Two-component Mixing Model Research Articles

Diurnal variation of atmospheric CO2 concentration and δ13C in an urban atmosphere during winter—role of the Nocturnal Boundary Layer

The paper presents the importance of the Nocturnal Boundary Layer in driving the diurnal variability of the atmospheric CO2 mixing ratio and the carbon isotope ratio at ground level from an urban station in India. Our observations are the first of their kind from this region. The atmospheric CO2 mixing ratio and the carbon isotopic ratio were measured for both the morning (05:30–07:30 IST) and afternoon time (16:00–18:00 IST) air samples at 5 m above ground level in Bangalore city, Karnataka State (12° 58′ N, 77° 38′ E, masl = 920 m) for a 10 day period during the winter of 2008. We observed a change of ~7% the in CO2 mixing ratio between the morning and afternoon time air samples. A stable isotope analysis of CO2 from morning samples showed a depletion in the carbon isotope ratio by ~2‰ compared to the afternoon samples. Along with the ground-based measurement of air samples, data of radiosonde measurements were also obtained from the Indian Meteorological Department to identify the vertical atmospheric structure at different time in a day. We proposed the presence or absence of the NBL as a controlling factor for the observed variability in the mixing ratio as well as its isotopic composition. Here we used the Keeling model approach to find out the carbon isotope ratio for the local sources. The local sources have further been characterized as anthropogenic and biological respiration (in %) using a two-component mixing model. We also used a vertical mixing model based on the concept of the mixing of isotopically depleted (carbon isotope) “polluted air” (PA) with isotopically enriched “free atmospheric air” (FA) above. Using this modeling approach, the contribution of FA at ground level is being estimated for both the morning and afternoon time air samples.

Bias and uncertainty of δ13CO2 isotopic mixing models

Patterns in the isotopic signal (stable C isotope composition; δ13C) of respiration (δ13CR) have led to important gains in understanding the C metabolism of many systems. Contained within δ13CR is a record of the C source mineralized, the metabolic pathway of C and the environmental conditions during which respiration occurred. Because gas samples used for analysis of δ13CR contain a mixture of CO2 from respiration and from the atmosphere, two-component mixing models are used to identify δ13CR. Measurement of ecosystem δ13CR, using canopy airspace gas samples, was one of the first applications of mixing models in ecosystem ecology, and thus recommendations and guidelines are based primarily on findings from these studies. However, as mixing models are applied to other experimental conditions these approaches may not be appropriate. For example, the range in [CO2] obtained in gas samples from canopy air is generally less than 100 μmol mol−1, whereas in studies of respiration from soil, foliage or tree stems, the range can span as much as 10,000 μmol mol−1 and greater. Does this larger range in [CO2] influence the precision and accuracy of δ13CR estimates derived from mixing models? Does the outcome from using different regression approaches and mixing models vary depending on the range of [CO2]? Our research addressed these questions using a simulation approach. We found that it is important to distinguish between large (>1,000 μmol mol−1) and small (<100 μmol mol−1) ranges of CO2 when applying a mixing model (Keeling plot or Miller–Tans) and regression approach (ordinary least squares or geometric mean regression) combination to isotopic data. The combination of geometric mean regression and the Miller–Tans mixing model provided the most accurate and precise estimate of δ13CR when the range of CO2 is ≥1,000 μmol mol−1.

Antarctic lunar meteorites Yamato-793169, Asuka-881757, MIL 05035, and MET 01210 (YAMM): Launch pairing and possible cryptomare origin

