Distribution, condition, and growth of newly settled southern flounder (Paralichthys lethostigma) in the Galveston Bay Estuary, TX

Several flatfish species, including southern flounder (Paralichthys lethostigma) recruit to estuaries during early life. Therefore, evaluation of estuarine sites and habitats that serve as nurseries is critical to conservation and management. The present study used density data in conjunction with biochemical condition and growth measurements to evaluate settlement sites used by southern flounder in the Galveston Bay Estuary (GBE). In 2005, beam-trawl collections were made in three major sections of the GBE (East Bay, Galveston Bay, West Bay). Three sites were sampled in each bay. Within each sampling site, replicate collections were taken from three habitats: 1) marsh edge (< 1 m depth), 2) intermediate zone (10–20 m from marsh interface;  1 m depth), and 3) bay zone (typically > 100 m from marsh interface; depth > 1 m). Average size of southern flounder collected was 12–19 mm standard length, and peak densities occurred in January and February. Catch data indicated that densities of southern flounder were significantly greater in East Bay (2.75 per 100 m²) than in Galveston Bay (0.91 per 100 m²) or in West Bay (0.45 per 100 m²). Densities were statistically similar among habitats. Otolith-based estimates of age indicated that the majority of southern flounder collected were 35–45 days old and derived from early December to early January hatch-dates. Growth rates were similar among bays and among habitats, with the average growth rate being 0.40 mm day^− 1 (range: 0.21–0.76 mm day^− 1). RNA:DNA was above the established baseline value for nutritional stress, indicating that newly settled southern flounder in the GBE were in relatively high condition. Habitat-specific differences in RNA:DNA ratios were not observed; however, ratios were significantly lower in West Bay (average 8.0) than in East Bay (average 9.5) or in Galveston Bay (average 9.8), suggesting the condition of new recruits may vary spatially within the GBE. Findings from the current study suggest density and condition of newly settled southern flounder vary at the bay scale, suggesting that parts of GBE do not function equally as nurseries.     

Dietary greenhouse gas emissions of meat-eaters,fish-eaters,vegetarians and vegans in the UK

The production of animal-based foods is associated with higher greenhouse gas (GHG) emissions than plant-based foods. The objective of this study was to estimate the difference in dietary GHG emissions between self-selected meat-eaters, fish-eaters, vegetarians and vegans in the UK. Subjects were participants in the EPIC-Oxford cohort study. The diets of 2,041 vegans, 15,751 vegetarians, 8,123 fish-eaters and 29,589 meat-eaters aged 20–79 were assessed using a validated food frequency questionnaire. Comparable GHG emissions parameters were developed for the underlying food codes using a dataset of GHG emissions for 94 food commodities in the UK, with a weighting for the global warming potential of each component gas. The average GHG emissions associated with a standard 2,000 kcal diet were estimated for all subjects. ANOVA was used to estimate average dietary GHG emissions by diet group adjusted for sex and age. The age-and-sex-adjusted mean (95 % confidence interval) GHG emissions in kilograms of carbon dioxide equivalents per day (kgCO₂e/day) were 7.19 (7.16, 7.22) for high meat-eaters (?>?=?100 g/d), 5.63 (5.61, 5.65) for medium meat-eaters (50-99 g/d), 4.67 (4.65, 4.70) for low meat-eaters (?<?50 g/d), 3.91 (3.88, 3.94) for fish-eaters, 3.81 (3.79, 3.83) for vegetarians and 2.89 (2.83, 2.94) for vegans. In conclusion, dietary GHG emissions in self-selected meat-eaters are approximately twice as high as those in vegans. It is likely that reductions in meat consumption would lead to reductions in dietary GHG emissions.     

Das Wachstum der Kontinente nach der Zyklustheorie

Ohne Zusammenfassung     

Multidecadal simulation of coastal fog with a regional climate model

In order to model stratocumulus clouds and coastal fog, we have coupled the University of Washington boundary layer model to the regional climate model, RegCM (RegCM-UW). By comparing fog occurrences observed at various coastal airports in the western United States, we show that RegCM-UW has success at modeling the spatial and temporal (diurnal, seasonal, and interannual) climatology of northern California coastal fog. The quality of the modeled fog estimate depends on whether coast-adjacent ocean or land grid cells are used; for the model runs shown here, the oceanic grid cells seem to be most appropriate. The interannual variability of oceanic northern California summertime fog, from a multi-decadal simulation, has a high and statistically significant correlation with the observed interannual variability (r = 0.72), which indicates that RegCM-UW is capable of investigating the response of fog to long-term climatological forcing. While RegCM-UW has a number of aspects that would benefit from further investigation and development, RegCM-UW is a new tool for investigating the climatology of coastal fog and the physical processes that govern it. We expect that with appropriate physical parameterizations and moderate horizontal resolution, other climate models should be capable of simulating coastal fog. The source code for RegCM-UW is publicly available, under the GNU license, through the International Centre for Theoretical Physics.     

