Intercalibration of Mg Isotope Delta Scales and Realisation of SI Traceability for Mg Isotope Amount Ratios and Isotope Delta Values     

Jochen Vogl  Martin Rosner  Simone A. Kasemann  Rebecca Kraft  Anette Meixner  Janine Noordmann  Savelas Rabb  Olaf Rienitz  Jan A. Schuessler  Michael Tatzel  Robert D. Vocke 《Geostandards and Geoanalytical Research》2020,44(3):439-457

The continuous improvement of analytical procedures using multi‐collector technologies in ICP‐mass spectrometry has led to an increased demand for isotope standards with improved homogeneity and reduced measurement uncertainty. For magnesium, this has led to a variety of available standards with different quality levels ranging from artefact standards to isotope reference materials certified for absolute isotope ratios. This required an intercalibration of all standards and reference materials, which we present in this interlaboratory comparison study. The materials Cambridge1, DSM3, ERM‐AE143, ERM‐AE144, ERM‐AE145, IRMM‐009 and NIST SRM 980 were cross‐calibrated with expanded measurement uncertainties (95% confidence level) of less than 0.030‰ for the δ^25/24Mg values and less than 0.037‰ for the δ^26/24Mg values. Thus, comparability of all magnesium isotope delta (δ) measurements based on these standards and reference materials is established. Further, ERM‐AE143 anchors all magnesium δ‐scales to absolute isotope ratios and therefore establishes SI traceability, here traceability to the SI base unit mole. This applies especially to the DSM3 scale, which is proposed to be maintained. With ERM‐AE144 and ERM‐AE145, which are product and educt of a sublimation–condensation process, for the first time a set of isotope reference materials is available with a published value for the apparent triple isotope fractionation exponent θ_app, the fractionation relationship ln α(^25/24Mg)/ln α(^26/24Mg).  相似文献   

Trace metal dynamics in the water column and pore waters in a temperate tidal system: response to the fate of algae-derived organic matter     

Nicole Kowalski  Olaf Dellwig  Melanie Beck  Maik Grunwald  Sibylle Fischer  Maike Piepho  Thomas Riedel  Holger Freund  Hans-Jürgen Brumsack  Michael E. Böttcher 《Ocean Dynamics》2009,59(2):333-350

Tidal and seasonal behaviour of the redox-sensitive trace metals Mn, Fe, Mo, U, and V have been investigated in the open-water column and shallow pore waters of the backbarrier tidal flats of the island of Spiekeroog (Southern North Sea) in 2002 and 2007. The purpose was to study the response of trace metal cycles on algae blooms, which are assumed to cause significant changes in the redox state of the entire ecosystem. Trace metal data were complemented by measurements of nutrients and enumeration of algae cells in 2007. Generally, Mn and V show a tidal cyclicity in the water column with maximum values during low tide which is most pronounced in summer due to elevated microbial activity in the sediments. Mo and U behave almost conservatively throughout the year with slightly increasing levels towards high tide. Exceptions are observed for both metals after summer algae blooms. Thus, the seasonal behaviour of the trace metals appear to be significantly influenced by productivity in the water column as the occurrence of algae blooms is associated with an intense release of organic matter (e.g. transparent exopolymer particles, TEP) thereby forming larger organic-rich aggregates. Along with elevated temperatures in summer, the deposition of such aggregates favours microbial activity within the surface sediments and release of DOC, nutrients and trace metals (Mn, Mo and V) during the degradation of the aggregates. Additionally, pronounced reducing conditions lead to the reduction of Mn(IV)-oxides and Fe(III)-(oxihydr)oxides, thereby releasing formerly scavenged compounds as V and phosphate. Therefore, pore-water profiles show significant enrichments in trace metals especially from July to September. Finally, the trace metals are released to the open water column via draining pore waters (esp. Mo, Mn, and V) and/or fixed in the sediment as sulphides (Fe, Mo) and bound to organic matter (U). Non-conservative behaviour of Mo in oxygenated seawater, first observed in the investigation area by Dellwig et al. (Geochim Cosmochim Acta 71:2745–2761, 2007a), was shown to be a recurrent phenomenon which is closely coupled to bacterial activity after the breakdown of algae blooms. In addition to the postulated fixation of Mo in oxygen-depleted micro-zones of the aggregates or by freshly formed organic matter, a direct removal of Mo from the water column by reduced sediment surfaces may also play an important role.  相似文献   

