Natural Cadmium Isotopic Variations in Eight Geological Reference Materials (NIST SRM 2711, BCR 176, GSS-1, GXR-1, GXR-2, GSD-12, Nod-P-1, Nod-A-1) and Anthropogenic Samples, Measured by MC-ICP-MS

In this study, the Cd isotopic composition of various geological reference materials and anthropogenic samples was investigated. The measurements were made by multicollector ICP-MS and instrumental mass fractionation was controlled using a "sample-standard bracketing" technique. Cadmium isotopic data are reported relative to an internal Cd solution (Cd Spex) and expressed as the ¹¹⁴ Cd/¹¹⁰Cd delta value. Two other Cd solutions (Prolabo and JMC) were analysed and yielded the same 0% delta value. A fractionated Cd metal sample (Münster Cd) was used as a secondary reference material for Cd isotopic measurements and we obtained a ¹¹⁴ Cd/¹¹⁰ Cd delta value of 4.48% relative to Cd Spex solution. As opposed to multi-stage Cd purification previously published in the literature, a new one step anionic exchange purification using dilute HCl for the analysis of Cd isotopes in geological samples was developed. This method enabled a high recovery (> 95%) and effective separation of the sample matrix to be achieved. The long-term external reproducibility was evaluated at 0.12% (2 standard deviations) for the ¹¹⁴ Cd/¹¹⁰Cd ratio, based on reference solutions and replicated measurements of samples over one year. The variation of Cd isotopic composition of natural terrestrial samples is restricted to a small range of 0.4%, which is similar to previously reported results. In contrast, large variations of Cd isotopic composition were found for anthropogenic samples with values as low as −0.64% for a dust sample issued from a lead smelter and values as high as +0.50% for NIST SRM 2711 (metal-rich soil). These variations are 10 times larger than the reproducibility and suggest that Cd isotopes can be useful as tracers of anthropogenic sources of Cd in the environment.     

Michigan basin regional ground water flow discharge to three Great Lakes

Ground water discharge to the Great Lakes around the Lower Peninsula of Michigan is primarily from recharge in riparian basins and proximal upland areas that are especially important to the northern half of the Lake Michigan shoreline. A steady-state finite-difference model was developed to simulate ground water flow in four regional aquifers in Michigan's Lower Peninsula: the Glaciofluvial, Saginaw, Parma-Bayport, and Marshall aquifers interlayered with the Till/"red beds," Saginaw, and Michigan confining units, respectively. The model domain was laterally bound by a continuous specified-head boundary, formed from lakes Michigan, Huron, St. Clair, and Erie, with the St. Clair and Detroit River connecting channels. The model was developed to quantify regional ground water flow in the aquifer systems using independently determined recharge estimates. According to the flow model, local stream stages and discharges account for 95% of the overall model water budget; only 50% enters the lakes directly from the ground water system. Direct ground water discharge to the Great Lakes' shorelines was calculated at 36 m3/sec, accounting for 5% of the overall model water budget. Lowland areas contribute far less ground water discharge to the Great Lakes than upland areas. The model indicates that Saginaw Bay receives only approximately 1.13 m3/sec ground water; the southern half of the Lake Michigan shoreline receives only approximately 2.83 m3/sec. In contrast, the northern half of the Lake Michigan shoreline receives more than 17 m3/sec from upland areas.     

Coral skeletal delta(15)N reveals isotopic traces of an agricultural revolution

This study introduces a new method of tracing the history of nutrient loading in coastal oceans via delta(15)N analysis of organic nitrogen preserved in the skeleton of the massive Porites coral. Four coral cores were collected in Bali, Indonesia, from reefs exposed to high levels of fertilizers in agricultural run-off, from lagoonal corals impacted by sewage, and from a reef located 30 km offshore. Skeletal delta(15)N in the agriculturally exposed coral declined from 10.7+/-0.4 per thousand in 1970-1971, when synthetic fertilizers (-0.8 per thousand+/-0.2 per thousand) were introduced to Bali, to a depleted "anthropogenic" baseline of 3.5 per thousand+/-0.4% in the mid-1990s. delta(15)N values were negatively correlated with rainfall, suggesting that marine delta(15)N lowers during flood-bourn influxes of waste fertilizers. Reef cores exposed to untreated sewage in terrestrial discharge were enriched (7.8 and 7.3+/-0.4 per thousand), while the offshore core reflected background oceanic signals (6.2+/-0.4 per thousand). delta(15)N, N concentration, and C:N systematics indicate that the N isotopic composition of skeletal organic matter was generally well preserved over 30 years. We suggest that skeletal organic delta(15)N can serve as a recorder of past nitrogen sources. In Bali, this tracer suggests that the intensification of Western style agricultural practices since 1970 are contributing to the degradation of coastal coral reefs.     

