Description: Discovery of seafloor volcanism west of Buldir Volcano, the westernmost emergent volcano in the Aleutian arc, demonstrates that surface expression of active Aleutian volcanism falls below sea level just west of 175·9°E longitude, but is otherwise continuous from mainland Alaska to Kamchatka. Lavas dredged from newly discovered seafloor volcanoes up to 300 km west of Buldir have end-member geochemical characteristics that provide new insights into the role of subducted basalt as a source component in Aleutian magmas. Western Aleutian seafloor lavas define a highly calc-alkaline series with 50–70% SiO2. Most samples have Mg-numbers [Mg# = Mg/(Mg + Fe)] greater than 0·60, with higher MgO and lower FeO* compared with average Aleutian volcanic rocks at all silica contents. Common basalts and basaltic andesites in the series are primitive, with average Mg# values of 0·67 (±0·02, n = 99, 1SD), and have Sr concentrations (423 ± 29 ppm, n = 99) and La/Yb ratios (4·5 ± 0·4, n = 29) that are typical of island arc basaltic lavas. A smaller group of basaltic samples is more evolved and geochemically more enriched, with higher and more variable Sr and La/Yb (average Mg# = 0·61 ± 0·1, n = 31; Sr = 882 ± 333 ppm, n = 31; La/Yb = 9·1 ± 0·9, n = 16). None of the geochemically enriched basalts or basaltic andesites has low Y (〈15 ppm) or Yb (〈1·5 ppm), so none show the influence of residual or cumulate garnet. In contrast, most western seafloor andesites, dacites and rhyodacites have higher Sr (〉1000 ppm) and are adakitic, with strongly fractionated trace element patterns (Sr/Y = 50–350, La/Yb = 8–35, Dy/Yb = 2·0–3·5) with low relative abundances of Nb and Ta (La/Ta 〉 100), consistent with an enhanced role for residual or cumulate garnet + rutile. All western seafloor lavas have uniformly radiogenic Hf and Nd isotopes, with εNd = 9·1 ± 0·3 (n = 31) and εHf = 14·5 ± 0·6 (n = 27). Lead isotopes are variable and decrease with increasing SiO2 from basalts with 206Pb/204Pb = 18·51 ± 0·05 (n = 11) to dacites and rhyodacites with 206Pb/204Pb = 18·43 ± 0·04 (n = 18). Western seafloor lavas form a steep trend in 207Pb/204Pb–206Pb/204Pb space, and are collinear with lavas from emergent Aleutian volcanoes, which mostly have 206Pb/204Pb 〉 18·6 and 207Pb/204Pb 〉 15·52. High MgO and Mg# relative to silica, flat to decreasing abundances of incompatible elements, and decreasing Pb isotope ratios with increasing SiO2 rule out an origin for the dacites and rhyodacites by fractional crystallization. The physical setting of some samples (erupted through Bering Sea oceanic lithosphere) rules out an origin for their garnet + rutile trace element signature by melting in the deep crust. Adakitic trace element patterns in the dacites and rhyodacites are therefore interpreted as the product of melting of mid-ocean ridge basalt (MORB) eclogite in the subducting oceanic crust. Western seafloor andesites, dacites and rhyodacites define a geochemical end-member that is isotopically like MORB, with strongly fractionated Ta/Hf, Ta/Nd, Ce/Pb, Yb/Nd and Sr/Y. This eclogite component appears to be present in lavas throughout the arc. Mass-balance modeling indicates that it may contribute 36–50% of the light rare earth elements and 18% of the Hf that is present in Aleutian volcanic rocks. Close juxtaposition of high-Mg# basalt, andesite and dacite implies widely variable temperatures in the western Aleutian mantle wedge. A conceptual model explaining this shows interaction of hydrous eclogite melts with mantle peridotite to produce buoyant diapirs of pyroxenite and pyroxenite melt. These diapirs reach the base of the crust and feed surface volcanism in the western Aleutians, but are diluted by extensive melting in a hotter mantle wedge in the eastern part of the arc.

