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  • National Academy of Sciences  (64,447)
  • International Union of Crystallography  (62,274)
  • ELSEVIER SCIENCE BV
  • 2020-2023  (49)
  • 2020-2022  (7,817)
  • 2020-2020
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  • 1
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    Washington, DC : National Academy of Sciences
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  • 2
    Publication Date: 2014-06-24
    Description: The early Pliocene warm phase was characterized by high sea surface temperatures and a deep thermocline in the eastern equatorial Pacific. A new hypothesis suggests that the progressive closure of the Panamanian seaway contributed substantially to the termination of this zonally symmetric state in the equatorial Pacific. According to this hypothesis, intensification of the Atlantic meridional overturning circulation (AMOC) – induced by the closure of the gateway – was the principal cause of equatorial Pacific thermocline shoaling during the Pliocene. In this study, twelve Panama seaway sensitivity experiments from eight ocean/climate models of different complexity are analyzed to examine the effect of an open gateway on AMOC strength and thermocline depth. All models show an eastward Panamanian net throughflow, leading to a reduction in AMOC strength compared to the corresponding closed-Panama case. In those models that do not include a dynamic atmosphere, deepening of the equatorial Pacific thermocline appears to scale almost linearly with the throughflow-induced reduction in AMOC strength. Models with dynamic atmosphere do not follow this simple relation. There are indications that in four out of five models equatorial wind-stress anomalies amplify the tropical Pacific thermocline deepening. In summary, the models provide strong support for the hypothesized relationship between Panama closure and equatorial Pacific thermocline shoaling.
    Repository Name: EPIC Alfred Wegener Institut
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  • 3
    Publication Date: 2018-02-05
    Description: Euphausiids constitute a major biomass component in shelf ecosystems and play a fundamental role in the rapid vertical transport of carbon from the ocean surface to the deeper layers during their daily vertical migration (DVM). DVM depth and migration patterns depend on oceanographic conditions with respect to temperature, light and oxygen availability at depth, factors that are highly dependent on season in most marine regions. Here we introduce a global krill respiration ANN (artificial neural network) model including the effect of latitude (LAT), the day of the year (DoY), and the number of daylight hours (DLh), in addition to the basal variables that determine ectothermal oxygen consumption (temperature, body mass and depth). The newly implemented parameters link space and time in terms of season and photoperiod to krill respiration. The ANN model showed a better fit (r2 = 0.780) when DLh and LAT were included, indicating a decrease in respiration with increasing LAT and decreasing DLh. We therefore propose DLh as a potential variable to consider when building physiological models for both hemispheres. For single Euphausiid species investigated in a large range of DLh and DoY, we also tested the standard respiration rate for seasonality with Multiple Linear Regression (MLR) and General Additive model (GAM). GAM successfully integrated DLh (r2 = 0.563) and DoY (r2 = 0.572) effects on respiration rates of the Antarctic krill, Euphausia superba, yielding the minimum metabolic activity in mid-June and the maximum at the end of December. We could not detect DLh or DoY effects in the North Pacific krill Euphausia pacifica, and our findings for the North Atlantic krill Meganyctiphanes norvegica remained inconclusive because of insufficient seasonal data coverage. We strongly encourage comparative respiration measurements of worldwide Euphausiid key species at different seasons to improve accuracy in ecosystem modeling.
    Repository Name: EPIC Alfred Wegener Institut
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  • 4
    Publication Date: 2019-07-16
    Description: Euphausiids constitute a major biomass component in shelf ecosystems and play a fundamental role in the rapid vertical transport of carbon from the ocean surface to the deeper layers during their daily vertical migration (DVM). DVM depth and migration patterns depend on oceanographic conditions with respect to temperature, light and oxygen availability at depth, factors that are highly dependent on season in most marine regions. Here we introduce a global krill respiration ANN (Artificial Neural Network) model including the effect of latitude (LAT), the day of the year (DoY), and the number of daylight hours (DLh), in addition to the basal variables that determine ectothermal oxygen consumption (temperature, body mass and depth). The newly implemented parameters link space and time in terms of season and photoperiod to krill respiration. The ANN model showed a better fit (r2=0.780) when DLh and LAT were included, indicating a decrease in respiration with increasing LAT and decreasing DLh. We therefore propose DLh as a potential variable to consider when building physiological models for both hemispheres. For single Euphausiid species investigated in a large range of DLh and DoY, we also tested the standard respiration rate for seasonality with Multiple Linear Regression (MLR) and General Additive model (GAM). GAM successfully integrated DLh (r2= 0.563) and DoY (r2= 0.572) effects on respiration rates of the Antarctic krill, Euphausia superba, yielding the minimum metabolic activity in mid-June and the maximum at the end of December. We could not detect DLh or DoY effects in the North Pacific krill Euphausia pacifica, and our findings for the North Atlantic krill Meganyctiphanes norvegica remained inconclusive because of insufficient seasonal data coverage. We strongly encourage comparative respiration measurements of worldwide Euphausiid key species at different seasons to improve accuracy in ecosystem modelling.
    Repository Name: EPIC Alfred Wegener Institut
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  • 5
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    ELSEVIER SCIENCE BV
    In:  EPIC3Earth and Planetary Science Letters, ELSEVIER SCIENCE BV, 403, pp. 446-455, ISSN: 0012-821X
    Publication Date: 2014-08-25
    Description: The transition from last glacial to deglacial and subsequently to modern interglacial climate conditions was accompanied by abrupt shifts in the palaeoceanographic setting in the subpolar North Atlantic. Knowledge about the role that sea ice coverage played during these rapid climate reversals is limited since most marine sediment cores from the higher latitudes provide only a coarse temporal resolution and often poorly preserved microfossils. Here we present a highly resolved reconstruction of sea ice conditions that characterised the eastern Fram Strait – a key area for water mass exchange between the Arctic Ocean and the North Atlantic – for the past 30 ka BP. This reconstruction is based on the distribution of the sea ice biomarker IP25 and phytoplankton derived biomarkers in a sediment core from the continental slope of western Svalbard. During the late glacial (30 ka to 19 ka BP), recurrent advances and retreats of sea ice characterised the study area and point to a hitherto less considered oceanic (and/or atmospheric) variability. A long-lasting perennial sea ice coverage in eastern Fram Strait persisted only at the very end of the Last Glacial Maximum (i.e. from 19.2 to 17.6 ka BP) and was abruptly reduced at the onset of Heinrich Event 1 – coincident with or possibly even inducing the collapse of the Atlantic Meridional Overturning Circulation (AMOC). Further maximum sea ice conditions prevailed during the Younger Dryas cooling event and support the assumption of an AMOC reduction due to increased formation and export of Arctic sea ice through Fram Strait. A significant retreat of sea ice and sea surface warming are observed for the Early Holocene.
    Repository Name: EPIC Alfred Wegener Institut
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  • 6
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    National Academy of Sciences
    In:  EPIC3PNAS, National Academy of Sciences, 111(34), pp. E3501-E3505, ISSN: 0027-8424
    Publication Date: 2016-12-09
    Description: A recent temperature reconstruction of global annual temperature shows Early Holocene warmth followed by a cooling trend through the Middle to Late Holocene [Marcott SA, et al., 2013, Science 339(6124):1198–1201]. This global cooling is puzzling because it is opposite from the expected and simulated global warming trend due to the retreating ice sheets and rising atmospheric greenhouse gases. Our critical reexamination of this contradiction between the reconstructed cooling and the simulated warming points to potentially significant biases in both the seasonality of the proxy reconstruction and the climate sensitivity of current climate models.
    Repository Name: EPIC Alfred Wegener Institut
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  • 7
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    ELSEVIER SCIENCE BV
    In:  EPIC3Palaeogeography Palaeoclimatology Palaeoecology, ELSEVIER SCIENCE BV, 414, pp. 1-19, ISSN: 0031-0182
    Publication Date: 2014-09-04
    Description: Here we present an improvement of paleotemperature reconstructions for the Southern Ocean by combining new diatom data from the Pacific sector with published Atlantic and Indian sector reference data. The statistical analysis of 336 surface sediment samples recovered from a wide area of Southern Ocean environments defines a supra-regional reference data set for quantitative summer sea surface temperature (SSST) estimations. In situ temperature measurements covering the time span from approx. 1900 to 1991 were used as reference instead of more recent time series of satellite-derived data, possibly biased by ocean warming. Different transfer function (TF) models for the Imbrie and Kipp Method (IKM), the Modern Analog Technique (MAT), Weighted Averaging (WA), and Weighted Averaging Partial Least Squares (WAPLS) were tested. Best performance for IKM was obtained using the D336 set with 29 diatom taxa and three factors, resulting in root mean square error of prediction (RMSEP) of 0.833°C for SSST. MAT estimates were best with six analogs resulting in the lowest RMSEP of 0.812°C. WAPLS applied to D336 resulted in a RMSEP of 0.782°C. WA performed less well, expressed by a RMSEP of 0.974°C. Furthermore, two subsets for the Atlantic (D151) and the Pacific sectors (D107) were applied with IKM to test for the advantages of localized TFs. IKM-D151 and IKM-D107 performed comparably good as IKM-D336, with RMSEP of 0.71°C and 0.68°C, respectively. Application of the augmented reference data sets on two Pleistocene sediment records from the Atlantic (PS1768-8) and Pacific (PS58/271-1) sectors led to the best performance of IKM with D336, expressed by high overall communalities (〉0.75) and fewer (PS1768-8) to no (PS58/271-1) no-analogs, compared to the regional data sets, proving IKM-D336 to deal better with higher assemblage variability. SSST estimates for both cores exhibit similar glacial/interglacial patterns for all four applied D336-based TF methods, with the best concordance between IKM and WAPLS.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , isiRev , info:eu-repo/semantics/article
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  • 8
    Publication Date: 2019-07-17
    Repository Name: EPIC Alfred Wegener Institut
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  • 9
    Publication Date: 2019-07-17
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  • 10
    Publication Date: 2019-07-17
    Repository Name: EPIC Alfred Wegener Institut
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  • 11
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    ELSEVIER SCIENCE BV
    In:  EPIC3Harmful Algae, ELSEVIER SCIENCE BV, 36, pp. 22-28, ISSN: 1568-9883
    Publication Date: 2019-07-17
    Description: Azadinium poporum is a small dinoflagellate from the family Amphidomataceae which is known for the production potential of azaspiracids (AZAs) causative of azaspiracid shellfish poisoning (AZP). A. poporum has been recorded from European and western Pacific waters. Here we report on the high variability of toxin profiles within this species in Chinese coastal waters. Out of 16 analyzed strains of A. poporum from different geographic locations along the Chinese coastline, three strains proved not to contain AZAs, whereas 13 strains contained different combinations of AZA-2, AZA-11, AZA-37, a yet unknown isomer of AZA-1 (named AZA-40) and new AZA with yet unreported molecular mass of 853 Da (named AZA-41). The new AZA-40, other than AZA-1 itself, belongs to the recently discovered “348-type” group, which in tandem mass spectrometry displays a group 4 fragment with m/z 348 instead of the group 4 fragment of the classic AZAs with m/z 362, indicating a shift of a methyl group from the C24-C40 part of the molecule (rings F-I) to the C2-C9 part (carboxylic side chain and ring A). AZA-41 apparently is a dehydro variant of AZA-2. In addition a previously reported AZA with a molecular mass 871 DA could be unambiguously assigned to AZA-11, which is known to be a shellfish metabolite of AZA-2. This is the first report of AZA-11 being also de novo synthetized by dinoflagellates.
    Repository Name: EPIC Alfred Wegener Institut
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  • 12
    Publication Date: 2019-07-16
    Repository Name: EPIC Alfred Wegener Institut
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  • 13
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    ELSEVIER SCIENCE BV
    In:  EPIC3Dynamics of Atmospheres and Oceans, ELSEVIER SCIENCE BV, 50(1), pp. 55-77, ISSN: 0377-0265
    Publication Date: 2018-12-07
    Description: A semi-analytical model of the Panama throughflow is presented. The model expresses the throughflow transport as a function of deep water formation in the North Pacific and in the North Atlantic, and of the Panama Gateway depth. The model is derived from the integral of the momentum equation along a circumpolar path, and can be interpreted from the point of view of the vorticity balance. The important conditions are whether the deep water, whose location is considered to be above the bottom water formed around Antarctica, originates from the North Atlantic or from the North Pacific, and whether the Panama Gateway is shallower than the lower boundary of the deep water. The present model indicates that the barotropic transport through the Panama Gateway is eastward, except for the case where the deep water is formed in the North Pacific and the sill of the Panama Gateway is shallow. The baroclinic structure of the Panama throughflow depends on whether the deep water is formed in the North Pacific or in the North Atlantic. These qualitative implications of the model are consistent with recent numerical studies and proxy-based paleoceanographic studies. Numerical experiments performed in the present study reinforce confidence in the semi-analytical model.
    Repository Name: EPIC Alfred Wegener Institut
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  • 14
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    ELSEVIER SCIENCE BV
    In:  EPIC3Palaeogeography Palaeoclimatology Palaeoecology, ELSEVIER SCIENCE BV, 539(109506), ISSN: 0031-0182
    Publication Date: 2019-12-22
    Description: Density-driven mass movement deposits (MMDs) were mapped throughout the Quaternary sedimentary record of Lake El'gygytgyn (NE Siberia) using high-resolution acoustic data. Three different acoustic facies types were identified in the lake: (1) pelagic sediment, (2) plastic flow deposits and (3) turbidites. Deposits from plastic flows are dominantly present proximal to the lakes' slopes, whereas deposits from turbidity currents occur more spatially distributed. During glacial times, the distribution of MMDs was more uniform, while during interglacial periods, MMDs were deposited predominantly close to the slope of the northwestern area. Furthermore, the overall number of MMDs and accumulated sediment volume significantly varies between glacial/interglacial periods. About 1.6 times more MMDs were mapped during interglacials, contributing to a 3.5 times higher sediment volume. The main reason for this large difference is that a significant increase in plastic flows were formed during interglacials, which account for a much larger volume of sediments when compared with the glacial intervals characterized by increased amount of turbidites. It appears that the most important source areas for MMDs are located at the northern and western shores. Cycles of lake level changes caused by variations in climate conditions between glacials and interglacials are likely the main trigger mechanism for the generation of these MMDs. The climate-dependent genesis and partly erosive potential influencing the sedimentary record contain implications to consider for future paleo-environmental reconstructions in lacustrine settings.
    Repository Name: EPIC Alfred Wegener Institut
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  • 15
    Publication Date: 2020-08-11
    Description: The Antarctic krill, Euphausia superba, has evolved seasonal rhythms of physiology and behaviour to survive under the extreme photoperiodic conditions in the Southern Ocean. However, the molecular mechanisms generating these rhythms remain far from understood. The aim of this study was to investigate seasonal differences in gene expression in three different latitudinal regions (South Georgia, South Orkneys/Bransfield Strait, Lazarev Sea) and to identify genes with potential regulatory roles in the seasonal life cycle of Antarctic krill. The RNA-seq data were analysed (a) for seasonal differences between summer and winter krill sampled from each region, and (b) for regional differences within each season. A large majority of genes showed an up-regulation in summer krill in all regions with respect to winter krill. However, seasonal differences in gene expression were less pronounced in Antarctic krill from South Georgia, most likely due to the milder seasonal conditions of the lower latitudes of this region, with a less extreme light regime and food availability between summer and winter. Our results suggest that in the South Orkneys/Bransfield Strait and Lazarev Sea region, Antarctic krill entered a state of metabolic depression and regressed development (winter quiescence) in winter. Moreover, seasonal gene expression signatures seems to be driven by a photoperiodic timing system that may adapt the flexible behaviour and physiology of Antarctic krill to the highly seasonal environment according to the latitudinal region. However, at the lower latitude South Georgia region, food availability might represent the main environmental cue influencing seasonal physiology.
