ALBERT

Description: In order to obtain new insight into the reliability of the ensemble prediction system of the European Centre for Medium-Range Weather Forecasts (ECMWF), we compare the ensemble spread-error relationship obtained from an observation-based verification to the one obtained from an analysis-based verification. Observations used in this study are mainly radiosonde temperatures and radiance measurements from the AMSU-A channel 5 microwave temperature sounder. The observation operators from the 4D-Var data assimilation scheme are used to map the forecasts into observation space. In “observation-space”, observed radiances are compared with forecast radiances, derived from the ensemble's atmospheric profiles of temperature, gas concentrations, cloud, and surface properties using the “RTTOV” radiative transfer code. The observation-space assessment yields different results than the analysis-based assessment in the extra-tropics for short-range forecasts (1-day), and in the tropics in general. In the extra-tropics, for 5-day forecasts the discrepancy between the analysis-based and observation-based verification is small and the ensemble variances are quite reliable. The observation-based diagnostic indicate that the stochastic model error schemes contribute to the well-tuned ensemble spread in the extra-tropics, but can degrade the reliability of the ensemble in the tropics. It is suggested that observation-based diagnostics should be used more routinely to diagnose the ensemble performance, and help diagnosing the effectiveness of model error schemes and estimating the amplitude of the initial perturbations.

Description: Mutnovsky Volcano, located in Kamchatka, Russia, is a young volcano that has formed a series of four overlapping stratocones over its approximately 80 ka history. Erupted products at Mutnovsky range in composition from basalts to dacites; basalts are the most common. In this study, melt inclusions from representative samples of all erupted compositions from all four eruptive centers were analyzed to investigate the causes of the compositional heterogeneity, melt evolution, and pre-eruptive magma dynamics. Melt inclusions from Mutnovsky were sampled in olivine, plagioclase, orthopyroxene, and clinopyroxene. The melt inclusion data represent a wide range of melt compositions, from basalt through rhyolite. Geochemical modeling of melt inclusion data, combined with field evidence and chemical zoning of plagioclase phenocrysts, indicates that fractional crystallization and magma mixing produced the range of erupted bulk rock compositions. The measured variability of melt inclusion compositions in each host mineral phase indicates that different host minerals trapped unique melts that evolved separately from one another. The melt inclusion data suggest that individual melt portions evolved by fractional crystallization, perhaps in different magma chambers, within the Mutnovsky plumbing system, and were mixed prior to eruption. Our data do not indicate whether the mixing events were the cause of eruption or are simply the manifestation of the eruption process. Melt inclusions trapped in plagioclase, clinopyroxene, orthopyroxene and olivine phenocrysts represent a wide range of melt compositions, from basalt through rhyolite. Melt inclusion data, combined with field evidence and chemical zoning of plagioclase phenocrysts, indicate that fractional crystallization and magma mixing produced the range of erupted bulk rock compositions. The melt inclusion data suggest that individual melt portions evolved by fractional crystallization, perhaps in different magma chambers, within the Mutnovsky plumbing system, and were mixed prior to eruption.

Description: Article Reconstructing past sea ice coverage in the Arctic is important for future climate predictions. Here, the authors present a new sea ice record from the Eurasian sector of the Arctic Ocean and report that Arctic sea ice reached its modern winter maximum for the first time 2.6 million years ago. Nature Communications doi: 10.1038/ncomms6608 Authors: Jochen Knies, Patricia Cabedo-Sanz, Simon T. Belt, Soma Baranwal, Susanne Fietz, Antoni Rosell-Melé

Description: During extratropical transition (ET) of tropical cyclones (TC) reduced predictability for the midlatitude flow is often observed. In this study we assess the sensitivity of the midlatitude flow response to ET. To this end, a simple novel metric, the “equivalent forecast hour difference”, is introduced and applied to experimental simulations for eight recent ET events, in which the TC has been removed or relocated. Early during ET, the midlatitude flow response is sensitive to ridgebuilding directly downstream of the transitioning TC. In cases with strong ridgebuilding and Rossby wave triggering, the sensitivity remains high. The midlatitude flow response is even more sensitive to error in the initial position of the TC. This study newly quantifies the high degree of sensitivity of the downstream midlatitude flow response to ET. It corroborates the need for correct tropical cyclogenesis and TC track forecasts for improving midlatitude numerical weather prediction during ET.