Photochemistry of flourine in the mesosphere of Venus

In the laboratory, reactions with flourine species proceed rapidly with high rates but under mesospheric conditions the effeciency of these compounds is low due to the rapid formation of HF and to the lack of reactivity of this species. Even if diffusion processes are included, the result of calculations leads to fluorie concentrations typically less than 20 cm^?3. The low photodissociation coeffecient of HF leads to the expectation of a scale height of HF greater than or equal to the mean scale height. If the troposphere appears to be a sink for hydrofluoric acid, the maximum value of fluorine is obtained with a downward flux of 1.3 × 10⁸ HF atoms cm^?2 sec^?1 at the level of the clouds.     

Radar constraints on asteroid regolith properties using 433 Eros as ground truth

Abstract— Radar data enable us to estimate an asteroid's near‐surface bulk density, thus providing a joint constraint on near‐surface porosity and solid density. We investigate two different approaches to simplifying this joint constraint: estimating solid densities by assuming uniform porosities for all asteroids; and estimating porosities by assuming uniform mineralogy within each taxonomic class. Methods used to estimate asteroids' near‐surface solid densities from radar data have not previously been calibrated via independent estimates. Recent spacecraft results on the chondritic nature of 433 Eros now permit such a check, and also support porosity estimation for S‐class objects. We use radar albedos and polarization ratios estimated for 36 main‐belt asteroids and nine near‐Earth asteroids to estimate near‐surface solid densities using two methods, one of which is similar to the uncalibrated algorithms used in previous studies, the other of which treats Eros as a calibrator. We also derive porosities for the same sample by assigning solid densities for each taxonomic class in advance. Density‐estimation results obtained for Eros itself are consistent with the uncalibrated method being valid in the mean; those derived for the full sample imply that uncalibrated solid densities are, at most, a few tens of percent too large on average. However, some derived densities are extremely low, whereas most porosity estimates are physically plausible. We discuss the relative merits of these two approaches.     

On the Role of Lightning NOx in the Formation of Tropospheric Ozone Plumes: A Global Model Perspective

A series of ozone transects measured each year from 1987 to 1990 over thewestern Pacific and eastern Indian oceans between mid-November andmid-Decembershows a prominent ozone maximum reaching 50–80 ppbv between 5 and 10 kmin the 20° S–40° S latitude band. This maximum contrasts with ozonemixing ratios lower than20 ppbv measured at the same altitudes in equatorial regions. Analyses witha globalchemical transport model suggest that these elevated ozone values are part ofa large-scale tropospheric ozone plume extending from Africa to the western Pacific acrosstheIndian ocean. These plumes occur several months after the peak in biomassburninginfluence and during a period of high lightning activity in the SouthernHemispheretropical belt. The composition and geographical extent of these plumes aresimilar to theozone layers previously encountered during the biomass burning season in thisregion.Our model results suggest that production of nitrogen oxides from lightningstrokes sustains the NO_x (= NO+NO₂) levels and the ozonephotochemical productionrequired in the upper troposphere to form these persistent elevated ozonelayers emanating from biomass burning regions.     

Global NOx Production by Lightning

Lightning is thought to represent an important source of tropospheric reactive nitrogen species NO_x (NO + NO₂),but estimates of global production of NO_x by lightning varyconsiderably. We evaluate the production of NO_x by lightning using a global chemical/transport model, satellite lightning observations, and airborne NO_x measurements. Various model calculations are conducted toassess the global NO_x production rate of lightning by comparing the model calculations with airborne measurements. The results show that the simulated NO_x in the tropical middle and upper troposphere are very sensitiveto the amount and altitude of the lightning NO_x used in the model. A global lightning NO_x production of 7 Tg N yr^–1uniformly distributed in convective clouds or 3.5 Tg N yr^–1 distributedin the upper cloud regions produces good agreement between calculated and measured NO_x concentrations in the tropics.     

Dynamical aspects of katabatic wind evolution in the Antarctic coastal zone

The spatial evolution of katabatic winds along idealized slopes representative of Antarctic terrain is examined using a hydrostatic, two-dimensional primitive equation model with high resolution. A downslope momentum-forces analysis is made of simulations in which katabatic flow reaches steady state, with emphasis on physical mechanisms in the coastal zone. The importance of the reversal of the pressure gradient force in the coastal zone, causing the sudden decay of katabatic winds, is discussed.