Distributions and characteristics of dissolved organic matter in temperate coastal waters (Southern North Sea)     

Andrea Lübben  Olaf Dellwig  Sandra Koch  Melanie Beck  Thomas H. Badewien  Sibylle Fischer  Rainer Reuter 《Ocean Dynamics》2009,59(2):263-275

The spatial and temporal distributions of chromophoric dissolved organic matter (CDOM) and dissolved organic carbon (DOC) was studied in the East-Frisian Wadden Sea (Southern North Sea) during several cruises between 2002 and 2005. The spatial distribution of CDOM in the German Bight shows a strong gradient towards the coast. Tidal and seasonal variations of dissolved organic matter (DOM) identify freshwater discharge via flood-gates at the coastline and pore water efflux from tidal flat sediments as the most important CDOM sources within the backbarrier area of the Island of Spiekeroog. However, the amount and pattern of CDOM and DOC is strongly affected by various parameters, e.g. changes in the amount of terrestrial run-off, precipitation, evaporation, biological activity and photooxidation. A decoupling of CDOM and DOC, especially during periods of pronounced biological activity (algae blooms and microbial activity), is observed in spring and especially in summer. Mixing of the endmembers freshwater, pore water, and open sea water results in the formation of a coastal transition zone. Whilst an almost conservative behaviour during mixing is observed in winter, summer data point towards non-conservative mixing.  相似文献   

Physical reworking by near-bottom flow alters the metazoan meiofauna of Fieberling Guyot (northeast Pacific)     

David Thistle  Lisa A. Levin  Andrew J Gooday  Olaf Pfannkuche  P John D. Lambshead 《Deep Sea Research Part I: Oceanographic Research Papers》1999,46(12):185

Although much of the deep sea is physically tranquil, some regions experience near-bottom flows that rework the surficial sediment. During periods of physical reworking, animals in the reworked layer risk being suspended, which can have both positive and negative effects. Reworking can also change the sediment in ecologically important ways, so the fauna of reworked sites should differ from that of quiescent locations. We combined data from two reworked, bathyal sites on the summit of Fieberling Guyot (32°27.631′N, 127°49.489′W; 32°27.581′N, 127°47.839′W) and compared the results with those of more tranquil sites. We tested for differences in the following parameters, which seemed likely to be sensitive to the direct or indirect effects of reworking: (1) the vertical distribution of the meiofauna in the sea bed, (2) the relative abundance of surface-living harpacticoids, (3) the proportion of the fauna consisting of interstitial harpacticoids, (4) the ratio of harpacticoids to nematodes. We found that the vertical distributions of harpacticoid copepods, ostracods, and kinorhynchs were deeper on Fieberling. In addition, the relative abundance of surface-living harpacticoids was less, the proportion of interstitial harpacticoids was greater, and the ratio of harpacticoids to nematodes was greater on Fieberling. These differences between Fieberling and the comparison sites suggest that physical reworking affects deep-sea meiofauna and indicate the nature of some of the effects.  相似文献   

The Baltica–lapetus passive margin dyke complex in the Sarektjåkkå Nappe,northern Swedish Caledonides     

Olaf M. Svenningsen 《Geological Journal》1994,29(4):323-354

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基于优化随机森林回归模型的土壤盐渍化反演   总被引：1，自引：0，他引：1  

