Geochemistry of a new enriched mantle type locality in the northern hemisphere: Implications for the origin of the EM-I source

Late Cretaceous (66.2 ± 0.5 Ma amphibole and 66.7 ± 0.2 Ma phlogopite ⁴⁰Ar/³⁹Ar ages) nephelinitic volcanic rocks from Godzilla Seamount in the eastern North Atlantic (34°N latitude) have trace element and Sr–Nd–Pb–Hf-isotope compositions similar to the Enriched Mantle I (EM-I) endmember, except for their low ²⁰⁷Pb/²⁰⁴Pb relative to ²⁰⁶Pb/²⁰⁴Pb ratios (²⁰⁶Pb/²⁰⁴Pb_in = 17.7, ²⁰⁷Pb/²⁰⁴Pb_in = 15.34) plotting below the Northern Hemisphere Reference Line on the uranogenic Pb isotope diagram. O isotope data on amphibole separates are mantle-like (δ¹⁸O = 5.6–5.8‰). Age and location of the isolated Godzilla Seamount, however, preclude it from being derived from the Madeira or Canary hotspots, making a lower-mantle origin unlikely. Therefore we propose derivation from a shallow (lithospheric/asthenospheric) melting anomaly. As observed in mid-ocean-ridge and ocean-island basalts, there is a systematic decrease of ²⁰⁷Pb/²⁰⁴Pb ratios (and Δ7/4) in the individual EM-I endmember type localities towards northern latitudes with Godzilla lying on the extension of this trend. This trend is mirrored in ultra-potassic volcanic rocks such as lamproites and kimberlites, which reflect the composition of enriched subcontinental lithospheric mantle. Therefore, a global pattern in ²⁰⁷Pb/²⁰⁴Pb ratios and Δ7/4 is suggested. The geochemical composition of EM-I endmember type localities, including Godzilla lavas, and the enriched (DUPAL) anomaly in the southern hemisphere could reflect derivation from ancient, metasomatized subcontinental lithospheric mantle. We propose a two-stage model to explain the trace element and isotopic composition of the EM-I mantle endmember localities worldwide: 1) during the early history of the Earth, subcontinental lithosphere was metasomatized by melts from subducted slabs along convergent margins generating high μ (²³⁸U/²⁰⁴Pb) sources, and 2) as the Earth cooled, hydrous fluids replaced hydrous melts as the main slab component metasomatizing the subcontinental lithospheric mantle (generating EM-I sources with lower μ). In accordance with this model, the global variations in ²⁰⁷Pb/²⁰⁴Pb ratios and Δ7/4 could reflect geographic differences in μ and/or the age at which the transition from stages 1 to 2 took place in the Archaean lithosphere. The model would require a re-definition of the EM-I endmember to low ²⁰⁶Pb/²⁰⁴Pb, high ²⁰⁸Pb/²⁰⁴Pb (positive Δ8/4) but variable ²⁰⁷Pb/²⁰⁴Pb (positive and negative Δ7/4).     

A 20 ka sediment record from the Hajar Mountain range in N-Oman,and its implication for detecting arid–humid periods on the southeastern Arabian Peninsula

Playa-like sediments from the Hajar Mountain range in northern Oman (22.83°N, 59.00°E; 1050 m asl) document variations of the paleoenvironmental and paleoclimate conditions over the last 20 ka. Based on high-resolution sediment sampling and their OSL dating, sedimentation rates were calculated and used as a proxy for paleorainfall. The results show that the Glacial to Lateglacial was characterized by arid conditions with a following transitional period of even less rainfall. At 10.5 ka, sedimentation rates increases abruptly, indicating the onset of the early Holocene humid period (EHHP). Rainfall reaches its maximum at 9–8 ka (EHHP-2) and a decreasing sedimentation rate after 8 ka characterizes the arid period of the middle to late Holocene. Variations of the hydrological regime are associated with the intensity of the boreal summer Indian monsoon and its related position of the ITCZ. For the onset of the EHHP, a northerly shift of the ITCZ is postulated, thus confirming earlier results from the southern Arabian Peninsula.     

Crustal scattering at the KTB from a combined microearthquake and receiver analysis

In December of 1994 a fluid injection experiment which triggered several hundreds of microearthquakes was conducted at the KTB main borehole (Oberpfalz, Germany). These events were recorded with a temporal seismic network at the surface. Out of the complete data set, a cluster of five events recorded at four mini-arrays consisting of eight or nine stations was used to investigate the crustal scattering properties in the vicinity of the KTB. For this purpose, the 'Double Beam Method' (DBM; Krüger et al . 1993 , 1995 , 1996) and the 'Double Beam Imaging Method' (Scherbaum, Krüger & Weber 1997) were extended to curved wave fronts to drop the restriction of plane-wave propagation. This technique is used for imaging the crustal scattering strength using earthquake clusters recorded at close-by mini-arrays. The results of the array analysis show that the composition of the P coda is mainly affected by the site location of the arrays. Near-surface and deeper crustal scattering contribute in a very complicated pattern. Furthermore, with the present data set it was possible to identify reflections from the top of the Erbendorf Body. This is a very pronounced arrival in most of the recorded traces. In one of the arrays its amplitudes are even greater than the direct P phases. Five to eight coherent phases could be identified by the mini-arrays. Using only these phases, synthetic P -coda traces were constructed, which only contain the coherent part of the observed wavefield. By subtracting the synthetic coherent wavefield from the original traces we achieve a variance reduction in the P coda of up to 37 per cent. This leads to the conclusion that a large amount of the P coda at the KTB can be modelled by a simple deterministic single-scattering model using a small number of individual scatterers.     

