Holocene records in the southeastern Bay of Biscay: global versus regional climate signals

Core KS10b (North East Atlantic, water depth 550 m) was recovered at a location of high sediment deposition including a high-resolution palaeoclimatic record for the southeastern Bay of Biscay (BoB) over the last 9.0 cal ka BP. The effect of global and regional climatic forcing factors (e.g. orbital forcing, North Atlantic Oscillation: NAO) and their subsequent control on water temperature, sea-level, hydrology and continental influence were investigated by studying foraminiferal faunas, sedimentology, and stable isotopes. Results indicate probable episodic incursions of the warm and salty Iberian Poleward Current (IPC) into the BoB by the intermittent presence of the subtropical species Globigerinoides ruber. These incursions seem to be triggered by negative NAO-like conditions. Our data show five main climatic periods, which are in general agreement with literature data on the climatic variability in the North Atlantic and the Iberian Peninsula: The early Holocene (~9.0–7.4 cal ka BP) is characterised by low sea-level, significant downslope transport, eutrophic benthic settings and high surface water productivity. These environmental characteristics are probably due to the general wet and warm climate under a prevailing negative NAO, increasing precipitation and river runoff and favouring the incursion of the IPC into the BoB. The climatic optimum appears between ~7.4 and 6.0 cal ka BP under a generally positive NAO index. In the following (~6.0–3.5 cal ka BP), surface water cooling is matching a steep decline of the Northern Hemisphere summer insolation. Meanwhile, benthic settings are changing progressively towards present day trophic conditions. The time interval from ~3.5 to 1.8 cal ka BP encompasses the Iberian-Roman Humid period characterised by warm and humid conditions, and increasing primary production under a prevailing negative NAO index. The last 1.8 ka were characterised by stable cool conditions, reflecting a change towards a positive NAO state

Sources and nature of ice-nucleating particles in the free troposphere at Jungfraujoch in winter 2017

Primary ice formation in mixed-phase clouds is initiated by a minute subset of the ambient aerosol population, called ice-nucleating particles (INPs). The knowledge about their atmospheric concentration, composition, and source in cloud-relevant environments is still limited. During the 2017 joint INUIT/CLACE (Ice Nuclei research UnIT/CLoud–Aerosol Characterization Experiment) field campaign, observations of INPs as well as of aerosol physical and chemical properties were performed, complemented by source region modeling. This aimed at investigating the nature and sources of INPs. The campaign took place at the High-Altitude Research Station Jungfraujoch (JFJ), a location where mixed-phase clouds frequently occur. Due to its altitude of 3580 m a.s.l., the station is usually located in the lower free troposphere, but it can also receive air masses from terrestrial and marine sources via long-range transport. INP concentrations were quasi-continuously detected with the Horizontal Ice Nucleation Chamber (HINC) under conditions representing the formation of mixed-phase clouds at −31 ∘C. The INP measurements were performed in parallel to aerosol measurements from two single-particle mass spectrometers, the Aircraft-based Laser ABlation Aerosol MAss Spectrometer (ALABAMA) and the laser ablation aerosol particle time-of-flight mass spectrometer (LAAPTOF). The chemical identity of INPs is inferred by correlating the time series of ion signals measured by the mass spectrometers with the time series of INP measurements. Moreover, our results are complemented by the direct analysis of ice particle residuals (IPRs) by using an ice-selective inlet (Ice-CVI) coupled with the ALABAMA. Mineral dust particles and aged sea spray particles showed the highest correlations with the INP time series. Their role as INPs is further supported by source emission sensitivity analysis using atmospheric transport modeling, which confirmed that air masses were advected from the Sahara and marine environments during times of elevated INP concentrations and ice-active surface site densities. Indeed, the IPR analysis showed that, by number, mineral dust particles dominated the IPR composition (∼58 %), and biological and metallic particles are also found to a smaller extent (∼10 % each). Sea spray particles are also found as IPRs (17 %), and their fraction in the IPRs strongly varied according to the increased presence of small IPRs, which is likely due to an impact from secondary ice crystal formation. This study shows the capability of combining INP concentration measurements with chemical characterization of aerosol particles using single-particle mass spectrometry, source region modeling, and analysis of ice residuals in an environment directly relevant for mixed-phase cloud formation.</p

High Precision Femtosecond Laser Ablation ICP‐MS Measurement of Benthic Foraminiferal Mn‐Incorporation for Paleoenvironmental Reconstruction: A Case Study From the Plio‐Pleistocene Caribbean Sea