杨练兵  陈春波  郑宏伟  罗格平  尚白军  Olaf Hellwich 《地球信息科学学报》2021,23(9):1662-1674

当前应用于土壤盐分含量（Soil Salinity Content, SSC）反演的随机森林回归（Random Forests Regression, RFR）较少关注对模型精度影响较大的反演参数子集和模型参数的同步优化。本研究选择渭-库绿洲和奇台绿洲为实验区,基于Landsat-5 TM、SRTM、MOD11A2.006遥感数据构建反演参数。首先,利用弹性网络（Elastic Net, EN）筛选出反演参数子集,然后利用遗传算法（Genetic Algorithm, GA）和贝叶斯优化算法（Bayesian Optimization Algorithm, BOA）分别优化随机森林回归（Random Forests Regression, RFR）参数,建立反演参数子集和模型参数分步优化的RFR模型（EN-GA-RFR、EN-BOA-RFR）。建立利用GA和BOA分别同步优化反演参数子集和模型参数的RFR模型（GA-RFR、BOA-RFR）。在每个实验区,对比EN-GA-RFR、EN-BOA-RFR、GA-RFR、BOA-RFR的预测精度。最后分析每个实验区各类盐渍土的空间分布,并对2个实验区的反演参数进行对比分析。结果表明：每个实验区模型预测精度由高到低的排序均为BOA-RFR>GA-RFR>EN-BOA-RFR=EN-GA-RFR,整体上BOA的优化性能均好于GA;渭-库绿洲和奇台绿洲面积占比最大的盐渍土类型分别为盐渍土和中度盐渍土;反演参数对SSC的表征能力存在空间分异性。  相似文献   

Available energy and energy balance closure at four coniferous forest sites across Europe   总被引：1，自引：0，他引：1  

Uta Moderow  Marc Aubinet  Christian Feigenwinter  Olaf Kolle  Anders Lindroth  Meelis Mölder  Leonardo Montagnani  Corinna Rebmann  Christian Bernhofer 《Theoretical and Applied Climatology》2009,98(3-4):397-412

The available energy (AE), driving the turbulent fluxes of sensible heat and latent heat at the earth surface, was estimated at four partly complex coniferous forest sites across Europe (Tharandt, Germany; Ritten/Renon, Italy; Wetzstein, Germany; Norunda, Sweden). Existing data of net radiation were used as well as storage change rates calculated from temperature and humidity measurements to finally calculate the AE of all forest sites with uncertainty bounds. Data of the advection experiments MORE II (Tharandt) and ADVEX (Renon, Wetzstein, Norunda) served as the main basis. On-site data for referencing and cross-checking of the available energy were limited. Applied cross checks for net radiation (modelling, referencing to nearby stations and ratio of net radiation to global radiation) did not reveal relevant uncertainties. Heat storage of sensible heat J _H, latent heat J _E, heat storage of biomass J _veg and heat storage due to photosynthesis J _C were of minor importance during day but of some importance during night, where J _veg turned out to be the most important one. Comparisons of calculated storage terms (J _E, J _H) at different towers of one site showed good agreement indicating that storage change calculated at a single point is representative for the whole canopy at sites with moderate heterogeneity. The uncertainty in AE was assessed on the basis of literature values and the results of the applied cross checks for net radiation. The absolute mean uncertainty of AE was estimated to be between 41 and 52 W m^?2 (10–11 W m^?2 for the sum of the storage terms J and soil heat flux G) during mid-day (approximately 12% of AE). At night, the absolute mean uncertainty of AE varied from 20 to about 30 W m^?2 (approximately 6 W m^?2 for J plus G) resulting in large relative uncertainties as AE itself is small. An inspection of the energy balance showed an improvement of closure when storage terms were included and that the imbalance cannot be attributed to the uncertainties in AE alone.  相似文献   

Extreme events,trends, and variability in Northern Hemisphere lake-ice phenology (1855–2005)     