    Repository Name: EPIC Alfred Wegener Institut
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  • 16
    Publication Date: 2020-09-02
    Repository Name: EPIC Alfred Wegener Institut
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  • 17
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    ELSEVIER SCIENCE BV
    In:  EPIC3Tectonophysics, ELSEVIER SCIENCE BV, 778(228370), ISSN: 0040-1951
    Publication Date: 2020-12-01
    Description: Some of the oldest surviving oceanic basins in the world, the Mozambique and West Somali basins, were created during the breakup of Gondwana, starting around 180 Ma. Between the two basins, relative movements of West Gondwana and East Gondwana, including Madagascar, created a shear zone, the Davie Fracture Zone (DFZ) with a topographic elevation (Davie Ridge - DR) marking its centre. The crustal composition of the DFZ and DR is a subject of speculation and debate. In this study, we present seismic refraction data across the prominent topography of the southern DR. Ray tracing of the wide-angle data as well as additional seismic amplitude modelling and 2.5D density modelling constrain its crustal structure and architecture. The data indicate that in the Mozambique Channel the DR consists of fragments of continental crust with a thickness of 10 to 12 km. An oceanic crust indenter extends northward from the Mozambique Basin into the area between the DR and the East African margin at 16.5°S. Northeast of the DR, at 41.8°W/14.5°S, the Somali Basin is probably floored by 6 km thick oceanic crust. Hence, the continental DR separates oceanic crust of the Somali and Mozambique basins. The transitional crustal area at the central Mozambican margin is underlain by high velocity lower crust (HVLC). The HVLC has velocities up to 7.3 km/s and extents along the margin, vanishing northward between 16.5° and 14.5°S. At the Madagascan side of the DR, at 16.5°S, the highly intruded stretched continental crust is 9 km thick and possibly underlain with a smaller HVLC of 2.9 km thickness and an E-W extent of 120 km. The oceanic crust at 14.5°S represents the oldest part the Somali Basin, which formed after the initial NW-SE rifting between East and West Gondwana.
    Repository Name: EPIC Alfred Wegener Institut
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  • 18
    Publication Date: 2020-12-16
    Repository Name: EPIC Alfred Wegener Institut
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  • 19
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    ELSEVIER SCIENCE BV
    In:  EPIC3Palaeogeography Palaeoclimatology Palaeoecology, ELSEVIER SCIENCE BV, 573, pp. 110437, ISSN: 0031-0182
    Publication Date: 2021-05-25
    Description: There have been a number of suggested driving factors for Late Miocene expansion of C4 plant coverage, including a decline in atmospheric CO2 concentrations, enhanced aridity and seasonality, shifts in fire regimes, and tectonic uplift. In order to identify and discriminate the driving factors of vegetation changes, continuous records from the same section or basin are required. We present micro-charcoal-based fire history and C4 vegetation abundance records spanning the Miocene from the Yanwan Section in the Tianshui Basin, on the northeastern Tibetan Plateau (NE TP). Based on statistical analyses, the micro-charcoal concentrations were relatively low before ~10Â Ma, and after that time, there was an exponential increase. The C4 plant abundance shows a strong increase after 8Â Ma, about 2 million years after the micro-charcoal concentrations started increasing. We compare our records with published CO2, pollen, seasonality, herbivorous mammalian fossil and tectonic records from the same section and basin. We find that C4 vegetation, fire intensities, and opening landscapes increased simultaneously after 8 Ma. This indicates that a fire-grassland feedback, initially driven by aridification, was the trigger for the Late Miocene expansion of C4 plants. We speculate that herbivorous mammalian species may also have played a minor role. During the Miocene, there is a trend towards enhanced seasonality and a decline in atmospheric CO2 concentrations, which were also necessary preconditions for the expansion.
    Repository Name: EPIC Alfred Wegener Institut
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  • 20
    Publication Date: 2020-11-17
    Repository Name: EPIC Alfred Wegener Institut
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  • 21
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    ELSEVIER SCIENCE BV
    In:  EPIC3Ecological Modelling, ELSEVIER SCIENCE BV, 442, ISSN: 0304-3800
    Publication Date: 2021-01-25
    Description: Antarctic krill up- and down-regulate their metabolism as a strategy to cope with the strong seasonal environmental fluctuations in the Southern Ocean. In this study, we investigate the impact of this light- and temperature dependent metabolic regulation on growth, reproduction and winter survival of krill. Therefore, we advance a bioenergetic growth model of krill by adding a data-derived scaling function of krill activity. With SERBIK (SEasonally Regulated BIoenergetic Krill growth model), we conduct a numerical experiment which tests the impact of such scaling on krill life history under two different winter food conditions: In the first scenario, we simulate life history of krill when winter food availability is low; in the second scenario, winter food availability is increased within realistic ranges. The results demonstrate that the scaling of metabolism is especially important during low food winters. Reducing metabolism during winter permits individuals to grow to larger body length, reproduce successfully and release a greater number of eggs. It further significantly reduces withinyear size fluctuations caused by starvation during months with low food availability. Finally, SERBIK can be used in future spatial modelling studies which include movement of krill along latitudinal gradients and thus spatiotemporal gradients in light- and temperature.
    Repository Name: EPIC Alfred Wegener Institut
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  • 22
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    ELSEVIER SCIENCE BV
    In:  EPIC3Geomorphology, ELSEVIER SCIENCE BV, 382, ISSN: 0169-555X
    Publication Date: 2021-03-17
    Description: Acoustic and detailed swath bathymetry data revealed a systematic picture of submarine landslides on the Siberian part of Lomonosov Ridge. Whereas numerous studies on mass movement exist along the margin of the Arctic Ocean less is known from central Arctic. A regional survey comprising swath bathymetry, sediment echo sounder and multichannel seismic profiling was performed on the southeastern Lomonosov Ridge. The data provide constraints on the present-day morphology of the Siberian part of Lomonosov Ridge, between 81°–84°N and 140°–146°E. We mapped twelve crescent-shaped escarpments located on both flanks on the crest of Lomonosov Ridge. The escarpments are 2.1 to 10.2 km wide, 1.7 to 8.2 km long and 125 to 851 m high from which 58 to 207 m are occupied by crescent-shaped headscarps. Subbottom data show chaotic reflections within most of the escarpment areas. The unit is overlain by ~110–340 m of semi-coherent parallel reflections. At its bottom the chaotic reflections are limited by a partly eroded high-amplitude reflection sequence that is inclined with 〈1° basinwards. We find the escarpments to be remnants of submarine landslide events that mobilized 0.09 to 7.58 km3 of sediments between mid Pliocene and mid Miocene. The relatively small amounts of mobilized sediments seem to be typical for the Lomonosov Ridge. The epoch corresponds to the ongoing subsidence of the Lomonosov Ridge below sea level. During that time deposition and the load of sediments changed. We suggest that changes in sediment type preconditioned, and co-occurring earthquakes finally triggered the submarine landslides.
    Repository Name: EPIC Alfred Wegener Institut
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  • 23
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    ELSEVIER SCIENCE BV
    In:  EPIC3Global and Planetary Change, ELSEVIER SCIENCE BV, 200, pp. 103474, ISSN: 0921-8181
    Publication Date: 2021-07-01
    Repository Name: EPIC Alfred Wegener Institut
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  • 24
    Publication Date: 2021-06-30
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  • 25
    Publication Date: 2019-10-20
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  • 26
    Publication Date: 2019-12-20
    Description: Bioturbation is one of the key mediators of biogeochemical processes in benthic habitats that can have a high contribution to seafloor functioning and benthic pelagic coupling in coastal waters. Previous studies on bioturbation were limited to point locations and extrapolations in single regions, but have not accounted for regional differences under changing environmental conditions, though there are indications that species contributions will differ across regions or with biotic and abiotic context. To capture those differences and assess global patterns and commonalities, multi-regional analyses are imperative. Here for the first time, bioturbation potential (BPc), a functional indicator of benthic community bioturbation, was estimated based on macrofauna data from four regions (i.e. German Baltic Sea, German North Sea, Belgian part of the North Sea and the Eastern English Channel). For each region and sediment type we identified key species contributing to BPc. Comparison within and across regions demonstrated regional differences, and both overlap and mismatch between species that are functionally important and those that are dominant in biomass. Knowledge on the functionally important species is crucial when management objectives include the protection of certain ecosystem functions. Available environmental layers were used as predictors to model the spatial distribution of BPc for each area and to explore the underlying drivers of differences. Random forest models were trained using as response variables either i) BPc initially calculated per station; or ii) BPp – the species-specific contribution to BPc – for key species (with subsequent summation of their predicted full-coverage distributions to BPc). Maps of BPc distribution predicted by random forest were compared with those generated using natural neighbour interpolation. Overall, derived BPc values increased towards the German parts of the North and Baltic Seas. The relevance of BPc for ecosystem processes and functions, however, vary with biotic and abiotic settings. Results revealed a strong association of BPc with species diversity and region, but less with sediment grain size. A large range of BPc occurred when species richness was low. This suggests that the provisioning of high bioturbation activity is possible also under low diversity, where it is vulnerable due to reduced resilience. The executed multi-regional analysis allowed identifying regional differences in performance of macrofauna, suggesting the need for regionspecific conservation and management strategies. https://doi.org/10.1016/j.ecolind.2019.105945 Received 26 July 2019; Received in revised form 12 November 2019; Accepted 14 November 2019 ⁎ Corresponding author. E-mail address: mayya.gogina@io-warnemuende.de (M. Gogina). Ecological Indicators 110 (2020) 105945 1470-160X/ Crown Copyright © 2019 Published by Elsevier Ltd. All rights reserved. T
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  • 27
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    ELSEVIER SCIENCE BV
    In:  EPIC3Science of The Total Environment, ELSEVIER SCIENCE BV, 707, ISSN: 0048-9697
    Publication Date: 2020-02-25
    Description: An increase in human Vibrio spp. infections has been linked to climate change related events, in particular to seawater warming and heatwaves. However, there is a distinct lack of research of pathogenic Vibrio spp. occurrences in the temperate North Sea, one of the fastest warming seas globally. Particularly in the German Bight, Vibrio investigations are still scarce. This study focuses on the spatio-temporal quantification and pathogenic characterization of V. parahaemolyticus, V. vulnificus and V. cholerae over the course of 14 months. Species-specific MPN-PCR (Most probable number – polymerase chain reaction) conducted on selectively enriched surface water samples revealed seasonal patterns of all three species with increased abundances during summer months. The extended period of warm seawater coincided with prolonged Vibrio spp. occurrences in the German Bight. Temperature and nitrite were the factors explaining variations in Vibrio spp. abundances after generalized additive mixed models. The specific detection of pathogenic markers via PCR revealed trh-positive V. parahaemolyticus, pathogenic V. vulnificus (nanA, manIIA, PRXII) and V. cholerae serotype O139 presence. Additionally, spatio-temporally varying virulence profiles of V. cholerae with multiple accessory virulence-associated genes, such as the El Tor variant hemolysin (hlyAET), acyltransferase of the repeats-in-toxin cluster (rtxC), Vibrio 7th pandemic island II (VSP-II), Type III Secretion System (TTSS) and the Cholix Toxin (chxA) were detected. Overall, this study highlights that environmental human pathogenic Vibrio spp. comprise a reservoir of virulence-associated genes in the German Bight, especially in estuarine regions. Due to their known vast genetic plasticity, we point to the possible emergence of highly pathogenic V. cholerae strains. Particularly, the presence of V. cholerae serotype O139 is unusual and needs urgent continuous surveillance. Given the predictions of further warming and more frequent heatwave events, human pathogenic Vibrio spp. should be seriously considered as a developing risk to human health in the German Bight.
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  • 28
    Publication Date: 2020-02-14
    Description: Numerous studies have provided compelling evidence that the Pacific Ocean has experienced substantial glacial/interglacial changes in bottom-water oxygenation associated with enhanced carbon dioxide storage in the glacial deep ocean. Under postulated low glacial bottom-water oxygen concentrations (O2bw), redox zonation, biogeochemical processes and element fluxes in the sediments must have been distinctively different during the last glacial period (LGP) compared to current well-oxygenated conditions. In this study, we have investigated six sites situated in various European contract areas for the exploration of polymetallic nodules within the Clarion-Clipperton Zone (CCZ) in the NE Pacific and one site located in a protected Area of Particular Environmental Interest (APEI3) north of the CCZ. We found bulk sediment Mn maxima of up to 1 wt% in the upper oxic 10 cm of the sediments at all sites except for the APEI3 site. The application of a combined leaching protocol for the extraction of sedimentary Mn and Fe minerals revealed that mobilizable Mn(IV) represents the dominant Mn(oxyhydr)oxide phase with more than 70% of bulk solid-phase Mn. Steady state transport-reaction modeling showed that at postulated glacial O2bw of 35 µM, the oxic zone in the sediments was much more compressed than today where upward diffusing pore-water Mn2+ was oxidized and precipitated as authigenic Mn(IV) at the oxic-suboxic redox boundary in the upper 5 cm of the sediments. Transient transport-reaction modeling demonstrated that with increasing O2bw during the last glacial termination to current levels of ~ 150 µM, (1) the oxic-suboxic redox boundary migrated deeper into the sediments and (2) the authigenic Mn(IV) peak was continuously mixed into subsequently deposited sediments by bioturbation causing the observed mobilizable Mn(IV) enrichment in the surface sediments. Such a distinct mobilizable Mn(IV) maximum was not found in the surface sediments of the APEI3 site, which indicates that the oxic zone was not as condensed during the LGP at this site due to two- to threefold lower organic carbon burial rates. Leaching data for sedimentary Fe minerals suggest that Fe(III) has not been diagenetically redistributed during the LGP at any of the investigated sites. Our results demonstrate that the basin-wide deoxygenation in the NE Pacific during the LGP was associated with (1) a much more compressed oxic zone at sites with carbon burial fluxes higher than 1.5 mg Corg m-2 d-1, (2) the authigenic formation of a sub-surface mobilizable Mn(IV) maximum in the upper 5 cm of the sediments and (3) a possibly intensified suboxic-diagenetic growth of polymetallic nodules. As our study provides evidence that authigenic Mn(IV) precipitated in the surface sediments under postulated low glacial O2bw, it contributes to resolving a long-standing controversy concerning the origin of widely observed Mn-rich layers in glacial/deglacial deep-sea sediments.
