Tracing effects of decalcification on solute sources in a shallow groundwater aquifer, NW Germany

δ⁸⁷Sr values and Ca/Sr ratios were employed to quantify solute inputs from atmospheric and lithogenic sources to a catchment in NW Germany. The aquifer consists primarily of unconsolidated Pleistocene eolian and fluviatile deposits predominated by >90% quartz sand. Accessory minerals include feldspar, glauconite, and mica, as well as disperse calcium carbonate in deeper levels. Decalcification of near-surface sediment induces groundwater pH values up to 4.4 that lead to enhanced silicate weathering. Consequently, low mineralized Ca–Na–Cl- and Ca–Cl-groundwater types are common in shallow depths, while in deeper located calcareous sediment Ca–HCO₃-type groundwater prevails. δ⁸⁷Sr values and Ca/Sr ratios of the dissolved pool range from 7.3 to −2.6 and 88 to 493, respectively. Positive δ⁸⁷Sr values and low Ca/Sr ratios indicate enhanced feldspar dissolution in shallow depths of less than 20 m below soil surface (BSS), while equilibrium with calcite governs negative δ⁸⁷Sr values and elevated Ca/Sr ratios in deep groundwater (>30 m BSS). Both positive and negative δ⁸⁷Sr values are evolved in intermediate depths (20–30 m BSS). For groundwater that is undersaturated with respect to calcite, atmospheric supplies range from 4% to 20%, while feldspar-weathering accounts for 8–26% and calcium carbonate for 62–90% of dissolved Sr²⁺. In contrast, more than 95% of Sr²⁺ is derived by calcium carbonate and less than 5% by feldspar dissolution in Ca–HCO₃-type groundwater. The surprisingly high content of carbonate-derived Sr²⁺ in groundwater of the decalcified portion of the aquifer may account for considerable contributions from Ca-containing fertilizers. Complementary tritium analyses show that equilibrium with calcite is restricted to old groundwater sources.     

Strontium stable isotopes fractionate in the soil environments?

This study shows that the stable isotopic composition of strontium (the ⁸⁸Sr/⁸⁶Sr ratio expressed as δ^88/86Sr value relative to the NBS987 standard) varies significantly in sedimentary terrestrial environments. The abundances of ⁸⁶Sr, ⁸⁸Sr isotopes were analyzed by MC-ICP-MS “Nu Plasma”. All studied rocks and waters show δ^88/86Sr values that are distinctly different from the measured NBS987 standard (yielding 0.01 ± 0.05‰, all errors are reported as 2σ). Modern corals from the northern Gulf of Aqaba, Red Sea yielded significantly different value than seawater (δ^88/86Sr = 0.22 ± 0.07‰, compared to 0.35 ± 0.06‰, respectively), in an excellent correlation with the δ^88/86Sr analyses reported by Fietzke and Eisenhauer [Fietzke, J., Eisenhauer, A., 2006. Determination of temperature-dependent stable strontium isotopes (⁸⁸Sr/⁸⁶Sr) fractionation via bracketing standard MC-ICP-MS. Geochm. Geophys. Geosyst. 7 (no. 8)] on other coral samples. All carbonate samples that originated in the marine environment: corals (porites and acropora from the northern Gulf of Aqaba); Cretaceous limestone and runoff from the Judea Mountains as well as lacustrine evaporitic aragonite (Dead Sea); and Red Sea and Atlantic seawater yield an average δ^88/86Sr value of 0.26 ± 0.1‰. On the other hand, secondary materials (products of chemical weathering) from the terrestrial environment of the Judea Mountain such as terra rossa soil and speleothem calcite (that derives its Sr from the above-lying soil) yielded significantly lower δ^88/86Sr value of − 0.17 ± 0.06‰. This indicates that strontium isotopes fractionate in the soil environment calling for a possible development of strontium isotopes as a tracer for processes of chemical weathering and pedogenesis.     

Geochemistry of coral from Papua New Guinea as a proxy for ENSO ocean–atmosphere interactions in the Pacific Warm Pool

