Anthropogenic Forcing of the Baltic Sea Thallium Cycle.

Anthropogenic activities have fundamentally changed the chemistry of the Baltic Sea. According to results reported in this study, not even the thallium (Tl) isotope cycle is immune to these activities. In the anoxic and sulfidic ("euxinic") East Gotland Basin today, Tl and its two stable isotopes are cycled between waters and sediments as predicted based on studies of other redox-stratified basins (e.g., the Black Sea and Cariaco Trench). The Baltic seawater Tl isotope composition (ε205Tl) is, however, higher than predicted based on the results of conservative mixing calculations. Data from a short sediment core from East Gotland Basin demonstrates that this high seawater ε205Tl value originated sometime between about 1940 and 1947 CE, around the same time other prominent anthropogenic signatures begin to appear in the same core. This juxtaposition is unlikely to be coincidental and suggests that human activities in the surrounding area have altered the seawater Tl isotope mass-balance of the Baltic Sea.

Sources of dehydration fluids underneath the Kamchatka arc.

Fluids mediate the transport of subducted slab material and play a crucial role in the generation of arc magmas. However, the source of subduction-derived fluids remains debated. The Kamchatka arc is an ideal subduction zone to identify the source of fluids because the arc magmas are comparably mafic, their source appears to be essentially free of subducted sediment-derived components, and subducted Hawaii-Emperor Seamount Chain (HESC) is thought to contribute a substantial fluid flux to the Kamchatka magmas. Here we show that Tl isotope ratios are unique tracers of HESC contribution to Kamchatka arc magma sources. In conjunction with trace element ratios and literature data, we trace the progressive dehydration and melting of subducted HESC across the Kamchatka arc. In succession, serpentine (<100 km depth), lawsonite (100-250 km depth) and phengite (>250 km depth) break down and produce fluids that contribute to arc magmatism at the Eastern Volcanic Front (EVF), Central Kamchatka Depression (CKD), and Sredinny Ridge (SR), respectively. However, given the Tl-poor nature of serpentine and lawsonite fluids, simultaneous melting of subducted HESC is required to explain the HESC-like Tl isotope signatures observed in EVF and CKD lavas. In the absence of eclogitic crust melting processes in this region of the Kamchatka arc, we propose that progressive dehydration and melting of a HESC-dominated mélange offers the most compelling interpretation of the combined isotope and trace element data.

Publisher Correction: Glacial-interglacial Nd isotope variability of North Atlantic Deep Water modulated by North American ice sheet.

An amendment to this paper has been published and can be accessed via a link at the top of the paper.

Glacial-interglacial Nd isotope variability of North Atlantic Deep Water modulated by North American ice sheet.

The Nd isotope composition of seawater has been used to reconstruct past changes in the contribution of different water masses to the deep ocean. In the absence of contrary information, the Nd isotope compositions of endmember water masses are usually assumed constant during the Quaternary. Here we show that the Nd isotope composition of North Atlantic Deep Water (NADW), a major component of the global overturning ocean circulation, was significantly more radiogenic than modern during the Last Glacial Maximum (LGM), and shifted towards modern values during the deglaciation. We propose that weathering contributions of unradiogenic Nd modulated by the North American Ice Sheet dominated the evolution of the NADW Nd isotope endmember. If water mass mixing dominated the distribution of deep glacial Atlantic Nd isotopes, our results would imply a larger fraction of NADW in the deep Atlantic during the LGM and deglaciation than reconstructed with a constant northern endmember.

Barium isotope evidence for pervasive sediment recycling in the upper mantle.

The upper mantle, as sampled by mid-ocean ridge basalts (MORBs), exhibits significant chemical variability unrelated to mechanisms of melt extraction at ridges. We show that barium isotope variations in global MORBs vary systematically with radiogenic isotopes and trace element ratios, which reflects mixing between depleted and enriched MORB melts. In addition, modern sediments and enriched MORBs share similar Ba isotope signatures. Using modeling, we show that addition of ~0.1% by weight of sediment components into the depleted mantle in subduction zones must impart a sedimentary Ba signature to the overlying mantle and induce low-degree melting that produces the enriched MORB reservoir. Subsequently, these enriched domains convect toward mid-ocean ridges and produce radiogenic isotope variation typical of enriched MORBs. This mechanism can explain the chemical and isotopic features of enriched MORBs and provide strong evidence for pervasive sediment recycling in the upper mantle.

Testosterone administration inhibits hepcidin transcription and is associated with increased iron incorporation into red blood cells.

Testosterone administration increases hemoglobin levels and has been used to treat anemia of chronic disease. Erythrocytosis is the most frequent adverse event associated with testosterone therapy of hypogonadal men, especially older men. However, the mechanisms by which testosterone increases hemoglobin remain unknown. Testosterone administration in male and female mice was associated with a greater increase in hemoglobin and hematocrit, reticulocyte count, reticulocyte hemoglobin concentration, and serum iron and transferrin saturation than placebo. Testosterone downregulated hepatic hepcidin mRNA expression, upregulated renal erythropoietin mRNA expression, and increased erythropoietin levels. Testosterone-induced suppression of hepcidin expression was independent of its effects on erythropoietin or hypoxia-sensing mechanisms. Transgenic mice with liver-specific constitutive hepcidin over-expression failed to exhibit the expected increase in hemoglobin in response to testosterone administration. Testosterone upregulated splenic ferroportin expression and reduced iron retention in spleen. After intravenous administration of transferrin-bound (58) Fe, the amount of (58) Fe incorporated into red blood cells was significantly greater in testosterone-treated mice than in placebo-treated mice. Serum from testosterone-treated mice stimulated hemoglobin synthesis in K562 erythroleukemia cells more than that from vehicle-treated mice. Testosterone administration promoted the association of androgen receptor (AR) with Smad1 and Smad4 to reduce their binding to bone morphogenetic protein (BMP)-response elements in hepcidin promoter in the liver. Ectopic expression of AR in hepatocytes suppressed hepcidin transcription; this effect was blocked dose-dependently by AR antagonist flutamide. Testosterone did not affect hepcidin mRNA stability. In conclusion, testosterone inhibits hepcidin transcription through its interaction with BMP/Smad signaling. Testosterone administration is associated with increased iron incorporation into red blood cells.

