Effects of Temperature and Humidity upon the Entrainment of Sedimentary Particles by Wind

Aeolian transport of sedimentary particles is a well-recognized phenomenon in cold regions, but the effect of low temperature (T) and specific humidity (q) upon particle entrainment has not previously been investigated. This study reports on wind-tunnel experiments (-12 °C T 32 °C, and 1 g kg^-1 q 10 g kg^-1) that suggest the aerodynamic drag required to entrain sand sized particles can be 30% lower in cold or high latitude settings, as compared to hot deserts. For any given regional wind velocity, this effect will increase the wind strength index and thereby the proportion of time a surface is active at low temperature.The influence of air temperature and humidity upon the threshold for particle motion is determined by three physical processes: (1) The effect of air viscosity and density on the fluid drag force acting to dislodge sedimentary particles; (2) the effect of viscosity on the turbulent wake shed from these particles, and the frequency and magnitude of burst-sweep events; and (3) the development of inter-particle cohesion via adsorbed water. This study considers the relative importance of each of these processes. The threshold friction velocity model of Shao and Lu is revised to incorporate the inter-particle force associated with hygroscopic water. It is found to perform well when tested against the experimental data obtained for this study.     

Cristobalite- and tridymite-bearing clasts in Parnallee (LL3) and Farmington (L5)

Abstract— A set of cristobalite- and tridymite-rich igneous clasts (CB1 to CB8) have been found in Parnallee (LL3.6). They consist of clinoenstatite, minor feldspathic mesostasis and cristobalite veined by endiopsideaugite. The largest clast, CB8, is 1.6 cm in diameter and contains veined tridymite and cristobalite, clinoenstatite (zoned to ferroaugite and pyroxferroite Fs_75.6Wo_20.0) and plagioclase. Compared to bulk ordinary chondrites (OC), the bulk clasts are depleted in Al (0.02–0.8× OC), Na and K and enriched in Si (1.6–2.0× OC) and Ca (1.3–4.5× OC). Bulk CB8 has LREE > HREE (La/Lu = 1.6) with a positive Eu anomaly (Eu/Eu^* = 2.4). Textural observations suggest that the clasts cooled rapidly (24–420 °C/h) above 1200 °C. Clasts CB1—CB8 contain the isotopically heaviest O yet found in ordinary chondrites (up to δ¹⁷O = +8.7%_o, δ¹⁸O = +11.6%_o). Enrichment in the heavy isotopes of O is dependent on the proportion of cristobalite (or tridymite) in the clasts. A regression line CRIL (Cristobalite Line), with slope 0.77, is defined by the isotopic compositions of CB1—CB8, the Farmington clast and ordinary chondrite chondrules. An ¹⁶O-poor gas reservoir, whose composition must lie at some point along the extension of CRIL, has undergone varying degrees of isotopic exchange with most ordinary chondrite material. Silica polymorphs have undergone the greatest degree of exchange because of their open, framework structures. Silicon in CB1—CB8 has normal isotopic ratios. A model is proposed that involves differentiation of H-group material through extraction of volatile elements in a vapour phase, loss of an Fe-Ni-S melt and metastable crystallisation (60–70%) of olivine. The calculated residual liquid is silica-oversaturated and its subsequent predicted crystallisation sequence resembles that preserved in CB1—CB8. This model may require two stages of heating, the second one prior to cristobalite crystallisation (if the silica polymorph crystallises within its predicted stability field of > 1500 °C). Isotopic exchange took place either when CB1—CB8 were ejected from their parent body due to impact or near the surface of the parent body, perhaps in an ejecta blanket setting. The latter option is preferred because it is more consistent with our igneous model.     

