ALBERT

Description: Molecular dynamics simulations unravel the association of citrate to (10–10) and (000–1) growth fronts of zinc oxide and demonstrate an unexpected mobility of the surfactant. Citrate association to perfectly planar (10–10) and (000–1) ZnO-ethanol interfaces was found to be favored over dissociation by 1.5–2 eV hence suggesting strongly bound, immobilized surfactants. However, intramolecular stress prevents binding of all three carboxyl groups to planar surfaces and the typical arrangement is that of two carboxyl-Zn contacts (including two salt bridges each) whilst the remaining carboxyl group is dangling into the solvent. As a consequence, the surfactant exhibits a “walking” mechanism to move along the surface by exchanging the role of its carboxyl groups. This finding has strong implications for the role of citrate during crystal growth as illustrated by a recently developed simulation scheme based on hundreds of individual Zn 2+ and OH – ion association steps. In particular, for the (10–10) surface – which grows via formation of ridges embedded by {10–10} faces – these simulations show how citrate ions move towards steps and bind to the growth front by additional 4 eV per surfactant molecule.

Description: Abstract The paper by Lee et al (J Am Ceram Soc 102:4555‐4561, 2019) reports on semiconductor quantum dots (QDs) obtained in a silicate glass matrix by a novel modification of the solid‐state precipitation technique and characterized by a variety of techniques. Based on their experimental data, we critically discuss their assessment of the QDs obtained as CdSe/Cd1−xZnxSe core/shell structures. By analyzing their results (in particular, Raman scattering data) and comparing them to other data available in literature, we show that the data presented give no evidence for the formation of core/shell structures and conclude that the authors obtained rather homogeneous Cd1−xZnxSe QDs without any noticeable compositional gradient.

Description: Polar lows are intense mesoscale cyclones that occur at high latitudes in both hemispheres during winter. Their sometimes evidently convective nature, fuelled by strong surface fluxes and with cloud-free centers, have led to some polar lows being referred to as ‘arctic hurricanes’. Idealized studies have shown that intensification by hurricane development mechanisms is theoretically possible in polar winter atmospheres, but the lack of observations and realistic simulations of actual polar lows have made it difficult to ascertain if this occurs in reality. Here the roles of surface heat fluxes and latent heat release in the development of a Barents Sea polar low, which in its cloud structures showed some similarities to hurricanes, are studied with an ensemble of sensitivity experiments, where latent heating and/or surface fluxes of sensible and latent heat were switched off before the polar low peaked in intensity. To ensure that the polar lows in the sensitivity runs did not track too far away from the actual environmental conditions, a technique known as spectral nudging was applied. This was shown to be crucial for enabling comparisons between the different model runs. The results presented here show that: 1) No intensification occurred during the mature, post-baroclinic stage of the simulated polar low; 2) Surface heat fluxes, i.e. air-sea interaction, were crucial processes both in order to attain the polar low's peak intensity during the baroclinic stage and to maintain its strength in the mature stage; and 3) Latent heat release played a less important role than surface fluxes in both stages.

Description: Multi-decadal to centennial planktic  18 O and Mg/Ca records were generated at ODP976 in the Alboran Sea. The site is in the flow path of Atlantic inflow waters entering the Mediterranean and captured North Atlantic signals through the surface inflow and the atmosphere. The records reveal similar climatic oscillations during the last two glacial-to-interglacial transitions, albeit with a different temporal pacing. Glacial termination 1 (T1) was marked by Heinrich event 1 (H1), post-H1 Bolling/Allerod (B/A) warming and Younger Dryas (YD) cooling. During T2 the H11  18 O anomaly was twice as high and lasted 30% longer than during H1. The post-H11 warming marked the start of MIS5e while the subsequent YD-style cooling occurred during early MIS5e. The post-H11 temperature increase at ODP976 matched the sudden Asian Monsoon Termination II at 129 ka BP. Extending the 230 Th-dated speleothem timescale to ODP976 suggests glacial conditions in the Northeast Atlantic region were terminated abruptly and interglacial warmth was reached in less than a millennium. The early-MIS5e cooling and freshening at ODP976 coincided with similar changes at North Atlantic sites suggesting this was a basin-wide event. By analogy with T1 we argue that this was a YD-type event that was shifted into the early stages of the last interglacial period. This scenario is consistent with evidence from northern North Atlantic and Nordic Sea sites that the continuing disintegration of the large Saalian Stage (MIS6) ice sheet in Eurasia delayed the advection of warm North Atlantic waters and full-strength convective overturn until later stages of MIS5e.