The Antarctic lunar meteorite Meteorite Hills (MET) 01210 is a polymict regolith breccia, dominantly composed of mare basalt components. One relatively large (2.7 × 4.7 mm) basalt clast in MET 01210 (MET basalt) shows remarkable mineralogical similarities to the lunar-meteorite crystalline mare basalts Yamato (Y)-793169, Asuka (A)-881757, and Miller Range (MIL) 05035. All four basalts have similar rock texture, mineral assemblage, mineral composition, pyroxene crystallization trend, and pyroxene exsolution lamellae. The estimated TiO 2 contents (∼2.0 wt%) of the MET basalt and MIL 05035 are close to the bulk-rock TiO 2 contents of Y-793169 and A-881757. These similarities suggest that Y-793169, A-881757, MIL 05035, and the MET basalt came from the same basalt flow, which we designate the YAMM basalt. The source-basalt pairing of the YAMM is also supported by their similar REE abundances, crystallization ages (approx. 3.8–3.9 Ga), and isotopic compositions (low U/Pb, low Rb/Sr, and high Sm/Nd). The pyroxene exsolution lamellae, which are unusually coarse (up to a few microns) by mare standards, imply a relatively slow cooling in an unusually thick lava and/or subsequent annealing within a cryptomare. Reported noble gas and CRE data with close launch ages (∼1 Ma) and ejection depths (deeper than several meters) among the four meteorites further indicate their simultaneous ejection from the moon. Despite the marginally close terrestrial ages, pairing in the conventional Earth-entry sense seems unlikely because of the remote recovery sites among the YAMM meteorites. The high abundance (68%) of mare components in MET 01210 estimated from a two-component mixing model calculation could have resulted from either lateral mixing at a mare-highland boundary or vertical mixing in a cryptomare. The proportion of mare materials in MET 01210 is greater than in Apollo core samples at the mare-highland boundary. The burial depth (>several meters deep) inferred from the lack of surface irradiation of MET 01210 exceeds the typical mare regolith thickness (a few meters). Thus, the source of the YAMM meteorites is likely a terrain of locally high mare-highland mixing within a cryptomare. We searched for a possible source crater of the YAMM meteorites within the well-defined cryptomare, based on the multiple constraints obtained from this study and published data. An unnamed 1.4 km-diameter crater (53°W, 44.5°S) on the floor of the Schickard crater is the most suitable source for the YAMM meteorites. The 238U/ 204Pb ( μ) value of the YAMM basalts is extremely low, relative to those of the Apollo mare basalts, but comparable to those of the Luna 24 very low-Ti basalts. The low- μ source indicates a derivation from a less differentiated mantle with a lack of KREEP components. Although the chemical sources of materials and heat source of melting might be independent, the heat source that generated the source magma of the YAMM and Luna 24 basalts may not be related to KREEP, unlike the case of the Apollo basalts. The distinct chemical and isotopic compositions of mantle sources between the Apollo basalts and the YAMM/Lunar 24 basalts imply differences in mantle composition and thermal evolution between the Procellarum KREEP Terrane (PKT) and non-PKT regions of the nearside.

Autochthonous origin of semi-labile dissolved organic carbon in a large monomictic lake (Lake Biwa): carbon stable isotopic evidence

Semi-labile dissolved organic carbon (DOC) plays an important role in the transport and hypolimnetic remineralization of carbon in large freshwater lakes. However, sources of semi-labile DOC in lakes remain unclear. This study used a carbon stable isotope approach to examine relative contributions of autochthonous and allochthonous sources to semi-labile DOC. Vertical and seasonal variations in the concentration and carbon stable isotope ratio (δ13C) of DOC were determined in large (surface area 674 km2; maximum depth 104 m), monomictic Lake Biwa. A sharp vertical gradient of δ13C of DOC (δ13C-DOC) during the stratification period [mean ± standard error (SE) −25.5 ± 0.1 and −26.0 ± 0.0‰ in the epi- and hypolimnion, respectively] indicated the accumulation of 13C-rich DOC in the epilimnion. Vertical mixing explained the intermediate values of δ13C-DOC (−25.7 ± 0.0‰) measured throughout the water column during the overturn period. Both DOC concentration and δ13C-DOC decreased in the hypolimnion during stratification, indicating selective remineralization of 13C-rich DOC. Using a two-component mixing model, we estimated the δ13C value of semi-labile DOC to be −22.2 ± 0.3‰, which was close to the δ13C of particulate organic carbon collected in the epilimnion during productive seasons (−22.7 ± 0.7‰) but much higher than the δ13C-DOC in river waters (−26.5 ± 0.1‰). Semi-labile DOC appeared to be mainly autochthonous in origin, produced by planktonic communities during productive seasons. The spatiotemporal uncoupling between production and remineralization of semi-labile DOC implies that hypolimnetic oxygen consumption may be affected by pelagic primary production during productive seasons of the preceding year.