A Porites sp. coral growing offshore from the Sepik and Ramu Rivers in equatorial northern Papua New Guinea has yielded an accurate 20-year history (1977–1996) of sea surface temperature (SST), river discharge, and wind-induced mixing of the upper water column. Depressions in average SSTs of about 0.5–1.0 °C (indicated by coral Sr/Ca) and markedly diminished freshwater runoff to the coastal ocean (indicated by coral δ¹⁸O, δ¹³C and UV fluorescence) are evident during the El Niño – Southern Oscillation (ENSO) events of 1982–1983, 1987 and 1991-1993. The perturbations recorded by the coral are in good agreement with changes in instrumental SST and river discharge/precipitation records, which are known to be diagnostic of the response of the Pacific Warm Pool ocean–atmosphere system to El Niño. Consideration of coastal ocean dynamics indicates that the establishment of northwest monsoon winds promotes mixing of near-surface waters to greater depths in the first quarter of most years, making the coral record sensitive to changes in the Asian–Australian monsoon cycle. Sudden cooling of SSTs by 1°C following westerly wind episodes, as indicated by the coral Sr/Ca, is consistent with greater mixing in the upper water column at these times. Furthermore, the coral UV fluorescence and oxygen isotope data indicate minimal contribution of river runoff to surface ocean waters at the beginning of most years, during the time of maximum discharge. This abrupt shift in flood-plume behaviour appears to reflect the duration and magnitude of northwest monsoon winds, which tend to disperse flood plume waters to a greater extent in the water column when wind-mixing is enhanced. Our results suggest that a multi-proxy geochemical approach to the production of long coral records should provide comprehensive reconstructions of tropical paleoclimate processes operating on interannual timescales.     

S, O and Sr isotope systematics of active vent materials from the Mariana backarc basin spreading axis at 18°N

Stable isotope ratios of S, O and Sr have been measured for active vent materials which were first found and sampled in April 1987 from the Mariana backarc spreading axis at 18°N. Chimneys consisted mostly of barite with a lesser proportion of sulfide minerals such as sphalerite, galena, chalcopyrite and pyrite. Theδ³⁴S values of sphalerite and galena taken from several chimneys and various parts of a chimney showed a narrow range from 2.1 to 3.1‰, suggesting uniform conditions of fluid chemistry during chimney growth. The sulfur isotopic results imply a contribution of hydrogen sulfide reduced from seawater sulfate in the deep hydrothermal reaction zone, considering that fresh glasses of the Mariana Trough basalts haveδ³⁴S= −0.6 ± 0.3‰. Sulfur isotopic compositions of hydrogen sulfide in the high temperature vent fluids (δ³⁴S= 3.6–4.8‰) which are higher than those of the sulfide minerals suggest the secondary addition of hydrogen sulfide partially reduced from entrained seawater SO₄²⁻ at a basal part of the chimneys. This interpretation is consistent with theδ³⁴S values of barite (21–22‰) that are higher than those of seawater sulfate. The residence time of the entrained SO₄²⁻ was an order of an hour on a basis of oxygen isotopic disequilibrium of barite. Strontium isotopic variations of barite and vent waters indicated that Sr in barite was mostly derived from the Mariana Trough basalts with a slight contribution from Sr in circulating sea-water, and that 10–20% mixing of seawater with ascending hydrothermal fluids induced precipitation of barite at the sea-floor.     

Very high-frequency and seasonal cave atmosphere PCO2 variability: Implications for stalagmite growth and oxygen isotope-based paleoclimate records

Cave air P_CO2 at two Irish sites varied dramatically on daily to seasonal timescales, potentially affecting the timing of calcite deposition and consequently climate proxy records derived from stalagmites collected at the same sites. Temperature-dependent biochemical processes in the soil control CO₂ production, resulting in high summer P_CO2 values and low winter values at both sites. Large Large-amplitude, high-frequency variations superimposed on this seasonal cycle reflect cave air circulation. Here we model stalagmite growth rates, which are controlled partly by CO₂ degassing rates from drip water, by considering both the seasonal and high-frequency cave air P_CO2 variations. Modeled hourly growth rates for stalagmite CC-Bil from Crag Cave in SW Ireland reach maxima in late December (0.063 μm h^− 1) and minima in late June/early July (0.033 μm h^− 1). For well-mixed ‘diffuse flow’ cave drips such as those that feed CC-Bil, high summer cave air P_CO2 depresses summer calcite deposition, while low winter P_CO2 promotes degassing and enhances deposition rates. In stalagmites fed by well-mixed drips lacking seasonal variations in δ¹⁸O, integrated annual stalagmite calcite δ¹⁸O is unaffected; however, seasonality in cave air P_CO2 may influence non-conservative geochemical climate proxies (e.g., δ¹³C, Sr/Ca). Stalagmites fed by ‘seasonal’ drips whose hydrochemical properties vary in response to seasonality may have higher growth rates in summer because soil air P_CO2 may increase relative to cave air P_CO2 due to higher soil temperatures. This in turn may bias stalagmite calcite δ¹⁸O records towards isotopically heavier summer drip water δ¹⁸O values, resulting in elevated calcite δ¹⁸O values compared to the ‘equilibrium’ values predicted by calcite–water isotope fractionation equations. Interpretations of stalagmite-based paleoclimate proxies should therefore consider the consequences of cave air P_CO2 variability and the resulting intra-annual variability in calcite deposition rates.     

