Dating prograde fluid pulses during subduction by in situ U–Pb and oxygen isotope analysis

Keywords High-pressure fluids · Whiteschists · U–Pb dating · Oxygen isotopes · Ion microprobe · Metasomatism Introduction The subduction of crustal material to mantle depths and its chemical modification during burial and exhumation contribute to element recycling in the mantle and the formation of new crust through arc magmatism. Crustal rocks that Abstract The Dora-Maira whiteschists derive from metasomatically altered granites that experienced ultrahighpressure metamorphism at ~750 °C and 40 kbar during the Alpine orogeny. In order to investigate the P–T–time– fluid evolution of the whiteschists, we obtained U–Pb ages from zircon and monazite and combined those with trace element composition and oxygen isotopes of the accessory minerals and coexisting garnet. Zircon cores are the only remnants of the granitic protolith and still preserve a Permian age, magmatic trace element compositions and δ18O of ~10 ‰. Thermodynamic modelling of Si-rich and Si-poor whiteschist compositions shows that there are two main fluid pulses during prograde subduction between 20 and 40 kbar. In Si-poor samples, the breakdown of chlorite to garnet + fluid occurs at ~22 kbar. A first zircon rim directly overgrowing the cores has inclusions of prograde phlogopite and HREE-enriched patterns indicating zircon growth at the onset of garnet formation. A second main fluid pulse is documented close to peak metamorphic conditions in both Si-rich and Si-poor whiteschist when talc + kyanite react to garnet + coesite + fluid. A second metamorphic overgrowth on zircon with HREE depletion was observed in the Si-poor whiteschists, whereas a single metamorphic overgrowth capturing phengite and talc inclusions was observed in the Si-rich whiteschists. Garnet rims, zircon rims and monazite are in chemical and isotopic equilibrium for oxygen, demonstrating that they all formed at peak metamorphism at 35 Ma as constrained by the age of monazite (34.7 ± 0.4 Ma) and zircon rims (35.1 ± 0.8 Ma). The prograde zircon rim in Si-poor whiteschists has an age that is within error indistinguishable from the age of peak metamorphic conditions, consistent with a minimum rate of subduction of 2 cm/year for the Dora-Maira unit. Oxygen isotope values for zircon rims, monazite and garnet are equal within error at 6.4 ± 0.4 ‰, which is in line with closed-system equilibrium fractionation during prograde to peak temperatures. The resulting equilibrium Δ18Ozircon-monazite at 700 ± 20 °C is 0.1 ± 0.7 ‰. The in situ oxygen isotope data argue against an externally derived input of fluids into the whiteschists. Instead, fluidassisted zircon and monazite recrystallisation can be linked to internal dehydration reactions during prograde subduction. We propose that the major metasomatic event affecting the granite protolith was related to hydrothermal seafloor alteration post-dating Jurassic rifting, well before the onset of Alpine subduction.

Localized Upregulation of a New Expansin Gene Predicts the Site of Leaf Formation in the Tomato Meristem

Expansins are extracellular proteins that increase plant cell wall extensibility in vitro and are thought to be involved in cell expansion. We showed in a previous study that administration of an exogenous expansin protein can trigger the initiation of leaflike structures on the shoot apical meristem of tomato. Here, we studied the expression patterns of two tomato expansin genes, LeExp2 and LeExp18. LeExp2 is preferentially expressed in expanding tissues, whereas LeExp18 is expressed preferentially in tissues with meristematic activity. In situ hybridization experiments showed that LeExp18 expression is elevated in a group of cells, called I1, which is the site of incipient leaf primordium initiation. Thus, LeExp18 expression is a molecular marker for leaf initiation, predicting the site of primordium formation at a time before histological changes can be detected. We propose a model for the regulation of phyllotaxis that postulates a crucial role for expansin in leaf primordium initiation.

High-Frequency in Situ Optical Measurements During a Storm Event: Assessing Relationships Between Dissolved Organic Matter, Sediment Concentrations, and Hydrologic Processes

