Development of Iron Speciation Reference Materials for Palaeoredox Analysis

The development and application of geochemical techniques to identify redox conditions in modern and ancient aquatic environments has intensified over recent years. Iron (Fe) speciation has emerged as one of the most widely used procedures to distinguish different redox regimes in both the water column and sediments, and is the main technique used to identify oxic, ferruginous (anoxic, Fe(II) containing) and euxinic (anoxic, sulfidic) water column conditions. However, an international sediment reference material has never been developed. This has led to concern over the consistency of results published by the many laboratories that now utilise the technique. Here, we report an interlaboratory comparison of four Fe speciation reference materials for palaeoredox analysis, which span a range of compositions and reflect deposition under different redox conditions. We provide an update of extraction techniques used in Fe speciation and assess the effects of both test portion mass, and the use of different analytical procedures, on the quantification of different Fe fractions in sedimentary rocks. While atomic absorption spectroscopy and inductively coupled plasma‐optical emission spectrometry produced comparable Fe measurements for all extraction stages, the use of ferrozine consistently underestimated Fe in the extraction step targeting mixed ferrous–ferric minerals such as magnetite. We therefore suggest that the use of ferrozine is discontinued for this Fe pool. Finally, we report the combined data of four independent Fe speciation laboratories to characterise the Fe speciation composition of the reference materials. These reference materials are available to the community to provide an essential validation of in‐house Fe speciation measurements.     

A test of J2000 model in a glacierized catchment in the central Tibetan Plateau

In this paper, the application of a fully distributed hydrological model J2000 with limited hydrological data was investigated in an alpine small and glacierized catchment, the Qugaqie (55 km² with 7.3% glacier area), in the central Tibetan Plateau (TP). The J2000 was examined to investigate the influence on model performance, as well as on data, parameters and sensitivities. The model was calibrated with time series of discharge at the basin outlet for the summers of 2006 and 2007 and validated for the summer of 2008 by examining multiple objective functions. The model coefficients of determination were 0.62 and 0.91 for the calibration periods in 2006 and 2007, respectively, and 0.56 for the validation period in 2008. Simulated discharge was generally less than the observed values for the calibration and validation periods. The sensitivity to alteration in meteorological parameter has revealed that a change in air temperature would cause a dramatic increase of discharge in the Qugaqie catchment. Hypothetical climate scenario experiments showed that the increase of air temperature by 1°C resulted in 14% increase in runoff, whereas 20% increase in precipitation caused 9% increase in runoff but 12% reduction in glacier melt.     

Magnetic fields in galaxies

Summary Recent years have seen an amazing development in our knowledge of the magnetic fields in the universe. The last ten years were crucial in our realization of the importance of the magnetic fields in galaxies. While a lot of the earlier data on our Galaxy depended on optical observations, the bulk of the recent results depend on radio measurements. The radio Zeeman effect gave us new information on magnetic fields in molecular clouds. The mapping of galaxies at several radio frequencies resulted in new knowledge about the large-scale magnetic fields in these basic building blocks of the universe. These exciting observations have led to new theoretical developments. In particular, the dynamo theory of flat objects received much attention since the observed large-scale structures can best be explained through the action of the dynamo effect. This review will attempt to summarise the observational evidence and to give viable explanations for the magnetic fields in galaxies.     

The impact of groundwater–surface water interactions on the water balance of a mesoscale lowland river catchment in northeastern Germany

The glacially formed northeastern German lowlands are characterized by extensive floodplains, often interrupted by relatively steep moraine hills. The hydrological cycle of this area is governed by the tight interaction of surface water dynamics and the corresponding directly connected shallow groundwater aquifer. Runoff generation processes, as well as the extent and spatial distribution of the interaction between surface water and groundwater, are controlled by floodplain topography and by surface water dynamics. A modelling approach based on extensive experimental analyses is presented that describes the specific water balance of lowland areas, including the interactions of groundwater and surface water, as well as reflecting the important role of time‐variable shallow groundwater stages for runoff generation in floodplains. In the first part, experimental investigations of floodplain hydrological characteristics lead to a qualitative understanding of the water balance processes and to the development of a conceptual model of the water balance and groundwater dynamics of the study area. Thereby model requirements which allow for an adequate simulation of the floodplain hydrology, considering also interactions between groundwater and surface water have been characterized. Based on these analyses, the Integrated Modelling of Water Balance and Nutrient Dynamics (IWAN) approach has been developed. This consists of coupling the surface runoff generation and soil water routines of the deterministic, spatially distributed hydrological model WASIM‐ETH‐I with the three‐dimensional finite‐difference‐based numerical groundwater model MODFLOW and Processing MODFLOW. The model was applied successfully to a mesoscale subcatchment of the Havel River in northeast Germany. It was calibrated for two small catchments (1·4 and 25 km²), where the importance of the interaction processes between groundwater and surface waters and the sensitivity of several controlling parameters could be quantified. Validation results are satisfying for different years for the entire 198 km² catchment. The model approach was further successfully tested for specific events. The experimental area is a typical example of a floodplain‐dominated landscape. It was demonstrated that the lateral flow processes and the interactions between groundwater and surface water have a major importance for the water balance and periodically superimposed on the vertical runoff generation. Copyright © 2006 John Wiley & Sons, Ltd.     

