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HTD2: a single‐crystal X‐ray diffractometer for combined high‐pressure/low‐temperature experiments at laboratory scale (2022)

Fischer, Andreas ; Langmann, Jan ; Vöst, Marcel ; [weitere]

International Union of Crystallography | 5 Abbey Square, Chester, Cheshire CH1 2HU, England

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Publikationsdatum: 2022-12-15

Beschreibung: High‐pressure (HP) X‐ray diffraction experiments at low temperature (LT) require dedicated instruments as well as non‐standard sample environments and measuring strategies. This is especially true when helium cryogenic temperatures below 80 K are targeted. Furthermore, only experiments on single‐crystalline samples provide the prerequisites to study subtle structural changes in the p–T phase diagram under extreme LT and HP conditions in greater detail. Due to special hardware requirements, such measurements are usually in the realm of synchrotron beamlines. This contribution describes the design of an LT/HP diffractometer (HTD2) to perform single‐crystal X‐ray diffraction experiments using a laboratory source in the temperature range 400 〉 T 〉 2 K while applying pressures of up to 20 GPa.

Beschreibung: The design and operation of a newly commissioned single‐crystal X‐ray diffractometer (HTD2) are presented. The device enables experiments under simultaneous low‐temperature and high‐pressure conditions using a laboratory X‐ray source.

Schlagwort(e): ddc:548 ; HTD2 ; low temperature ; high pressure ; single crystals ; instrumentation

Sprache: Englisch

Materialart: doc-type:article

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Site dependence of the magnetocaloric effect in Mn5−xFexSi3 (2022)

Ait Haddouch, Mohammed ; Abboushi, Nour ; Sharma, Neetika ; [weitere]

International Union of Crystallography | 5 Abbey Square, Chester, Cheshire CH1 2HU, England

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Publikationsdatum: 2022-12-06

Beschreibung: The nuclear and magnetic structures of Mn3Fe2Si3 are investigated in the temperature range from 20 to 300 K. The magnetic properties of Mn3Fe2Si3 were measured on a single crystal. The compound undergoes a paramagnetic to antiferromagnetic transition at TN2 ≃ 120 K and an antiferromagnetic to antiferromagnetic transition at TN1 ≃ 69 K. A similar sequence of magnetic phase transitions is found for the parent compound Mn5Si3 upon temperature variation, but the field‐driven transition observed in Mn5Si3 is not found in Mn3Fe2Si3, resulting in a strongly reduced magnetocaloric effect. Structurally, the hexagonal symmetry found for both compounds under ambient conditions is preserved in Mn3Fe2Si3 through both magnetic transitions, indicating that the crystal structure is only weakly affected by the magnetic phase transition, in contrast to Mn5Si3 where both transitions distort the nuclear structure. Both compounds feature a collinear high‐temperature magnetic phase AF2 and transfer into a non‐collinear phase AF1 at low temperature. While one of the distinct crystallographic sites remains disordered in the AF2 phase in the parent compound, the magnetic structure in the AF2 phase involves all magnetic atoms in Mn3Fe2Si3. These observations imply that the distinct sites occupied by the magnetic atoms play an important role in the magnetocaloric behaviour of the family.

Beschreibung: The nuclear and magnetic structures of Mn3Fe2Si3 are determined and the magnetic properties are compared with those of the parent compound Mn5Si3. The results imply that the distinct magnetic sites play an important role in the magnetocaloric behaviour of the family. image

Schlagwort(e): ddc:548 ; magnetocaloric effect ; magnetic structure ; neutron diffraction ; synchrotron diffraction ; site dependence

Sprache: Englisch

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Southern Ocean biogenic blooms freezing-in Oligocene colder climates (2022)

Hochmuth, Katharina ; Whittaker, Joanne M ; Sauermilch, Isabel ; [weitere]

Springer Nature

In: EPIC3Nature Communications, Springer Nature, 13(1), pp. 1-10, ISSN: 2041-1723

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Publikationsdatum: 2022-11-24

