Changes in Coral Skeleton Growth Recorded by Density Band Stratigraphy, Crystalline Structure, and Hiatuses

Next-generation high resolution brightfield microscopy, x-radiography, and microcomputed tomography (microCT) analyses indicate that coral skeleton high density band (HDB) and low density band (LDB) stratigraphic sequences record dynamic changes in coral growth history. HDB-LDB sequences were studied within three small heads of Orbicella annularis, an ecological keystone species in the Caribbean Sea, collected from the leeward fringing reefs on Curaçao. Results indicate that HDB layers are formed by the thickening of exothecal and endothecal dissepiments, costae, and theca located at the margin and external to individual skeletal cups (corallites). Conversely, septa and columellas located inside individual corallites do not change in thickness. HDB-LDB stratigraphic sequences were laterally traced from the center to the margins of individual coral heads, demonstrating that shifts took place in the trajectory of coral skeleton growth. Normal HDB layers in the center of individual coral heads are formed at the same time (age-equivalent) as surfaces of erosion and no skeleton growth (hiatuses) on the margins of the heads. These hiatus surfaces within HDB-LDB stratal geometries indicate that multiple marine ecological and environmental processes affect the orientation, size, shape, and geometry of coral skeletons during coral growth history. The presence of these hiatus surfaces in other large coral heads would strongly impact sclerochronology and the interpretation of multiple environmental factors including sea surface temperature (SST).

Highly selective adsorption on WX2 (X=S, Se, Te) monolayer and effect of strain engineering: A DFT Study

A model of SO2 molecule was established, and the adsorption of SO2 by intrinsic graphene was first studied by the first principles study. The calculation results show that the intrinsic WX2 (X = S, Se, Te) has a weak adsorption of SO2 and belongs to physical adsorption. Then compare the adsorption of SO2 by the WX2 systems doped with As and Ge, and calculated by first-principles: the doped WX2 has a stronger adsorption effect on SO2. From the perspective of the degree of change in the adsorption structure, single-doped Ge/WTe2 has stronger stability when adsorbing gas molecules; from the perspective of adsorption energy, charge density, band structure, and density of states diagrams, single-doped Ge/WTe2 has a greater effect on SO2 gas has better adsorption effect.

Persistent Turbulence in the Samoan Passage

Abyssal waters forming the lower limb of the global overturning circulation flow through the Samoan Passage and are modified by intense mixing. Thorpe-scale-based estimates of dissipation from moored profilers deployed on top of two sills for 17 months reveal that turbulence is continuously generated in the passage. Overturns were observed in a density band in which the Richardson number was often smaller than ¼, consistent with shear instability occurring at the upper interface of the fast-flowing bottom water layer. The magnitude of dissipation was found to be stable on long time scales from weeks to months. A second array of 12 moored profilers deployed for a shorter duration but profiling at higher frequency was able to resolve variability in dissipation on time scales from days to hours. At some mooring locations, near-inertial and tidal modulation of the dissipation rate was observed. However, the modulation was not spatially coherent across the passage. The magnitude and vertical structure of dissipation from observations at one of the major sills is compared with an idealized 2D numerical simulation that includes a barotropic tidal forcing. Depth-integrated dissipation rates agree between model and observations to within a factor of 3. The tide has a negligible effect on the mean dissipation. These observations reinforce the notion that the Samoan Passage is an important mixing hot spot in the global ocean where waters are being transformed continuously.

Marine Reservoir Corrections for the Brazilian Northern Coast Using Modern Corals

ABSTRACTThe Abrolhos bank, in southern Bahia State (BA), is the largest coral reef system in the southwestern Atlantic. It is highly influenced by the Brazil Current (BC), since it is located in the continental shelf. By contrast, Todos os Santos Bay (TSB), in Salvador, capital of Bahia State (BA) has an important coral biodiversity, located in a bay inlet with restricted water circulation. Coral cores were collected in those sites and were analyzed for density band counting and by Th/U dating to estimate growth rates and age. In this work, we present 14C ages of some of these bands in order to evaluate the marine reservoir effect (MRE) to which the colonies were subjected during growth. It is the first study making use of coral skeleton samples for MRE determination for the Brazilian coast. ΔR was calculated to be –151±23 14C yr, while that for the TSB was –107±51 14C yr.

