Evaluation of aeolian dust records obtained from Polar Ice Cores

When an ice core sample is analysed for its aeolian dust content, it is melted and the particles detected are suspended in water. Consequently, dust measurement techniques employed in the ice core community differ from those used for in-situ studies of airborne dust. Methods commonly used to classify insolubles suspended in a liquid are either based on the particles’ interaction with light or on the detection of resistive pulses by means of Coulter counting. Data sets obtained with Coulter counters are widely accepted as references and other techniques are judged against their ability to reproduce these. Unfortunately, optically acquired ice core dust records were found to differ. By analyzing two sections of the NEEM dust record, two different evaluation procedures are discussed before a third protocol is proposed. It is found that relative changes in the archived dust load can be reproduced, while the simultaneous attainment of absolute concentrations or changes in the grain size frequency histograms in high resolution remains difficult.

“Unconformity-Bounded” Stratigraphic Units in the South Polar Layered Deposits (Promethei Lingula, Mars)

We conducted a stratigraphic analysis of the South Polar Layered Deposits (SPLDs) in Promethei Lingula (PL, Mars) based on the identification of regional unconformities at visible and radar wavelengths. According to the terrestrial classification, this approach constrains the stratigraphy of the region and remedies the ambiguous interpretation of stratigraphy through marker layers, bypassing the problem related to the morphologic and radiometric appearance of the layers. Thus, the approach does not exclude diverse classifications, but complements them, whereas other discriminant elements are doubtful or difficult/impossible to be defined. Using this approach, we defined two stratigraphic units (or synthems: PL1 and PL2) in PL, which are morphologically different and divided by a regional unconformity (AuR1). This stratigraphic architecture implies that the geological history of PL has been conditioned by periodic changes in climate, which in turn are related to orbital variations of Mars.

The impacts of volcanic aerosol on stratospheric ozone and the Northern Hemisphere polar vortex: separating radiative-dynamical changes from direct effects due to enhanced aerosol heterogeneous chemistry

After major volcanic eruptions the enhanced aerosol causes ozone changes due to greater heterogeneous chemistry on the particle surfaces (HET-AER) and from dynamical effects related to the radiative heating of the lower stratosphere (RAD-DYN). We carry out a series of experiments with an atmosphere–ocean–chemistry–climate model to assess how these two processes change stratospheric ozone and Northern Hemispheric (NH) polar vortex dynamics. Ensemble simulations are performed under present day and preindustrial conditions, and with aerosol forcings representative of different eruption strength, to investigate changes in the response behaviour. We show that the halogen component of the HET-AER effect dominates under present-day conditions with a global reduction of ozone (−21 DU for the strongest eruption) particularly at high latitudes, whereas the HET-AER effect increases stratospheric ozone due to N2O5 hydrolysis in a preindustrial atmosphere (maximum anomalies +4 DU). The halogen-induced ozone changes in the present-day atmosphere offset part of the strengthening of the NH polar vortex during mid-winter (reduction of up to −16 m s-1 in January) and slightly amplify the dynamical changes in the polar stratosphere in late winter (+11 m s-1 in March). The RAD-DYN mechanism leads to positive column ozone anomalies which are reduced in a present-day atmosphere by amplified polar ozone depletion (maximum anomalies +12 and +18 DU for present day and preindustrial, respectively). For preindustrial conditions, the ozone response is consequently dominated by RAD-DYN processes, while under present-day conditions, HET-AER effects dominate. The dynamical response of the stratosphere is dominated by the RAD-DYN mechanism showing an intensification of the NH polar vortex in winter (up to +10 m s-1 in January). Ozone changes due to the RAD-DYN mechanism slightly reduce the response of the polar vortex after the eruption under present-day conditions.

Polar Nature of Biomimetic Fluorapatite/Gelatin Composites: A Comparison of Bipolar Objects and the Polar State of Natural Tissue

The correspondence of the state of alignment of macromolecules in biomimetic materials and natural tissues is demonstrated by investigating a mechanism of electrical polarity formation: An in vitro grown biomimetic FAp/gelatin composite is investigated for its polar properties by second harmonic (SHGM) and scanning pyroelectric microscopy (SPEM). Hexagonal prismatic seed crystals formed in gelatin gels represent a monodomain polar state, due to aligned mineralized gelatin molecules. Later growth stages, showing dumbbell morphologies, develop into a bipolar state because of surface recognition by gelatin functionality: A reversal of the polar alignment of macromolecules, thus, takes place close to that basal plane of the seed. In natural hard tissues (teeth and bone investigated by SPEM) and the biomimetic FAp/gelatin composite, we find a surprising analogy in view of growth-induced states of polarity: The development of polarity in vivo and in vitro can be explained by a Markov-type mechanism of molecular recognition during the attachment of macromolecules.

Comment on “Low time resolution analysis of polar ice cores cannot detect impulsive nitrate events” by D.F. Smart et al.

Smart et al. (2014) suggested that the detection of nitrate spikes in polar ice cores from solar energetic particle (SEP) events could be achieved if an analytical system with sufficiently high resolution was used. Here we show that the spikes they associate with SEP events are not reliably recorded in cores from the same location, even when the resolution is clearly adequate. We explain the processes that limit the effective resolution of ice cores. Liquid conductivity data suggest that the observed spikes are associated with sodium or another nonacidic cation, making it likely that they result from deposition of sea salt or similar aerosol that has scavenged nitrate, rather than from a primary input of nitrate in the troposphere. We consider that there is no evidence at present to support the identification of any spikes in nitrate as representing SEP events. Although such events undoubtedly create nitrate in the atmosphere, we see no plausible route to using nitrate spikes to document the statistics of such events.