Sr, Nd, O and H isotopic ratios in Ascension Island lavas and plutonic inclusions; cogenetic origin

Eighteen basic rocks from Ascension Island (South Atlantic) give a mean⁸⁷Sr/⁸⁶Sr ratio of 0.70311 ± 17 for both volcanics and plutonic inclusions. The late-stage differentiated rocks (rhyolites and granitic inclusions) have much higher⁸⁷Sr/⁸⁶Sr ratios, up to 0.712. All these rocks display the same range of Nd isotopic compositions (ε_Ndvalues from6.9to11.1with a mean on12samples of8.4 ± 0.6) implying a cogenetic relation between the two sequences. The D/H systematics lead to the same conclusion.In the NdSr diagram, the data plot close to the mantle array and show a positive correlation. This suggests a mixing between a depleted MORB-type mantle, i.e. the upper mantle, and a hot-spot with less depleted geochemical characteristics, i.e. the OIB mantle source.The total range of δ¹⁸O values lies between 4.8‰ for plagioclase cumulates and 6.7‰ for the most evolved rocks (peralkaline granites and comendites). The basic rocks have values around 5.3‰, typical of mantle-derived material. These oxygen data indicate that the high⁸⁷Sr/⁸⁶Sr ratios in the most evolved rocks (both volcanic and plutonic terms) result from the combination of two different processes: incorporation of slight amounts (< 1%) of high-temperature altered oceanic crust by the magma in the late stages of the differentiation process and then in-situ Rb decay since the time of formation of these rocks. Both processes were very effective because of the high Rb and low Sr contents of these evolved rocks.Oxygen isotope systematics in the Ascension Island granites and rhyolites indicate that a fractional crystallization process alone does not produce δ¹⁸O values higher than 6.7‰, i.e. that the ultimate δ¹⁸O enrichment, relative to the initial basic magma, is not greater than 1.5‰.     

Oxygen isotopic composition of alkaline anorogenic granites as a clue to their origin: the problem of crustal oxygen

The primary isotopic characteristics of alkaline granites are often obscured by secondary processes enhanced by their unusual chemical compositions. This is true for radiogenic as well as for stable isotopes. For example, the ⁸⁷Sr/⁸⁶Sr ratios can vary drastically in closed systems because of very high Rb/Sr ratios and can also be easily modified by direct or indirect interaction with continental crust because of low Sr concentrations. Moreover, the frequent occurrence of the granitic massifs as hypovolcanic complexes increases the probability of interaction with meteoric waters which is a common source of important isotopic variability.The investigation of oxygen isotope systematics in alkaline acidic rocks from various environments shows the¹⁸O content of their quartz to be highly invariable, and the δ¹⁸O values to be close to the mantle range of values. This is due to the resistance of quartz to isotopic exchange, which makes it a good tracer of primary isotopic composition. If we eliminate the quartz δ¹⁸O values for which interaction with meteoric water is well documented (five samples), the total range of variation (seventeen samples) is from 6.0 to 7.3‰ relative to SMOW. The values can easily be accounted for by, and correspond to, equilibrium with mantle-type material in a temperature range of 1200-800°C. If we consider possible effects of fractional crystallization, this temperature range can probably be reduced to its lower limit which is much more likely for rocks of acidic composition.The present oxygen isotope study strongly supports an origin for alkaline anorogenic granites from mantle-dominated sources.     

Geochemical approach to magmatic evolution of Mt. Erciyes stratovolcano Central Anatolia, Turkey