Description: Western Aleutian seafloor lavas define a highly calc-alkaline series, with Mg numbers (Mg#, Mg/Mg+Fe) greater than 0.65 in dacitic lavas with 2-4% MgO at 63-70% SiO2. These lavas have uniformly radiogenic Hf and Nd and variable, but relatively unradiogenic, Sr and Pb, at the MORB-like end of the spectrum of island-arc lavas. Andesites and dacites have high Sr 〉1000 ppm, fractionated trace element patterns (Sr/Y=50-350, La/Yb=8-35, Dy/Yb=2-3.5), and low relative abundances of Nb and Ta (La/Ta=100-300), consistent with an enhanced role for residual or cumulate garnet + rutile. MORB-like isotope compositions and high MgO and Mg# relative to silica, rule out an origin for the andesites and dacites by fractional crystallization from basalt, except perhaps, by a process of melt-rock reaction with peridotite. The most fractionated trace element patterns are in western seafloor rhyodacites (69-70% SiO2), which were dredged from volcanic cones built on Bering Sea oceanic lithosphere, where the crust is probably no more than 10 km thick, and so unlikely to produce garnet during crustal melting. We interpret the western seafloor andesites and dacites to have been produced by melting of subducted MORB-like basalt in the eclogite facies, followed by interaction of the resulting high-silica melt with mantle peridotite. This interpretation is consistent with the tectonic setting in the western Aleutians, which is dominated by oblique convergence, capable of producing a relatively hot subducting plate. Western seafloor lavas define an end-member composition with MORB-like isotope compositions and fractionated trace element ratios, which falls at the end of the continuum of compositions for all Aleutian lavas. The end-member character of western seafloor lavas is clearest in plots highlighting their radiogenic Hf, Nd and strong relative depletions in Ta and Yb. The western seafloor lavas also define an end-member composition for Pb isotopes Some western seafloor samples have high Nd/Hf, as required by Hf-Nd mixing scenarios, which indicate that a source component with radiogenic Hf and Nd and Nd/Hf greater than ~8, is present in lavas throughout the Aleutian arc (Brown et al., 2005 Fall AGU). Abundances of radiogenic Nd and Hf in the eclogite-melt component are relatively high, and so offset the unradiogenic Hf and Nd from subducted sediment. The result is a source mixture with much higher contributions of both subducted basalt and subducted sediment relative to the mantle end-member, than is produced when these elements are modeled as binary mixtures of mantle and sediment.

Description: Sr provides unique constraints on subduction magma source models because it is a fluid-mobile element that is abundant and relatively unradiogenic in arc volcanic rocks. It is common for arc basalts to be 3-4-times more Sr-rich than similarly evolved MORB (Sr/Nd = 30-50 vs 10-15 in MORB) yet Sr isotopes in arc basalts are usually offset from MORB only slightly ( Sr/ Sr ~0.7034 vs 0.7028 for MORB). This is a puzzle because abundant sources of subducted Sr in sediment (GLOSS II Sr/ Sr = 0.712) and altered oceanic crust ( Sr/ Sr = 0.704-0.705) are more radiogenic than average arc basalts globally ( Sr/ Sr ~ 0.7034)...