Origin and fate of particulate organic matter in the southern Beaufort Sea – Amundsen Gulf region, Canadian Arctic

To establish the relative importance of terrigenous and marine organic matter in the southern Beaufort Sea, we measured the concentrations and the stable isotopic compositions of organic carbon and total nitrogen in sediments and in settling particles intercepted by sediment traps. The organic carbon content of surface sediment in the Chukchi and southern Beaufort Seas ranged from 0.6 to 1.6% dry wt., without a clear geographical pattern. The C ORG:N TOT ratio ranged from 7.0 to 10.4 and did not vary significantly downcore at any one station. Values of δ 13C ORG and δ 15N TOT in the sediment samples were strongly correlated, with the highest values, indicative of a more marine contribution, in the Amundsen Gulf. In contrast, the organic matter content, elemental (C ORG:N TOT ratio) and isotopic ( δ 13C ORG and δ 15N TOT) composition of the settling particles was different from and much more variable than in the bottom sediments. The isotopic signature of organic matter in the Beaufort Sea is well constrained by three distinct end-members: a labile marine component produced in situ by planktonic organisms, a refractory marine component, the end product of respiration and diagenesis, and a refractory terrigenous component. A three-component mixing model explains the scatter observed in the stable isotope signatures of the sediment trap samples and accommodates an apparent two-component mixing model of the organic matter in sediments. The suspended matter in the water column contains organic matter varying from essentially labile and marine to mostly refractory and terrigenous. As it settles through the water column, the labile marine organic matter is degraded, and its original stable isotope signature changes towards the signature of the marine refractory component. This process continues in the bottom sediment with the result that the sedimentary organic matter becomes dominated by the refractory terrigenous and marine components.

Dynamics of stream nitrate sources and flow pathways during stormflows on urban, forest and agricultural watersheds in central Pennsylvania, USA

AbstractUnderstanding the influence of storm events on nitrate (NO3−) dynamics is important for efficiently managing NO3− pollution. In this study, five sites representing a downstream progression of forested uplands underlain by resistant sandstone to karst lowlands with agricultural, urban and mixed land‐use were established in Spring Creek, a 201 km2 mixed land‐use watershed in central Pennsylvania, USA. At each site, stream water was monitored during six storm events in 2005 to assess changes in stable isotopes of NO3− (δ15N‐NO3− and δ18O‐NO3−) and water (δ18O‐H2O) from baseflow to peakflow. Peakflow fractions of event NO3− and event water were then computed using two‐component mixing models to elucidate NO3− flow pathway differences among the five sites. For the forested upland site, storm size appeared to affect NO3− sources and flow pathways. During small storms (&lt;35 mm rainfall), greater event NO3− fractions than event water fractions indicated the prevalence of atmospheric NO3− source contributions at peakflow. During larger storms (&gt;35 mm rainfall), event NO3− fractions were less than event water fractions at peakflow suggesting that NO3− was flushed from stored sources via shallow subsurface flow pathways. For the urbanized site, wash‐off of atmospheric NO3− was an important NO3− source at peakflow, especially during short‐duration storms where event water contributions indicated the prevalence of overland flow. In the karst lowlands, very low fractions of event water and even lower fractions of event NO3− at peakflow suggested the dominance of ground water flow pathways during storms. These ground water flow pathways likely flushed stored NO3− sources into the stream, while deep soils in the karst lowlands also may have promoted NO3− assimilation. The results of this study illustrated how NO3− isotopes and δ18O‐H2O could be combined to show key differences in water and NO3− delivery between forested uplands, karst valleys and fully urbanized watersheds. Copyright © 2009 John Wiley &amp; Sons, Ltd.

Temporal trends of pollution Pb and other metals in east-central Baffin Island inferred from lake sediment geochemistry

Concentrations and stable isotope ratios of lead (Pb) from lake sediments were used to quantify temporal patterns of anthropogenic Pb pollution in the Clyde River region of Baffin Island, Arctic Canada. Surface sediments from eight lakes on eastern Baffin Island and one from northern-most Greenland, spanning a gradient of 20° latitude, showed great variability with respect to Pb concentration and stable isotopic Pb ratios, with little apparent latitudinal trend. To constrain the temporal evolution of regional Pb pollution, a well-dated core from one of the sites, Lake CF8 on east-central Baffin Island, was analyzed geochemically at high stratigraphic resolution. A pronounced decrease in the 206Pb/ 207Pb ratio occurs in sediments deposited between 1923 and the mid-1970s, likely reflecting alkyl-Pb additives derived from the combustion of fossil fuels at a global scale. A two-component mixing model indicates that 17–26% of the Pb in the labile fraction of sediments deposited in Lake CF8 between 2001 and 2005 is from anthropogenic input. A Pb–Pb co-isotopic plot ( 206Pb/ 207Pb vs. 208Pb/ 206Pb ratios) of the Lake CF8 time series data indicates multiple possible sources of industrial Pb pollution. Despite widespread reductions in industrial Pb emissions since the 1970s, there is no evidence for attendant reductions of pollution Pb at Lake CF8. Enhanced scavenging from increased primary production as well as changing precipitation rates as climate warms may represent important factors that modulate Pb deposition to Lake CF8, and Arctic lakes elsewhere.

