Abstract. Millimetre-sized plastics are numerically abundant and widespread across the world's ocean surface. These buoyant macroscopic particles can be mixed within the upper water column by turbulent transport. Models indicate that the largest decrease in their concentration occurs within the first few metres of water, where in situ observations are very scarce. In order to investigate the depth profile and physical properties of buoyant plastic debris, we used a new type of multi-level trawl at 12 sites within the North Atlantic subtropical gyre to sample from the air-seawater interface to a depth of 5 m, at 0.5 m intervals. Our results show that plastic concentrations drop exponentially with water depth, and decay rates decrease with increasing Beaufort number. Furthermore, smaller pieces presented lower rise velocities and were more susceptible to vertical transport. This resulted in higher depth decays of plastic mass concentration (milligrams m −3 ) than numerical concentration (pieces m −3 ). Further multilevel sampling of plastics will improve our ability to predict at-sea plastic load, size distribution, drifting pattern, and impact on marine species and habitats.

The effects of surface morphology, defects, texture and energy on carbon steel corrosion are elucidated along with relevant characterization methods.

We studied the layer-by-layer collapse of molecularly thin films of a model lubricant confined between two atomically smooth substrates. The dynamics of the consecutive expulsion of four molecular layers were found to slow down with decreasing film thickness but showed no evidence for confinement-induced solidification. Using a hydrodynamic model, we show that the sliding friction of liquid layers on top of the solid substrates is approximately 18 times higher than the mutual friction between adjacent liquid layers. The latter was independent of film thickness and in close agreement with the bulk viscosity.

Iron single atom catalysts (Fe SACs) are the best‐known nonprecious metal (NPM) catalysts for the oxygen reduction reaction (ORR) of polymer electrolyte membrane fuel cells (PEMFCs), but their practical application has been constrained by the low Fe SACs loading (<2 wt%). Here, a one‐pot pyrolysis method is reported for the synthesis of iron single atoms on graphene (FeSA‐G) with a high Fe SAC loading of ≈7.7 ± 1.3 wt%. The as‐synthesized FeSA‐G shows an onset potential of 0.950 V and a half‐wave potential of 0.804 V in acid electrolyte for the ORR, similar to that of Pt/C catalysts but with a much higher stability and higher phosphate anion tolerance. High temperature SiO 2 nanoparticle‐doped phosphoric acid/polybenzimidazole (PA/PBI/SiO 2 ) composite membrane cells utilizing a FeSA‐G cathode with Fe SAC loading of 0.3 mg cm −2 delivers a peak power density of 325 mW cm −2 at 230 °C, better than 313 mW cm −2 obtained on the cell with a Pt/C cathode at a Pt loading of 1 mg cm −2 . The cell with FeSA‐G cathode exhibits superior stability at 230 °C, as compared to that with Pt/C cathode. Our results provide a new approach to developing practical NPM catalysts to replace Pt‐based catalysts for fuel cells.

A water-soluble, chiral calix[4]arene has been found to form hydrogels when triggered by the presence of specific anions, with efficacy linked to the Hofmeister series; the gel properties are modified by the associated cations, and gelation can be reversibly switched off by increasing pH.

Zircon (U-Th)/He thermochronometry is an established radiometric dating technique used to place temporal constraints on a range of thermally sensitive geological events, such as crustal exhumation, volcanism, meteorite impact, and ore genesis. Isotopic, crystallographic, and/or mineralogical heterogeneities within analyzed grains can result in dispersed or anomalous (U-Th)/He ages. Understanding the effect of these grain-scale phenomena on the distribution of He in analyzed minerals should lead to improvements in data interpretation. We combine laser ablation microsampling and noble gas and trace element mass spectrometry to provide the first twodimensional, grain-scale zircon He "maps" and quantify intragrain He distribution. These maps illustrate the complexity of intracrystalline He distribution in natural zircon and, combined with a correlated quantification of parent nuclide (U and Th) distribution, provide an opportunity to assess a number of crystal chemistry processes that can generate anomalous zircon (U-Th)/He ages. The technique provides new insights into fluid inclusions as potential traps of radiogenic He and confirms the effect of heterogeneity in parent-daughter isotope abundances and metamictization on (U-Th)/He systematics. Finally, we present a new inversion method where the He, U, and Th mapping data can be used to constrain the high-and low-temperature history of a single zircon crystal.

Abstract. Quantifying the saturation state of aragonite ( Ar ) within the calcifying fluid of corals is critical for understanding their biomineralization process and sensitivity to environmental changes including ocean acidification. Recent advances in microscopy, microprobes, and isotope geochemistry enable the determination of calcifying fluid pH and [CO ]/K sp ) has proved elusive. Here we test a new technique for deriving Ar based on Raman spectroscopy. First, we analysed abiogenic aragonite crystals precipitated under a range of Ar from 10 to 34, and we found a strong dependence of Raman peak width on Ar with no significant effects of other factors including pH, Mg/Ca partitioning, and temperature. Validation of our Raman technique for corals is difficult because there are presently no direct measurements of calcifying fluid Ar available for comparison. However, Raman analysis of the international coral standard JCp-1 produced Ar of 12.3 ± 0.3, which we demonstrate is consistent with published skeletal Mg/Ca, Sr/Ca, B/Ca, δ 11 B, and δ 44 Ca data. Raman measurements are rapid (≤ 1 s), high-resolution (≤ 1 µm), precise (derived Ar ± 1 to 2 per spectrum depending on instrument configuration), accurate ( ±2 if Ar < 20), and require minimal sample preparation, making the technique well suited for testing the sensitivity of coral calcifying fluid Ar to ocean acidification and warming using samples from natural and laboratory settings. To demonstrate this, we also show a high-resolution time series of Ar over multiple years of growth in a Porites skeleton from the Great Barrier Reef, and we evaluate the response of Ar in juvenile Acropora cultured under elevated CO 2 and temperature.

Background Implant surface roughness after air abrasive therapy has not been measured precisely in previous research. Debridement with air abrasion facilitates the mechanical removal of bacterial biofilms but may damage implant surfaces on a microscopic level. Purpose This study aimed to investigate the cleaning potential of various air abrasive powders and their effect on titanium implant surfaces. Materials and Methods Twenty implants coated with red ink were inserted into three‐dimensional printed circumferential bone defect models. Treatment was completed with three types of air abrasive powders: sodium bicarbonate (SB), glycine, and erythritol for 60 seconds. Water alone was used as control. The percentage of remaining ink was assessed using digital photography and graphic software. Implant surface topography/roughness was quantified using optical profilometry and examined via scanning electron microscopy. The microscopic analysis was performed at two implant areas: collar (Laser‐Lok surface) and threads. Results The cleaned surfaces (%, mean ± SD) after treatment with SB, glycine, and erythritol accounted for 49.3 ± 3.6%, 33.1 ± 1.2%, and 25.1 ± 0.7%, respectively. Statistically significant differences were found between all groups (P < .001). SB was the only powder that significantly increased the implant roughness (Sa) on both the implant collar (1.53‐2.10 μm) and threads (3.53‐4.20 μm). Regardless of the abrasive powder used, the collar, emerging implant surfaces from the defect base, and surfaces beneath implants threads exhibited more post‐treatment residual ink. Conclusion Large‐sized powder showed the greatest cleaning capacity, but caused more alterations to the implant surface. Glycine and erythritol displayed no significant changes in surface roughness, however, demonstrated a limited ink removal capacity.