Description: Discovery of seafloor volcanism west of Buldir Volcano, the westernmost emergent volcano in the Aleutian arc, demonstrates that surface expression of active Aleutian volcanism falls below sea level just west of 175·9°E longitude, but is otherwise continuous from mainland Alaska to Kamchatka. Lavas dredged from newly discovered seafloor volcanoes up to 300 km west of Buldir have end-member geochemical characteristics that provide new insights into the role of subducted basalt as a source component in Aleutian magmas. Western Aleutian seafloor lavas define a highly calc-alkaline series with 50–70% SiO 2 . Most samples have Mg-numbers [Mg# = Mg/(Mg + Fe)] greater than 0·60, with higher MgO and lower FeO* compared with average Aleutian volcanic rocks at all silica contents. Common basalts and basaltic andesites in the series are primitive, with average Mg# values of 0·67 (±0·02, n = 99, 1SD), and have Sr concentrations (423 ± 29 ppm, n = 99) and La/Yb ratios (4·5 ± 0·4, n = 29) that are typical of island arc basaltic lavas. A smaller group of basaltic samples is more evolved and geochemically more enriched, with higher and more variable Sr and La/Yb (average Mg# = 0·61 ± 0·1, n = 31; Sr = 882 ± 333 ppm, n = 31; La/Yb = 9·1 ± 0·9, n = 16). None of the geochemically enriched basalts or basaltic andesites has low Y (〈15 ppm) or Yb (〈1·5 ppm), so none show the influence of residual or cumulate garnet. In contrast, most western seafloor andesites, dacites and rhyodacites have higher Sr (〉1000 ppm) and are adakitic, with strongly fractionated trace element patterns (Sr/Y = 50–350, La/Yb = 8–35, Dy/Yb = 2·0–3·5) with low relative abundances of Nb and Ta (La/Ta 〉 100), consistent with an enhanced role for residual or cumulate garnet + rutile. All western seafloor lavas have uniformly radiogenic Hf and Nd isotopes, with Nd = 9·1 ± 0·3 ( n = 31) and Hf = 14·5 ± 0·6 ( n = 27). Lead isotopes are variable and decrease with increasing SiO 2 from basalts with 206 Pb/ 204 Pb = 18·51 ± 0·05 ( n = 11) to dacites and rhyodacites with 206 Pb/ 204 Pb = 18·43 ± 0·04 ( n = 18). Western seafloor lavas form a steep trend in 207 Pb/ 204 Pb– 206 Pb/ 204 Pb space, and are collinear with lavas from emergent Aleutian volcanoes, which mostly have 206 Pb/ 204 Pb 〉 18·6 and 207 Pb/ 204 Pb 〉 15·52. High MgO and Mg# relative to silica, flat to decreasing abundances of incompatible elements, and decreasing Pb isotope ratios with increasing SiO 2 rule out an origin for the dacites and rhyodacites by fractional crystallization. The physical setting of some samples (erupted through Bering Sea oceanic lithosphere) rules out an origin for their garnet + rutile trace element signature by melting in the deep crust. Adakitic trace element patterns in the dacites and rhyodacites are therefore interpreted as the product of melting of mid-ocean ridge basalt (MORB) eclogite in the subducting oceanic crust. Western seafloor andesites, dacites and rhyodacites define a geochemical end-member that is isotopically like MORB, with strongly fractionated Ta/Hf, Ta/Nd, Ce/Pb, Yb/Nd and Sr/Y. This eclogite component appears to be present in lavas throughout the arc. Mass-balance modeling indicates that it may contribute 36–50% of the light rare earth elements and 18% of the Hf that is present in Aleutian volcanic rocks. Close juxtaposition of high-Mg# basalt, andesite and dacite implies widely variable temperatures in the western Aleutian mantle wedge. A conceptual model explaining this shows interaction of hydrous eclogite melts with mantle peridotite to produce buoyant diapirs of pyroxenite and pyroxenite melt. These diapirs reach the base of the crust and feed surface volcanism in the western Aleutians, but are diluted by extensive melting in a hotter mantle wedge in the eastern part of the arc.

Description: Background HIV infection is associated with increased risk of cardiovascular disease (CVD) in men. Whether HIV is an independent risk factor for CVD in women has not yet been established. Methods and Results We analyzed data from the Veterans Aging Cohort Study on 2187 women (32% HIV infected [HIV + ]) who were free of CVD at baseline. Participants were followed from their first clinical encounter on or after April 01, 2003 until a CVD event, death, or the last follow-up date (December 31, 2009). The primary outcome was CVD (acute myocardial infarction [AMI], unstable angina, ischemic stroke, and heart failure). CVD events were defined using clinical data, International Classification of Diseases, Ninth Revision, Clinical Modification codes, and/or death certificate data. We used Cox proportional hazards models to assess the association between HIV and incident CVD, adjusting for age, race/ethnicity, lipids, smoking, blood pressure, diabetes, renal disease, obesity, hepatitis C, and substance use/abuse. Median follow-up time was 6.0 years. Mean age at baseline of HIV + and HIV uninfected (HIV – ) women was 44.0 versus 43.2 years ( P 〈0.05). Median time to CVD event was 3.1 versus 3.7 years ( P =0.11). There were 86 incident CVD events (53%, HIV + ): AMI, 13%; unstable angina, 8%; ischemic stroke, 22%; and heart failure, 57%. Incident CVD/1000 person-years was significantly higher among HIV + (13.5; 95% confidence interval [CI]=10.1, 18.1) than HIV – women (5.3; 95% CI=3.9, 7.3; P 〈0.001). HIV + women had an increased risk of CVD, compared to HIV – (hazard ratio=2.8; 95% CI=1.7, 4.6; P 〈0.001). Conclusions HIV is associated with an increased risk of CVD in women.