Distribution of Crenarchaeota tetraether membrane lipids in surface sediments from the Red Sea

The Red Sea represents an extreme marine environment, with high salinity, high temperature and low level of nutrients, complicating the application of standard geochemical palaeotemperature proxies. In order to investigate the applicability of the TEX86 (TetraEther indeX of GDGTs with 86 carbons) proxy for sea surface temperature (SST) in the Red Sea, the distribution of glycerol dialkyl glycerol tetraether membrane lipids (GDGTs) in sediments from the Red Sea and the Gulf of Aden were examined. Against expectations, TEX86 values for the Red Sea do not show a simple linear relationship with SST and deviate from the global core top calibration. In the northern Red Sea, at temperatures between 25 and 28°C, the values increase linearly with SST, whereas in the southern Red Sea, at temperatures above 28°C, TEX86 decreases with increasing temperature. Factors like seasonality and depth of production, salinity and nutrient availability, as well as diagenetic overprint or influence of allochtonous terrestrial lipids, cannot explain this pattern. However, the observed TEX86 relationship with SST could be explained by the presence of a hypothetical endemic Crenarchaeota population in the Red Sea with a specific TEX86 vs. SST relationship. In the Southern Red Sea, a two-component mixing model implies an exponential decrease in the endemic population towards the Gulf of Aden. Thus, the application of the TEX86 as a palaeotemperature proxy in the Red Sea is likely only possible for the northern Red Sea area with the specific SST vs. TEX86 relationship determined in this study and potentially for the whole Red Sea basin during glacials, when water exchange with the Indian Ocean was more restricted than today and the endemic archaeal lipid distribution was not affected by transport from the Indian Ocean. Our results suggest that distinct populations of Crenarchaeota in extreme environments such as evaporitic basins may have different membrane composition, necessitating application of another calibration than the global core top calibration for TEX86 palaeothermometry.

Phosphorus losses from an artificially drained rural lowland catchment in North-Eastern Germany

In a small, extensively artificially drained lowland catchment (15.5 km 2) in Mecklenburg-Vorpommern (North-Eastern Germany), the dynamics and the extent of total phosphorus (TP) and total reactive phosphorus (TRP) losses as well as the discharge were monitored at different scales for three winter seasons of 6 months each. Ranging from 0.036 to 0.044 mg TP l −1 and from 0.030 to 0.037 mg TRP l −1, average phosphorus concentrations in the discharge of a collector drain, a ditch draining arable land and a small brook were low. Elevated concentrations occurred during intensive snowmelt events. Probably due to the re-mobilisation of phosphorus under anaerobic conditions, concentrations (0.137 mg TP l −1 and 0.076 mg TRP l −1) in a ditch draining grassland on degraded peat were significantly higher than at the other sites characterised by mineral soils. Generally, phosphorus concentrations increased with discharge at all sites except for the grassland, although not during each single discharge event. Surprisingly, a dependency on the fertilisation practices could not be found. The phosphorus losses per winter season were low, with a maximum of 270 g TP ha −1 and 211 g TRP ha −1. Using a two-component mixing model based on baseflow separation and parameter optimisation, it was estimated that around 53, 60 and 56% of the TP losses from the collector drain, from the ditch and from the brook as well as 53, 68 and 45% of the TRP loads were exported via a fast flow component. This component accounted for 18–23% of the total discharge. At all measurement stations, there were large differences between the partitioning patterns of the single discharge events. Our study has not only shown the event-based behaviour of the P losses and the possible occurrence of high P concentrations due to preferential flow, but also that the highest potential of eutrophication in this lowland landscape originates from drained, degraded, and intensively used peatlands.

Use of oxygen-18 isotope to quantify flows in the upriver and middle reaches of the Heihe River, Northwestern China

In recharge areas, the Heihe River flow was separated into components of ice-snowmelt and precipitation according to 14 gauging stations and to monthly hydrograph using oxygen-18. As shown by the result of the two-component mixing model, on average, 19.8% of the runoff comes from ice-snowmelt. At three stations which are closer to glaciers and with headstream of ice-snow melted water, the ice-snowmelt runoff is larger than 28% of stream water. In addition, because most of the ice-snowmelt infiltrates the groundwater, which later discharges into the river at mountain outlets, the ice-snowmelt percentage in runoff is lower than average at these stations with the elevation higher than 3,600 m. According to monthly hydrograph, the lowest percentage of ice-snowmelt in runoff is in July (6.46%), whereas during November it is the largest (26.1%). In the middle basin, the fraction of groundwater in runoff had a marked increase from 23.57% near Zhangye City to 60.28% near Gaotai City, and then a dramatic drop to 13.61% near Zhengyixia Station because of agricultural flood irrigation in Zhangye Basin.