Barbara J. Benson  John J. Magnuson  Olaf P. Jensen  Virginia M. Card  Glenn Hodgkins  Johanna Korhonen  David M. Livingstone  Kenton M. Stewart  Gesa A. Weyhenmeyer  Nick G. Granin 《Climatic change》2012,112(2):299-323

Often extreme events, more than changes in mean conditions, have the greatest impact on the environment and human well-being. Here we examine changes in the occurrence of extremes in the timing of the annual formation and disappearance of lake ice in the Northern Hemisphere. Both changes in the mean condition and in variability around the mean condition can alter the probability of extreme events. Using long-term ice phenology data covering two periods 1855–6 to 2004–5 and 1905–6 to 2004–5 for a total of 75 lakes, we examined patterns in long-term trends and variability in the context of understanding the occurrence of extreme events. We also examined patterns in trends for a 30-year subset (1975–6 to 2004–5) of the 100-year data set. Trends for ice variables in the recent 30-year period were steeper than those in the 100- and 150-year periods, and trends in the 150-year period were steeper than in the 100-year period. Ranges of rates of change (days per decade) among time periods based on linear regression were 0.3−1.6 later for freeze, 0.5−1.9 earlier for breakup, and 0.7−4.3 shorter for duration. Mostly, standard deviation did not change, or it decreased in the 150-year and 100-year periods. During the recent 50-year period, standard deviation calculated in 10-year windows increased for all ice measures. For the 150-year and 100-year periods changes in the mean ice dates rather than changes in variability most strongly influenced the significant increases in the frequency of extreme lake ice events associated with warmer conditions and decreases in the frequency of extreme events associated with cooler conditions.  相似文献   

Depleted subcontinental lithospheric mantle and its tholeiitic melt metasomatism beneath NE termination of the Eger Rift (Europe): the case study of the Steinberg (Upper Lusatia,SE Germany) xenoliths     

Anna Kukuła  Jacek Puziewicz  Magdalena Matusiak-Małek  Theodoros Ntaflos  Jörg Büchner  Olaf Tietz 《Mineralogy and Petrology》2015,109(6):761-787

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Water balance estimation under the challenge of data scarcity in a hyperarid to Mediterranean region          下载免费PDF全文

Agnes Sachse  Christian Fischer  Jonathan B. Laronne  Hanna Hennig  Amer Marei  Olaf Kolditz  Tino Rödiger 《水文研究》2017,31(13):2395-2411

Water budget analyses are important for the evaluation of the water resources in semiarid and arid regions. The lack of observed data is the major obstacle for hydrological modelling in arid regions. The aim of this study is the analysis and calculation of the natural water resources of the Western Dead Sea subsurface catchment, one which is highly sensitive to rainfall resulting in highly variable temporal and spatial groundwater recharge. We focus on the subsurface catchment and subsequently apply the findings to a large‐scale groundwater flow model to estimate the groundwater discharge to the Dead Sea. We apply a semidistributed hydrological model (J2000g), originally developed for the Mediterranean, to the hyperarid region of the Western Dead Sea catchment, where runoff data and meteorological records are sparsely available. The challenge is to simulate the water budget, where the localized nature of extreme rainstorms together with sparse runoff data results in few observed runoff and recharge events. To overcome the scarcity of climate input data, we enhance the database with mean monthly rainfall data. The rainfall data of 2 satellites are shown to be unsuitable to fill the missing rainfall data due to underrepresentation of the steep hydrological gradient and temporal resolution. Hydrological models need to be calibrated against measured values; hence, the absence of adequate data can be problematic. Therefore, our calibration approach is based on a nested strategy of diverse observations. We calculate a direct surface runoff of the Western Dead Sea surface area (1,801 km²) of 3.4 mm/a and an average recharge (36.7 mm/a) for the 3,816 km² subsurface drainage basin of the Cretaceous aquifer system.  相似文献