Prospective modelling of 3D hyporheic exchange based on high‐resolution topography and stream elevation

River managers and scientists interested in hyporheic processes need adequate tools for characterizing hyporheic exchange flow (HEF) at local sites where only poor information on subsurface properties are available. This study evaluates a three‐dimensional modelling approach, on the basis of detailed surface parameterization and a simplified subsurface structure, for comparison of potential HEF characteristics at three experimental reaches at the channel‐unit scale. First, calibration is conducted to determine the best fit‐of‐heads given the model simplification, then the structure of residuals are used to evaluate the origin of the misfit, and finally, a sensitivity analysis is conducted to identify inter‐site differences in HEF. Results show that such an approach can highlight potential magnitude differences in HEF characteristics between reaches. The sensitivity analysis is successful in delineating the small area of exchange that remains under conditions of high groundwater discharge. In this case, however, the calibrated model performs poorly in representing the exchange pattern at the sediment–water interface, thus suggesting that the approach is less adequate for a deterministic simulation of observed heads. The summary statistics are in the range of similar published models, for which the reported indicator is the root mean square error on heads normalized by the head drop over the reach. We recommend, however, that modellers use a more comparable indicator, such as a measure of the residuals normalized by a measure of observed vertical head differences. Overall, when subsurface data are unavailable or sparse, a three‐dimensional groundwater model based on high‐resolution topographic data combined with a sensitivity analysis appears as a useful tool for a preliminary characterization of HEF. Copyright © 2013 John Wiley & Sons, Ltd.     

Trading more food: Implications for land use,greenhouse gas emissions,and the food system

The volume of agricultural trade increased by more than ten times throughout the past six decades and is likely to continue with high rates in the future. Thereby, it largely affects environment and climate. We analyse future trade scenarios covering the period of 2005–2045 by evaluating economic and environmental effects using the global land-use model MAgPIE (“Model of Agricultural Production and its Impact on the Environment”). This is the first trade study using spatially explicit mapping of land use patterns and greenhouse gas emissions. We focus on three scenarios: the reference scenario fixes current trade patterns, the policy scenario follows a historically derived liberalisation pathway, and the liberalisation scenario assumes a path, which ends with full trade liberalisation in 2045.Further trade liberalisation leads to lower global costs of food. Regions with comparative advantages like Latin America for cereals and oil crops and China for livestock products will export more. In contrast, regions like the Middle East, North Africa, and South Asia face the highest increases of imports. Deforestation, mainly in Latin America, leads to significant amounts of additional carbon emissions due to trade liberalisation. Non-CO₂ emissions will mostly shift to China due to comparative advantages in livestock production and rising livestock demand in the region. Overall, further trade liberalisation leads to higher economic benefits at the expense of environment and climate, if no other regulations are put in place.     

Biogeochemical responses to late-winter storms in the Sargasso Sea,I—Pulses of primary and new production

We have hypothesized that the weekly/biweekly passage of winter storms in the subtropical open ocean destabilizes the water column leading to pulsed NO₃^? inputs, resulting in new production that is not accounted for in most annual estimates. This paper presents data on nitrogen and carbon cycling in the Sargasso Sea at approximately daily resolution, during the period prior to seasonal stratification in 2004 and 2005; these data permit us to assess the importance of winter storms for introducing NO₃^? and the contribution of these inputs to annual new and export production. The two sampling years were in stark contrast to each other with 2004 characterized by periods of relative calm between winter storms, and 2005 characterized by nearly continuous storm activity. As a result, temporal variability in mixed layer depth (MLD) and euphotic zone [NO₃^?] were very different between years. MLDs in 2004 increased to >150 m in response to the passage of storms and then rapidly shoaled to <100 m leading to the pulsed injection of NO₃^? (～100 nmol l^?1) into the lower half of the euphotic zone, while in 2005 MLDs were consistently >300 m and euphotic zone [NO₃^?]>100 nmol l^?1. Despite the very different [NO₃^?], rates of daily NO₃^? uptake were similar from year to year because of significant nocturnal uptake in 2004. Similar rates of new production did not translate into similar rates of particulate nitrogen and carbon export however, as observed export from the upper 200 m was 2–5-fold greater in 2004 than in 2005. Furthermore, the decrease of particulate nitrogen and carbon flux with depth between 200 and 400 m in 2004 was substantially lower than in 2005; this is consistent with the observed biological response in which diatoms and coccolithophores exhibited rapid growth following pulsed NO₃^? inputs in 2004. A combination of data from the Bermuda Testbed Mooring, which provides a longer temporal record than the cruise, and the observations presented in this study show that in the winter of 2004, there were 8–10 storm events that likely resulted in pulsed NO₃^? inputs. Summed over all the events, new production prior to seasonal stratification was estimated to be ～0.12–0.18 mol N m^?2 or ～14–21% of current annual estimates.     

Biogeochemical responses to late-winter storms in the Sargasso Sea. IV. Rapid succession of major phytoplankton groups

In this paper, we present multi-parameter data on phytoplankton community composition, and its response to storm events in the Sargasso Sea in late February and early March of 2 years (2004 and 2005). Observed physical conditions spanned a continuum from pulsed destratification/stratification to continuous mixing, with a corresponding range of phytoplankton growth responses. The pulsed destratification/stratification condition resulted in a rapid (1–2 d) doubling of euphotic zone chlorophyll (Chl-a) along with a rapid succession, days timescale, from diatoms to haptophytes and then to cyanobacteria. Deep (>300 m) continuous mixing led to a slow (8–9 d) doubling of autotrophic biomass with no observed succession in the phytoplankton community. These different temporal responses appear to be due to differences between nutrient-limited and light-limited phytoplankton growth, although differences in grazing rates or selective grazing cannot be ruled out. Unexpectedly, we found that flow cytometrically enumerated picoeukaryotes were not accounted for in HPLC-pigment derived phytoplankton classifications and did not covary with any of the pigments quantified. Yet, the picoeukaryotes were positively related to increases in total Chl-a and increased carbon export, suggesting an important but as yet unknown role in the Sargasso Sea carbon cycle.