Description: Geochemical, mineralogical and biological indicators preserved in sediments are widely used to reconstruct past climate change, but proxies differ in the degree to which their utility as climate indicators has been validated via laboratory experiments, modern spatial calibrations, or down-core comparisons with instrumental climate data. Multi-proxy studies provide another means of evaluating interpretations of proxies. This paper presents a multi-proxy assessment comparing 19 sub-centennially resolved late Holocene proxy records, covering the period 300–1900 AD, from seven Icelandic marine and lacustrine core sites. We employ simple statistical comparisons between proxy reconstructions to evaluate their correlations over time and, ultimately, their utility as proxies for regional climate. Proxies examined include oxygen isotopic composition of benthic and planktonic foraminifera, abundance of the sea-ice biomarker IP 25 , allochthonous quartz in marine sediments (a proxy for drift ice around Iceland), marine carbonate abundance, total organic carbon concentration, chironomid assemblages, lacustrine biogenic silica and carbon/nitrogen ratios in lake sediments. Most of the examined proxy records, including temperature and sea-ice proxies, correlate strongly with each other over multi-centennial timescales, and thus do appear to record changes in regional climate. Copyright © 2011 John Wiley & Sons, Ltd.

Description: Abstract Holocene paleoceanographic reconstructions along the North Iceland Shelf have employed a variety of sea surface temperature and sea ice proxies. However, these surface proxies tend to have a seasonal bias toward spring/summer and thus only provide a discrete snapshot of surface conditions during one season. Furthermore, sea surface temperature proxies can be influenced by additional confounding variables resulting in markedly different Holocene temperature reconstructions. Here, we expand Iceland's marine paleoclimate toolkit with TEX86L: a temperature proxy based on the distribution of archaeal glycerol dibiphytanyl glycerol tetraether (GDGT) lipids. We develop a local Icelandic calibration from 21 surface sediment samples covering a wide environmental gradient across Iceland's insular shelves. Locally calibrated GDGT results demonstrate that (1) TEX86L reflects winter subsurface (0–200 m) temperatures on the North Iceland Shelf and (2) our calibration produces more realistic temperature estimates with substantially lower uncertainty (S.E. ±4 °C) over global calibrations. We then apply this new calibration to a high‐resolution marine sediment core (last millennium) collected from the central NIS with age control constrained by 14C‐dated mollusks. To test the veracity of the GDGT subsurface temperatures, we analyze quartz and calcite wt% and a series of highly branched isoprenoid alkenes, including the sea ice biomarker IP25, from the same core. The sediment records demonstrate that the development of thick sea ice during the Little Ice Age warmed the subsurface due to winter insulation. Importantly, this observation reflects a seasonal component of the sea ice/ocean feedback to be considered for the nonlinear cooling of the Little Ice Age in and around Iceland.

Description: A novel environment-evoked transcriptional signature predicts reactivity in single dentate granule neurons A novel environment-evoked transcriptional signature predicts reactivity in single dentate granule neurons, Published online: 06 August 2018; doi:10.1038/s41467-018-05418-8 Single nuclei RNA-seq has been used to characterize transcriptional signature of environment-related activity in cells of the dentate gyrus. Here the authors use this approach to show that whether a neuron will be reactivated in response to re-exposure to a previous environment can be predicted by its transcriptional signature.

Description: Biomass is a meaningful energy source for the decentralized power generation. The combination of a 2-stage thermochemical conversion unit with an Inverse Brayton Cycle (IBC) is subject to present research activities. Several advantages are expected compared to commercial available concepts. A commercially proven turbocharger from the automotive industry is used for the IBC unit. No cost-intensive gas cleaning is required due to an almost dust and tar free biomass conversion. The influence of feedstock characteristics on the thermochemical conversion, emissions and overall plant performance is subject to process optimization studies. Furthermore validation of the concept is target of a demonstration phase which is planned at later stage of the research activities.

Description: ABSTRACT Semi-quantitative estimates of early to late Holocene spring sea ice concentration (SpSIC) and occurrence of summer sea ice for the northern Barents Sea have been obtained by analysing the biomarkers IP 25 , brassicasterol and a tri-unsaturated highly branched isoprenoid lipid in a Holocene marine sediment core. Sub-surface water mass variations were derived from planktic foraminiferal assemblages and stable isotopes (δ 18 O, δ 13 C). The record indicates paleoceanographic changes over three intervals. During Period I (ca. 9500–5900 cal a BP), the study location experienced the lowest recorded SpSIC (ca. 25%) with short spring seasons and long productive summers, resulting partly from increased Atlantic Water inflow that caused a stronger ocean–atmosphere heat exchange. Throughout Period II (ca. 5900–2700 cal a BP), the winter sea ice margin migrated southwards and an overall cooling trend resulted in higher SpSIC (ca. 60%) and increased delivery of cold Arctic Water. During Period III (ca. 2700 cal a BP to present), SpSIC increased further (ca. 75%) and some sea ice remained during summer months. A sub-surface warming probably indicates a decoupling of heat exchange between the ocean and the atmosphere. Longer springs and shorter summers were accompanied by the most southerly location of the winter sea ice margin.