Dissolved organic matter (DOM) dynamics during storm events has received considerable attention in forested watersheds, but the extent to which storms impart rapid changes in DOM concentration and composition in highly disturbed agricultural watersheds remains poorly understood. In this study, we used identical in situ optical sensors for DOM fluorescence (FDOM) with and without filtration to continuously evaluate surface water DOM dynamics in a 415 km(2) agricultural watershed over a 4 week period containing a short-duration rainfall event. Peak turbidity preceded peak discharge by 4 h and increased by over 2 orders of magnitude, while the peak filtered FDOM lagged behind peak turbidity by 15 h. FDOM values reported using the filtered in situ fluorometer increased nearly fourfold and were highly correlated with dissolved organic carbon (DOC) concentrations (r(2) = 0.97), providing a highly resolved proxy for DOC throughout the study period. Discrete optical properties including specific UV absorbance (SUVA(254)), spectral slope (S(290-350)), and fluorescence index (FI) were also strongly correlated with in situ FDOM and indicate a shift toward aromatic, high molecular weight DOM from terrestrially derived sources during the storm. The lag of the peak in FDOM behind peak discharge presumably reflects the draining of watershed soils from natural and agricultural landscapes. Field and experimental evidence showed that unfiltered FDOM measurements underestimated filtered FDOM concentrations by up to similar to 60% at particle concentrations typical of many riverine systems during hydrologic events. Together, laboratory and in situ data provide insights into the timing and magnitude of changes in DOM quantity and quality during storm events in an agricultural watershed, and indicate the need for sample filtration in systems with moderate to high suspended sediment loads.

Estimates of in situ Larval Development Time for the Lobster, Homarus Americanus

Larval development time is a critical factor in assessing the potential for larval transport, mortality. and subsequently, the connectivity of marine populations through larval exchange. Most estimates of larval duration are based on laboratory studies and may not reflect development times in nature. For larvae of the American lobster (Homarus americanus), temperature-dependent development times have been established in previous laboratory studies. Here, we used the timing of seasonal abundance curves for newly hatched larvae (stage 1) and the final plankonic instar (postlarva), coupled with a model of temperature-dependent development to assess development time in the field. We were unable to reproduce the timing of the seasonal abundance curves using laboratory development rates in our model. Our results suggest that larval development in situ may be twice as fast as reported laboratory rates. This will result in reduced estimates of larval transport potential, and increased estimates of instantaneous mortality rate and production.

Proliferation index in ductal carcinoma in situ of the breast: Relation to estrogen, progesterone and HER2/neu receptors

Background. Ductal carcinoma in situ (DCIS) is the most prevalent precursor to invasive breast cancer (IBC), the second leading cause of death in women in the United States. The three most important prognostic markers for IBC are Estrogen receptor (ER), Progesterone receptor (PR) and HER2/neu. The four groups (IBC) defined as (1) ER and/or PR positive and HER2/neu negative, (2) ER and/or PR positive and HER2/neu positive (3) ER and/or PR negative and HER2/neu positive and (4) negative for all three of these receptors (Triple negative). However, they have not been well studied in DCIS. This is an exploratory study with a primary objective to examine the prevalence of ER, PR, and HER2/neu in DCIS, to explore if the defined groups of IBC occur in DCIS and to consider the biological relationship between these four groups and the proliferative activity of the tumor. A secondary goal of this study is to examine the relationship between grade and proliferative activity. Methods. Using immunohistochemistry, I have measured Ki-67, ER, PR and HER2/neu positivity for a series of cases of DCIS. Results. 20 ER and/or PR positive and HER2/neu negative (50%) with average PI of 0.05, 7 ER and/or PR positive and HER2/neu positive (17.5%) with average PI of 0.14, 10 ER and/or PR negative and HER2/neu positive (25%) with average PI of 0.18, and three triple negative (7.5%) with average PI of 0.18. ER and/or PR positive and HER2/neu positive group has the highest PI (p<0.001). Further, the ER and/or PR positive and HER2/neu positive group show a linear relationship between PI and average ER/PR positivity (R=0.6). PI increases with higher grades. Conclusion. PI appears to depend upon the average fraction of positive ER/PR tumor cells, possibly with a synergistic dependence when HER2/neu is positive. If ER/PR is negative, then both HER2/neu positive and the triple negative cases appear to cluster around an average PI that is higher than the average PI in HER2/neu negative ER/PR positive negative cases. In the triple negative tumors there must be another driver of proliferation.^

Intercellular adhesion and membrane polarity in rat hepatocytes: Localization of cell -CAM 105 and other domain-specific membrane proteins {\it in situ\/} and {\it in vitro\/} by electron microscopy