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  • 29
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    In:  EPIC3Palaeogeography Palaeoclimatology Palaeoecology, ELSEVIER SCIENCE BV, 546(109633), ISSN: 0031-0182
    Publication Date: 2020-04-03
    Repository Name: EPIC Alfred Wegener Institut
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  • 30
    Publication Date: 2020-02-24
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  • 31
    Publication Date: 2021-01-10
    Description: Deep-sea regions provide vast ecosystem services such as biological habitat and nutrient cycling. Even though being threatened by climate change and facing possible biodiversity loss, these deep-sea ecosystems are poorly understood. So are macrobenthic communities and their functions within these ecosystems. Biodiversity and ecosystem function relationships as well as their link to environmental drivers can be assessed with the biological trait analysis. We used this approach for the first time for macrofauna assemblages across the deep Fram Strait between Greenland and Svalbard (1000–5500 m water depth) to evaluate their community-specific function from the upper continental slope down to the deepest known Arctic depression, the Molloy Deep. We aimed to investigate whether there are changes in benthic functioning along the bathymetric gradient and if so, which environmental stressors may drive these changes. In total, 16 stations were sampled with a giant box corer (0.25 m2) in 2016 and 2018. Sediments were sieved through a 0.5 mm mesh size sieve and fauna was identified to lowest possible taxonomic entity. Functions of species were characterized by using six traits split in 24 modalities gathered in a fuzzy coded species × traits array. Environmental parameters shaping the benthic habitat and reflecting food availability were gathered from remote sensing, mooring deployments, and sediment sampling. A distance-based redundancy analysis indicated near-bottom water temperature, seabed inclination, water depth as well as phytodetritial matter at the sea surface and seafloor (indicating food availability) to be the best variables explaining the trait and station distribution. Stations clustered into three groups based on their trait composition. Shallower stations characterized by high chlorophyll a concentration with large organisms, living within the sediment as well as predating specimens clustered in one group. A second group was characterized by stations with low chlorophyll a concentration and medium-sized, suspension feeding, epifaunal living macrofauna. A third group comprised stations with water depths ≥ 3000 m and was dominated by medium sized, surface deposit feeding and infaunal living specimens. Overall, the functional structure of macrofauna communities in the Fram Strait followed a food availability-driven gradient. Based on the relationship between sea ice, surface water primary production and food availability at the seafloor, these results point to macrobenthos being sensible to predicted anthropogenically generated environmental variations in polar regions. Alterations in benthic ecosystem functions might be expected when environmental conditions change.
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  • 32
    Publication Date: 2020-06-17
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  • 33
    Publication Date: 2020-09-02
    Description: In this study, organic geochemical analyses of two sediment cores (BL16 and LV63–23) recovered from the western Bering Sea were carried out to examine the sea-ice variability and its relationship to phytoplankton community evolution over the past century. Bulk stable organic carbon isotopic composition (δ13CTOC) showed pronounced depletion on the northern shelf since the late 1970s, indicating greater terrigenous organic matter (OM) under warming during recent decades. Variation in sedimentary OM in the southward core was closely associated with marine primary productivity and regional deposition processes. Arctic sea-ice proxy IP25 throughout the two cores with different temporal profile patterns demonstrated sea-ice presence with the spatiotemporal variability across the study area over the past century. The phytoplankton marker-IP25 index (PIP25), a proxy for estimating semi-quantitatively sea-ice concentrations, reflected a decreased sea-ice cover with more distinct interannual fluctuations between 0.7 and 0.2 (especially in core BL16) after the late 1970s, coinciding with the recent warming scenario. Increased concentrations of phytoplankton biomarkers (brassicasterol and dinosterol) and their ratios as well as the PIP25 record in core BL16 indicated a synchronous variability of reduced sea-ice cover with the enhancement of phytoplankton productivity since the late 1970s. These results suggested a coupled interaction of the sea-ice condition and planktonic ecosystem in the north Bering shelf. Our results also revealed recent (since the 2000s) spatial heterogeneity in sea-ice coverage between the northern and southern parts of the Bering Sea.
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  • 34
    Publication Date: 2020-10-12
    Description: recent study using Fe-limited phytoplankton strains, showed that iron (Fe) uptake rates normalized by cellular surface area were best related to dissolved iron (dFe) concentrations as the inorganic Fe (Fe’) supply rates were not sufficient to satisfy the Fe biological demand. Short-term (24 h) shipboard incubations with the in-situ phytoplankton community were used to measure Fe uptake rates that were normalized per biomass (as particulate organic carbon, POC). Fe uptake rates measured following 55FeCl3 additions (0.05 to 0.9 nM) were fitted to different Fe pools (dFe, Felabile, and Fe’) using the Michaelis-Menten equation. Data showed a similar high conditional stability constant for biological transporters across all sites and phytoplankton size classes, with only a 2-fold variation in the concentrations of cellular transporters. These observations are in line with previous reports that eukaryotic phytoplankton takes up Fe close to the limit imposed by transporters cellular density and uses similar high-affinity Fe uptake systems. To further explore the link between Fe uptake rates and Fe chemistry, we also studied the effect of Fe additions preequilibrated with different Fe-binding ligands (L) including: the siderophore desferrioxamine B, two carbohydrates (glucuronic acid and carrageenan) and two different bacterial exopolycarbohydrates (L6 and L22, referred as EPS). For all stations, phytoplankton were able to acquire Fe associated to DFB as previously reported, however, different Fe:L ratios prevent quantitative comparison with other studies. Iron bound to carbohydrates, glucuronic acid, carrageenan and EPS could enhance or decrease Fe uptake rates in comparison to equimolar FeCl3 addition. These results illustrate that the effect of such L on Fe uptake rates will depend on the in-situ plankton community and their chemical structure. The variation of the Fe’ concentrations was able to explain up to 69% of the Fe uptake rates observed for the Antarctic communities. This relationship with Fe’ was related to the fact that the Fe’ maximal supply, due to the dissociation of FeL, was enough to satisfy the measured Fe uptakes rates. Calculations using previous reports in contrasted regions of the Southern Ocean, showed that Fe’ maximal supply was greater than Fe uptake rates measured in 80% of the cases. Moreover, considering photo- and redox-chemistry as well as kinetical situations prevailing in the field, Fe’ should not be overlooked as a pool able to satisfy most of the Fe biological demand. Finally, this study points towards the potential that the GEOTRACES Fe chemical speciation data represent to explore Fe uptake rates at a larger scale in this vast Fe-limited oceanic region.
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  • 35
    Publication Date: 2020-12-01
    Description: We assessed the qualitative composition of fluorescent dissolved organic matter (FDOM) in Arctic Ocean surface water and in sea ice north of the Svalbard Archipelago (in the Sophia Basin, the Yermak Plateau and the north Spitsbergen shelf) in May and June 2015, during the “TRANSSIZ” expedition (Transitions in the Arctic Seasonal Sea Ice Zone). Samples collected in open lead waters (OW), under-ice waters (UIW) and from the sea ice (ICE) were analyzed by fluorescence spectroscopy and subsequently by multivariate statistical methods using Parallel Factor Analysis (PARAFAC). Statistical analyses of all measured DOM fluorescence excitation and emission matrices (EEMs) enabled four components to be identified and validated. The spectral characteristics of the first component C1 (λEx/λEm 282(270)/335) corresponded to those of tryptophan. The spectral properties of the other three components corresponded to those of humic-like substances: components two (C2 − λEx/λEm 315(252)/395) and three (C3 − λEx/λEm 357(258)/446) corresponded to humic-like substances of marine origin, whereas component four (C4 − λEx/λEm 261(399)/492) resembled terrestrial humic-like substances. Changes in FDOM composition were recorded in OW, in contrast to UIW and sea ice. In the OW the sum of fluorescence intensities of humic-like components (C2, C3 and C4) was two times higher than the fluorescence intensity of protein-like component (C1). Component C2 exhibited the highest fluorescence intensity. In the UIW and particularly in the sea ice the fluorescence intensity of the protein-like component, IC1, was the highest. The IC1 in the sea ice increased toward the sea ice bottom, reaching maximum values at the sea ice-water interface. The calculated spectral indices (SUVA(254) and HIX) and ratios of fluorescence intensities of protein-like to humic-like components, Ip/Ih, suggested that FDOM in water and sea ice was predominantly autochthonous, characterized by low molecular weight organic compounds and low aromatic ring saturation. Enrichment factors Dc, calculated from salinity-normalized values of the optical DOM properties and dissolved organic carbon concentrations, indicated the significant fractionation of FDOM in the sea ice relative to the parent open waters. The humic-like terrestrial component C4 was enriched the least, whereas the protein-like component C1 was enriched the most. A statistically significant (p 〈 0.0001) and relatively strong (R = 63) correlation between IC1 and the total chlorophyll a concentration Tchla was found in the sea ice, which suggests that sympagic algal communities were producers of the protein-like FDOM fraction.
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  • 36
    Publication Date: 2020-12-12
    Description: Scotia Sea and the Drake Passage is key towards understanding the development of modern oceanic circulation patterns and their implications for ice sheet growth and decay. The sedimentary record of the southern Scotia Sea basins documents the regional tectonic, oceanographic and climatic evolution since the Eocene. However, a lack of accurate age estimations has prevented the calibration of the reconstructed history. The upper sedimentary record of the Scotia Sea was scientifically drilled for the first time in 2019 during International Ocean Discovery Program (IODP) Expedition 382, recovering sediments down to ∼643 and 676 m below sea floor in the Dove and Pirie basins respectively. Here, we report newly acquired high resolution physical properties data and the first accurate age constraints for the seismic sequences of the upper sedimentary record of the Scotia Sea to the late Miocene. The drilled record contains four basin-wide reflectors – Reflector-c, -b, -a and -a' previously estimated to be ∼12.6 Ma, ∼6.4 Ma, ∼3.8 Ma and ∼2.6 Ma, respectively. By extrapolating our new Scotia Sea age model to previous morpho-structural and seismic-stratigraphic analyses of the wider region we found, however, that the four discontinuities drilled are much younger than previously thought. Reflector-c actually formed before 8.4 Ma, Reflector-b at ∼4.5/3.7 Ma, Reflector-a at ∼1.7 Ma, and Reflector-a' at ∼0.4 Ma. Our updated age model of these discontinuities has major implications for their correlation with regional tectonic, oceanographic and cryospheric events. According to our results, the outflow of Antarctic Bottom Water to northern latitudes controlled the Antarctic Circumpolar Current flow from late Miocene. Subsequent variability of the Antarctic ice sheets has influenced the oceanic circulation pattern linked to major global climatic changes during early Pliocene, Mid-Pleistocene and the Marine Isotope Stage 11.
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  • 37
    Publication Date: 2020-12-16
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  • 38
    Publication Date: 2021-01-06
    Description: Aquaculture development in Europe, while critical to the European Union (EU) Blue Growth strategy, has stagnated over the past decades due largely to high competition for space in the nearshore coastal zone among potential uses and the lack of clear priorities, policy, and planning at EU and national scales. Broad Marine Spatial Planning, including the designation of Allocated Zones for Aquaculture, requires spatial data at the corresponding broad spatial scale, which has not been readily available, as well as model projections to assess potential impacts of climate change. Here, daily chlorophyll-a, water temperature, salinity, and current speed outputs from a marine ecosystem model encompassing the coastal North East Atlantic, the North Sea, and the Mediterranean Sea (the pan-European POLCOMS-ERSEM model configuration) are used to drive a Dynamic Energy Budget growth model of Pacific oyster (Crassostrea gigas). Areas broadly suitable for growth were identified using threshold tolerance range masking applied using the model variables mentioned above, as well as bathymetry data. Oyster growth time series were transformed into simplified indicators that are meaningful to the industry (e.g., time to market weight) and mapped. In addition to early-century indicator maps, modelling and mapping were also carried out for two contrasting late-century climate change projections, following representative concentration pathways 4.5 and 8.5. Areas found to have good oyster growth potential now and into the future were further assessed in terms of their climate robustness (i.e., where oyster growth predictions are comparable between different future climate scenarios). Several areas within Europe were highlighted as priority areas for the development of offshore Pacific oyster cultivation, including coastal waters along the French Atlantic, the southern North Sea, and western Scotland and Ireland. A large potential growth hot spot was also identified along northwestern Africa, associated with a cool, productive upwelling coastal zone. The framework proposed here offers a flexible approach to include a large range of ecological input data, climate and ecosystem model scenarios, aquaculture-related models, species of interest, indicator types, and tolerance thresholds. Such information is suggested to be included in more extensive spatial assessments and planning, along with further socioeconomic and environmental data.
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  • 39
    Publication Date: 2021-01-06
    Description: Millennial scale variations of terrigenous provenance in marine realm are closely related to regional environment and climate changes. Therefore, a wealth of information of past environment and climate can be constrained via fingerprinting sediment provenance. The Sea of Japan is a unique marginal sea in the North Pacific due to its high sill and distinct thermohaline circulation. The modern hydrography in the Sea of Japan is mainly affected by the East Asian Monsoon and Tsushima Warm Current, one branch of the Kuroshio Current. The Sea of Japan communicates with neighboring seas through four shallow and narrow straits, indicating great effects of global eustatic sea level change on its environment over glacial-interglacial cycles. Here we examine the terrigenous provenance in fine-grained fraction (〈63 μm) of core KCES1, located near one end of the Tsushima Strait of the Sea of Japan over the last 48 ka, using radiogenic isotopes of strontium (Sr) and neodymium (Nd). Our data suggest that the terrigenous provenance in core KCES1 was mainly derived from the Yangtze River after 7 ka and a mixture of Yangtze and Yellow Rivers during the last glacial and deglacial periods. Notably, pronounced negative excursions of εNd values at HS1 were attributed to minor additions of unradiogenic Nd contribution from China-Korea cratonic hinterland. A binary mixing model further reveals that 〉85% terrigenous material is derived from the Yangtze and Yellow Rivers over the last 48 ka. Moreover, abrupt variations in sediment provenance occurred at ~18 ka and ~ 7 ka, which coincide with variations in oceanic surface circulation and deep ventilation recorded in the Sea of Japan. We suggest that paleo-Tsushima Warm Current invaded into the Sea of Japan with reopening of the Tsushima Strait at HS1 and the Tsushima Warm Current substantially entered the Sea of Japan after 7 ka due to intensified Kuroshio Current and rising eustatic sea level. The inflow of Tsushima Warm Current gives rise to a range of changes in surface hydrography, deep ventilation, ecological communities and productivity and sediment texture. The combination of fluxes of paleo-rivers and the intensity of Kuroshio Current, which are closely tied to the eustatic sea level and the East Asian Monsoon, plays a key role in controlling the variations in sediment provenance in the Ulleung Basin. Our study provides unique insight into the tight coupling between changes in sediment provenance and oceanic environment over the last 48 ka in the Sea of Japan.