Erciyes stratovolcano, culminating at 3917 m, is located in the Cappadocian region of central Anatolia. During its evolution, this Quaternary volcano produced pyroclastic deposits and lava flows. The great majority of these products are calc-alkaline in character and they constitute Kocdag and Erciyes sequences by repeated activities. Alkaline activity is mainly observed in the first stages of Kocdag and approximately first-middle stages of Erciyes sequences. Generally, Kocdag and Erciyes stages terminate by pyroclastic activities. The composition of lavas ranges from basalt to rhyolite (48.4–70.5 wt.% SiO₂). Calc-alkaline rocks are represented mostly by andesites and dacites. Some compositional differences between alkaline basaltic, basaltic and andesitic rocks were found; while the composition of dacites remain unchanged. All these volcanics are generally enriched in LIL and HFS elements relative to the orogenic values except Rb, Ba, Nb depleted alkaline basalt. ⁸⁷Sr/⁸⁶Sr and ¹⁴³Nd/¹⁴⁴Nd isotopic composition of the volcanics range between 0.703344–0.703964, 0.512920–0.512780 for alkaline basalts and change between 0.704322–0.705088, 0.512731–0.512630 for alkaline basaltic rocks whereas calc-alkaline rocks have relatively high Sr and Nd isotopic ratios (0.703434–0.705468, 0.512942–0.512600). Low Rb, Ba, Nb content with high Zr/Nb, low Ba/Nb, La/Yb ratio and low Sr isotopic composition suggest an depleted source component, while high Ba, Rb, Nb content with high La/Yb, Ba/Nb, low Zr/Nb and low ⁸⁷Sr/⁸⁶Sr ratios indicate an OIB-like mantle source for the generation of Erciyes alkaline magma. These elemental and ratio variations also indicate that the different mantle sources have undergone different degree of partial melting episodes. The depletion in Ba, Rb, Nb content may be explained by the removal of these elements from the source by slab-derived fluids which were released from pre-collisional subduction, modified the asthenospheric mantle. The chemically different mantle sources interacted with crustal materials to produce calc-alkaline magma. The Ba/Nb increase of calc-alkaline samples indicates the increasing input of crustal components to Erciyes volcanics. Sr and Nd isotopic compositions and elevated LIL and HFS element content imply that calc-alkaline magma may be derived from mixing of an OIB-like mantle melts with a subduction-modified asthenospheric mantle and involvement of crustal materials in intraplate environments.     

Oxygen and strontium isotopic characteristics of calc-alkalic volcanic rocks from the central and western Japan arcs: Evaluation of contribution of crustal components to the magmas

¹⁸O/¹⁶O and ⁸⁷Sr/⁸⁶Sr ratios were determined for Quaternary calc-alkalic volcanic rocks from six volcanic rock suites in the central and western Japan arcs. The δ¹⁸O values relative to SMOW and ⁸⁷Sr/⁸⁶Sr ratios range from +6.3 to +9.9⁰/₀₀ and 0.70357 to 0.70684, respectively. Both the O- and Sr-isotopic compositions are higher than those for island-arc primitive magmas and their differentiates. The isotopic compositions of the calc-alkalic rocks cannot be derived by a simple fractional crystallization of the primitive magmas. On the other hand, the ¹⁸O- and ⁸⁷Sr-enrichment is confined to the rock suites located in well-developed island arcs having thick continental-type crust with low or negative Bouguer anomalies. Involvement of ¹⁸O- and ⁸⁷Sr-rich crustal material in the magma formation is suggested.The isotopic compositions vary remarkably within individual rock suites as well as from volcano to volcano. The data points in δ¹⁸O vs. ⁸⁷Sr/⁸⁶Sr plot accord with a mixing model between primitive magmas and crustal material of dioritic composition on an average, assuming their comparative Sr contents. The primitive magmas involved could not be low-Sr tholeiites, but magmas more or less enriched in incompatible elements including Sr, which correspond to high-alkali tholeiites or alkali basalts and their evolved magmas. The nature of the primitive magmas seems to change from tholeiitic to more alkalic with progressing island-arc evolution.Mixing of crust-derived melts is more plausible than assimilation of solid-rocks for involving 20 to 30% crustal material in the magmas along simple mixing curves. Isotopic variations between the rock suites are ascribed to variable Sr concentration radio of the end-members, variable isotopic compositions of crustal material or variable mixing ratio of the end-members. Extremely high-δ ¹⁸O rocks with moderate increase in ⁸⁷Sr/⁸⁶Sr ratio suggest another mixing process in shallower magma chambers between andesite magmas and metasedimentary rocks having high δ ¹⁸O and ⁸⁷Sr/⁸⁶Sr values but low Sr content. Subsequent fractional crystallization of once-derived magmas would be the prominent process for the rock suites showing gradual increase in ¹⁸O up to 1⁰/₀₀ with uniform ⁸⁷Sr/⁸⁶Sr ratios.     

Efficient trapping of organic carbon in sediments on the continental margin with high fluvial sediment input off southwestern Taiwan