青藏高原东部兴措湖生物壳体元素及同位素记录的气候环境信息

通过对青藏高原东部若尔盖盆地兴措湖50年来Gyraulus sibirica壳体元素及同位素分析,并与器测气象资料的比较,建立了兴措湖记录与对应的降水和气温间的函数关系,探讨了湖泊记录所指示的气候环境意义,结果表明：青藏高原东部兴措湖地区腹足类生物在夏半年形成壳体,它所记录的是夏半年而不是全年的气候环境信息,Gyraulus Sibria壳体Mg/Ca比及δ^18O指标与夏半年气温有一定的相关性,其中壳体δ^18O指标对气温变化更敏感,δ^18O与夏半年气温滑动平均间的变率为1．64‰／℃,均值比为0．28‰/℃,Sr/Ca比,δ^13C指标与夏半年的降水量关系较密切,尤其是Sr/Ca比随降水量波动呈显著相关变化,Sr/Ca变化与降水间的平均变率（d(Sr/Ca)/dP)为－0．045/mm。     

Biodegradation of NOM in Rapid Sand Filters for Removing Iron and Manganese

In order to examine the Corg flow in rapid sand filter columns for the elimination of iron and manganese, reduced groundwater was treated in a pilot plant consisting of a trickling filter column (TF I) followed by a wet type filter column (WF II) and a separate wet type filter column (WF sep). Additionally the effect of filtration on BOM was studied by measuring AOC and BDOC. The biological processes in TF I and WF sep led to an elimination of iron, ammonia, and manganese. Moreover, the filtration decreased the NOM content. 21% and 23% of the TOC were eliminated in TF I and in WF sep, respectively. WF II caused no significant Corg reduction. The calculation of the Corg flow in the filter columns showed that bacteria took part in the TOC elimination. From the TOC removed, about 24% was eliminated by metabolic activities of the bacterial population whereas 86% was adsorbed onto iron sludge. Similar results were obtained for the TF I column and for the WF sep column as well. The calculated Corg flow was confirmed by the BDOC measurements. The filtration process led to a BDOC decrease. TF I and WF sep reduced appoximately 35% of the biodegradable organic carbon. In contrast there was no significant elimination by WF II. The AOC results suggest that an AOC production and an AOC elimination process exist in rapid sand filters for groundwater treatment. In the trickling filter column significant AOC production was found, whereas in the wet type filter columns AOC elimination was predominating.     

Area-Averaged Surface Fluxes Over the Litfass Region Based on Eddy-Covariance Measurements

Micrometeorological measurements (including eddy-covariance measurements of the surface fluxes of sensible and latent heat) were performed during the LITFASS-2003 experiment at 13 field sites over different types of land use (forest, lake, grassland, various agricultural crops) in a 20 × 20 km² area around the Meteorological Observatory Lindenberg (MOL) of the German Meteorological Service (Deutscher Wetterdienst, DWD). Significant differences in the energy fluxes could be found between the major land surface types (forest, farmland, water), but also between the different agricultural crops (cereals, rape, maize). Flux ratios between the different surfaces changed during the course of the experiment as a result of increased water temperature of the lake, changing soil moisture, and of the vegetation development at the farmland sites. The measurements over grass performed at the boundary-layer field site Falkenberg of the MOL were shown to be quite representative for the farmland part of the area. Measurements from the 13 sites were composed into a time series of the area-averaged surface flux by taking into account the data quality of the single flux values from the different sites and the relative occurrence of each surface type in the area. Such composite fluxes could be determined for about 80% of the whole measurement time during the LITFASS-2003 experiment. Comparison of these aggregated surface fluxes with area-averaged fluxes from long-range scintillometer measurements and from airborne measurements showed good agreement.     

Low-Level Atmospheric Jets And Inversions Over The Western Weddell Sea

For four months in the fall and earlywinter of 1992, as Ice Station Weddell (ISW) driftednorthward through the ice-covered western Weddell Sea,ice station personnel profiled the atmosphericboundary layer (ABL) with radiosondes. These showedthat the ABL was virtually always stably stratifiedduring this season: 96% of the soundings found anear-surface inversion layer. Forty-four percent ofthese inversions were surface-based. Eighty percentof the soundings that yielded unambiguous windprofiles showed an atmospheric jet with speeds as highas 14 m s^-1 in a core below an altitude of 425 m. This paper documents the features of these inversionsand low-level jets. Because the inversion statistics,in particular, are like those reported in and aroundthe Arctic Ocean, similar local processes seem tocontrol the ABL over sea ice regions in bothhemispheres. A simple two-layer model, in which anelevated layer becomes frictionally decoupled from thesurface, does well in explaining the ISW jetstatistics. This model also implies a new geostrophicdrag parameterization for sea-ice regions that dependson the magnitude of the geostrophic wind, the 10-mdrag coefficient C_DN10, and the ABL height, butnot explicitly on any stratification parameter.     