Some limitations in using 222Rn to assess river–groundwater interactions: the case of Castel di Sangro alluvial plain (central Italy)

222Rn was used to assess river–groundwater interactions within Castel di Sangro alluvial aquifer (Italy). The effectiveness of results obtained through this indicator was verified by also analyzing δ18O, major ions and temperature in both surface and groundwater, and carrying out piezometric head monitoring and discharge measurements. Hydrogeological investigations suggested that the river infiltrates into the aquifer in the south-eastern aquifer portion, while groundwater discharges into the river in the north-eastern portion. The latter phenomenon is supported by 222Rn data. Nevertheless, flow-through conditions cause the modelled discharge along this river reach, estimated by 222Rn data in a degassing-corrected two-component mixing model, to be greater than the measured discharge. Concerning river infiltration into the aquifer, δ18O, major ions and temperature data show that the river contribution is negligible in terms of aquifer recharge. Thus, the observed increase in 222Rn concentration in that portion of the aquifer is due to the enrichment process caused by infiltration of rainwater (222Rn free) which flows from the local divide area. Hence, in the study site, the use of only 222Rn to predict river–groundwater interactions causes some estimation inaccuracies and it must be coupled with other hydrochemical and hydrogeological parameters to gain a thorough understanding of such interactions.

Use of Chemical Fingerprinting to Establish the Presence of Spilled Crude Oil in a Residential Area Following Hurricane Katrina, St. Bernard Parish, Louisiana

Hurricane Katrina's storm surge displaced and damaged a 250,000 barrel storage tank causing a Nigerian crude oil blend (API 36.4 degrees) to be released and dispersed into the adjacent evacuated residential area by the retreating floodwaters. The subsequent environmental assessment involved sampling and chemical fingerprinting of nearly 15,000 wipe and soil samples collected both inside and outside of buildings to determine which properties were impacted by the spilled crude oil. Tier 1 qualitative analysis of gas chromatograms and Tier 2 quantitative (revised Nordtest-type) and qualitative (ASTM D5739-type) analysis of petroleum biomarkers revealed the extent of crude oil contamination-as well as the widespread occurrence of hydrocarbons derived from (i) lubricating, hydraulic, and transmission oils, most likely from vehicles in the flooded area, and (ii) allochthonous natural organic matter (NOM) from the surrounding bayous. Conventional oil spill fingerprinting protocols and two-component mixing models (crude oil/lube oil and crude oil/NOM) were used to confirm the presence of the spilled crude oil-even when mixed at low concentrations with other hydrocarbon sources-as a means to develop and govern a settlement and remedial program with the affected property owners.

Two-component white color synthesis using diffractive structures

The work presented deals with the possibilities of synthesizing white color, which is of great interest for diffractive image devices. The method of additive mixing is utilized for synthesizing arbitrary nonspectral colors using diffracted light. The suggested solution is based on employing only two complementary colors as primaries for additive mixing, which is simpler and offers better energy efficiency than color-mixing models using three or more primaries. For comparison, two different two-component mixing models are considered together with a three-component RGB model. First, the theory of additive color mixing is modified for the case of diffracted light, and equations for relative areas of primary gratings are derived. Using colorimetry, a method of measurement and determination of diffracted light color is proposed and practically tested. Finally, a set of available primary gratings was used for experimental preparation of white color, and results of the two approaches to color mixing models are compared.