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  • 40
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    In:  EPIC3Journal of Sea Research, ELSEVIER SCIENCE BV, 170, pp. 102020, ISSN: 1385-1101
    Publication Date: 2021-03-02
    Description: Brown shrimp, Crangon crangon, inhabit highly productive sandy and muddy grounds of the southern North Sea. The stomachs of the shrimp contain variable and often high numbers of sediment grains. The function of sediment grains inside the stomach and the purpose of their ingestion are only poorly understood. We tested in laboratory experiments whether sediment and associated organic material complement the natural food of C. crangon or if sand grains may be used by the shrimp to support trituration and maceration of ingested food. The shrimp showed no notable preference for sediment with natural organic content over sediment with reduced organic content, limited ingestion of sediment upon starvation, and no additional uptake of sand grains after feeding. Instead, C. crangon took up sediment only while feeding on regular food, suggesting that sand grains are not ingested intentionally but rather incidentally as a side effect of hasty gobbling. This conclusion is supported by the highly variable uptake of sand grains among individuals. Under experimental conditions, sand grains from sediments do not seem to have a crucial function in food processing and digestion in brown shrimp.
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  • 41
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    In:  EPIC3Palaeogeography Palaeoclimatology Palaeoecology, ELSEVIER SCIENCE BV, 572, ISSN: 0031-0182
    Publication Date: 2021-04-25
    Description: Ocean sediment drifts contain important information about past bottom currents but a direct link between the study of sedimentary archives and ocean dynamics is not always possible. To close this gap for the North Atlantic, we set up a new coupled Ice-Ocean-Sediment Model of the N. Atlantic - Arctic region. In order to evaluate the potential dynamics of the model, we conducted decadal sensitivity experiments. In our model contouritic sedimentation shows a significant sensitivity towards climate variability for most of the contourite drift locations in the model domain. We observe a general decrease of sedimentation rates during warm conditions with decreasing atmospheric and oceanic gradients and an extensive increase of sedimentation rates during cold conditions with respective increased gradients. We can relate these results to changes in the dominant bottom circulation supplying deep water masses to the contourite sites under different climate conditions. A better understanding of northern deep water pathways in the Atlantic Meridional Overturning Circulation (AMOC) is crucial for evaluating possible consequences of climate change in the ocean.
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  • 42
    Publication Date: 2021-06-30
    Description: Rivers are an important transport route of anthropogenic litter from inland sources toward the sea. A citizen science approach was used to evaluate the litter pollution of rivers in Germany: schoolchildren within the project “Plastic Pirates” observed floating macrolitter at 282 sites and took meso-/microplastic samples (i.e. particles 1 mm - 25 mm) at over 164 sites across the entire country during the years 2016 and 2017. Floating macrolitter quantities ranged from 0 to 8.25 items m -1 h -1 (average of 0.34 ± 0.89 litter items m -1 h -1 ) and floating macrolitter was sighted at 54% of sampling sites. The quantities of floating meso-/microplastics ranged from 0 to 220 particles h -1 (average of 6.86 ± 24.11 meso-/microplastics h -1 ). They were present at 57% of the sampling sites. Given that only particles 〉 1 mm were sampled and analyzed, the pollution of rivers in Germany by microplastics is likely a ubiquitous problem, regardless of the size of the river. We identified six plastic pollution hotspots where 60% of all meso-/microplastics collected in the present study were found. The composition of the particles at these hotspots indicates plastic producers and possibly the construction industry and wastewater treatment plants as point sources. An identification of litter hotspots would enable specific mitigation measures, adapted to the respective source, and thereby prevent the release of large quantities of small plastic particles in rivers. The adopted large-scale citizen science approach was especially suitable to detect pollution hotspots by sampling a variety of rivers, large and small, and enabled a national overview of litter pollution in German rivers.
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  • 43
    Publication Date: 2017-01-27
    Description: High acoustic seafloor-backscatter signals characterize hundreds of patches of methane-derived authigenic carbonates and chemosynthetic communities associated with hydrocarbon seepage on the Nile Deep Sea Fan (NDSF) in the Eastern Mediterranean Sea. During a high-resolution ship-based multibeam survey covering a ~ 225 km2 large seafloor area in the Central Province of the NDSF we identified 163 high-backscatter patches at water depths between 1500 and 1800 m, and investigated the source, composition, turnover, flux and fate of emitted hydrocarbons. Systematic Parasound single beam echosounder surveys of the water column showed hydroacoustic anomalies (flares), indicative of gas bubble streams, above 8% of the high-backscatter patches. In echosounder records flares disappeared in the water column close to the upper limit of the gas hydrate stability zone located at about 1350 m water depth due to decomposition of gas hydrate skins and subsequent gas dissolution. Visual inspection of three high-backscatter patches demonstrated that sediment cementation has led to the formation of continuous flat pavements of authigenic carbonates typically 100 to 300 m in diameter. Volume estimates, considering results from high-resolution autonomous underwater vehicle (AUV)-based multibeam mapping, were used to calculate the amount of carbonate-bound carbon stored in these slabs. Additionally, the flux of methane bubbles emitted at one high-backscatter patch was estimated (0.23 to 2.3 × 106 mol a− 1) by combined AUV flare mapping with visual observations by remotely operated vehicle (ROV). Another high-backscatter patch characterized by single carbonate pieces, which were widely distributed and interspaced with sediments inhabited by thiotrophic, chemosynthetic organisms, was investigated using in situ measurements with a benthic chamber and ex situ sediment core incubation and allowed for estimates of the methane consumption (0.1 to 1 × 106 mol a− 1) and dissolved methane flux (2 to 48 × 106 mol a− 1). Our comparison of dissolved and gaseous methane fluxes as well as methane-derived carbonate reservoirs demonstrates the need for quantitative assessment of these different methane escape routes and their interaction with the geo-, bio-, and hydrosphere at cold seeps.
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  • 44
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    In:  EPIC3Palaeogeography Palaeoclimatology Palaeoecology, ELSEVIER SCIENCE BV, (402), pp. 44-54, ISSN: 0031-0182
    Publication Date: 2016-10-22
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  • 45
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    In:  EPIC3Earth-Science Reviews, ELSEVIER SCIENCE BV, 135, pp. 48-58, ISSN: 0012-8252
    Publication Date: 2016-12-23
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  • 46
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    In:  EPIC3Ecological Modelling, ELSEVIER SCIENCE BV, 220(18), pp. 2173-2186, ISSN: 0304-3800
    Publication Date: 2018-02-16
    Description: We present a five-year (1997-2001) numerical simulation of daily mean chlorophyll a concentrations at station Geesthacht Weir on the lower Elbe River (Germany) using an extremely simple Lagrangian model driven by (a) water discharge, global radiation, water temperature, and (b) silica observations at station Schmilka in the upper reach of the Elbe River. Notwithstanding the lack of many mechanistic details, the model is able to reproduce observed chlorophyll a variability surprisingly well, including a number of sharp valleys and ascents/descents in the observed time series. The model's success is based on the assumption of three key effects: prevailing light conditions, sporadic limitation of algal growth due to lack of silica and algae loss rates that increase above an empirically specified temperature threshold of 20 degrees C. Trimmed-down model versions are studied to analyse the model's success in terms of these mechanisms. In each of the five years the model consistently fails, however, to properly simulate characteristic steep increases of chlorophyll a concentrations after pronounced spring minima. Curing this model deficiency by global model re-calibration was found to be impossible. However, suspension of silica consumption by algae for up to 10 days in spring is shown to serve as a successful placeholder for processes that are disregarded in the model but apparently play an important role in the distinctly marked period of model failure. For the remainder of the year the very simple model was found to be adequate
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  • 47
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    In:  EPIC3Ecological Modelling, ELSEVIER SCIENCE BV, 213(2), pp. 229-244, ISSN: 0304-3800
    Publication Date: 2018-02-16
    Description: A simple Lagrangian water quality model was designed to investigate the hypothesis of sporadic silica limitations of diatom growth in the lower Elbe River in Germany. For each fluid parcel a limited reservoir of silica was specified to be consumed by diatoms. The model's simplicity notwithstanding, a set of six selected model parameters could not be fully identified from existing observations at one station. After the introduction of prior knowledge of the ranges of meaningful parameter values, calibration of the over-parameterised model manifested itself primarily in the generation of posterior parameter covariances. Estimations of the covariance matrix based on (a) second order partial derivatives of a quadratic cost function at its optimum and (b) Monte Carlo simulations exploring the whole space of parameter values gave consistent results. Diagonalisation of the covariance matrix yielded two linear parameter combinations that were most effectively controlled by data from periods with and without lack of silica, respectively. The two parameter combinations were identified as the essential inputs that govern the successful simulation of intermittently decreasing chlorophyll a concentrations in summer. A satisfactory simulation of the pronounced chlorophyll a minimum in spring, by contrast, was found to be beyond the means of the simple model.
    Repository Name: EPIC Alfred Wegener Institut
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  • 48
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    National Academy of Sciences
    In:  EPIC3Proceedings of the National Academy of Sciences, National Academy of Sciences, ISSN: 0027-8424
    Publication Date: 2017-02-08
    Description: The variability of sea surface temperatures (SSTs) at multidecadal and longer timescales is poorly constrained, primarily because instrumental records are short and proxy records are noisy. Through applying a new noise filtering technique to a global network of late Holocene SST proxies, we estimate SST variability between annual and millennial timescales. Filtered estimates of SST variability obtained from coral, foraminifer, and alkenone records are shown to be consistent with one another and with instrumental records in the frequency bands at which they overlap. General circulation models, however, simulate SST variability that is systematically smaller than instrumental and proxy-based estimates. Discrepancies in variability are largest at low latitudes and increase with timescale, reaching two orders of magnitude for tropical variability at millennial timescales. This result implies major deficiencies in observational estimates or model simulations, or both, and has implications for the attribution of past variations and prediction of future change.
    Repository Name: EPIC Alfred Wegener Institut
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  • 49
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    ELSEVIER SCIENCE BV
    In:  EPIC3Precambrian Research, ELSEVIER SCIENCE BV, 250, pp. 143-150, ISSN: 0301-9268
    Publication Date: 2017-10-17
    Description: We report a strong magnetic high over the Giæverryggen at the Grunehogna craton in western DronningMaud Land, East Antarctica. The anomaly was coarsely mapped by previous surveys. Recently acquiredmagnetic data (2012/13) better constrain its spatial extent and permit the estimate of a theoretical ampli-tude value of +4000 to +4200 nT at bedrock surface. From the magnetic data, we estimated a minimummagnetic susceptibility in a spherical source body with a midpoint depth of ∼5.6 km to be greater than193 × 10−3SI, in the absence of relevant remanent magnetization. An exemplary 2.75-D forward mod-eling is carried out. Comparisons with neighboring magnetic highs in a plate tectonic reconstruction ofwestern Dronning Maud Land and southern Africa reveal clear similarities to the magnetic signature ofthe Paleoproterozoic banded iron formation in the Mhlapitsi fold and thrust belt near Polokwane (for-merly Pietersburg) in South Africa, suggesting a similar source for the Giæver Magnetic Anomaly andallow the interpretation that both regions were juxtaposed in Archaean and Paleoproterozoic times.
    Repository Name: EPIC Alfred Wegener Institut
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  • 50
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    ELSEVIER SCIENCE BV
    In:  EPIC3Global and Planetary Change, ELSEVIER SCIENCE BV, 123(Part A), pp. 67-76, ISSN: 0921-8181
    Publication Date: 2014-11-17
    Description: A multiproxy analysis based on planktic foraminiferal abundances, derived SSTs, and stable planktic isotopes measurements together with alkenone abundances and Uk′37 SSTs was performed on late MIS 6 to early MIS 5d sediment recovered fromSite 975 (ODP Leg 161) in the South Balearic Islands Basin(Western Mediterranean) with emphasis on reconstructing the climate progression of the last interglacial period. A number of abrupt climate changes related to alternative influence of nutrient rich northern and oligotrophic southernwater masses was revealed. Heinrich event 11 and cooling events C27, C26, C25, C24, and C23, which have been previously described in the North Atlantic, were recognized. However, in comparison to the eastern North Atlantic midlatitude region, events C27 and C26 at Site 975 seem to be significantly more pronounced. Together with evidence of a two-phase climate optimum with maximum SSTs reached during its later phase, this implies a close similarity in climate dynamics between the Western Mediterranean and the Nordic seas. We propose that postglacial effects in the Nordic seas had an influence on the westernMediterranean climate via atmospheric circulation and that these effects competed with the insolation force.
    Repository Name: EPIC Alfred Wegener Institut
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  • 51
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    ELSEVIER SCIENCE BV
    In:  EPIC3Polar Science, ELSEVIER SCIENCE BV, ISSN: 1873-9652
    Publication Date: 2014-11-13
    Description: The Arctic mid-ocean ridge system constitutes the most active source of earthquakes in the north polar region. However, the characteristics of its earthquake activity at teleseismic and local scales are not well studied because of the remote location of the ridge. We present here a comprehensive seismicity analysis that compares the teleseismic earthquake record of 35 years drawn from the catalogue of the International Seismological Centre with reconnaissance-style local earthquake records at six locations along the ridge that were instrumented either with ocean bottom seismometers or with seismometers on drifting ice floes. The teleseismic earthquake activity varies along the ridge and reflects ultraslow spreading processes with more and larger earthquakes produced in magma-rich regions than in magma-starved areas. Large magnitude earthquakes M〉5.5 are common along this ultraslow spreading ridge. Locally recorded earthquakes are of small magnitude (M〈2) and probably reflect the formation of the pronounced topographic relief. Their size and event rate is not as variable along the ridge as that of teleseismic events. Locally recorded earthquakes in the upper mantle are generated at several locations. Their focal depths do not depend on spreading rate but reflect the thermal state of the lithosphere with very deep earthquakes indicating an exceptionally cold lithosphere.
    Repository Name: EPIC Alfred Wegener Institut
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  • 52
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    ELSEVIER SCIENCE BV
    In:  EPIC3Tectonophysics, ELSEVIER SCIENCE BV, 630, pp. 300-312, ISSN: 0040-1951
    Publication Date: 2014-11-17
    Description: The Natal Valley (southwest Indian Ocean) has a complicated and protracted opening history, as has the surrounding southwest Indian Ocean. Recently collected multibeam swath bathymetry and 3.5 kHz seismic data from the Natal Valley reveal anomalous sea floor mounds in the northern Natal Valley. The significance, of these domes,as recorders of the geological history of the Natal Valley and SE African Margin has been overlooked with little attempt made to identify their origin, evolution or tectonic significance. This paper aims to describe these features from a morphological perspective and to use their occurrence as a means to better understand the geological and oceanographic evolution of this basin. The sea floor mounds are distinct in both shallow seismic and morphological character from the surrounding sea floor of the Natal Valley. Between 25 km and 31 km long, and 16 km and 18 km wide, these features rise some 400 m above the sedimentary deposits that have filled in the Natal Valley. Such macro-scale features have not previously been described from the Natal Valley or from other passive margins globally. They are not the result of bottom water circulation, salt tectonics; rather, igneous activity is favoured as the origin for these anomalous sea floor features. We propose a hypothesisthat the anomalous seafloor mounds observed in the Natal Valley are related to igneous activity associated with the EARS. The complicated opening history and antecedent geology, coupled with the southward propagation of the East African Rift System creates a unique setting where continental rift associated features have been developed in a marine setting.