Description: The hydrography of the Indian-Atlantic Ocean gateway has been connected to high-latitude climate dynamics by oceanic and atmospheric teleconnections on orbital and sub-orbital timescales. A wealth of sedimentary records aiming at reconstructing the late Pleistocene paleoceanography around the Southern Africa Continent has been devoted to understanding these linkages. Most of the records are, however, clustered close to the southern South African tip, with comparatively less attention devoted to areas under the direct influence of frontal zones of the Southern Ocean/South Atlantic. Here we present data of the composition and concentration of the diatom assemblage together with bulk biogenic content and the alkenone-based sea surface temperature (SST) variations for the past 350 kyr in the marine sediment core MD02-2588 (ca. 41°S, 26°E) recovered from the southern Agulhas Plateau. Variations in biosiliceous productivity show a varying degree of coupling with Southern Hemisphere paleoclimate records following a glacial-interglacial cyclicity. Ecologically well-constrained groups of diatoms record the glacial-interglacial changes in water masses dynamics, nutrient availability, and stratification of the upper ocean. The good match between the glacial maxima of total diatoms concentration, Chaetoceros spores abundance, and opal content with the maximum seasonal cover of Antarctic ice and the atmospheric dust records points to a dominant Southern Hemisphere forcing of diatom production. Sub-orbital variability of SST suggests rapid latitudinal migrations of the Subtropical Front and associated water masses over the southern Agulhas Plateau, following millennial contractions and expansions of the subtropical gyres. Warmings of the upper ocean over site MD02-2588 during Terminations IV to I occurred earlier than in the Antarctic Vostok, which is indicative of a Northern Hemisphere lead. Our multi-parameter reconstruction highlights how high latitude atmospheric and hydrographic processes modulated orbital highs and lows in primary production and SST as triggered by northward transport of Si, eolian dust input, and latitudinal migrations of frontal zones.

Description: A variety of observations-based hydrological variables from different data sets are used to investigate interannual variability and changes in the summertime hydrological cycle over four European regions – Iberian Peninsula (IP), British Isles (BI), Central Europe (CE) and European Russia (ER). An analysis performed on seasonal means (June, July and August: JJA) suggests that soil moisture variability is impacted almost equally by precipitation and air temperature in BI and ER regions. However, stronger links between soil moisture and precipitation are revealed for CE region and between soil moisture and air temperature for IP region. In all except IP regions summertime interannual variability of column-integrated water vapour is strongly linked to air temperature consistent with the dominating influence of the Clausius-Clapeyron equation. In BI, CE and ER interannual variability of regional precipitation is driven by variations in atmospheric moisture transport into these regions. In IP the link between precipitation and moisture transport is relatively weak. Based on monthly data, analysis of the lag-lead correlations revealed specific regional relationships between different hydrological variables. In particular, it is shown that in some regions (and months) interannual variability of soil moisture is linked more strongly to precipitation and air temperature anomalies in the previous month, rather than in the coinciding month. An analysis of the vertical structure of regional atmospheric moisture transport has revealed that the more continental the climate of the region is, the larger deviation from the mean (i.e., climatological) profile might be observed during anomalously dry/wet summers.

Description: With the aim of obtaining a general local formulation for anisotropic growth in soft biological tissues, a model based on the multiplicative decomposition of the growth tensor is formulated. The two parts of the growth tensor are associated with the main anisotropy directions. Together with an anisotropic driving force, the model enables an effective stress reduction by including growth-induced residual stresses, which is demonstrated in a numerical example of an idealized arterial segment. (© 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)

Description: Novel airborne in-situ measurements of inorganic chlorine, nitrogen oxide species and ozone were performed inside the lower Antarctic polar vortex and at its edge in September 2012. We focus on one flight during the TACTS/ESMVal campaign with the German research aircraft HALO, reaching latitudes of 65° S and potential temperatures up to 405 K. Using the early-winter correlations of reactive trace gases with N 2 O from ACE-FTS, we find high depletion of chlorine reservoir gases up to ∼ 40 % (0.8 ppbv) at 12 km to 14 km altitude in the vortex and 0.4 ppbv at the edge in subsided stratospheric air with mean ages up to 4.5 years. We observe denitrification of up to 4 ppbv, while ozone was depleted by 1.2 ppmv at potential temperatures as low as 380 K. The advanced instrumentation aboard HALO enables high resolution measurements with implications for the oxidation capacity of the lowermost stratosphere.

Description: The influence of downwelling stratospheric sulfurous aerosol on the UT (upper troposphere) aerosol concentrations and on cirrus clouds is investigated using CARIBIC (Civil aircraft for regular investigation of the atmosphere based on an instrument container) observations (between 1999–2002 and 2005–2013) and the cirrus reflectance product from MODIS. The initial period, 1999–2002, was volcanically quiescent after which the sulfurous aerosol in the LMS (Lowermost stratosphere) (S LMS ) became enhanced by several volcanic eruptions starting 2005. From 2005 to 2008 and in 2013, volcanic aerosol from several tropical eruptions increased S LMS . Due to consequent subsidence, the sulfur loading of the upper troposphere (S UT ) was increased by a factor of 2.5 compared to background levels. Comparison of S LMS and S UT during the seasons March-July and August-November show a close coupling of the UT and LMS. Finally, the relationship between S LMS and the cirrus cloud reflectance (CR) retrieved from MODIS spectrometer (onboard the satellites Terra and Aqua) is studied. S LMS and CR show a strong anti-correlation, with a factor of 3.5 increase in S LMS and decrease of CR by 8±2% over the period 2001 to 2011. We propose that the increase of S LMS due to volcanism has caused the coinciding cirrus CR decrease, which would be associated with a negative radiative forcing in the Northern Hemisphere midlatitudes.