Analysing nitrate losses from an artificially drained lowland catchment (North-Eastern Germany) with a mixing model

Tile drainage shortens the residence time of water in the soil and may therefore aggravate the diffuse pollution of adjacent surface water bodies. To assess the environmental impacts of tile drainage on surface water bodies, it is important to assess how the drainage discharge and its solute signal translate from the frequently studied plot scale to the catchment scale. We used results from the automated hydrograph separation method ‘recursive digital filter’ in combination with a two-component mixing model to quantify the role of the different flow components and flow paths for the nitrate-nitrogen losses at three different scales – collector drain outlet (4.2 ha), ditch (179 ha) and brook catchment (15.5 km 2) – in a pleistocene lowland area in North-Eastern Germany. Measured and modelled NO 3-N concentrations of three 6-months winter seasons agreed reasonably well. At the tile drainage plot, the fast flow component was responsible for 63–91% of the total simulated nitrate-nitrogen losses. The stated ranges were derived from all accepted model runs. This flow component was interpreted as a fast component bearing nitrate from the nutrient-enriched topsoil. Tile drainage itself delivered 89–95% of the total nitrate losses in the ditch catchment. In the brook catchment, at most 25% of the area was responsible for 54–85% of the NO 3-N losses. Although the mixing model is limited by the assumption of constant component concentrations and conservative behaviour of the solutes, it has shown to be a useful tool for hydrochemical studies. Overall, the results emphasise the importance of tile drainage for the catchments’ hydrochemistry and its environmental impact on the larger scale. Consequently, it will be difficult to significantly reduce diffuse pollution in an artificially drained lowland landscape on the catchment scale without addressing the issue of tile drainage. As a next step for model validation, other solutes such as sulphate and chloride could be added to reduce the uncertainty, and grassland should be explicitly included into the mixing model.

Spatial and temporal variability of downward particle fluxes on a continental slope: Lessons from an 8-yr experiment in the Gulf of Lions (NW Mediterranean)

A long-term experiment of downward particle fluxes and currents has been initiated in 1993 on the continental slope of the Gulf of Lions (NW Mediterranean) and pursued within the frame of several French and European projects (PNEC, Euromarge-NB, MTP II-MATER, EUROSTRATAFORM). Sediment traps and current meters were deployed at several locations on this slope deeply incised by numerous canyons, with an extensive spatial coverage for the first 2 years (canyons at the entrance, middle and exit of the gulf with respect to the general along-slope circulation, head and mid-canyon depths, adjacent open slope). From late 1995 onwards, this design was reduced to the two mid-canyon moorings at the entrance and exit of the gulf. Monthly fluxes and hourly temperatures and currents were recorded at 500 m (30 m above bottom, mab) in the canyon heads, at 500 and 1000 m (respectively 530 and 30 mab) nominal depths at the mid-canyon sites, and at 750 m (30 mab) open slope. This study aims at describing the spatial, seasonal and interannual variability of flux intensity and composition of settling particles, and at analyzing the role of diverse forcings in the control of particle exchange across the margin. Results from the first 8 years (1993–2001) show that total mass fluxes – in the 10 1–10 4 mg m − 2 d − 1 range – increase along slope, particularly for the near-bottom traps, between the NE (Planier Canyon) and the SW (Lacaze-Duthiers Canyon) limits of the Gulf of Lions, indicating an increased shelf export of particulate matter in the western part of the system. Bulk chemical composition (organic matter, carbonate, opal and lithogenic fraction) remained rather stable during the course of the experiment, tending towards values typical of superficial shelf sediments at higher mass fluxes. First-order calculations using a simple two-component mixing model suggest a decreasing contribution of primary particles settling out of the overlying waters to the total flux from the entrance towards the exit of the system. Particulate material transferred to the deeper slope in the southwestern part of the Gulf of Lions appears therefore to predominantly originate in resuspended shelf and/or upper slope sediment. Downward particle fluxes and potential forcing parameters exhibit a high seasonal variability, with higher values from late autumn to early spring. Furthermore, unprecedented winter flux peaks observed in 1999 dominated the interannual differences, which otherwise were quite limited. Correlations between sources of particulate material on the shelf (i.e., river and atmospheric inputs, phytoplankton biomass and sediment resuspension), cross-slope exchange mechanisms (derived from in situ temperature and current records) and flux data indicate a predominant effect of dense cold water cascading on the exchange of particulate matter between the shelf and the slope.