Lead isotopes in marine surface sediments reveal historical use of leaded fuel.

Analyses of lead (Pb) isotopes have been performed in terrestrial and fresh water environments to estimate historical uses of leaded fuel, but so far this method has not been employed in studies of world-wide marine surface sediments. We analyzed Pb and its isotopes in 23 surface sediments from four continents collected during the Galathea 3 expedition in 2006-2007. To enhance the anthropogenic signal, a partial digestion using nitric acid was performed. The concentrations of Pb, Th, U and Al were determined with an ICP-Quadrupole MS, and Pb-isotope ratios with an ICP-multi-collector MS. The samples could be divided into three groups: Harbor areas in larger cities with concentrations of 150 to 265 mg kg(-1) dry weight, smaller towns with concentrations between 20 and 40 mg kg(-1) dry weight, and remotely located sites with concentrations below 15 mg kg(-1) dry weight. Pb-isotope ratios were compared to literature values for gasoline and local or geological background values, and the contribution of leaded-gasoline to total concentrations was calculated for contaminated sites using both a one-dimensional and a novel two-dimensional (vector) method. The North American sites had Pb-isotope ratios corresponding to the US leaded gasoline, with 24-88% of the Pb from leaded gasoline. Samples from Oceania showed Pb-isotope ratios corresponding to Australian gasoline, with 60% attributed to leaded gasoline in Sydney and 21% in Christchurch. Outside Cape Town, 15 to 46% of Pb in sediments was from leaded gasoline.

Evidence for the survival of the oldest terrestrial mantle reservoir.

Helium is a powerful tracer of primitive material in Earth's mantle. Extremely high (3)He/(4)He ratios in some ocean-island basalts suggest the presence of relatively undegassed and undifferentiated material preserved in Earth's mantle. However, terrestrial lavas with high (3)He/(4)He ratios have never been observed to host the primitive lead-isotopic compositions that are required for an early (roughly 4.5 Gyr ago) formation age. Here we show that Cenozoic-era Baffin Island and West Greenland lavas, previously found to host the highest terrestrial-mantle (3)He/(4)He ratios, exhibit primitive lead-isotope ratios that are consistent with an ancient mantle source age of 4.55-4.45 Gyr. The Baffin Island and West Greenland lavas also exhibit (143)Nd/(144)Nd ratios similar to values recently proposed for an early-formed (roughly 4.5 Gyr ago) terrestrial mantle reservoir. The combined helium-, lead- and Nd-isotopic compositions in Baffin Island and West Greenland lavas therefore suggest that their source is the most ancient accessible reservoir in the Earth's mantle, and it may be parental to all mantle reservoirs that give rise to modern volcanism.

The return of subducted continental crust in Samoan lavas.

Substantial quantities of terrigenous sediments are known to enter the mantle at subduction zones, but little is known about their fate in the mantle. Subducted sediment may be entrained in buoyantly upwelling plumes and returned to the Earth's surface at hotspots, but the proportion of recycled sediment in the mantle is small, and clear examples of recycled sediment in hotspot lavas are rare. Here we report remarkably enriched 87Sr/86Sr and 143Nd/144Nd isotope signatures in Samoan lavas from three dredge locations on the underwater flanks of Savai'i island, Western Samoa. The submarine Savai'i lavas represent the most extreme 87Sr/86Sr isotope compositions reported for ocean island basalts to date. The data are consistent with the presence of a recycled sediment component (with a composition similar to the upper continental crust) in the Samoan mantle. Trace-element data show affinities similar to those of the upper continental crust--including exceptionally low Ce/Pb and Nb/U ratios--that complement the enriched 87Sr/86Sr and 143Nd/144Nd isotope signatures. The geochemical evidence from these Samoan lavas significantly redefines the composition of the EM2 (enriched mantle 2; ref. 9) mantle endmember, and points to the presence of an ancient recycled upper continental crust component in the Samoan mantle plume.

Reorganization of the western Himalayan river system after five million years ago.

Uplift of mountains driven by tectonic forces can influence regional climate as well as regional drainage patterns, which in turn control the discharge of eroded sediment to the ocean. But the nature of the interactions between tectonic forces, climate and drainage evolution remains contested. Here we reconstruct the erosional discharge from the Indus river over the past 30 million years using seismic reflection data obtained from drill core samples from the Arabian Sea and neodymium isotope data. We find that the source of the Indus sediments was dominated by erosion within and north of the Indus suture zone until five million years ago; after that, the river began to receive more erosional products from Himalayan sources. We propose that this change in the erosional pattern is caused by a rerouting of the major rivers of the Punjab into the Indus, which flowed east into the Ganges river before that time. Seismic reflection profiles from the Indus fan suggest high mass accumulation rates during the Pleistocene epoch partly driven by increased drainage to the Indus river after five million years ago and partly by faster erosion linked to a stronger monsoon over the past four million years. Our isotope stratigraphy for the Indus fan provides strong evidence for a significant change in the geometry of western Himalayan river systems in the recent geologic past.