Accumulation rates of marine and terrigenous organic carbon in the continental margin sediments off southwestern Taiwan were estimated from the measured concentrations and isotopic compositions of total organic carbon (TOC) and previously reported sedimentation rates. Surficial sediments were collected from the study area spanning from the narrow shelf near the Kaoping River mouth to the deep slope with depths reaching almost 3000 m. The average sediment loading of Kaoping River is 17 Mt/yr, which yields high sediment accumulation rates ranging from 0.08 to 1.44 g cm⁻² yr⁻¹ in the continental margin. About half of the discharged sediments were deposited on the margin within 120 km of the river mouth. Carbon isotopic compositions of terrestrial and marine end-members of organic matter were determined, respectively, based on suspended particulate matter (SPM) collected from three major rivers in the southwestern Taiwan and from an offshore station. All samples were analyzed for the TOC content and its isotopic composition (δ¹³C_org). The SPM samples were also analyzed for the total nitrogen (TN) content. TOC content in marine sediments ranges from 0.45% to 1.35% with the highest values on the upper slope near the Kaoping River mouth. The TOC/TN ratio of the SPM samples from the offshore station is 6.8±0.6, almost identical to the Redfield ratio, indicating their predominantly marine origin; their δ¹³C_org values are also typically marine with a mean of −21.5±0.3‰. The riverine SPM samples exhibit typical terrestrial δ¹³C_org values around −25‰. The δ¹³C_org values of surficial sediments range from −24.8‰ to −21.2‰, showing a distribution pattern influenced by inputs from the Kaoping River. The relative contributions from marine and terrestrial sources to sedimentary organic carbon were determined by the isotope mixing model with end-member compositions derived from the riverine and marine SPM. High fluvial sediment inputs lead to efficient trapping of organic carbon over a wide range of water depth in this continental margin. The marine organic accumulation rate ranges from 1.6 to 70 g C m⁻² yr⁻¹ with an area weighted mean of 4.2 g C m⁻² yr⁻¹, which is on a par with the mean terrestrial contribution and accounts for 2.3% of mean primary production. The depth-dependent accumulation rate of marine organic carbon can be simulated with a function involving primary productivity and mineral accumulation rate, which may be applicable to other continental margins with high sedimentation rates. Away from the nearshore area, the content of terrigenous organic carbon in surficial sediments decreases with distance from the river mouth, indicating its degradation in marine environments.     

Biogeochemistry of dissolved carbon,major, and trace elements during spring flood periods on the Ob River

Detailed knowledge of the flood period of Arctic rivers remains one of the few factors impeding rigorous prediction of the effect of climate change on carbon and related element fluxes from the land to the Arctic Ocean. In order to test the temporal and spatial variability of element concentration in the Ob River (western Siberia) water during flood period and to quantify the contribution of spring flood period to the annual element export, we sampled the main channel year round in 2014–2017 for dissolved C, major, and trace element concentrations. We revealed high stability (approximately ≤10% relative variation) of dissolved C, major, and trace element concentrations in the Ob River during spring flood period over a 1‐km section of the river channel and over 3 days continuous monitoring (3‐hr frequency). We identified two groups of elements with contrasting relationship to discharge: (a) DIC and soluble elements (Cl, SO₄, Li, B, Na, Mg, Ca, P, V, Cr, Mn, As, Rb, Sr, Mo, Ba, W, and U) negatively correlated (p < 0.05) with discharge and exhibited minimal concentrations during spring flood and autumn high flow and (b) DOC and particle‐reactive elements (Al, Fe, Ti, Y, Zr, Nb, Cs, REEs, Hf, Tl, Pb, and Th), some nutrients (K), and metalloids (Ge, Sb, and Te), positively correlated (p < 0.05) with discharge and showed the highest concentrations during spring flood. We attribute the decreased concentration of soluble elements with discharge to dilution by groundwater feeding and increased concentration of DOC and particle‐reactive metals with discharge to leaching from surface soil, plant litter, and suspended particles. Overall, the present study provides first‐order assessment of fluxes of major and trace elements in the middle course of the Ob River, reveals their high temporal and spatial stability, and characterizes the mechanism of river water chemical composition acquisition.     

O, S, Sr, and Pb isotope variations in volcanic rocks from the Northern Mariana Islands: implications for crustal recycling in intra-oceanic arcs

Quaternary lavas from the Northern Mariana Islands have respective O- and S-isotope ranges ofδ¹⁸O = +5.7 to +6.6 (‰ SMOW) andδ³⁴S = +2.0to+20.7 (‰ CDT). Chemically evolved andesites and dacites with meanδ¹⁸O = +6.3 ± 0.2 are slightly enriched in¹⁸O with respect to unfractionated basalts of<53%SiO₂ with meanδ¹⁸O = +6.0 ± 0.1. This¹⁸O enrichment can be explained in terms of differentiation of parental mafic magmas havingδ¹⁸O values between +5.7 to +6.2‰ through closed-system crystal fractionation because the lavas from all nine islands of the arc define a coherentδ¹⁸OSiO₂ trend. The S-isotope composition of oxidized magmas is not modified extensively through the degassing of SO₂; therefore, the meanδ³⁴S value of ca. +11‰ for the Mariana lavas is considered to be representative of their source region.The enrichment of¹⁸O and³⁴S in Mariana Arc parental magmas relative to ocean floor basalts withδ¹⁸O ca. + 5.7‰ andδ³⁴S = ca.0.3‰ is attributed to the recycling of¹⁸O- and³⁴S-rich crustal components (sediment withδ¹⁸O = ca. + 25‰ and seawater sulfate withδ³⁴S = ca. +20‰ into the upper mantle source region for these arc magmas. This interpretation is consistent with enrichments of radiogenic Sr and Pb in the same lavas relative to ocean-floor basalts erupted either side of the arc, which are presumed to share a common upper mantle source. This enrichment is considered to reflect the mixing of two components, one having a typical upper mantle composition and the other having a more radiogenic character similar to that of western Pacific pelagic sediments.     