Closure of the Central American Seaway (CAS) and hydrology of the Caribbean Sea triggered Northern Hemisphere Glaciation and played an important role in the Pliocene to modern-day climate re-establishing the deep and surface ocean currents. New data on Mn/Ca obtained with femtosecond laser ablation inductively coupled plasma mass spectrometry on well-preserved tests of the epibenthic foraminifer Cibicidoides wuellerstorfi and infaunal C. mundulus contribute to the interpretation of paleoenvironmental conditions of the Caribbean Sea between 5.2 and 2.2 Ma (million years) across the closure of the CAS. Hydrothermal activity at the Lesser Antilles may be a primary source of Mn in the well-oxygenated Plio-Pleistocene Caribbean Sea. Incorporation of Mn in the benthic foraminifer shell carbonate is assumed to be affected by surface ocean nutrient cycling, and may hence be an indicator of paleoproductivity. Key Points - Femtosecond-laser ablation inductively coupled plasma mass spectrometry provides a new approach on distinguishing Mn of the ontogenetic shell calcite from Mn of the authigenic coatings - Ontogenetic Mn within the foraminifer shell calcite may result from the regional nutrient cycle - Mn in the deep eastern Caribbean Sea may mainly derive from hydrothermal sources along the Antilles Island Ar

Observation of viscosity transition in α-pinene secondary organic aerosol

Under certain conditions, secondary organic aerosol (SOA) particles can exist in the atmosphere in an amorphous solid or semi-solid state. To determine their relevance to processes such as ice nucleation or chemistry occurring within particles requires knowledge of the temperature and relative humidity (RH) range for SOA to exist in these states. In the CLOUD experiment at CERN, we deployed a new in-situ optical method to detect the viscosity of α-pinene SOA particles and measured their transition from the amorphous viscous to liquid state. The method is based on the depolarising properties of laboratory-produced non-spherical SOA particles and their transformation to non-depolarising spherical liquid particles during deliquescence. We found that particles formed and grown in the chamber developed an asymmetric shape through coagulation. A transition to spherical shape was observed as the RH was increased to between 35 % at −10 °C and 80 % at −38 °C, confirming previous calculations of the viscosity transition conditions. Consequently, α-pinene SOA particles exist in a viscous state over a wide range of ambient conditions, including the cirrus region of the free troposphere. This has implications for the physical, chemical and ice-nucleation properties of SOA and SOA-coated particles in the atmosphere

A comprehensive characterization of ice nucleation by three different types of cellulose particles immersed in water

We present the laboratory results of immersion freezing efficiencies of cellulose particles at supercooled temperature (T) conditions. Three types of chemically homogeneous cellulose samples are used as surrogates that represent supermicron and submicron ice-nucleating plant structural polymers. These samples include microcrystalline cellulose (MCC), fibrous cellulose (FC) and nanocrystalline cellulose (NCC). Our immersion freezing dataset includes data from various ice nucleation measurement techniques available at 17 different institutions, including nine dry dispersion and 11 aqueous suspension techniques. With a total of 20 methods, we performed systematic accuracy and precision analysis of measurements from all 20 measurement techniques by evaluating T-binned (1 ∘C) data over a wide T range (−36 ∘C <T<−4 ∘C). Specifically, we intercompared the geometric surface area-based ice nucleation active surface site (INAS) density data derived from our measurements as a function of T, ns,geo(T). Additionally, we also compared the ns,geo(T) values and the freezing spectral slope parameter (Δlog(ns,geo)/ΔT) from our measurements to previous literature results. Results show all three cellulose materials are reasonably ice active. The freezing efficiencies of NCC samples agree reasonably well, whereas the diversity for the other two samples spans ≈ 10 ∘C. Despite given uncertainties within each instrument technique, the overall trend of the ns,geo(T) spectrum traced by the T-binned average of measurements suggests that predominantly supermicron-sized cellulose particles (MCC and FC) generally act as more efficient ice-nucleating particles (INPs) than NCC with about 1 order of magnitude higher ns,geo(T)

The Structure of an RNAi Polymerase Links RNA Silencing and Transcription

RNA silencing refers to a group of RNA-induced gene-silencing mechanisms that developed early in the eukaryotic lineage, probably for defence against pathogens and regulation of gene expression. In plants, protozoa, fungi, and nematodes, but apparently not insects and vertebrates, it involves a cell-encoded RNA-dependent RNA polymerase (cRdRP) that produces double-stranded RNA triggers from aberrant single-stranded RNA. We report the 2.3-Å resolution crystal structure of QDE-1, a cRdRP from Neurospora crassa, and find that it forms a relatively compact dimeric molecule, each subunit of which comprises several domains with, at its core, a catalytic apparatus and protein fold strikingly similar to the catalytic core of the DNA-dependent RNA polymerases responsible for transcription. This evolutionary link between the two enzyme types suggests that aspects of RNA silencing in some organisms may recapitulate transcription/replication pathways functioning in the ancient RNA-based world

Strategies to improve the signal and noise performance of active matrix, flatâ panel imagers for diagnostic xâ ray applications

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/134928/1/mp8831.pd

Empirical and theoretical investigation of the noise performance of indirect detection, active matrix flatâ panel imagers (AMFPIs) for diagnostic radiology

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/134855/1/mp7919.pd