Polarization studies of the Venus uv contrasts: Cloud height and haze variability

Polarimetry is able to show direct evidence for compositional differences in the Venus clouds. We present observations (collected during $\text{2}\text{1}\text{2}$ Venus years by the Pioneer Venus Orbiter) of the polarization in four colors of the bright and dark ultraviolet features. We find that the polarization is significantly different between the bright and dark areas. The data show that the “null” model of L. W. Esposito (1980, J. Geophys. Res.85, 8151–8157) and the “overlying haze” model of J. B. Pollack et al. (1980, J. Geophys. Res.85, 8223–8231) are insufficient. Exact calculations of the polarization, including multiple scattering and vertical inhomogeneity near the Venus cloud tops, are able to match the observations. Our results give a straightforward interpretation of the polarization differences in terms of known constituents of the Venus atmosphere. The submicron haze and uv absorbers are anticorrelated: for haze properties as given by K. Kawabata et al. (1980, J. Geophys. Res.85, 8129–8140) the excess haze depth at 9350 Å over the bright regions is Δτ_h = 0.03 ± 0.02. The cloud top is slightly lower in the dark features: the extra optical depth at 2700 Å in Rayleigh scattering above the darker areas is Δτ_R = 0.010 ± 0.005. This corresponds to a height difference of 1.2 ± 0.6 km at the cloud tops. The calculated polarization which matches our data also explains the relative polarization of bright and dark features observed by Mariner 10. The observed differential polarization cannot be explained by differential distribution of haze, if the haze aerosols have an effective size of 0.49 μm, as determined by K. Kawabata et al. (1982, submitted) for the aerosols overlying the Venus equator. We propose two models for the uv contrasts consistent with our results. In a physical model, the dark uv regions are locations of vertical convergence and horizontal divergence. In a chemical model, we propose that the photochemistry is limited by local variations in water vapor and molecular oxygen. The portions of the atmosphere where these constituents are depleted at the cloud tops are the dark uv features. Strong support for this chemical explanation is the observation that the number of sulfur atoms above the cloud tops is equal over both the bright and dark areas. The mass budget of sulfur at these altitudes is balanced between excess sulfuric acid haze over the bright regions and excess SO₂ in the dark regions.     

A whole-moon thermal history model of Europa: Impact of hydrothermal circulation and salt transport

A whole-moon numerical model of Europa is developed to simulate its thermal history. The thermal evolution covers three phases: (i) an initial, roughly 0.5 Gyr-long period of radiogenic heating and differentiation, (ii) a long period from 0.5 Gyr to 4 Gyr with continuing radiogenic heating but no tidal dissipative heating (TDH), and (iii) a final period covering the last 0.5 Gyr until the present, during which TDH is active. Hydrothermal plumes develop after the initial period of heating and differentiation and transport heat and salt from Europa’s silicate mantle to its ice shell. We find that, even without TDH, vigorous hydrothermal convection in the rocky mantle can sustain flow in an ocean layer throughout Europa’s history. When TDH becomes active, the ice shell melts quickly to a thickness of about 20 km, leaving an ocean 80 km or more deep. Parameterized convection in the ice shell is non-uniform spatially, changes over time, and is tied to the deeper ocean–mantle dynamics. We also find that the dynamics are affected by salt concentrations. An initially non-uniform salt distribution retards plume penetration, but is homogenized over time by turbulent diffusion and time-dependent flow driven by initial thermal gradients. After homogenization, the uniformly distributed salt concentrations are no longer a major factor in controlling plume transport. Salt transport leads to the formation of a heterogeneous brine layer and salt inclusions at the bottom of the ice shell; the presence of salt in the ice shell could strongly influence convection in that layer.     

Intermineral oxygen three‐isotope systematics of silicate minerals in equilibrated ordinary chondrites

High‐precision oxygen three‐isotope ratios were measured for four mineral phases (olivine, low‐Ca and high‐Ca pyroxene, and plagioclase) in equilibrated ordinary chondrites (EOCs) using a secondary ion mass spectrometer. Eleven EOCs were studied that cover all groups (H, L, LL) and petrologic types (4, 5, 6), including S1–S4 shock stages, as well as unbrecciated and brecciated meteorites. SIMS analyses of multiple minerals were made in close proximity (mostly <100 μm) from several areas in each meteorite thin section, to evaluate isotope exchange among minerals. Oxygen isotope ratios in each mineral become more homogenized as petrologic type increases with the notable exception of brecciated samples. In type 4 chondrites, oxygen isotope ratios of olivine and low‐Ca pyroxene are heterogeneous in both δ¹⁸O and Δ¹⁷O, showing similar systematics to those in type 3 chondrites. In type 5 and 6 chondrites, oxygen isotope ratios of the four mineral phases plot along mass‐dependent fractionation lines that are consistent with the bulk average Δ¹⁷O of each chondrite group. The δ¹⁸O of three minerals, low‐Ca and high‐Ca pyroxene and plagioclase, are consistent with equilibrium fractionation at temperatures of 700–1000 °C. In most cases the δ¹⁸O values of olivine are higher than those expected from pyroxene and plagioclase, suggesting partial retention of premetamorphic values due to slower oxygen isotope diffusion in olivine than pyroxene during thermal metamorphism in ordinary chondrite parent bodies.