance of site history and spatial heterogeneity