The Energy Balance Experiment EBEX-2000. Part I: overview and energy balance

An overview of the Energy Balance Experiment (EBEX-2000) is given. This experiment studied the ability of state-of-the-art measurements to close the surface energy balance over a surface (a vegetative canopy with large evapotranspiration) where closure has been difficult to obtain. A flood-irrigated cotton field over uniform terrain was used, though aerial imagery and direct flux measurements showed that the surface still was inhomogeneous. All major terms of the surface energy balance were measured at nine sites to characterize the spatial variability across the field. Included in these observations was an estimate of heat storage in the plant canopy. The resultant imbalance still was 10%, which exceeds the estimated measurement error. We speculate that horizontal advection in the layer between the canopy top and our flux measurement height may cause this imbalance, though our estimates of this term using our measurements resulted in values less than what would be required to balance the budget. The National Center for Atmospheric Research is supported by the National Science Foundation     

The Critical Richardson Number and Limits of Applicability of Local Similarity Theory in the Stable Boundary Layer

Measurements of atmospheric turbulence made over the Arctic pack ice during the Surface Heat Budget of the Arctic Ocean experiment (SHEBA) are used to determine the limits of applicability of Monin–Obukhov similarity theory (in the local scaling formulation) in the stable atmospheric boundary layer. Based on the spectral analysis of wind velocity and air temperature fluctuations, it is shown that, when both the gradient Richardson number, Ri, and the flux Richardson number, Rf, exceed a ‘critical value’ of about 0.20–0.25, the inertial subrange associated with the Richardson–Kolmogorov cascade dies out and vertical turbulent fluxes become small. Some small-scale turbulence survives even in this supercritical regime, but this is non-Kolmogorov turbulence, and it decays rapidly with further increasing stability. Similarity theory is based on the turbulent fluxes in the high-frequency part of the spectra that are associated with energy-containing/flux-carrying eddies. Spectral densities in this high-frequency band diminish as the Richardson–Kolmogorov energy cascade weakens; therefore, the applicability of local Monin–Obukhov similarity theory in stable conditions is limited by the inequalities Ri < Ri _cr and Rf < Rf _cr. However, it is found that Rf _cr  =  0.20–0.25 is a primary threshold for applicability. Applying this prerequisite shows that the data follow classical Monin–Obukhov local z-less predictions after the irrelevant cases (turbulence without the Richardson–Kolmogorov cascade) have been filtered out.     

Possible Effects of Altered Growth Behaviour of Norway Spruce (Picea abies) on Carbon Accounting

Implementing the Kyoto Protocol necessitates precise and practical inventory methods for estimating the carbon reservoir in forests. An analysis of the German state North Rhine-Westphalia forest inventory data showed enormous deviations from the yield tables of Wiedemann (1936, 1942). Specifically the ratio of height/diameter at breast height was up to 30% lower than in the yield tables, which indicated wider annual rings and a lower basic density. Such differences most likely pose consequences for the calculation of the amount of carbon in these forests. In this study the aboveground green weight, moisture and the carbon content of fifteen 46-year old Norway spruces (Picea abies) were measured, and two approaches for calculating the aboveground carbon content of trees were discussed: the common methodology of applying expansion and conversion factors as well as using optimized regression equations. The average expansion factor deviated approximately 1.2% from the yield tables of Grundner and Schwappach (1906). The wood density was 368 kg/m³ and within the European scope of 320–420 kg/m³ (Bosshard, 1984; Hakkila, 1989; Knigge and Schulz, 1966; Trendelenburg and Mayer-Wegelin, 1955). The woody carbon content was found to be 50.42%, which corresponded well with reference values of 50.3% (Bosshard, 1984) and 51.4% (Knigge and Schulz, 1966). However, the average percentage of crown material carbon content was 0.75% higher than in the tree boles. This study demonstrated that the most reliable methodology for calculating aboveground tree carbon was a power regression function, which calculated the growing stock volume, converting it directly into tree carbon content. The results deviated by less than 1.3% (R² = 0.99) from the measured tree carbon. Using volume expansion factors and factors of basic density and carbon percentage, as in Burschel et al. (1993), the calculated results diverged –3.7% from the measured outcome. The adapted form according to Fang et al. (2001) deviated –1.2% (R² = 0.63) and the form following Brown and Schroeder (1999) about –2.5% (R² = 0.61) from the measured carbon of the sample trees. However, coefficients of variation from 12% and 13% for the presented algorithm illustrated that in reality the calculated carbon of single trees could diverge considerably from the model results.