Strontium in rivers of the Baltic Basin

The rivers in the Baltic Basin drain a mixture of bedrocks ranging from Mesozoic-Paleozoic sediments in the south to Proterozoic-Archean intrusives in the north. The rivers in the sedimentary basin in the south have high concentrations of Sr, in the interval 100–500 µg l^–1 while the⁸⁷Sr/⁸⁶Sr ratio is close to that of seawater, i.e. 0.71. The northern rivers in the Precambrian shield area on the other hand have low Sr concentrations of 15–50 µg l^–1 with high⁸⁷Sr/⁸⁶Sr ratios of about to 0.73 (0.721–0.745). The riverine input of dissolved Sr to the brackish Baltic Sea approaches 60 tons year^–1, with a weighted mean concentration approaching 130 µg l^–1 and a weighted mean⁸⁷Sr/⁸⁶Sr ratio close to 0.712. Although the sedimentary area in the south supplies only about 43% of the total river discharge, it gives about 88% of the total Sr input. Because of this and the strong regional riverine variation in⁸⁷Sr/⁸⁶Sr ratio, Sr and its isotopes seem to be a convenient tool to unveil mixing relations of water masses in the northern Baltic Sea, provided high resolution analyses are applied. For an overall characterization of water mixing in the Baltic Sea, the Nd system will be superior to that of Sr.     

Isotope characteristics of submarine lavas from the Philippine Sea: implications for the origin of arc and basin magmas of the Philippine tectonic plate

Igneous rocks from the Philippine tectonic plate recovered on Deep Sea Drilling Project Legs 31, 58 and 59 have been analyzed for Sr, Nd and Pb isotope ratios. Samples include rocks from the West Philippine Basin, Daito Basin and Benham Rise (40–60 m.y.), the Palau-Kyushu Ridge (29–44 m.y.) and the Parece Vela and Shikoku basins (17–30 m.y.). Samples from the West Philippine, Parece Vela and Shikoku basins are MORB (mid-ocean ridge basalt)-like with ⁸⁷Sr/⁸⁶Sr= 0.7026−0.7032, ¹⁴³Nd/¹⁴⁴Nd= 0.51300−0.51315, and ²⁰⁶Pb/²⁰⁴Pb= 17.8−18.1. Samples from the Daito Basin and Benham Rise are OIB (oceanic island basalt)-like with ⁸⁷Sr/⁸⁶Sr= 0.7038−0.7040, ¹⁴³Nd/¹⁴⁴Nd= 0.51285−0.51291 and ²⁰⁶Pb/²⁰⁴Pb= 18.8−19.2. All of these rocks have elevated ²⁰⁷Pb/²⁰⁴Pb and ²⁰⁸Pb/²⁰⁴Pb compared to the Northern Hemisphere Regression Line (NHRL) and have δ²⁰⁷Pb values of 0 to +6 and δ²⁰⁸Pb values of +32 to +65. Lavas from the Palau-Kyushu Ridge, a remnant island arc, have ⁸⁷Sr/⁸⁶Sr= 7032−0.7035, ¹⁴³Nd/¹⁴⁴Nd= 0.51308−0.51310 and ²⁰⁶Pb/²⁰⁴Pb= 18.4−18.5. Unlike the basin magmas erupted before and after them, these lavas plot along the NHRL and have Pb-isotope ratios similar to modern Pacific plate MORB's. This characteristic is shared by other Palau-Kyushu Arc volcanic rocks that have been sampled from submerged and subaerial portions of the Mariana fore-arc.At least four geochemically distinct magma sources are required for these Philippine plate magmas. The basin magmas tap Source 1, a MORB-mantle source that was contaminated by EMI (enriched mantle component 1 [31]) and Source 2, an OIB-like mantle source with some characteristics of EMII (enriched mantle component 2 [31]). The arc lavas are derived from Source 3, a MORB-source or residue mantle including Sr and Pb from the subducted oceanic crust, and Source 4, MORB-source or residue mantle including a component with characteristics of HIMU (mantle component with high U/Pb [31]). These same sources can account for many of the isotopic characteristics of recent Philippine plate arc and basin lavas. The enriched components in these sources which are associated with the DUPAL anomaly were probably introduced into the asthenosphere from the deep mantle when the Philippine plate was located in the Southern Hemisphere 60 m.y.b.p.     