Beschreibung: 〈jats:title〉Abstract〈/jats:title〉〈jats:p〉Crossing a key atmospheric CO〈jats:sub〉2〈/jats:sub〉 threshold triggered a fundamental global climate reorganisation ~34 million years ago (Ma) establishing permanent Antarctic ice sheets. Curiously, a more dramatic CO〈jats:sub〉2〈/jats:sub〉 decline (~800–400 ppm by the Early Oligocene(~27 Ma)), postdates initial ice sheet expansion but the mechanisms driving this later, rapid drop in atmospheric carbon during the early Oligocene remains elusive and controversial. Here we use marine seismic reflection and borehole data to reveal an unprecedented accumulation of early Oligocene strata (up to 2.2 km thick over 1500 × 500 km) with a major biogenic component in the Australian Southern Ocean. High-resolution ocean simulations demonstrate that a tectonically-driven, one-off reorganisation of ocean currents, caused a unique period where current instability coincided with high nutrient input from the Antarctic continent. This unrepeated and short-lived environment favoured extreme bioproductivity and enhanced sediment burial. The size and rapid accumulation of this sediment package potentially holds ~1.067 × 10〈jats:sup〉15〈/jats:sup〉 kg of the ‘missing carbon’ sequestered during the decline from an Eocene high CO〈jats:sub〉2〈/jats:sub〉-world to a mid-Oligocene medium CO〈jats:sub〉2〈/jats:sub〉-world, highlighting the exceptional role of the Southern Ocean in modulating long-term climate.〈/jats:p〉

Repository-Name: EPIC Alfred Wegener Institut

Materialart: Article , isiRev

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Evidence for late glacial oceanic carbon redistribution and discharge from the Pacific Southern Ocean (2022)

Iwasaki, Shinya ; Lembke-Jene, Lester ; Nagashima, Kana ; [weitere]

Springer Nature

In: EPIC3Nature Communications, Springer Nature, 13, 12 p., ISSN: 2041-1723

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Publikationsdatum: 2022-11-14

Beschreibung: Southern Ocean deep-water circulation plays an important role in the global carbon cycle. On geological time-scales, upwelling along the Chilean continental margin likely contributed to the deglacial atmospheric carbon dioxide rise, but little quantitative evidence exists of carbon storage. Here, we use a new X-ray Micro-Computer-Tomography method to assess foraminiferal test dissolution as proxy for paleo-carbonate ion concentrations [CO3^2−]. Our subantarctic Southeast Pacific sediment core depth transect shows significant deep-water [CO3^2−] variations during the Last Glacial Maximum and Deglaciation (10 – 22 ka BP). We provide evidence for an increase in [CO3^2−] during the early deglacial period (15-19 ka BP), followed by a ca. 40 µmol kg^-1 reduction in Lower Circumpolar Deepwater (CDW). This decreased Pacific to Atlantic export of low-carbon CDW contributed to significantly lowered carbon storage within the Southern Ocean, highlighting the importance of a dynamic Pacific–Southern Ocean deep-water reconfiguration for shaping late-glacial oceanic carbon storage, and subsequent deglacial oceanic-atmospheric CO2 transfer.

Repository-Name: EPIC Alfred Wegener Institut

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Energy threshold changes in volcanic activity at Mt. Etna (Italy) inferred from volcanic tremor (2022)

Langer, Horst ; Falsaperla, Susanna ; Spampinato, Salvatore ; [weitere]

Springer Nature

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Publikationsdatum: 2022-10-28

Beschreibung: From the 2010s on, pattern classification has proven an effective method for flagging alerts of volcano unrest before eruptive activity at Mt. Etna, Italy. The analysis has been applied online to volcanic tremor data, and has supported the surveillance activity of the volcano that provides timely information to Civil Protection and other authorities. However, after declaring an alert, no one knows how long the volcano unrest will last and if a climactic eruptive activity will actually begin. These are critical aspects when considering the effects of a prolonged state of alert. An example of longstanding unrest is related to the Christmas Eve eruption in 2018, which was heralded by several months of almost continuous Strombolian activity. Here, we discuss the usage of thresholds to detect conditions leading to paroxysmal activity, and the challenges associated with defining such thresholds, leveraging a dataset of 52 episodes of lava fountains occurring in 2021. We were able to identify conservative settings regarding the thresholds, allowing for an early warning of impending paroxysm in almost all cases (circa 85% for the first 4 months in 2021, and over 90% for the whole year). The chosen thresholds also proved useful to predict that a paroxysmal activity was about to end. Such information provides reliable numbers for volcanologists for their assessments, based on visual information, which may not be available in bad weather or cloudy conditions.