    Repository Name: EPIC Alfred Wegener Institut
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  • 53
    Publication Date: 2017-02-01
    Description: The Fram Strait is the main gateway for water, heat and sea-ice exchanges between the Arctic Ocean and the North Atlantic. The complex physical environment results in a highly variable primary production in space and time. Previous regional studies have defined key bottom-up (ice cover and stratification from melt water controlling the light availability, and wind mixing and water transport affecting the supply of nutrients) and top-down processes (heterotrophic grazing). In this study, in situ field data, remote sensing and modeling techniques were combined to investigate in detail the influence of melting sea-ice and ocean properties on the development of phytoplankton blooms in the Fram Strait region for the years 1998–2009. Satellite-retrieved chlorophyll-a concentrations from temporarily ice-free zones were validated with contextual field data. These were then integrated per month on a grid size of 20 × 20 km, resulting in 10 grids/fields. Factors tested for their influence on spatial and temporal variation of chlorophyll-a were: sea-ice concentration from satellite and sea-ice thickness, ocean stratification, water temperature and salinity time-series simulated by the ice-ocean model NAOSIM. The time series analysis for those ten ice-free fields showed a regional separation according to different physical processes affecting phytoplankton distribution. At the marginal ice zone the melting sea-ice was promoting phytoplankton growth by stratifying the water column and potentially seeding phytoplankton communities. In this zone, the highest mean chlorophyll concentration averaged for the productive season (April–August) of 0.8 mgC/m3 was observed. In the open ocean the phytoplankton variability was correlated highest to stratification formed by solar heating of the upper ocean layers. Coastal zone around Svalbard showed processes associated with the presence of coastal ice were rather suppressing than promoting the phytoplankton growth. During the twelve years of observations, chlorophyll concentrations significantly increased in the southern part of the Fram Strait, associated with an increase in sea surface temperature and a decrease in Svalbard coastal ice.
    Repository Name: EPIC Alfred Wegener Institut
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  • 54
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    ELSEVIER SCIENCE BV
    In:  Capponi, G., Crispini, L., Scambelluri, M., 2008. Comment on “Subduction polarity reversal at the junction between the Western Alps and the Northern Apennines, Italy”, by G. Vignaroli, C. Faccenna, L. Jolivet, C. Piromallo, F. Rossetti Tectonophysics, Volume 465, Issues 1-4, 20 February 2009, Pages 221-226
    Publication Date: 2017-04-04
    Description: We first would like to thank Capponi et al. (2008) for their comments and criticisms on our paper, offering us the opportunity to discuss the data and the model presented in Vignaroli et al. (2008a) and clarify the geological rationale behind our manuscript. Vignaroli et al. (2008a) presented a large-scale reconstruction on the evolution of the Western Alpine–Northern Apennine junction, based on shallow geological information derived from the Northern Apennines, the Western and Ligurian Alps coupled with deep mantle structures from seismic tomography and tectonic reconstructions. The aim of this paper is then to give an alternative, though simplified, tectonic solution to the long-standing debate concerning the polarity of the subduction zone in the central Mediterranean and its linkage with the Alpine orogeny and the formation of the arcs belt. We condensed and simplified the huge wealth of geological information using cross-sections along the three orogenic segments. One of the main points of the paper is that the Voltri Massif of the Ligurian Alps is reinterpreted as an eclogitic-bearing domain exhumed by means of ductile-to-brittle extensional detachment tectonics with a top-to-the-W sense of shear. In this view, the orogenic architecture and evolution of the Ligurian Alps presents affinities (both for geometry and timing of deformation) with the widely accepted extensional structures recognized in the Western Alps, in the Northern Apennines and, in general, in Alpine-type orogenic belts of the Mediterranean. The detailed comment made by Capponi et al. (2008) is indeed centred on the tectonic structure of the Voltri Massif (probably this comment should have been addressed to our companion paper, Vignaroli et al., 2008b, focused on the Voltri Massif structures and available on-line on March 2008). The main point of the comment is that the exhumation of High-Pressure (HP) metamorphic units exposed in the Voltri Massif was produced by thrusts rather than by syn-orogenic extensional detachments. In this reply, we would first like to make some general considerations on the criteria/concepts adopted for the interpretation of the exhumation-related structures and we will then discuss point-by-point the criticism of Capponi et al., 2008 Capponi, G., Crispini, L., Scambelluri, M., 2008. Comment on "Subduction polarity reversal at the junction between the Western Alps and the Northern Apennines, Italy", by G. Vignaroli, C. Faccenna, L. Jolivet, C. Piromallo, F. Rossetti. Tectonophysics.Capponi et al. (2008).
    Description: Published
    Description: 227-231
    Description: 3.3. Geodinamica e struttura dell'interno della Terra
    Description: JCR Journal
    Description: reserved
    Keywords: HIGH-PRESSURE ROCKS ; METAMORPHIC CORE COMPLEX ; SCHISTES-LUSTRES COMPLEX ; ECLOGITES LIGURIAN ALPS ; VOLTRI-MASSIF ; CRUSTAL EXTENSION ; TYRRHENIAN SEA ; POSTOROGENIC EXTENSION ; CONTINENTAL EXTENSION ; SHEAR ZONE ; 04. Solid Earth::04.07. Tectonophysics::04.07.02. Geodynamics
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
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  • 55
    Publication Date: 2019-08-23
    Repository Name: EPIC Alfred Wegener Institut
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  • 56
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    ELSEVIER SCIENCE BV
    In:  EPIC3Marine Geology, ELSEVIER SCIENCE BV, 254(3-4), pp. 197-215, ISSN: 0025-3227
    Publication Date: 2019-07-17
    Description: We studied the impact of the last glacial (late Weichselian) sea level cycle on sediment architecture in theinner Kara Sea using high-resolution acoustic sub-bottom profiling. The acoustic lines were ground-truthedwith dated sediment cores. Furthermore we refined the location of the eastern LGM ice margin, by new subbottom profiles. New model results of post-Last Glacial Maximum (LGM) isostatic rebound for this area allowa well-constrained interpretation of acoustic units in terms of sequence stratigraphy. The lowstand (orregressive) system tract sediments are absent but are represented by an unconformity atop of Pleistocenesediments on the shelf and by a major incised dendritic paleo-river network. The subsequent transgressiveand highstand system tracts are best preserved in the incised channels and the recent estuaries while onlyminor sediment accumulation on the adjacent shelf areas is documented. The Kara Sea can be subdividedinto three areas: estuaries (A), the shelf (B) and (C) deeper lying areas that accumulated a total of 114 x1010 t of Holocene sediments.
    Repository Name: EPIC Alfred Wegener Institut
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  • 57
    Publication Date: 2021-03-30
    Description: In the past two decades, most of the steps in a macromolecular crystallography experiment have undergone tremendous development with respect to speed, feasibility and increase of throughput. The part of the experimental workflow that is still a bottleneck, despite significant efforts, involves the manipulation and harvesting of the crystals for the diffraction experiment. Here, a novel low‐cost device is presented that functions as a cover for 96‐well crystallization plates. This device enables access to the individual experiments one at a time by its movable parts, while minimizing evaporation of all other experiments of the plate. In initial tests, drops of many typically used crystallization cocktails could be successfully protected for up to 6 h. Therefore, the manipulation and harvesting of crystals is straightforward for the experimenter, enabling significantly higher throughput. This is useful for many macromolecular crystallography experiments, especially multi‐crystal screening campaigns.
    Description: A simple and low‐cost device has been developed to minimize evaporation in microtiter plates for easy crystal handling and harvesting. image
    Keywords: 548 ; evaporation reduction ; crystal handling ; crystal harvesting ; crystallographic fragment screening
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  • 58
    Publication Date: 2021-03-30
    Description: Multiple‐Edge Anomalous Diffraction (MEAD) has been applied to various quaternary sulfosalts belonging to the adamantine compound family in order to validate the distribution of copper, zinc and iron cations in the structure. Semiconductors from this group of materials are promising candidates for photovoltaic applications. Their properties strongly depend on point defects, in particular related to cation order–disorder. However, Cu+, Zn2+ and Fe2+ have very similar scattering factors and are all but indistinguishable in usual X‐ray diffraction experiments. Anomalous diffraction utilizes the dependency of the atomic scattering factors f′ and f′′ of the energy of the radiation, especially close to the element‐specific absorption edges. In the MEAD technique, individual Bragg peaks are tracked over an absorption edge. The intensity changes depending on the structure factor can be highly characteristic for Miller indices selected for a specific structural problem, but require very exact measurements. Beamline KMC‐2 at synchrotron BESSY II, Berlin, has been recently upgraded for this technique. Anomalous X‐ray powder diffraction and XAFS compliment the data. Application of this technique confirmed established cation distribution in Cu2ZnSnSe4 (CZTSe) and Cu2FeSnS4 (CFTS). In contrast to the literature, cation distribution in Cu2ZnSiSe4 (CZSiSe) is shown to adopt a highly ordered wurtz‐kesterite structure type.
    Description: Multiple‐Edge Anomalous Diffraction (MEAD) has been applied to various quaternary sulfosalts belonging to the adamantine compound family in order to validate the distribution of copper, zinc and iron cations in the structure. Application of this technique confirms established cation distribution in Cu2ZnSnSe4 (CZTSe) and Cu2FeSnS4 (CFTS), but in Cu2ZnSiSe4 (CZSiSe) the cation distribution is shown to adopt a highly ordered wurtz‐kesterite structure type in contrast to the literature. image
    Keywords: 548 ; synchrotron ; anomalous diffraction ; semiconductor ; MEAD
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  • 59
    Publication Date: 2021-03-27
    Description: The growth of diffraction‐quality crystals and experimental phasing remain two of the main bottlenecks in protein crystallography. Here, the high‐affinity copper(II)‐binding tripeptide GHK was fused to the N‐terminus of a GFP variant and an MBP‐FG peptide fusion. The GHK tag promoted crystallization, with various residues (His, Asp, His/Pro) from symmetry molecules completing the copper(II) square‐pyramidal coordination sphere. Rapid structure determination by copper SAD phasing could be achieved, even at a very low Bijvoet ratio or after significant radiation damage. When collecting highly redundant data at a wavelength close to the copper absorption edge, residual S‐atom positions could also be located in log‐likelihood‐gradient maps and used to improve the phases. The GHK copper SAD method provides a convenient way of both crystallizing and phasing macromolecular structures, and will complement the current trend towards native sulfur SAD and MR‐SAD phasing.
    Description: A novel three‐residue tag containing the residues GHK that can be used to promote crystallization and in SAD phasing experiments using its tightly bound copper ion is described. image
    Keywords: 548 ; phasing ; crystallization ; GHK ; SAD
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  • 60
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    International Union of Crystallography | 5 Abbey Square, Chester, Cheshire CH1 2HU, England
    Publication Date: 2021-03-30
    Description: Recently, the authors reported on the development of crystallinity in mixed‐tacticity polyhydroxybutyrates. Comparable values reported in the literature vary depending on the manner of determination, the discrepancies being partially attributable to scattering from paracrystalline portions of the material. These portions can be qualified by peak profile fitting or quantified by allocation of scattered X‐ray intensities. However, the latter requires a good quality of the former, which in turn must additionally account for peak broadening inherent in the measurement setup, and due to limited crystallite sizes and the possible presence of microstrain. Since broadening due to microstrain and paracrystalline order both scale with scattering vector, they are easily confounded. In this work, a method to directionally discern these two influences on the peak shape in a Rietveld refinement is presented. Allocating intensities to amorphous, bulk and paracrystalline portions with changing tactic disturbance provided internal validations of the obtained directional numbers. In addition, the correlation between obtained thermal factors and Young's moduli, determined in earlier work, is discussed.
    Description: A method to robustly determine paracrystalline contents from Rietveld‐refined powder X‐ray data is presented and discussed for the example of mixed‐tacticity polyhydroxybutyrates. image
    Keywords: 548 ; polyhydroxybutyrates ; mixed tacticity ; paracrystallinity ; Rietveld refinement ; thermal factors
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  • 61
    Publication Date: 2021-03-27
    Description: Two evaluation concepts for nondestructive depth‐resolved X‐ray residual stress analysis in the near‐surface region of materials with cubic symmetry and nearly single crystalline structure are introduced by simulated examples. Both concepts are based on the same data acquisition strategy, which consists in the determination of lattice‐spacing depth profiles along the ⟨hkl⟩ poles by stepwise sample rotation around the scattering vector. Segmentation of these profiles parallel to the sample surface provides the lattice strain state as a function of depth. The first evaluation concept extends the crystallite group method developed for materials with pronounced crystallographic texture by the feature of depth resolution and can be applied to samples with arbitrary orientation. The second evaluation concept, which adapts the linear regression approach of the sin2ψ method for the case of single crystalline materials, is restricted to samples with (001) orientation. The influence of the strain‐free lattice parameter a0 on residual stress analysis using both evaluation concepts is discussed on the basis of explicitly derived relations.
    Description: Two data evaluation concepts are proposed for nondestructive and depth‐resolved X‐ray residual stress analysis by means of energy‐dispersive diffraction on materials featuring cubic symmetry and a nearly single crystalline structure. image
    Keywords: 548 ; residual stress ; X‐ray diffraction ; depth‐resolved analysis ; mosaic crystals
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  • 62
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    International Union of Crystallography | 5 Abbey Square, Chester, Cheshire CH1 2HU, England
    Publication Date: 2021-03-30
    Description: Dichroism is one of the most important optical effects in both the visible and the X‐ray range. Besides absorption, scattering can also contribute to dichroism. This paper demonstrates that, based on the example of polyimide, materials can show tiny dichroism even far from electronic resonances due to scattering. Although the effect is small, it can lead to a measurable polarization change and might have influence on highly sensitive polarimetric experiments.
    Description: Aligned molecules, for example in polyimide foils, lead to small dichroism even far from resonances, which can be revealed by high‐precision X‐ray polarimetry. image
    Keywords: 548 ; polyimide ; polarization ; X‐ray polarimetry ; wide‐angle scattering ; X‐ray dichroism
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  • 63
    Publication Date: 2021-03-27
    Description: The complete elastic stiffness tensor of thiourea has been determined from thermal diffuse scattering (TDS) using high‐energy photons (100 keV). Comparison with earlier data confirms a very good agreement of the tensor coefficients. In contrast with established methods to obtain elastic stiffness coefficients (e.g. Brillouin spectroscopy, inelastic X‐ray or neutron scattering, ultrasound spectroscopy), their determination from TDS is faster, does not require large samples or intricate sample preparation, and is applicable to opaque crystals. Using high‐energy photons extends the applicability of the TDS‐based approach to organic compounds which would suffer from radiation damage at lower photon energies.
    Description: The elastic stiffness coefficients of thiourea are determined from thermal diffuse scattering. image
    Keywords: 548 ; thermal diffuse scattering ; elastic stiffness ; thiourea
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  • 64
    Publication Date: 2021-07-03
    Description: X‐ray reflectivity (XRR) is a powerful and popular scattering technique that can give valuable insight into the growth behavior of thin films. This study shows how a simple artificial neural network model can be used to determine the thickness, roughness and density of thin films of different organic semiconductors [diindenoperylene, copper(II) phthalocyanine and α‐sexithiophene] on silica from their XRR data with millisecond computation time and with minimal user input or a priori knowledge. For a large experimental data set of 372 XRR curves, it is shown that a simple fully connected model can provide good results with a mean absolute percentage error of 8–18% when compared with the results obtained by a genetic least mean squares fit using the classical Parratt formalism. Furthermore, current drawbacks and prospects for improvement are discussed.