Stream–air temperature relations to classify stream–ground water interactions in a karst setting, central Pennsylvania, USA

Stream–ground water interactions in karst vary from complete losses through swallow holes, to reemergences from springs. Our study objective was to compare stream–air temperature and energy exchange relationships across various stream–ground water relationships in a carbonate watershed. It was hypothesized that ground water-fed stream segments could be distinguished from perched/losing segments using stream–air temperature relationships. Two types of computations were conducted: (1) comparisons of stream–air temperature relationships for the period of October 1999–September 2002 at 12 sites in the Spring Creek drainage and (2) detailed energy budget computations for the same period for ground water-dominated Thompson Run and Lower Buffalo Run, a stream with negligible ground water inputs. Weekly average air temperatures and stream temperatures were highly correlated, but slopes and intercepts of the relationship varied for the 12 sites. Slopes ranged from 0.19 to 0.67 and intercepts ranged from 3.23 to 9.07 °C. A two-component mixing model with end members of ground water and actual stream temperatures indicated that the slope and intercept of the stream–air temperature relationship was controlled by ground water inputs. Streams with large ground water inputs had greater intercepts and lesser slopes than streams that were seasonally losing, perched, and/or distant from ground water inputs. Energy fluxes across the air–water interface were greatest for the ground water-fed stream due to increased longwave, latent, and sensible heat losses from the stream in winter when large temperature and vapor pressure differences existed between the stream and air. Advection of ground water was an important source and sink for heat in the ground water-fed stream, depending on season. In contrast, along the seasonally losing stream reach, advection was of minimal importance and stream temperatures were dominated by energy exchange across the air- water interface. Overall, results showed that stream temperatures and energy exchange in this carbonate watershed were strongly related to stream–ground water interactions.

Geochemistry and time-series analyses of orbitally forced Upper Cretaceous marl–limestone rhythmites (Lehrte West Syncline, northern Germany)

A cyclic marl–limestone succession of Middle–Late Campanian age has been investigated with respect to a Milankovitch-controlled origin of geochemical data. In general, the major element geochemistry of the marl–limestone rhythmites can be explained by a simple two-component mixing model with the end-members calcium carbonate and ‘average shale’-like material. Carbonate content varies from 55 to 90%. Non-carbonate components are clay minerals (illite, smectite) and biogenic silica from sponge spicules, as well as authigenically formed zeolites (strontian heulandite) and quartz. The redox potential suggests oxidizing conditions throughout the section. Trace element and stable isotopic data as well as SEM investigations show that the carbonate mud is mostly composed of low-magnesium calcitic tests of planktic coccolithophorids and calcareous dinoflagellate cysts (calcispheres). Diagenetic overprint results in a decrease of 2% δ18O and an increase in Mn of up to 250 ppm. However, the sediment seems to preserve most of its high Sr content compared to the primary low-magnesium calcite of co-occurring belemnite rostra. The periodicity of geochemical cycles is dominated by 413 ka and weak signals between 51 and 22.5 ka, attributable to orbital forcing. Accumulation rates within these cycles vary between 40 and 50 m/Ma. The resulting cyclic sedimentary sequence is the product of (a) changes in primary production of low-magnesium calcitic biogenic material in surface waters within the long eccentricity and the precession, demonstrated by the CaCO3 content and the Mg/Al, Mn/Al and Sr/Al ratios, and (b) fluctuations in climate and continental weathering, which changed the quality of supplied clay minerals (the illite/smectite ratio), demonstrated by the K/Al ratio. High carbonate productivity correlates with smectite-favouring weathering (semi-arid conditions, conspicuously dry and moist seasonal changes in warmer climates). Ti as the proxy indicator for the detrital terrigenous influx, as well as Rb, Si, Zr and Na, shows only low frequency signals, indicating nearly constant rates of supply throughout the more or less pure pelagic carbonate deposition of the long-lasting third-order Middle–Upper Campanian sedimentary cycle.

Petrological and geochemical evidences for magma mixing in the Palgongsan Pluton

Cretaceous Palgongsan pluton in the Gyeongsang basin is composed of coarse-grained porphyritic granite, medium-grained equigranular granite and aplite. The granites are designated to cale-alkaline I-type granites. Mafic enclaves are easily found in the pluton, and they are textually classified into fine-grained microgranular mafic enclaves and medium-grained mafic enclaves. The mafic enclaves in the granites are igneous in origin and comprise plagioclase, amphibole, biotite, and small amount of apatite, opaque, pyroxene and quartz. The mafic enclaves characteristically show petrographical features such as fine-grained texture, mafic clots, acicular amphibole, acicular apatite, plagioclase xenocryst, rapakivi texture and ocellar quartz. This observation demonstrates that the mafic enclaves are derived from mafic magma injection into crystallizing granitic magma chamber. There are good linear correlations in major oxide contents vs. SiO2 content in the Palgongsan pluton. Particularly the compositional variation between the granites and the mafic enclaves is possibly ascribed to two-component mixing model. Highly linear compositional variation trends between the Palgongsan porphyritic granite and the fine-grained mafic microgranular enclaves can be best explained by the compositional mixing of granitic magma with mafic magma which injected into the crystallizing granitic magma chamber. However the compositions of the equigranular granite and the aplite are characteristically of highly fractionated rock, and they are caused by later stage fractionation of granitic magma independent on the two-component mixing