Beschreibung: Project IMPACT (A multidisciplinary Insight on the kinematics and dynamics of Magmatic Processes at Mt. Etna Aimed at identifying preCursor phenomena and developing early warning sysTems). IMPACT belongs to the Progetti Dipartimentali INGV [DIP7], https://progetti.ingv.it/index.php/it/progetti-dipartimentali/vulcani/impact#informazioni-sul-progetto.

Beschreibung: Published

Beschreibung: 17895

Beschreibung: 4V. Processi pre-eruttivi

Beschreibung: JCR Journal

Schlagwort(e): Volcanic tremor ; Volcano monitoring ; Pattern recognition ; Self Organizing maps ; Fuzzy clustering ; Mt. Etna ; 04.06. Seismology ; 04.08. Volcanology ; 05.01. Computational geophysics

Repository-Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)

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Robust approaches for model‐free small‐angle scattering data analysis (2022)

Bender, Philipp ; Honecker, Dirk ; Bersweiler, Mathias ; [weitere]

International Union of Crystallography | 5 Abbey Square, Chester, Cheshire CH1 2HU, England

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Publikationsdatum: 2022-10-04

Beschreibung: The small‐angle neutron scattering data of nanostructured magnetic samples contain information regarding their chemical and magnetic properties. Often, the first step to access characteristic magnetic and structural length scales is a model‐free investigation. However, due to measurement uncertainties and a restricted q range, a direct Fourier transform usually fails and results in ambiguous distributions. To circumvent these problems, different methods have been introduced to derive regularized, more stable correlation functions, with the indirect Fourier transform being the most prominent approach. Here, the indirect Fourier transform is compared with the singular value decomposition and an iterative algorithm. These approaches are used to determine the correlation function from magnetic small‐angle neutron scattering data of a powder sample of iron oxide nanoparticles; it is shown that with all three methods, in principle, the same correlation function can be derived. Each method has certain advantages and disadvantages, and thus the recommendation is to combine these three approaches to obtain robust results.

Beschreibung: Three different approaches are compared for determination of the correlation function from the small‐angle neutron scattering data of a powder sample of iron oxide nanoparticles.

Schlagwort(e): ddc:548

Sprache: Englisch

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Mid-Pliocene El Niño/Southern Oscillation suppressed by Pacific intertropical convergence zone shift (2022)

Pontes, Gabriel M. ; Taschetto, Andréa S. ; Sen Gupta, Alex ; [weitere]

Springer Nature

In: EPIC3Nature Geoscience, Springer Nature, ISSN: 1752-0908

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Publikationsdatum: 2022-08-16

Beschreibung: The El Niño/Southern Oscillation (ENSO), the dominant driver of year-to-year climate variability in the equatorial Pacific Ocean, impacts climate pattern across the globe. However, the response of the ENSO system to past and potential future temperature increases is not fully understood. Here we investigate ENSO variability in the warmer climate of the mid-Pliocene (~3.0–3.3 Ma), when surface temperatures were ~2–3 °C above modern values, in a large ensemble of climate models—the Pliocene Model Intercomparison Project. We show that the ensemble consistently suggests a weakening of ENSO variability, with a mean reduction of 25% (±16%). We further show that shifts in the equatorial Pacific mean state cannot fully explain these changes. Instead, ENSO was suppressed by a series of off-equatorial processes triggered by a northward displacement of the Pacific intertropical convergence zone: weakened convective feedback and intensified Southern Hemisphere circulation, which inhibit various processes that initiate ENSO. The connection between the climatological intertropical convergence zone position and ENSO we find in the past is expected to operate in our warming world with important ramifications for ENSO variability.