    Description: Artificial neural networks trained with simulated data are shown to correctly and quickly determine film parameters from experimental X‐ray reflectivity curves.
    Keywords: 548 ; X‐ray reflectivity ; machine learning ; organic semi‐conductors ; neural networks
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  • 65
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    International Union of Crystallography | 5 Abbey Square, Chester, Cheshire CH1 2HU, England
    Publication Date: 2021-06-05
    Description: Coordinate‐free expressions for the form factors of arbitrary polygons and polyhedra are derived using the divergence theorem and Stokes's theorem. Apparent singularities, all removable, are discussed in detail. Cancellation near the singularities causes a loss of precision that can be avoided by using series expansions. An important application domain is small‐angle scattering by nanocrystals.
    Description: Coordinate‐free expressions for the form factors of arbitrary polygons and polyhedra are derived using the divergence theorem and Stokes's theorem. Series expansions are used to ensure numeric precision close to apparent singularities. image
    Keywords: 548 ; form factors ; polyhedra ; Fourier shape transform
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  • 66
    Publication Date: 2021-06-30
    Description: ROBL‐II provides four different experimental stations to investigate actinide and other alpha‐ and beta‐emitting radionuclides at the new EBS storage ring of ESRF within an energy range of 3 to 35 keV. The XAFS station consists of a highly automatized, high sample throughput installation in a glovebox, to measure EXAFS and conventional XANES of samples routinely at temperatures down to 10 K, and with a detection limit in the sub‐p.p.m. range. The XES station with its five bent‐crystal analyzer, Johann‐type setup with Rowland circles of 1.0 and 0.5 m radii provides high‐energy resolution fluorescence detection (HERFD) for XANES, XES, and RIXS measurements, covering both actinide L and M edges together with other elements accessible in the 3 to 20 keV energy range. The six‐circle heavy duty goniometer of XRD‐1 is equipped for both high‐resolution powder diffraction as well as surface‐sensitive CTR and RAXR techniques. Single crystal diffraction, powder diffraction with high temporal resolution, as well as X‐ray tomography experiments can be performed at a Pilatus 2M detector stage (XRD‐2). Elaborate radioprotection features enable a safe and easy exchange of samples between the four different stations to allow the combination of several methods for an unprecedented level of information on radioactive samples for both fundamental and applied actinide and environmental research.
    Description: ROBL‐II at ESRF provides four experimental stations to investigate actinides with X‐ray absorption and emission spectroscopy, and with surface, high‐resolution powder, and single‐crystal X‐ray diffractometry.
    Keywords: 549 ; actinides ; EXAFS ; XANES ; HERFD‐XANES ; XAS ; XES ; RIXS ; XRD ; CTR ; RAXR ; surface diffraction
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  • 67
    Publication Date: 2021-03-30
    Description: The ATSAS software suite encompasses a number of programs for the processing, visualization, analysis and modelling of small‐angle scattering data, with a focus on the data measured from biological macromolecules. Here, new developments in the ATSAS 3.0 package are described. They include IMSIM, for simulating isotropic 2D scattering patterns; IMOP, to perform operations on 2D images and masks; DATRESAMPLE, a method for variance estimation of structural invariants through parametric resampling; DATFT, which computes the pair distance distribution function by a direct Fourier transform of the scattering data; PDDFFIT, to compute the scattering data from a pair distance distribution function, allowing comparison with the experimental data; a new module in DATMW for Bayesian consensus‐based concentration‐independent molecular weight estimation; DATMIF, an ab initio shape analysis method that optimizes the search model directly against the scattering data; DAMEMB, an application to set up the initial search volume for multiphase modelling of membrane proteins; ELLLIP, to perform quasi‐atomistic modelling of liposomes with elliptical shapes; NMATOR, which models conformational changes in nucleic acid structures through normal mode analysis in torsion angle space; DAMMIX, which reconstructs the shape of an unknown intermediate in an evolving system; and LIPMIX and BILMIX, for modelling multilamellar and asymmetric lipid vesicles, respectively. In addition, technical updates were deployed to facilitate maintainability of the package, which include porting the PRIMUS graphical interface to Qt5, updating SASpy – a PyMOL plugin to run a subset of ATSAS tools – to be both Python 2 and 3 compatible, and adding utilities to facilitate mmCIF compatibility in future ATSAS releases. All these features are implemented in ATSAS 3.0, freely available for academic users at https://www.embl‐hamburg.de/biosaxs/software.html.
    Description: ATSAS is a comprehensive software suite for the processing, visualization, analysis and modelling of small‐angle scattering data. This article describes developments in the ATSAS 3.0 release, including new programs for data simulation and for the structural modelling of lipids, nucleic acids and polydisperse systems. image
    Keywords: 548 ; small‐angle scattering ; data analysis ; biological macromolecules ; structural modelling ; ATSAS
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  • 68
    Publication Date: 2021-03-27
    Description: Serial crystallography records still diffraction patterns from single, randomly oriented crystals, then merges data from hundreds or thousands of them to form a complete data set. To process the data, the diffraction patterns must first be indexed, equivalent to determining the orientation of each crystal. A novel automatic indexing algorithm is presented, which in tests usually gives significantly higher indexing rates than alternative programs currently available for this task. The algorithm does not require prior knowledge of the lattice parameters but can make use of that information if provided, and also allows indexing of diffraction patterns generated by several crystals in the beam. Cases with a small number of Bragg spots per pattern appear to particularly benefit from the new approach. The algorithm has been implemented and optimized for fast execution, making it suitable for real‐time feedback during serial crystallography experiments. It is implemented in an open‐source C++ library and distributed under the LGPLv3 licence. An interface to it has been added to the CrystFEL software suite.
    Description: A description and evaluation are given of XGANDALF, extended gradient descent algorithm for lattice finding, an algorithm developed for fast and accurate indexing of snapshot diffraction patterns. image
    Keywords: 548 ; indexing ; XGANDALF ; CrystFEL ; multiple lattices ; serial crystallography
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  • 69
    Publication Date: 2021-03-27
    Description: A crystallographic indexing algorithm, pinkIndexer, is presented for the analysis of snapshot diffraction patterns. It can be used in a variety of contexts including measurements made with a monochromatic radiation source, a polychromatic source or with radiation of very short wavelength. As such, the algorithm is particularly suited to automated data processing for two emerging measurement techniques for macromolecular structure determination: serial pink‐beam X‐ray crystallography and serial electron crystallography, which until now lacked reliable programs for analyzing many individual diffraction patterns from crystals of uncorrelated orientation. The algorithm requires approximate knowledge of the unit‐cell parameters of the crystal, but not the wavelengths associated with each Bragg spot. The use of pinkIndexer is demonstrated by obtaining 1005 lattices from a published pink‐beam serial crystallography data set that had previously yielded 140 indexed lattices. Additionally, in tests on experimental serial crystallography diffraction data recorded with quasi‐monochromatic X‐rays and with electrons the algorithm indexed more patterns than other programs tested.
    Description: pinkIndexer, an algorithm developed for indexing of snapshot diffraction patterns recorded with pink‐beam X‐rays, monochromatic X‐rays and electrons, is described and its use evaluated. image
    Keywords: 548 ; indexing ; pinkIndexer ; CrystFEL ; pink X‐ray beam ; serial electron diffraction
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  • 70
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    International Union of Crystallography | 5 Abbey Square, Chester, Cheshire CH1 2HU, England
    Publication Date: 2021-06-17
    Description: CRM1 is a nuclear export receptor that has been intensively targeted over the last decade for the development of antitumor and antiviral drugs. Structural analysis of several inhibitor compounds bound to CRM1 revealed that their mechanism of action relies on the covalent modification of a critical cysteine residue (Cys528 in the human receptor) located in the nuclear export signal‐binding cleft. This study presents the crystal structure of human CRM1, covalently modified by 2‐mercaptoethanol on Cys528, in complex with RanGTP at 2.58 Å resolution. The results demonstrate that buffer components can interfere with the characterization of cysteine‐dependent inhibitor compounds.
    Description: The covalent modification of human CRM1 by 2‐mercaptoethanol interferes with the characterization of cysteine‐dependent inhibitor compounds. image
    Keywords: 548 ; nuclear export ; cancer ; exportin 1 ; cysteine modification
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  • 71
    Publication Date: 2021-06-26
    Description: Owing to the development of X‐ray focusing optics during the past decades, synchrotron‐based X‐ray microscopy techniques allow the study of specimens with unprecedented spatial resolution, down to 10 nm, using soft and medium X‐ray photon energies, though at the expense of the field of view (FOV). One of the approaches to increase the FOV to square millimetres is raster‐scanning of the specimen using a single nanoprobe; however, this results in a long data acquisition time. This work employs an array of inclined biconcave parabolic refractive multi‐lenses (RMLs), fabricated by deep X‐ray lithography and electroplating to generate a large number of long X‐ray foci. Since the FOV is limited by the pattern height if a single RML is used by impinging X‐rays parallel to the substrate, many RMLs at regular intervals in the orthogonal direction were fabricated by tilted exposure. By inclining the substrate correspondingly to the tilted exposure, 378000 X‐ray line foci were generated with a length in the centimetre range and constant intervals in the sub‐micrometre range. The capability of this new X‐ray focusing device was first confirmed using ray‐tracing simulations and then using synchrotron radiation at BL20B2 of SPring‐8, Japan. Taking account of the fact that the refractive lens is effective for focusing high‐energy X‐rays, the experiment was performed with 35 keV X‐rays. Next, by scanning a specimen through the line foci, this device was used to perform large FOV pixel super‐resolution scanning transmission hard X‐ray microscopy (PSR‐STHXM) with a 780 ± 40 nm spatial resolution within an FOV of 1.64 cm × 1.64 cm (limited by the detector area) and a total scanning time of 4 min. Biomedical implant abutments fabricated via selective laser melting using Ti–6Al–4V medical alloy were measured by PSR‐STHXM, suggesting its unique potential for studying extended and thick specimens. Although the super‐resolution function was realized in one dimension in this study, it can be expanded to two dimensions by aligning a pair of presented devices orthogonally.
    Description: A new X‐ray focusing device generates hundreds of thousands of line foci, periodically spaced in the sub‐micrometre range, with centimetre length. It enables to achieve large FOV pixel super‐resolution scanning transmission hard X‐ray microscopy. image
    Keywords: 502.82 ; inclined refractive X‐ray multi‐lens array ; pixel super‐resolution ; scanning transmission hard X‐ray microscopy ; deep X‐ray lithography and electroplating
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  • 72
    Publication Date: 2021-07-02
    Description: A new concept for temporal gating of synchrotron X‐ray pulses based on laser‐induced thermal transient gratings is presented. First experimental tests of the concept yield a diffraction efficiency of 0.18%; however, the calculations indicate a theoretical efficiency and contrast of 〉30% and 10−5, respectively. The full efficiency of the pulse picker has not been reached yet due to a long‐range thermal deformation of the sample after absorption of the excitation laser. This method can be implemented in a broad spectral range (100 eV to 20 keV) and is only minimally invasive to an existing setup.
    Description: A new concept for temporal gating of synchrotron X‐ray pulses based on laser‐induced thermal transient gratings is presented.
    Keywords: 548 ; synchrotron ; time‐resolved ; thermal deformation ; transient grating ; pulse picking
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  • 73
    Publication Date: 2021-06-06
    Description: The time‐resolved hard X‐ray diffraction endstation KMC‐3 XPP for optical pump/X‐ray probe experiments at the electron storage ring BESSY II is dedicated to investigating the structural response of thin film samples and heterostructures after their excitation with ultrashort laser pulses and/or electric field pulses. It enables experiments with access to symmetric and asymmetric Bragg reflections via a four‐circle diffractometer and it is possible to keep the sample in high vacuum and vary the sample temperature between ∼15 K and 350 K. The femtosecond laser system permanently installed at the beamline allows for optical excitation of the sample at 1028 nm. A non‐linear optical setup enables the sample excitation also at 514 nm and 343 nm. A time‐resolution of 17 ps is achieved with the `low‐α' operation mode of the storage ring and an electronic variation of the delay between optical pump and hard X‐ray probe pulse conveniently accesses picosecond to microsecond timescales. Direct time‐resolved detection of the diffracted hard X‐ray synchrotron pulses use a gated area pixel detector or a fast point detector in single photon counting mode. The range of experiments that are reliably conducted at the endstation and that detect structural dynamics of samples excited by laser pulses or electric fields are presented.
    Description: The KMC‐3 XPP endstation of the synchrotron BESSY II is dedicated to time‐resolved studies of structural dynamics of matter upon optical and/or electrical excitation using hard X‐ray diffraction with an accessible time range from 17 ps to several microseconds. image
    Keywords: 548 ; beamline instrumentation ; time‐resolved X‐ray diffraction ; optical excitation ; thermal transport ; ferroelectric switching
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  • 74
    Publication Date: 2021-03-27
    Description: The crystal structures of sodium ethoxide (sodium ethanolate, NaOEt), sodium n‐propoxide (sodium n‐propanolate, NaOnPr), sodium n‐butoxide (sodium n‐butanolate, NaOnBu) and sodium n‐pentoxide (sodium n‐amylate, NaOnAm) were determined from powder X‐ray diffraction data. NaOEt crystallizes in space group P421m, with Z = 2, and the other alkoxides crystallize in P4/nmm, with Z = 2. To resolve space‐group ambiguities, a Bärnighausen tree was set up, and Rietveld refinements were performed with different models. In all structures, the Na and O atoms form a quadratic net, with the alkyl groups pointing outwards on both sides (anti‐PbO type). The alkyl groups are disordered. The disorder becomes even more pronounced with increasing chain length. Recrystallization from the corresponding alcohols yielded four sodium alkoxide solvates: sodium ethoxide ethanol disolvate (NaOEt·2EtOH), sodium n‐propoxide n‐propanol disolvate (NaOnPr·2nPrOH), sodium isopropoxide isopropanol pentasolvate (NaOiPr·5iPrOH) and sodium tert‐amylate tert‐amyl alcohol monosolvate (NaOtAm·tAmOH, tAm = 2‐methyl‐2‐butyl). Their crystal structures were determined by single‐crystal X‐ray diffraction. All these solvates form chain structures consisting of Na+, –O− and –OH groups, encased by alkyl groups. The hydrogen‐bond networks diverge widely among the solvate structures. The hydrogen‐bond topology of the iPrOH network in NaOiPr·5iPrOH shows branched hydrogen bonds and differs considerably from the networks in pure crystalline iPrOH.