Bottom-water Hypoxia Effects on Sediment–Water Interface Nitrogen Transformations in a Seasonally Hypoxic,Shallow Bay (Corpus Christi Bay,TX, USA)

Bottom-water hypoxia effects on sediment–water interface nitrogen (N) transformations in Corpus Christi Bay (TX, USA) were examined using continuous-flow intact sediment core incubations. Sediment cores were collected from three sites in August 2002 (summer hypoxia) and April 2003 (normoxia). Oxygen (O₂) and hydrogen sulfide (H₂S) depth profiles were generated with microelectrodes. Membrane inlet mass spectrometry was used to measure sediment O₂ demand and net N₂ flux and combined with isotope pairing to determine potential denitrification and N fixation. Potential dissimilatory nitrate reduction to ammonium (DNRA) was measured using high-performance liquid chromatography. Sediment O₂ penetration depths ranged from 5 to 10 mm. H₂S ranged from being present in overlying water and throughout the sediment column in August to not detectable in overlying water or sediment in April. Sediment O₂ demand was higher during bottom-water normoxia conditions versus hypoxia. Sediments were a significant source of \textNH_\text4^{\text +} {\text{NH}}_{\text{4}}^{\text{ + }} to overlying water during hypoxia but not during normoxia. Net N₂ fixation was observed at one station in August and all stations in April. Denitrification rates were significantly higher during hypoxia at two of three sites. Potential DNRA was observed during both oxic states, but rates were significantly higher during hypoxia, which may reflect sulfide enhancement and absence of cation exchange with ^\text14 \textNH_\text4^{\text +} ^{{\text{14}}} {\text{NH}}_{\text{4}}^{\text{ + }} . DNRA may contribute to formation and maintenance of bottom-water hypoxic events in this system. These results show that N transformation pathways and rates change when bottom-water O₂ concentrations drop to hypoxic levels. Since south Texas is a semiarid region with few episodic runoff events, these results indicate that Corpus Christi Bay sediments are a N source most of the year, and denitrification may drive N limitation between episodic runoff events.     

Pivotal principles for digital earth development in the twenty-first century

ABSTRACT

Reductionist thinking will no longer suffice to address contemporary, complex challenges that defy sectoral, national, or disciplinary boundaries. Furthermore, lessons learned from the past cannot be confidently used to predict outcomes or guide future actions. The authors propose that the confluence of a number of technology and social disruptors presents a pivotal moment in history to enable real time, accelerated, and integrated action that can adequately support a ‘future earth’ through transformational solutions. Building on more than a decade of dialogues hosted by the International Society for Digital Earth (ISDE), and evolving a briefing note presented to delegates of Pivotal 2015, the paper presents an emergent context for collectively addressing spatial information, sustainable development, and good governance through three guiding principles for enabling prosperous living in the twenty-first century. These are: (1) open data, (2) real-world context, and (3) informed visualization for decision support. The paper synthesizes an interdisciplinary dialogue to create a credible and positive future vision of collaborative and transparent action for the betterment of humanity and planet. It is intended that these Pivotal Principles can be used as an elegant framework for action toward the Digital Earth vision, across local, regional, and international communities and organizations.     

Accumulation of cadmium in extracellular granules in the kidney of the bivalve mollusc Mercenaria mercenaria (L.)

As part of an ongoing investigation of the transport, accumulation and excretion of metals in the infaunal eulamellibranch Mercenaria mercenaria (L.) organisms were exposed to radioactive cadmium followed by an autoradiographic study of the kidney tissue to determine the morphological sites of cadmium accumulation. Preliminary results of these studies indicate that cadmium is associated with large extracellular granules in the lumina of the kidneys. The presence of radioactive cadmium was determined morphometrically by counting developed silver grains on sections coated with a photographic emulsion. The results were statistically significant (99·9 % confidence—Student's t-test) to show that more radioactive cadmium was associated with large granules than with the background tissue.     

The Taylor Dome Antarctic O Record and Globally Synchronous Changes in Climate

The ¹⁸O/¹⁶O profile of a 554-m long ice core through Taylor Dome, Antarctica, shows the climate variability of the last glacial–interglacial cycle in detail and extends at least another full cycle. Taylor Dome shares the main features of the Vostok record, including the early climatic optimum with later cool phase of the last interglacial period in Antarctica. Taylor Dome δ¹⁸O fluctuations are more abrupt and larger than those at Vostok and Byrd Station, although still less pronounced than those of the Greenland GISP2 and GRIP records. The influence of the Atlantic thermohaline circulation on regional ocean heat transport explains the partly “North Atlantic” character of this Antarctic record. Under full glacial climate (marine isotope stage 4, late stage 3, and stage 2), this marine influence diminished and Taylor Dome became more like Vostok. Varying degrees of marine influence produce climate heterogeneity within Antarctica, which may account for conflicting evidence regarding the relative phasing of Northern and Southern Hemisphere climate change.     