Description: Article The organic geochemical biomarker IP 25 has been widely applied in the reconstruction of Arctic sea ice, yet its source remains undetermined. Here, the authors report the identification of IP 25 in common pan-Arctic sea ice diatoms, thus establishing its applicability as a palaeo Arctic sea ice proxy. Nature Communications doi: 10.1038/ncomms5197 Authors: T. A. Brown, S. T. Belt, A. Tatarek, C. J. Mundy

Description: Fetal nicotine exposure causes impaired adrenal catecholamine secretion and increased neonatal mortality during acute hypoxic challenges. Both effects are attributable to upregulation of ATP-sensitive K + channels (K ATP channels) and can be rescued by pretreatment with the blocker, glibenclamide. Although use of in vitro models of primary and immortalized, fetal-derived rat adrenomedullary chromaffin cells (i.e., MAH cells) demonstrated the involvement of α7 nicotinic ACh receptor (nAChR) stimulation and the transcription factor, HIF-2α, the latter's role was unclear. Using Western blots, we show that chronic nicotine causes a progressive, time-dependent induction of HIF-2α in MAH cells that parallels the upregulation of K ATP channel subunit, Kir6.2. Moreover, a common HIF target, VEGF mRNA, was also upregulated after chronic nicotine. All the above effects were prevented during co-incubation with α-bungarotoxin (100 nM), a specific α7 nAChR blocker, and were absent in HIF-2α-deficient MAH cells. Chromatin immunoprecipitation (ChIP) assays demonstrated binding of HIF-2α to a putative hypoxia response element in Kir6.2 gene promoter. Specificity of this signaling pathway was validated in adrenal glands from pups born to dams exposed to nicotine throughout gestation; the upregulation of both HIF-2α and Kir6.2 was confined to medullary, but not cortical, tissue. This study has uncovered a signaling pathway whereby a nonhypoxic stimulus (nicotine) promotes HIF-2α-mediated transcriptional upregulation of a novel target, Kir6.2 subunit. The data suggest that the HIF pathway may be involved in K ATP channel-mediated neuroprotection during brain ischemia, and in the effects of chronic nicotine on ubiquitous brain α7 nAChR.

Description: End-Permian (ca. 252 Ma) carbon isotope, paleobiological, and sedimentary data suggest that changes in ocean carbonate chemistry were directly linked to the mass extinction of marine organisms. Calcium isotopes provide a geochemical means to constrain the nature of these changes. The 44/40 Ca of carbonate rocks from southern China exhibits a negative excursion across the end-Permian extinction horizon, consistent with either a negative shift in the 44/40 Ca of seawater or a change in the calcite/aragonite ratio of carbonate sediments at the time of deposition. To test between these possibilities, we measured the 44/40 Ca of hydroxyapatite conodont microfossils from the global stratotype section and point (GSSP) for the Permian-Triassic boundary at Meishan, China. The conodont 44/40 Ca record shows a negative excursion similar in stratigraphic position and magnitude to that previously observed in carbonate rocks. Parallel negative excursions in the 44/40 Ca of carbonate rocks and conodont microfossils cannot be accounted for by a change in carbonate mineralogy, but are consistent with a negative shift in the 44/40 Ca of seawater. Such a shift is best accounted for by an episode of ocean acidification, pointing toward strong similarities between the greatest catastrophe in the history of animal life and anticipated global change during the twenty-first century.