    Description: The crystal structures of NaOEt, NaOPr, NaOBu and NaOAm (Am = amyl = pentyl) were determined from powder data. These compounds crystallize in an anti‐PbO structure in the space groups P21m and P4/nmm. Additionally, solvates with the composition NaOEt·2EtOH, NaOPr·2PrOH, NaOiPr·5iPrOH and NaOtAm·tAmOH were synthesized, and their structures were determined from single crystals. They form interesting chain structures of different compositions and topologies. image
    Keywords: 548 ; sodium alkoxide ; powder data ; solvate ; isopropanol ; Bärnighausen tree ; PXRD
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  • 75
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    International Union of Crystallography | 5 Abbey Square, Chester, Cheshire CH1 2HU, England
    Publication Date: 2021-03-27
    Description: Small‐angle X‐ray scattering from GaN nanowires grown on Si(111) is measured in the grazing‐incidence geometry and modelled by means of a Monte Carlo simulation that takes into account the orientational distribution of the faceted nanowires and the roughness of their side facets. It is found that the scattering intensity at large wavevectors does not follow Porod's law I(q) ∝ q−4. The intensity depends on the orientation of the side facets with respect to the incident X‐ray beam. It is maximum when the scattering vector is directed along a facet normal, reminiscent of surface truncation rod scattering. At large wavevectors q, the scattering intensity is reduced by surface roughness. A root‐mean‐square roughness of 0.9 nm, which is the height of just 3–4 atomic steps per micrometre‐long facet, already gives rise to a strong intensity reduction.
    Description: The intensity of small‐angle X‐ray scattering from GaN nanowires on Si(111) depends on the orientation of the side facets with respect to the incident beam. This reminiscence of truncation rod scattering gives rise to a deviation from Porod's law. A roughness of just 3–4 atomic steps per micrometre‐long side facet notably changes the intensity curves. image
    Keywords: 548 ; nanowires ; Porod's law ; facet truncation rods ; small‐angle X‐ray scattering ; SAXS ; grazing‐incidence small‐angle X‐ray scattering ; GISAXS
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  • 76
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    International Union of Crystallography | 5 Abbey Square, Chester, Cheshire CH1 2HU, England
    Publication Date: 2021-06-28
    Description: Recent developments in cryogenic electron microscopy (cryo‐EM) have enabled structural studies of large macromolecular complexes at resolutions previously only attainable using macromolecular crystallography. Although a number of methods can already assist in de novo building of models into high‐resolution cryo‐EM maps, automated and reliable map interpretation remains a challenge. Presented here is a systematic study of the accuracy of models built into cryo‐EM maps using ARP/wARP. It is demonstrated that the local resolution is a good indicator of map interpretability, and for the majority of the test cases ARP/wARP correctly builds 90% of main‐chain fragments in regions where the local resolution is 4.0 Å or better. It is also demonstrated that the coordinate accuracy for models built into cryo‐EM maps is comparable to that of X‐ray crystallographic models at similar local cryo‐EM and crystallographic resolutions. The model accuracy also correlates with the refined atomic displacement parameters.
    Keywords: 548 ; ARP/wARP ; model building ; cryo‐EM ; model accuracy ; sequence assignment
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  • 77
    Publication Date: 2021-06-05
    Description: Carbonates containing CO4 groups as building blocks have recently been discovered. A new orthocarbonate, Sr2CO4 is synthesized at 92 GPa and at a temperature of 2500 K. Its crystal structure was determined by in situ synchrotron single‐crystal X‐ray diffraction, selecting a grain from a polycrystalline sample. Strontium orthocarbonate crystallizes in the orthorhombic crystal system (space group Pnma) with CO4, SrO9 and SrO11 polyhedra as the main building blocks. It is isostructural to Ca2CO4. DFT calculations reproduce the experimental findings very well and have, therefore, been used to predict the equation of state, Raman and IR spectra, and to assist in the discussion of bonding in this compound.
    Description: A new orthocarbonate, Sr2CO4, was synthesized under extreme pressure and temperature conditions of 92 GPa and 2500 K, respectively. The crystal structure of the compound s fully characterized in situ by synchrotron single‐crystal X‐ray diffraction and DFT calculations were employed to provide insight into its equation of state, Raman and IR spectra, and bonding. image
    Keywords: 548 ; orthocarbonates ; crystal structure ; single‐crystal X‐ray diffraction ; high pressure ; Sr2CO4
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  • 78
    Publication Date: 2021-06-28
    Description: Small‐angle X‐ray scattering (SAXS) is an established method for studying nanostructured systems and in particular biological macromolecules in solution. To obtain element‐specific information about the sample, anomalous SAXS (ASAXS) exploits changes of the scattering properties of selected atoms when the energy of the incident X‐rays is close to the binding energy of their electrons. While ASAXS is widely applied to condensed matter and inorganic systems, its use for biological macromolecules is challenging because of the weak anomalous effect. Biological objects are often only available in small quantities and are prone to radiation damage, which makes biological ASAXS measurements very challenging. The BioSAXS beamline P12 operated by the European Molecular Biology Laboratory (EMBL) at the PETRA III storage ring (DESY, Hamburg) is dedicated to studies of weakly scattering objects. Here, recent developments at P12 allowing for ASAXS measurements are presented. The beamline control, data acquisition and data reduction pipeline of the beamline were adapted to conduct ASAXS experiments. Modelling tools were developed to compute ASAXS patterns from atomic models, which can be used to analyze the data and to help designing appropriate data collection strategies. These developments are illustrated with ASAXS experiments on different model systems performed at the P12 beamline.
    Keywords: 548 ; ASAXS ; biological SAXS ; metalloproteins ; gold nanoparticles ; anomalous scattering ; beamline development
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  • 79
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    ELSEVIER SCIENCE BV
    In:  EPIC3Sedimentary Geology, ELSEVIER SCIENCE BV, 263-26, pp. 36-44, ISSN: 0037-0738
    Publication Date: 2014-09-17
    Repository Name: EPIC Alfred Wegener Institut
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  • 80
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    ELSEVIER SCIENCE BV
    In:  EPIC3Earth and Planetary Science Letters, ELSEVIER SCIENCE BV, ISSN: 0012-821X
    Publication Date: 2019-07-17
    Repository Name: EPIC Alfred Wegener Institut
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  • 81
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    ELSEVIER SCIENCE BV
    In:  EPIC3Earth and Planetary Science Letters, ELSEVIER SCIENCE BV, 300, pp. 112-124, ISSN: 0012-821X
    Publication Date: 2019-07-17
    Description: The Mediterranean Sea is at the transition between temperate and tropical air masses and as such of importance for studying climate change. The Gulf of Taranto and adjacent SW Adriatic Sea are at the heart of this region. Their sediments are excellently suited for generating high quality environmental records for the last millennia with a sub-decadal resolution. The quality of these records is dependent on a careful calibration of the transfer functions used to translate the sedimentary lipid signals to the local environment. Here, we examine and calibrate the UK′37 and TEX86 lipid-based temperature proxies in 48 surface sediments and relate these to ambient sea surface temperatures and other environmental data. The UK′37 -based temperatures in surface sediments reflect winter/spring sea surface temperatures in agreement with other studies demonstrating maximum haptophyte production during the colder season. The TEX86-based temperatures for the nearshore sites also reflect winter sea surface temperatures. However, at the most offshore sites, they correspond to summer sea surface temperatures. Additional lipid and environmental data including the distribution of the BIT index and remote-sensed chlorophyll-a suggest a shoreward increase of the impact of seasonal and spatial variability in nutrients and control of planktonic archaeal abundance by primary productivity, particle loading in surface waters and/or overprint by a cold-biased terrestrial TEX86 signal. As such the offshore TEX86 values seem to reflect a true summer signal to the effect that offshore UK′37 and TEX86 reconstruct winter and summer temperature, respectively, and hence provide information on the annual temperature amplitude.
    Repository Name: EPIC Alfred Wegener Institut
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  • 82
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    ELSEVIER SCIENCE BV
    In:  EPIC3Earth and Planetary Science Letters, ELSEVIER SCIENCE BV, 301, pp. 373-381, ISSN: 0012-821X
    Publication Date: 2019-07-17
    Description: In locations of rapid sediment accumulation receiving substantial amounts of laterally transported material the timescales of transport and accurate quantification of the transportedmaterial are at the focus of intense research. Here we present radiocarbon data obtained on co-occurring planktic foraminifera, marine haptophyte biomarkers (alkenones) and total organic carbon (TOC) coupled with excess Thorium-230 (230Thxs)measurements on four sediment cores retrieved in 1649–2879 mwater depth fromtwo such high accumulation drift deposits in the Northeast Atlantic, Björn and Gardar Drifts.While 230Thxs inventories imply strong sediment focussing, no age offsets are observed between planktic foraminifera and alkenones, suggesting that redistribution of sediments is rapid and occurs soon after formation ofmarine organic matter, or that transported material contains negligible amounts of alkenones. An isotopic mass balance calculation based on radiocarbon concentrations of co-occurring sediment components leads us to estimate that transported sediment components contain up to 12% of fossil organic matter that is free of or very poor in alkenones, but nevertheless appears to consist of a mixture of fresh and eroded fossil material. Considering all available constraints to characterize transported material, our results showthat although focussing factors calculated frombulk sediment 230Thxs inventoriesmay allowuseful approximations of bulk redeposition, they do not provide a unique estimate of the amount of each laterally transported sediment component. Furthermore, our findings provide evidence that the occurrence of lateral sediment redistribution alone does not always hinder the use ofmultiple proxies but that individual sediment fractions are affected to variable extents by sediment focussing.
    Repository Name: EPIC Alfred Wegener Institut
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  • 83
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    ELSEVIER SCIENCE BV
    In:  EPIC3Global and Planetary Change, ELSEVIER SCIENCE BV, 79(1-2), pp. 48-60, ISSN: 0921-8181
    Publication Date: 2019-07-17
    Description: The Arctic hydrological cycle throughout the Holocene is analyzed based on the results of transient simulations with the coupled atmosphere-ocean circulation model ECHO-G. The results suggest a ~ 2% increase of mid-Holocene to preindustrial Arctic river discharges for the Eurasian continent. However, rivers of the North America Arctic realm show a moderate runoff decline of approximately 4 to 5% for the same period. The total river discharge into the Arctic Ocean has remained at an approximately constant preindustrial level since the mid-Holocene. The positive discharge trend within Eurasia is caused by a more rapid decrease in local net evaporation compared to a smaller decline in advected moisture and hence precipitation. This effect is neither recognized within the North American Arctic domain nor in the far eastern part of the Eurasian Arctic realm. A detailed comparison of these model findings with a variety of proxy studies is conducted. The collected proxy records show trends of continental surface temperatures and precipitation rates that are consistent with the simulations. A continuation of the transient Holocene runs for the 19th and 20th century with increased greenhouse gasses indicates an increase of the total river influx into the Arctic Ocean of up to 7.6%. The Eurasian river discharges increase by 7.5%, the North American discharges by up to 8.4%. The most rapid increases have been detected since the beginning of the 20th century. These results are corroborated by the observed rising of Arctic river discharges during the last century which is attributed to anthropogenic warming. The acceleration of the Arctic hydrological cycle in the 20th century is without precedence in the Holocene.
    Repository Name: EPIC Alfred Wegener Institut
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  • 84
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    ELSEVIER SCIENCE BV
    In:  EPIC3Geomorphology, ELSEVIER SCIENCE BV, 187, pp. 135-152, ISSN: 0169-555X
    Publication Date: 2019-07-17
    Repository Name: EPIC Alfred Wegener Institut
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  • 85
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    ELSEVIER SCIENCE BV
    In:  EPIC3Marine Geology, ELSEVIER SCIENCE BV, 299-30, pp. 51-62, ISSN: 0025-3227
    Publication Date: 2019-07-16
    Description: Drift deposits document stages of particular dynamic bottom-currents and associated sedimentary transport activities. The analysis of seismic reflection data from the Amundsen Sea, southern Pacific Ocean, reveals sediment drift formation already in Eocene/Oligocene times. This observation indicates bottom current activity and hence a cold climate for the late Palaeogene in an area, which today lies under the influence of Antarctic Bottom Water (AABW) originating in the Ross Sea. The generation of sediment drifts is accompanied by the occurrence of mass transport deposits leading to the identification of a phase of strong ice sheet expansion (15-4 Ma), which due to a change in ice regime from wet- to dry-based was followed by less material input during the last  4 Ma.
    Repository Name: EPIC Alfred Wegener Institut
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  • 86
    Publication Date: 2019-07-17
    Description: The Sr and Nd isotopic composition of dust extracted from recentsnowlayers at the top of BerknerIslandicesheet (located within the Filchner–Ronne Ice Shelf at the southern end of the Weddell Sea) enables us, for the first time, to document dust provenance in Antarctica outside the East Antarctic Plateau (EAP) where all previous studies based on isotopic fingerprinting were carried out. Berknerdust displays an overall crust-like isotopic signature, characterized by more radiogenic 87Sr/86Sr and much less radiogenic 143Nd/144Nd compared to dust deposited on the EAP during glacial periods. Differences with EAP interglacial dust are not as marked but still significant, indicating that present-day Berknerdust provenance is distinct, at least to some extent, from that of the dust reaching the EAP. The fourteen snow-pit sub-seasonal samples that were obtained span a two-year period (2002–2003) and their dust Sr and Nd isotopic composition reveals that multiplesources are at play over a yearly time period. Southern South America, Patagonia in particular, likely accounts for part of the observed spring/summer dust deposition maxima, when isotopic composition is shifted towards “younger” isotopic signatures. In the spring, possible additional inputs from Australian sources would also be supported by the data. Most of the year, however, the measured isotopic signatures would be best explained by a sustained background supply from putative local sources in East Antarctica, which carry old-crust-like isotopic fingerprints. Whether the restricted East Antarctic ice-free areas produce sufficient eolian material has yet to be substantiated however. The fact that large (〉 5 μm) particles represent a significant fraction of the samples throughout the entire time-series supports scenarios that involve contributions from proximal sources, either in Patagonia and/or Antarctica (possibly including snow-free areas in the Antarctic Peninsula and other areas as well). This also indicates that additional dust transport, which does not reach the EAP, must occur at low-tropospheric levels to this coastalsector of Antarctica.
    Repository Name: EPIC Alfred Wegener Institut
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  • 87
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    ELSEVIER SCIENCE BV
    In:  EPIC3Global and Planetary Change, ELSEVIER SCIENCE BV, 80-81, pp. 180-189, ISSN: 0921-8181
    Publication Date: 2019-07-16
    Repository Name: EPIC Alfred Wegener Institut
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  • 88
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    ELSEVIER SCIENCE BV
    In:  EPIC3Tectonophysics, ELSEVIER SCIENCE BV, 585, pp. 113-123, ISSN: 0040-1951
    Publication Date: 2019-07-17
    Repository Name: EPIC Alfred Wegener Institut
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  • 89
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    ELSEVIER SCIENCE BV
    In:  EPIC3Ecological Complexity, ELSEVIER SCIENCE BV, 11, pp. 75-83, ISSN: 1476-945X
    Publication Date: 2019-07-17
    Description: Classifying species into functional groups is a way to understand the functioning of species-rich ecosystems, or to model the dynamics of such ecosystems. Many statistical techniques have been defined to classify species into groups, and a question is whether different techniques bring consistent classifications. In a tropical rain forest in French Guiana, five species classifications have been defined by different authors for the purpose of forest growth modelling but using different data sets and different statistical techniques. The correspondence between the five classifications was measured using four indices that are generalizations of existing indices to compare two classifications. A multiple correspondence analysis was used to identify associations between groups of different classifications. In a second step, two-table multivariate analyses were used to characterize the relationships between species classifications and eight species traits (consisting of seven populational traits and one functional trait). We evidenced a consensus on the potential size of trees: species were similarly clustered by the five classifications along this trait that is correlated to turnover rate. More surprisingly, no consensus was found for growth rate, nor wood density, traits that are correlated with light requirement.
