Evaluating U-series tools for weathering rate and duration on a soil sequence of known ages

Four soil profiles of known age (40, 250, 600 and 3000ka) from the Merced soil chronosequence in California were analysed for U and Th isotopes, and for major- and trace-element compositions, to test the assumption that leaching of U-series isotopes is a first order process with an invariant rate constant, as frequently assumed when applying this isotopic tool to determine weathering duration and sediment residence time. Average (230Th/238U) values for each profile decrease from a high of 1.28 in the youngest soil (40ka) to 1.09, 0.99 and 0.98 in the 250ka, 600ka and 3000ka soils respectively. (234U/238U) values also show variation across the 4 soils. The simultaneous variation in (230Th/238U) and (234U/238U) cannot be explained by a first-order kinetic model with invariant rate constants and instead requires that leaching coefficients for the U-series isotopes change with time. The observed data is consistent with a two-stage model that reflects an initial period of fast leaching of U and Th from a readily weathered soil pool (such as grain boundaries or defects), followed by slow leaching from a more resistant soil pool. Application of such a two-stage model may lead to significantly shorter calculated timescales of weathering than those obtained by the widely applied single-stage model of U-series weathering, which assumes no change in leaching coefficients over time. The results of this study have wide implications for published and future use of U-series tools in weathering studies. © 2013 Elsevier B.V

Nitrogen loss from soil through anaerobic ammonium oxidation coupled to iron reduction

The oxidation of ammonium is a key step in the nitrogen cycle, regulating the production of nitrate, nitrous oxide and dinitrogen. In marine and freshwater ecosystems, anaerobic ammonium oxidation coupled to nitrite reduction, termed anammox, accounts for up to 67% of dinitrogen production. Dinitrogen production through anaerobic ammonium oxidation has not been observed in terrestrial ecosystems, but the anaerobic oxidation of ammonium to nitrite has been observed in wetland soils under iron-reducing conditions. Here, we incubate tropical upland soil slurries with isotopically labelled ammonium and iron(iii) to assess the potential for anaerobic ammonium oxidation coupled to iron(iii) reduction, otherwise known as Feammox, in these soils. We show that Feammox can produce dinitrogen, nitrite or nitrate in tropical upland soils. Direct dinitrogen production was the dominant Feammox pathway, short-circuiting the nitrogen cycle and resulting in ecosystem nitrogen losses. Rates were comparable to aerobic nitrification and to denitrification, the latter being the only other process known to produce dinitrogen in terrestrial ecosystems. We suggest that Feammox could fuel nitrogen losses in ecosystems rich in poorly crystalline iron minerals, with low or fluctuating redox conditions. Includes Supplementary Information

Color prediction modeling for five-channel CMYLcLm printing

In printing, halftoning algorithms are applied in order to reproduce a continuous-tone image by a binary printing system. The image is transformed into a bitmap composed of dots varying in size and/or frequency. Nevertheless, this causes that the sparse dots found in light shades of cyan (C) and magenta (M) appear undesirably noticeable against white substrate. The solution is to apply light cyan (Lc) and light magenta (Lm) inks in those regions. In order to predict the color of CMYLcLm prints, we make use of the fact that Lc and Lm have similar spectral characteristics as C and M respectively. The goal of this paper is to present a model to characterize a five-channel CMYLcLm printing system using a three-channel color prediction model, where we treat the ink combinations Lc+C and Lm+M as new compound inks. This characterization is based on our previous three-channel CMY color prediction model that is capable of predicting both colorimetric tri-stimulus values and spectral reflectance. The drawback of the proposed model in this paper is the requirement of large number of training samples. Strategies are proposed to reduce this number, which resulted in expected larger but acceptable color differences

Subcellular metal imaging identifies dynamic sites of Cu accumulation in Chlamydomonas.

We identified a Cu-accumulating structure with a dynamic role in intracellular Cu homeostasis. During Zn limitation, Chlamydomonas reinhardtii hyperaccumulates Cu, a process dependent on the nutritional Cu sensor CRR1, but it is functionally Cu deficient. Visualization of intracellular Cu revealed major Cu accumulation sites coincident with electron-dense structures that stained positive for low pH and polyphosphate, suggesting that they are lysosome-related organelles. Nano-secondary ion MS showed colocalization of Ca and Cu, and X-ray absorption spectroscopy was consistent with Cu(+) accumulation in an ordered structure. Zn resupply restored Cu homeostasis concomitant with reduced abundance of these structures. Cu isotope labeling demonstrated that sequestered Cu(+) became bioavailable for the synthesis of plastocyanin, and transcriptome profiling indicated that mobilized Cu became visible to CRR1. Cu trafficking to intracellular accumulation sites may be a strategy for preventing protein mismetallation during Zn deficiency and enabling efficient cuproprotein metallation or remetallation upon Zn resupply