Zur Systematik der Kohlenstoff-Schwefel-Eisen-Verhältnisse in Auftriebssedimenten

Abundances of organic carbon, sulfur, and reactive iron in sediments of three upwelling environments (Peru, Oman and Benguela) suggest that organic carbon/reduced sulfur ratios (C/S-ratios) in this category of marine sediments deviate considerably from previously established empirical ratios in normal marine sediments. To clarify the discrepancies, we investigated those components of the diagenetic system that limit the formation of pyrite: sulfate concentrations and reduction rates in pore waters, availability of reactive iron, and the quantity and quality of organic matter. All three limitations are evident in our sample pools. The results suggest that C/S-ratios in recent and fossil marine sediments rich in organic matter may be unsuitable as paleoenvironmental indicators.

     

Kiglapait geochemistry V: Strontium

The Kiglapait intrusion contains 330 ppm Sr and has $\text{Sr}\text{Ca}\text{= 5 × 10}{}^{\mathrm{?3}}$ and $\text{Rb}\text{Sr}\text{= 3 × 10}{}^{\mathrm{?3}}$, as determined by summation over the Layered Group of the intrusion. Wholerocks in the Lower Zone contain 403 F_L^0.141 ppm Sr, where F_L is the fraction of liquid remaining; Sr drops to 180 ppm at the peak of augite production (F_L = 0.11) and rises to a maximum of 430 ppm in the Upper Zone before decreasing to 172 ppm at the end of crystallization. Feldspars in the Lower Zone contain 532 F_L^0.090 ppm Sr, increasing to 680 ppm in the Upper Zone before decreasing to 310 ppm at the end. Clinopyroxenes contain 15 to 30 ppm Sr and have a mineral-melt distribution coefficient D = 0.06 except near the top of the intrusion where D = 0.10.The calculated feldspar-liquid distribution coefficient has an average value near 1.75 but shows four distinct trends when plotted against X_An of feldspar. The first two of these are strongly correlated with the modal augite content of the liquid, on average by the relation D = 1.4 + 0.02 Aug^L. The third (decreasing) trend is due to co-crystallization of apatite, and the fourth (increasing) trend can best be attributed to a triclinic-monoclinic symmetry change in the feldspar at An₂₆, 1030°C. The compound feldspar-liquid distribution coefficient K_D for $\text{Sr}\text{Ca}$ bears out these deductions in detail and yields ΔG_r for the Sr-Ca exchange ranging from nearly zero at the base of the Lower Zone to ?26 kJ/gramatom at the end of crystallization. The compound feldspar-liquid distribution coefficient K_D for $\text{Rb}\text{Sr}$ varies from 0.3 in the Lower Zone to 1.1 at the end of crystallization.The ratio $\text{Ca}{}^{\mathrm{F}}\text{Ca}{}^{\mathrm{L}}$ is about 1.45 for troctolitic liquids containing 5% augite, for which K_D (Sr-Ca) = 1.0 and D_Ca = D_Sr. For common basaltic liquids containing 20% augite, the Kiglapait data predict $\text{solSr}{}^{\mathrm{F}}\text{Sr}{}^{\mathrm{L}}\text{= 1.8}$, as commonly found elsewhere. The strong dependence of D_sr on augite content of the liquid illuminates the role of liquid composition and structure in determining the feldspar-liquid distribution coefficient. Conversely, a discontinuous change in the trend of D_Sr when apatite arrives shows that the effect is due to apatite crystallization itself, not to the continuous variation of the liquid as it becomes enriched in apatite component.