    Repository Name: EPIC Alfred Wegener Institut
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  • 90
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    National Academy of Sciences
    In:  EPIC3Proc. of the National Academy of Sciences of the United States of America (PNAS), National Academy of Sciences, 109(16), pp. 5967-5971
    Publication Date: 2019-07-17
    Description: Understanding the temporal variation of cosmic radiation and solar activity during the Holocene is essential for studies of the solar-terrestrial relationship. Cosmic-ray produced radionuclides, such as 10Be and 14C which are stored in polar ice cores and tree rings, offer the unique opportunity to reconstruct the history of cosmic radiation and solar activity over many millennia. Although records from different archives basically agree, they also show some deviations during certain periods. So far most reconstructions were based on only one single radionuclide record, which makes detection and correction of these deviations impossible. Here we combine different 10Be ice core records from Greenland and Antarctica with the global 14C tree ring record using principal component analysis. This approach is only possible due to a new high-resolution 10Be record from Dronning Maud Land obtained within the European Project for Ice Coring in Antarctica in Antarctica. The new cosmic radiation record enables us to derive total solar irradiance, which is then used as a proxy of solar activity to identify the solar imprint in an Asian climate record. Though generally the agreement between solar forcing and Asian climate is good, there are also periods without any coherence, pointing to other forcings like volcanoes and greenhouse gases and their corresponding feedbacks. The newly derived records have the potential to improve our understanding of the solar dynamics and to quantify the solar influence on climate.
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  • 91
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    ELSEVIER SCIENCE BV
    In:  EPIC3Marine Micropaleontology, ELSEVIER SCIENCE BV, 92 - 9, pp. 16-28, ISSN: 0377-8398
    Publication Date: 2016-03-18
    Repository Name: EPIC Alfred Wegener Institut
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  • 92
    Publication Date: 2014-12-10
    Description: We investigated how physical incorporation, brine dynamics and bacterial activity regulate the distribution of inorganic nutrients and dissolved organic carbon (DOC) in artificial sea ice during a 19-day experiment that included periods of both ice growth and decay. The experiment was performed using two series of mesocosms: the first consisted of seawater and the second consisted of seawater enriched with humic-rich river water. We grew ice by freezing the water at an air temperature of −14 °C for 14 days after which ice decay was induced by increasing the air temperature to −1 °C. Using the ice temperatures and bulk ice salinities, we derived the brine volume fractions, brine salinities and Rayleigh numbers. The temporal evolution of these physical parameters indicates that there was two main stages in the brine dynamics: bottom convection during ice growth, and brine stratification during ice decay. The major findings are: (1) the incorporation of dissolved compounds (nitrate, nitrite, ammonium, phosphate, silicate, and DOC) into the sea ice was not conservative (relative to salinity) during ice growth. Brine convection clearly influenced the incorporation of the dissolved compounds, since the non-conservative behavior of the dissolved compounds was particularly pronounced in the absence of brine convection. (2) Bacterial activity further regulated nutrient availability in the ice: ammonium and nitrite accumulated as a result of remineralization processes, although bacterial production was too low to induce major changes in DOC concentrations. (3) Different forms of DOC have different properties and hence incorporation efficiencies. In particular, the terrestrially-derived DOC from the river water was less efficiently incorporated into sea ice than the DOC in the seawater. Therefore the main factors regulating the distribution of the dissolved compounds within sea ice are clearly a complex interaction of brine dynamics, biological activity and in the case of dissolved organic matter, the physico-chemical properties of the dissolved constituents themselves.
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  • 93
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    ELSEVIER SCIENCE BV
    In:  EPIC3Review of Palaeobotany and Palynology, ELSEVIER SCIENCE BV, 211, pp. 97-106, ISSN: 0034-6667
    Publication Date: 2015-03-08
    Repository Name: EPIC Alfred Wegener Institut
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  • 94
    Publication Date: 2015-04-10
    Description: Unmixing of grain-size distributionswithmultivariate statistical analysis gives indications of themain sediment transport processes and related environmental conditions in an area. We performed end-member mixing analysis (EMMA) of sedimentological data from 912 terrestrial sediment samples collected in the Donggi Cona catchment, north-eastern Tibetan Plateau. Up to the present, this is the largest sedimentological dataset on the Tibetan Plateau. EMMA resulted in the characterisation of three end-members that explain 88% of the variance within the dataset. The end-members all represent aeolian deposits. The first end-member EM 1 represents very fine dune sediments that were deflated from a former lake system. EM 2 represents medium sand deposits that were blown out from playa and alluvial fan sediments. EM 3 represents fine loess(−like) sediments mainly found at higher elevations. Different transformations, adding of a fourth end-member and adding of up to 200 loess samples do not change the composition of the end-members, demonstrating the robustness of themodel. EMMA allows the synchronous interpretation of very large datasets, resulting in a general characterisation of sediment transport in a particular area. Performing EMMA on the dataset demonstrates the importance of aeolian transport in this part of the world.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , isiRev
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  • 95
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    Unknown
    ELSEVIER SCIENCE BV
    In:  EPIC3Cold Regions Science and Technology, ELSEVIER SCIENCE BV, 83-84, pp. 13-19, ISSN: 0165-232X
    Publication Date: 2020-08-03
    Description: Precise knowledge of the absolute value and frequency dependence of the dielectric permittivity of ice is the basis for interpretation of radio echo sounding data on glaciers and ice sheets. However, in the range of radio-frequencies, data from direct measurements of the permittivity are sparse, and partially lacking uncertainty estimates. Here, we present new results for artificial and natural ice samples obtained by means of frequency-dependent measurements from 10 MHz to 1.5 GHz with a coaxial transmission line cell. Measurements on eight artificial ice samples grown from ultra-pure water within the cell yield a mean value for the real part of the relative permittivity of 3.18 ± 0.01 at − 20 °C. Sole evidence for dispersion is detected for frequencies below 10 MHz, possibly attributed to the Debye-type relaxation behavior. Investigation of the crystal orientation of the artificial ice samples reveals the c-axes to be predominantly parallel to the electric field inside the cell and allows to calculate a value representative for isotropic crystal orientation of 3.16 ± 0.01. Measurements on acid-doped artificial ice show a linear dependence of the real part with acidity with a gradient of (21.1 ± 3.9) [1/M]. The real part of the relative permittivity of natural firn and ice samples from a high Alpine glacier range from 2.02 at a density of 0.515 g/cm3 to 3.08 at 0.875 g/cm3. Quasi-continuous measurements with the present setup on an alpine firn core are now possible, with resolution depending on the coaxial cell's length, for direct comparison with the established dielectric profiling method.
    Repository Name: EPIC Alfred Wegener Institut
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  • 96
    Publication Date: 2014-04-17
    Description: Organic geochemical proxy data from surface sediment samples and a sediment core from Lake Donggi Cona were used to infer environmental changes on the northeastern Tibetan Plateau spanning the last 18.4 kyr. Long-chain n-alkanes dominate the aliphatic hydrocarbon fraction of the sediment extract from most surface sediment samples and the sediment core. Unsaturated mid-chain n-alkanes (nC23:1 and nC25:1) have high abundances in some samples, especially in core samples from the late glacial and early Holocene. TOC contents, organic biomarker and non-pollen-palynomorph concentrations and results from organic petrologic analysis on selected samples suggest three major episodes in the history of Lake Donggi Cona. Before ca. 12.6 cal ka BP samples contain low amounts of organic matter due to cold and arid conditions during the late glacial. After 12.6 cal ka BP, relatively high contents of TOC and concentrations of Botryococcus fossils, as well as enhanced concentrations of mid-chain n-alkanes and n-alkenes suggest a higher primary and macrophyte productivity than at present. This is supported by high contents of palynomorphs derived from higher plants and algae and was possibly triggered by a decrease of salinity and amelioration of climate during the early Holocene. Since 6.8 cal ka BP Lake Donggi Cona has been an oligotrophic freshwater lake. Proxy data suggest that variations in insolation drive ecological changes in the lake, with increased aquatic productivity during the early Holocene summer insolation maximum. Short-term drops of TOC contents or biomarker concentrations (at 9.9 cal ka BP, after 8.0 and between 3.5 and 1.7 cal ka BP) can possibly be related to relatively cool and dry episodes reported from other sites on the north-eastern Tibetan Plateau, which are hypothesized to occur in phase with Northern Hemisphere cooling events.
    Repository Name: EPIC Alfred Wegener Institut
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  • 97
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    Unknown
    ELSEVIER SCIENCE BV
    In:  EPIC3Review of Palaeobotany and Palynology, ELSEVIER SCIENCE BV, 168(1), pp. 31-40, ISSN: 0034-6667
    Publication Date: 2019-07-17
    Description: Previous studies based on fossil pollen data have reported significant changes in vegetation on the alpine Tibetan Plateau during the Holocene. However, since the relative proportions of fossil pollen taxa are largely influenced by individual pollen productivities and the dispersal characteristics, such inferences on vegetation have the potential to be considerably biased. We therefore examined the modern pollen–vegetation relationships for four common pollen species on the Tibetan Plateau, using Extended R-value (ERV) models. Assuming an average radius of 100 m for the sampled lakes, we estimated the relevant source area of pollen (RSAP) to be 2200 m (which represents the distance from the lake). Using Poaceae as the reference taxa (Pollen Productivity Estimate, PPE = 1), ERV Submodel 2 derived relative high PPEs for the steppe and desert taxa: 2.079 ± 0.432 for Artemisia and 5.379 ± 1.077 for Chenopodiaceae. Low PPEs were estimated for the Cyperaceae (1.036 ± 0.012), whose plants are characteristic of the alpine Kobresia meadows. Applying these PPEs to four fossil pollen sequences since the Late Glacial, the plant abundances on the central and north-eastern Tibetan Plateau were quantified using the “Regional Estimates of Vegetation Abundance from Large Sites” (REVEALS) model. The proportions of Artemisia and Chenopodiaceae were greatly reduced compared to their original pollen percentages in the reconstructed vegetation, owing to their high productivities and their dispersal characteristics, while Cyperaceae showed a relative increase in the vegetation reconstruction. The reconstructed vegetation assemblages of the four pollen sequence sites always yielded smaller compositional species turnovers than suggested by the pollen spectra, as revealed by Detrended Canonical Correspondence Analyses (DCCA) of the Holocene sections. The strength of the previously reported vegetation changes may therefore have been overestimated, which indicates the importance of taking into account pollen–vegetation relationships when discussing the potential drivers (such as climate, land use, atmospheric CO2 concentrations) and implications (such as for land surface–climate feedbacks, carbon storage, and biodiversity) of vegetation change.
    Repository Name: EPIC Alfred Wegener Institut
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  • 98
    facet.materialart.
    Unknown
    ELSEVIER SCIENCE BV
    In:  EPIC3Journal of Applied Geophysics, ELSEVIER SCIENCE BV, 75(1), pp. 87-98, ISSN: 0926-9851
    Publication Date: 2017-10-20
    Description: In this paper, the noise sources of an airborne electromagnetic frequency domain instrument used to measure sea-ice thickness are studied. The antennas are mounted on the wings of an aircraft. The paper presents real data examples showing that strong noise limited the accuracy of the thickness measurement to +/-0.5 m in the best case. Even drift correction and frequency filtering did not reduce the noise to a level necessary for sea ice thickness measurements with an accuracy of 0.1 m. We show results of 3D finite element modeling of the coupling between transmitter and receiver coils and the aircraft, which indicate that wing flexure is the primary cause of the strong noise. Wing deflection angles below 5° relative to the fuselage are large enough to cause changes higher than the wanted signal from the seawater under the ice. Wing flexure noise can be divided into an inductive and geometric contribution, both of the same order. Most of the wing flexure signal appears on the inphase component only, hence the quadrature component should be taken for sea ice thickness retrievals when wing flexure is present even when the inphase produces a larger ocean signal. Results also show that pitch and roll movements of the aircraft and electromagnetic coupling between seawater and aircraft can contribute significantly to the total noise. For flight heights of 30 m over the ocean these effects can change the signal by about 10% or more. For highly quantitative measurements like sea-ice thickness all these effects must be taken into account. We conclude that a fixed wing electromagnetic instrument for the purpose of measurements in a centimeter scale must include instrumentation to measure the relative position of the antenna coils with an accuracy of 1/10 mm. Furthermore the antenna separation distance should be as large as possible in order to increase the measured ratio of secondary to primary magnetic field strength.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , isiRev
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  • 99
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    Unknown
    International Union of Crystallography | 5 Abbey Square, Chester, Cheshire CH1 2HU, England
    Publication Date: 2021-06-27
    Description: Binary III–V nitrides such as AlN, GaN and InN in the wurtzite‐type structure have long been considered as potent semiconducting materials because of their optoelectronic properties, amongst others. With rising concerns over the utilization of scarce elements, a replacement of the trivalent cations by others in ternary and multinary nitrides has led to the development of different variants of nitrides and oxide nitrides crystallizing in lower‐symmetry variants of wurtzite. This work presents the symmetry relationships between these structural types specific to nitrides and oxide nitrides and updates some prior work on this matter. The non‐existence of compounds crystallizing in Pmc21, formally the highest subgroup of the wurtzite type fulfilling Pauling's rules for 1:1:2 stoichiometries, has been puzzling scientists for a while; a rationalization is given, from a crystallographic basis, of why this space group is unlikely to be adopted.
    Keywords: 548 ; group–subgroup relationships ; nitride materials ; wurtzite type
    Type: article
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  • 100
    facet.materialart.
    Unknown
    International Union of Crystallography | 5 Abbey Square, Chester, Cheshire CH1 2HU, England
    Publication Date: 2021-06-20
    Description: An approach for the comparison of pair distribution functions (PDFs) has been developed using a similarity measure based on cross‐correlation functions. The PDF is very sensitive to changes in the local structure, i.e. small deviations in the structure can cause large signal shifts and significant discrepancies between the PDFs. Therefore, a comparison based on pointwise differences (e.g. R values and difference curves) may lead to the assumption that the investigated PDFs as well as the corresponding structural models are not in agreement at all, whereas a careful visual inspection of the investigated structural models and corresponding PDFs may reveal a relatively good match. To quantify the agreement of different PDFs for those cases an alternative approach is introduced: the similarity measure based on cross‐correlation functions. In this paper, the power of this application of the similarity measure to the analysis of PDFs is highlighted. The similarity measure is compared with the classical Rwp values as representative of the comparison based on pointwise differences as well as with the Pearson product‐moment correlation coefficient, using polymorph IV of barbituric acid as an example.
    Description: A novel approach to the quantification of the agreement between pair distribution functions by a similarity measure based on cross‐correlation functions is introduced and evaluated. image
    Keywords: 548 ; pair distribution functions ; similarity measures ; total scattering techniques ; cross‐correlation functions ; R values
    Type: article
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