Carbon and oxygen isotope composition of shell carbonate of desert land snails

Variation in¹³C/¹²C and¹⁸O/¹⁶O ratios in the shell carbonate of several species of land snails was studied along a climatic gradient in semi-arid to arid areas in the southern Levant.¹³C was found to be enriched in snails from communities having plants with a C₄ photosynthetic pathway. Depleted δ¹³C values were found in areas with high mean annual rainfall, apparently due to higher input of metabolic CO₂ as a result of greater snail activity. Shell carbonate δ¹⁸O values show a weak relation to the δ¹⁸O values of rainwater. The shell δ¹⁸O values are enriched by 2–8‰ relative to isotopic equilibrium with environmental waters. Enrichment is suggested to result from metabolic effects on body water (with lower activity producing greater enrichment) but evaporation could also be a factor. Consistent differences in both¹³C and¹⁸O were found among species and may relate to the time when shell deposition occurs. As with most paleoenvironmental indicators, the application of shell isotopes is complicated by the multiplicity of controls of isotopic composition.     

Madagascar basalts: tracking oceanic and continental sources

Extensive Upper Cretaceous volcanism in southern Madagascar was fed in part by mantle sources resembling those expressed today in the Indian Ocean at Marion and Prince Edward islands and on the central Southwest Indian Ridge. In addition, very low ε_Nd(T) (to −17.4), high(⁸⁷Sr/⁸⁶Sr)_T (to 0.72126) tholeiites in southwestern Madagascar were variably but highly contaminated by ancient continental material broadly like that affecting the Bushe and Poladpur Formations of the later Deccan Traps in India. Alkalic dikes in southwestern Madagascar have a rough analogue in the Mahabaleshwar Formation of the Deccan, in that they document the influence of a low ²⁰⁶Pb/²⁰⁴Pb, negative ε_Nd, relatively low ⁸⁷Sr/⁸⁶Sr reservoir. A very similar reservoir is manifested at present in mid-ocean ridge basalts on the central Southwest Indian Ridge near 40°E. The original location of this end-member appears likely to have been in the Madagascan lithospheric mantle, a portion of which may have been removed in the Middle Cretaceous by the action of the Marion hotspot or the rifting of Indo-Madagascar. An origin within the hotspot itself also may be possible; however, recent products of the hotspot appear to lack completely the necessary low ²⁰⁶Pb/²⁰⁴Pb, low ε_Nd signatures.     

Orographic controls on rain water isotope distribution in the Mount Lofty Ranges of South Australia

Hydrogen and oxygen isotopes of water are common environmental tracers used to investigate hydrological processes, such as evaporation, vegetation water use, surface water–groundwater interaction, and groundwater recharge. The water isotope signature in surface water and groundwater evolves from the initial rain signature. In mountain terrain, rain water stable isotope composition spatially varies due to complex orographic precipitation processes. Many studies have examined the isotope–elevation relationships, while few have quantitatively investigate the terrain aspect and slope effect on rain isotope distribution. In this paper, we examine the orographic effects more completely, including elevation, terrain slope and aspect, on stable isotope distribution in the Mount Lofty Ranges (MLR) of South Australia, using a multivariate regression model. The regression of precipitation isotope composition suggests that orographic effects are the dominant controls on isotope spatial variability. About 75% of spatial variability in δ¹⁸O and deuterium excess is represented by the regression using solely orography-related variables (elevation, terrain aspect and slope), with about 25% of δ¹⁸O spatial variability attributed to the terrain aspect and slope effect. The lapse rate is about −0.25‰ for every 100 m at both windward and leeward slopes. However, at the same elevation, δ¹⁸O at the leeward slope (eastern MLR) is 0.5‰ larger than that at the windward slope. The difference can be explained by different mechanisms – continuous rain-out processes on the windward side and sub-cloud evaporation on the leeward side. Both δ¹⁸O and deuterium excess maps (1 km resolution) are constructed based on the regression results for the MLR. Both maps are consistent with groundwater of local precipitation origin, and useful to examine groundwater recharge.     

Small-scale,patchy distributions of infauna in hydrodynamically mobile continental shelf sands: Do ripple crests and troughs support different communities?