Repository-Name: EPIC Alfred Wegener Institut

Materialart: Article , NonPeerReviewed

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Environmental stability and phenotypic plasticity benefit the cold-water coral Desmophyllum dianthus in an acidified fjord (2022)

Beck, Kristina K. ; Schmidt-Grieb, Gertraud M. ; Laudien, Jürgen ; [weitere]

Springer Nature

In: EPIC3Communications Biology, Springer Nature, 5(683)

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Publikationsdatum: 2022-07-13

Beschreibung: The stratified Chilean Comau Fjord sustains a dense population of the cold-water coral (CWC) Desmophyllum dianthus in aragonite supersaturated shallow and aragonite under- saturated deep water. This provides a rare opportunity to evaluate CWC fitness trade-offs in response to physico-chemical drivers and their variability. Here, we combined year-long reciprocal transplantation experiments along natural oceanographic gradients with an in situ assessment of CWC fitness. Following transplantation, corals acclimated fast to the novel environment with no discernible difference between native and novel (i.e. cross-transplanted) corals, demonstrating high phenotypic plasticity. Surprisingly, corals exposed to lowest ara- gonite saturation (Ωarag 〈 1) and temperature (T 〈 12.0 °C), but stable environmental condi- tions, at the deep station grew fastest and expressed the fittest phenotype. We found an inverse relationship between CWC fitness and environmental variability and propose to consider the high frequency fluctuations of abiotic and biotic factors to better predict the future of CWCs in a changing ocean.

Repository-Name: EPIC Alfred Wegener Institut

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Intracellular nitrate storage by diatoms can be an important nitrogen pool in freshwater and marine ecosystems (2022)

Stief, Peter ; Schauberger, Clemens ; Lund, Marie B. ; [weitere]

Springer Nature

In: EPIC3Communications Earth & Environment, Springer Nature, 3(1), ISSN: 2662-4435

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Publikationsdatum: 2022-07-06

Beschreibung: Identifying and quantifying nitrogen pools is essential for understanding the nitrogen cycle in aquatic ecosystems. The ubiquitous diatoms represent an overlooked nitrate pool as they can accumulate nitrate intracellularly and utilize it for nitrogen assimilation, dissipation of excess photosynthetic energy, and Dissimilatory Nitrate Reduction to Ammonium (DNRA). Here, we document the global co-occurrence of diatoms and intracellular nitrate in phototrophic microbial communities in freshwater (n = 69), coastal (n = 44), and open marine (n = 4) habitats. Diatom abundance and total intracellular nitrate contents in water columns, sediments, microbial mats, and epilithic biofilms were highly significantly correlated. In contrast, diatom community composition had only a marginal influence on total intracellular nitrate contents. Nitrate concentrations inside diatom cells exceeded ambient nitrate concentrations ∼100–4000-fold. The collective intracellular nitrate pool of the diatom community accounted for 〈1% of total nitrate in pelagic habitats and 65–95% in benthic habitats. Accordingly, nitrate-storing diatoms are emerging as significant contributors to benthic nitrogen cycling, in particular through Dissimilatory Nitrate Reduction to Ammonium activity under anoxic conditions.

Repository-Name: EPIC Alfred Wegener Institut

Materialart: Article , NonPeerReviewed , info:eu-repo/semantics/article

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Sea ice surface temperatures from helicopter-borne thermal infrared imaging during the MOSAiC expedition (2022)

Thielke, Linda ; Huntemann, Marcus ; Hendricks, Stefan ; [weitere]

Springer Nature

In: EPIC3Scientific Data, Springer Nature, 9(1), ISSN: 2052-4463

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Publikationsdatum: 2022-06-27

Beschreibung: The sea ice surface temperature is important to understand the Arctic winter heat budget. We conducted 35 helicopter flights with an infrared camera in winter 2019/2020 during the Multidisciplinary Drifting Observatory for the Study of Arctic Climate (MOSAiC) expedition. The flights were performed from a local, 5 to 10 km scale up to a regional, 20 to 40 km scale. The infrared camera recorded thermal infrared brightness temperatures, which we converted to surface temperatures. More than 150000 images from all flights can be investigated individually. As an advanced data product, we created surface temperature maps for every flight with a 1 m resolution. We corrected image gradients, applied an ice drift correction, georeferenced all pixels, and corrected the surface temperature by its natural temporal drift, which results in time-fixed surface temperature maps for a consistent analysis of one flight. The temporal and spatial variability of sea ice characteristics is an important contribution to an increased understanding of the Arctic heat budget and, in particular, for the validation of satellite products.

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