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: New high resolution sea surface temperature (SST) and sea surface salinity (SSS) estimates are presented from the Agulhas Bank slope in the Atlantic sector of the Agulhas Corridor using planktic foraminiferal ( Globigerinoides ruber ) δ 18 O and Mg/Ca derived SST. By focusing on the last 80,000 years this is the first fine-scale Agulhas leakage record that overlaps in time with much of the Greenland ice core record of abrupt climate changes in the North Atlantic region. The multi-centennial profiles indicate instances of warm SST and/or increased SSS coincident with Northern Hemisphere cool periods, followed by Northern Hemisphere warming. These periods of enhanced SST and SSS in the Agulhas Corridor occur at the last glacial termination (T1) and during North Atlantic cold episodes associated with Heinrich (H) meltwater events. To a first-order approximation, the timing of maximal salinity events in relation to periods of North Atlantic freshwater perturbation is consistent with the concept suggested by climate models that enhanced Agulhas leakage provides for buoyancy compensation and can potentially trigger increased convective activity in the North Atlantic, thereby restoring Atlantic overturning circulation after relatively weak states.

Description: [1]  Past water column stratification can be assessed through comparison of the δ 18 O of different planktonic foraminiferal species. The underlying assumption is that different species form their shellssimultaneously, but at different depths in the water column. We evaluate thisassumption using a sediment trap time-series of Neogloboquadrinapachyderma (s) and Globigerina bulloides from the NWNorth Atlantic. We determined fluxes, δ 18 O and δ 13 C of shells from two size fractionsto assess size-related effects on shell chemistry and to better constrain the underlying causes of isotopic differences between foraminifera in deep-sea sediments. Our data indicate that in the subpolar North Atlantic differences in the seasonality of the shell flux, and not in depth habitat or test size, determine the interspecies Δδ 18 O. N . pachyderma (s) preferentially forms from early spring to late summer, whereas the flux of G . bulloides peaks later in the season and is sustained until autumn.Likewise, seasonality influences large and small specimens differently, with large shells settling earlier in the season. [2]  The similarity of the seasonal δ 18 O patterns between the two species indicatesthat theycalcify in an overlapping depth zone close to the surface. However, their δ 13 C patterns are markedly different (〉1 ‰). Bothspecies have a seasonally variable offset from δ 13 C DIC that appears to be governed primarily by temperature, with larger offsets associated with higher temperatures. The variable offset from δ 13 C DIC implies that seasonality of the flux affects the fossil δ 13 C signal, which has implications for reconstruction of the past oceanic carbon cycle.

Description: Carbon monoxide (CO) and other atmospheric trace constituents were measured from onboard an Airbus 340-600 passenger aircraft in the upper troposphere (UT) between south China and the Philippines during Civil Aircraft for the Regular Investigation of the Atmosphere Based on an Instrument Container (CARIBIC) flights from May 2005 until March 2008. A total of 132 events having CO enhancements were observed in the UT over the region during the 81 CARIBIC flights from Frankfurt, Germany, to Manila, Philippines, with a stopover in Guangzhou, China. Among these, 51 high-CO events with enhancements more than 50 ppb above background were observed. For these events enhancements ranged from 52.7 to 221.3 ppb and persisted for 3 to 78 min (∼40 to 1200 km), indicating an influence of strong pollution from biomass/biofuel/fossil fuel burning on the trace gas composition of the UT. Back trajectory analysis shows that south China, the Indochinese Peninsula, and the Philippines/Indonesia are the main source regions of the high-CO events. The composition of air parcels originating from south China was found to be primarily influenced by anthropogenic urban/industrial emissions, while emissions from biomass/biofuel burning contributed substantially to CO enhancements from the Indochinese Peninsula. During the Philippines/Indonesia events, air parcel composition suggests contributions from both biomass/biofuel burning and urban/industrial sources. Long-range transport of air parcels from northeast Asia and India also contributed to CO enhancements in the UT over the region. The general features of regional influence, typical cases, and the contributions of biomass/biofuel burning and anthropogenic emissions are presented and discussed to characterize the air parcels during the observed high-CO events.