Spatial variability of infauna with respect to distribution of topographic habitat features was examined in hydrodynamically mobile sandy sediments on the inner continental shelf off New Jersey, USA (39° 27.69′ N, 74° 15.81′W). Sediment cores for infauna were taken by SCUBA divers at multiple spatial scales over time at 12-m depth in the LEO-15 research area on Beach Haven Ridge. Crests, troughs and less consistently flanks of sand ripples 5–15-cm in height, were characterized by different infaunal community patterns at spatial scales of centimeters to kilometers on several sampling dates. Overall, infaunal community differences among ripple crests, troughs, and/or flanks within areas <1-m² were greater than those found for each of these habitats (i.e., either crests, troughs, or flanks) that were separated by distances of 2 m–4 km. Infaunal density and species richness were consistently higher in troughs compared to crests. Indirect measures of food resources such as particulate organic carbon, chl a, and pheophytin were associated with ripple crests and troughs. Troughs contained significantly higher levels of particulate organic carbon (~1.2 times higher) associated with finer sediments, compared with crests and flanks. Various combinations of taxa had higher densities in either crests or troughs of sand ripples depending on date, and the relative abundances of three taxa, the deposit-feeding polychaete Polygordius jouinae, the suspension-feeding surfclam Spisula solidissima, and predatory nemerteans were important in distinguishing between crests and troughs on most dates. Thus, a priori knowledge of whether a benthic sample comes from a crest or trough helped to explain small-scale infaunal patchiness in relatively homogeneous, subtidal sandy sediments. Consideration of such topographic features in sampling designs can help in explaining variation in species’ distributions at several spatial and temporal scales.     

Composition of back-arc basin volcanics, Valu Fa Ridge, Lau Basin: Evidence for a slab-derived component in their mantle source

Samples dredged from 2 localities near the crest of the Valu Fa ridge, an active back-arc basin spreading centre in the Lau Basin, consist of highly vesicular lava fragments of andesitic composition. The samples are characterized by rare, euhedral An₈₅ plagioclase phenocrysts in a hypocrystalline groundmass of An₆₀ plagioclase laths, brown glass and rare subhedral clinopyroxene. Samples from within and, to a lesser extent, between the dredge hauls show remarkable isotopic and chemical homogeneity, with: ⁸⁷Sr/⁸⁶Sr − 0.70330 ± 2; ¹⁴³Nd/¹⁴⁴Nd − 0.51303 ± 2; ²⁰⁶Pb/²⁰⁴Pb − 18.65 ± 2; ²⁰⁷Pb/²⁰⁴Pb − 15.55 ± 1; ²⁰⁸Pb/²⁰⁴Pb − 38.34 ± 4; Sr − 165 ppm; Rb − 7 ppm; Cs − 0.17 ppm; K − 3300 to 4200 ppm; Ba − 96 ppm; and REE — LREE depleted with 12–18 × chondritic abundances. On Sr-Nd, Pb-Pb and Sr-Pb plots the volcanics lie just within or on the edge of the MORB fields, overlapping with island-arc volcanics from the Marianas and Tonga. Compared with MORB and ocean-island basalts, the samples show alkali-element enrichment relative to REE and higher Cs relative to Rb. The isotopic and geochemical characteristics of the Valu Fa Ridge volcanics clearly indicate a minor, but significant, slab-derived component in the back-arc basin mantle source.     

Cloning and expression of alpha class glutathione S-transferase gene from the small hermaphroditic fish Rivulus marmoratus (Cyprinodontiformes, Rivulidae)

In order to assess its potential as a biomarker of aquatic pollution, an alpha class glutathione S-transferase gene (GSTα gene) was cloned from the small hermaphroditic fish Rivulus marmoratus. The R. marmoratus GSTα gene spanned 1.3 kb, consisting of 6 exons encoding 221 amino acid residues. It showed high similarity to zebrafish GST. We named this R. marmoratus GSTα gene as rm-GSTα. The cDNA of the rm-GSTα gene was also investigated for its phylogeny, tissue-specific and chemical-induced expression. Rm-GSTα was subcloned into a 6 × His-tagged pCR^®T7 TOPO TA expression vector to produce the recombinant 6 × His-tagged rm-GST protein. This will be used in future to raise an rm-GSTα antibody for use in the study of phase II metabolism involved in detoxification. We also exposed R. marmoratus to 300 μg/l of 4-nonylphenol in water, and found approximately 4-fold induction of R. marmoratus GSTα mRNA in the treated animals. In this paper, we discuss the characteristics of the R. marmoratus GSTα gene as well as its potential use in relation to environmental pollution.