Tritium hydrology of the Mississippi River basin

AbstractIn the early 1960s, the US Geological Survey began routinely analysing river water samples for tritium concentrations at locations within the Mississippi River basin. The sites included the main stem of the Mississippi River (at Luling Ferry, Louisiana), and three of its major tributaries, the Ohio River (at Markland Dam, Kentucky), the upper Missouri River (at Nebraska City, Nebraska) and the Arkansas River (near Van Buren, Arkansas). The measurements cover the period during the peak of the bomb‐produced tritium transient when tritium concentrations in precipitation rose above natural levels by two to three orders of magnitude. Using measurements of tritium concentrations in precipitation, a tritium input function was established for the river basins above the Ohio River, Missouri River and Arkansas River sampling locations. Owing to the extent of the basin above the Luling Ferry site, no input function was developed for that location. The input functions for the Ohio and Missouri Rivers were then used in a two‐component mixing model to estimate residence times of water within these two basins. (The Arkansas River was not modelled because of extremely large yearly variations in flow during the peak of the tritium transient.) The two components used were: (i) recent precipitation (prompt outflow) and (ii) waters derived from the long‐term groundwater reservoir of the basin. The tritium concentration of the second component is a function of the atmospheric input and the residence times of the groundwaters within the basin. Using yearly time periods, the parameters of the model were varied until a best fit was obtained between modelled and measured tritium data. The results from the model indicate that about 40% of the flow in the Ohio River was from prompt outflow, as compared with 10% for the Missouri River. Mean residence times of 10 years were calculated for the groundwater component of the Ohio River versus 4 years for the Missouri River. The mass flux of tritium through the Mississippi Basin and its tributaries was calculated during the years that tritium measurements were made. The cumulative fluxes, calculated in grams of 3H were: (i) 160 g for the Ohio (1961–1986), (ii) 98 g for the upper Missouri (1963–1997), (iii) 30 g for the Arkansas (1961–1997) and (iv) 780 g for the Mississippi (1961–1997). Copyright © 2004 John Wiley &amp; Sons, Ltd.

Resolving Chernobyl vs. global fallout contributions in soils from Poland using Plutonium atom ratios measured by inductively coupled plasma mass spectrometry

Plutonium in Polish forest soils and the Bór za Lasem peat bog is resolved between Chernobyl and global fallout contributions via inductively coupled plasma mass spectrometric measurements of 240Pu/ 239Pu and 241Pu/ 239Pu atom ratios in previously prepared NdF 3 α spectrometric sources. Compared to global fallout, Chernobyl Pu exhibits higher abundances of 240Pu and 241Pu. The ratios 240Pu/ 239Pu and 241Pu/ 239Pu co-vary and range from 0.186 to 0.348 and 0.0029 to 0.0412, respectively, in forest soils ( 241Pu/ 239Pu=0.2407×[ 240Pu/ 239Pu]−0.0413; r 2=0.9924). Two-component mixing models are developed to ap portion 239+240Pu and 241Pu activities; various estimates of the percentage of Chernobyl-derived 239+240Pu activity in forest soils range from <10% to >90% for the sample set. The 240Pu/ 239Pu– 241Pu/ 239Pu atom ratio mixing line extrapolates to estimate 241Pu/ 239Pu and the 241Pu/ 239+240Pu activity ratio for the Chernobyl source term (0.123±0.007; 83±5; 1 May 1986). Sample 241Pu activities, calculated using existing alpha spectrometric 239+240Pu activities, and the 240Pu/ 239Pu and 241Pu/ 239Pu atom ratios, agree relatively well with previous liquid scintillation spectrometry measurements. Chernobyl Pu is most evident in locations from northeastern Poland. The 241Pu activities and/or the 241Pu/ 239Pu atom ratios are more sensitive than 240Pu/ 239Pu or 238Pu/ 239+240Pu activity ratios at detecting small Chernobyl 239+240Pu inputs, found in southern Poland. The mass spectrometric data show that the 241Pu activity is 40–62% Chernobyl-derived in southern Poland, and 58–96% Chernobyl in northeastern Poland. The Bór za Lasem peat bog (49.42° N, 19.75° E), located in the Orawsko-Nowotarska valley of southern Poland, consists of global fallout Pu.