ANNUAL SKELETAL EXTENSION OF TWO REEF-BUILDING CORALS FROM THE COLOMBIAN CARIBBEAN SEA

The skeletal growth of the scleractinian corals Diploria labyrinthiformis (Linnaeus 1758) and Montastraea annularis (Ellis and Solander 1786) from Isla Grande (north of Rosario islands), Colombian Caribbean, was determined from annual extension increments revealed by X-radiography of 4-6 mm thick slabs obtained along the axis of maximum growth. The skeletal extension average rate for the last 22 years for D. labyrinthiformis was 3.8 mm year-1 (SE 0.10; N = 87). The correlation between growth of D. labyrinthiformi s and hours of sunlight was significantly negative. The annual variances of sunlight enhanced annual statistically significant differences of growth in this species. M. annularis showed an average extension growth of 10.6 mm year-1 (SE 0.32; N = 55) during the last 14 years. The increase of M. annularis growth was coincident with the end of nearby dredging activities as well as the decrease of nutrient levels. Nevertheless, the growth rate of this species showed no statistically significant differences through the years and no correlation with variation in sunlight. Alow density annual band, wider than high density band in D. labyrinthiformis and narrower in M. annularis, seems to form approximately during April and May in both species, which is coincident with the end of dry season (increase of sea surface temperature, decrease of hours of sunlight and high influence of Dique Channel waters over Rosario islands). The annual bands forming on both species at the study site might be highly related with time of reproduction of each species. Further investigation will permit a better understanding of how some local conditions or coral physiology are related with coral growth at Rosario islands.

Influence of interface properties on charge density, band edge shifts and kinetics of the photoelectrochemical process in p-type NiO photocathodes

The surface structure of NiO is correlated to observed changes in the band energy, energetic distribution of the trap states density, charge interface transfer, charge transport, and as a result the p-type DSSC device performance.

CONDUCTIVITY OF GAPPED GRAPHENE WITHIN RANDOM PHASE APPROXIMATION

The gapped graphene is technologically more important as electronic devices made up of conventional semiconductors are based on the presence of a gap between the valence and conduction bands. In this paper, we report our analytical and numerical calculation of conductivity of gapped graphene on SiO 2 substrate and its variation with the governing parameters of carrier density, band gap, long range charge impurity scatterers, short range neutral defect scatterers, impurity distance from the graphene interface and potential strength of short range scattering centers. We find that the conductivity for unscreened potential decreases with increasing band gap but when screening is incorporated the trend is not only reversed but there is a sharp enhancement in its magnitude also. The sub linear behavior seen in conductivity in the case of gapless graphene at high carrier concentration due to enhanced scattering from the short range neutral defects is also observed for gapped graphene, and it is further observed that increasing the potential strength of the defect scatterers brings in the same behavior at relatively smaller carrier densities.

H2 ADSORPTION ON LiB (001) SURFACE: A FIRST PRINCIPLES CALCULATION

The adsorption behavior of H2 on the LiB (001) surface was investigated with density functional theory (DFT) method. It was found that the site of H2 adsorbed on the Li-B bridge II was easier than the other four sites ( Li top, B top, hollow vertical and Li-B bridge I). H2 adsorbed on the Li-B bridge II site was a strong chemical adsorption. The adsorption energy was 2.190 eV, and the H , B atoms exhibited covalent characteristics, the H – H atoms have a little interaction, and the H2 was 0.331 Å below the surface of Li-B bridge II. The charge density, band structure, totals and partial density of states were calculated utilizing the first principle method. These calculations showed that the H interacted with the surface atoms, and partially saturated the dangling bonds with the surface atoms. The interaction between H and the surface atoms were mainly attributed to the H 1 s, B 2 s and B 2 p states. The calculated band gap was 0.075 eV and 0.199 eV before and after adsorption.