Cell-CAM 105 has been identified as a cell adhesion molecule (CAM) based on the ability of monospecific and monovalent anti-cell-CAM 105 antibodies to inhibit the reaggregation of rat hepatocytes. Although one would expect to find CAMs concentrated in the lateral membrane domain where adhesive interactions predominate, immunofluorescence analysis of rat liver frozen sections revealed that cell-CAM 105 was present exclusively in the bile canalicular (BC) domain of the hepatocyte. To more precisely define the in situ localization of cell-CAM 105, immunoperoxidase and electron microscopy were used to analyze intact and mechanically dissociated fixed liver tissue. Results indicate that although cell-CAM 105 is apparently restricted to the BC domain in situ, it can be detected in the pericanalicular region of the lateral membranes when accessibility to lateral membranes is provided by mechanical dissociation. In contrast, when hepatocytes were labeled following incubation in vitro under conditions used during adhesion assays, cell-CAM 105 had redistributed to all areas of the plasma membrane. Immunofluorescence analysis of primary hepatocyte cultures revealed that cell-CAM 105 and two other BC proteins were localized in discrete domains reminscent of BC while cell-CAM 105 was also present in regions of intercellular contact. These results indicate that the distribution of cell-CAM 105 under the experimental conditions used for cell adhesion assays differs from that in situ and raises the possibility that its adhesive function may be modulated by its cell surface distribution. The implications of these and other findings are discussed with regard to a model for BC formation.^ Analysis of molecular events involved in BC formation would be accelerated if an in vitro model system were available. Although BC formation in culture has previously been observed, repolarization of cell-CAM 105 and two other domain-specific membrane proteins was incomplete. Since DMSO had been used by Isom et al. to maintain liver-specific gene expression in vitro, the effect of this differentiation system on the polarity of these membrane proteins was examined. Based on findings presented here, DMSO apparently prolongs the expression and facilitates polarization of hepatocyte membrane proteins in vitro. ^

In-situ Iron isotope measurements and mineral compositions from ODP Hole 206-1256D and IODP Hole 335-U1256D

In-situ Fe isotope measurements have been carried out to estimate the impact of the hydrothermal metamorphic overprint on the Fe isotopic composition of Fe-Ti-oxides and Fe-sulfides of the different lithologies of the drilled rocks from IODP Hole 1256D (eastern equatorial Pacific; 15 Ma crust formed at the East Pacific Rise). Most igneous rocks normally have a very restricted range in their 56Fe/54Fe ratio. In contrast, Fe isotope compositions of hot fluids (> 300 °C) from mid-ocean-ridge spreading centers define a narrow range that is shifted to lower delta 56Fe values by 0.2 per mil - 0.5 per mil as compared to igneous rocks. Therefore, it is expected that mineral phases that contain large amounts of Fe are especially affected by the interaction with a fluid that fractionates Fe isotopes during exsolution/precipitation of those minerals. We have used a femtosecond UV-Laser ablation system to determine mineral 56Fe/54Fe ratios of selected samples with a precision of < 0.1 per mil (2 sigma level) at micrometer-scale. We have found significant variations of the delta 56Fe (IRMM-014) values in the minerals between different samples as well as within samples and mineral grains. The overall observed scale of delta 56Fe (magnetite) in 1256D rocks ranges from - 0.12 to + 0.64 per mil, and of delta 56Fe (ilmenite) from - 0.77 to + 0.01 per mil. Pyrite in the lowermost sheeted dike section is clearly distinguishable from the other investigated lithological units, having positive delta 56Fe values between + 0.29 and + 0.56 per mil, whereas pyrite in the other samples has generally negative delta 56Fe values from - 1.10 to - 0.59 permil. One key observation is that the temperature dependent inter-mineral fractionations of Fe isotopes between magnetite and ilmenite are systematically shifted towards higher values when compared to theoretically expected values, while synthesized, well equilibrated magnetite-ilmenite pairs are compatible with the theoretical predictions. Theoretical considerations including beta-factors of different aqueous Fe-chlorides and Rayleigh-type fractionations in the presence of a hydrous, chlorine-bearing fluid can explain this observation. The disagreement between observed and theoretical equilibrium fractionation, the fact that magnetite, in contrast to ilmenite shows a slight downhole trend in the delta 56Fe values, and the observation of small scale heterogeneities within single mineral grains imply that a general re-equilibration of the magnetite-ilmenite pairs is overprinted by kinetic fractionation effects, caused by the interaction of magnetite/ilmenite with hydrothermal fluids penetrating the upper oceanic crust during cooling, or incomplete re-equilibration at low temperatures. Furthermore, the observation of significant small-scale variations in the 56Fe/54Fe ratios of single minerals in this study highlights the importance of high spatial-resolution-analyses of stable isotope ratios for further investigations.

Seaweed - epiphyte - mesograzer communities were tested for their responses to elevated seawater temperature and [CO2] in benthic mesocosms experiments across four consecutive seasons of one year in Kiel, Germany

Rising seawater temperature and CO2 concentrations (ocean acidification) represent two of the most influential factors impacting marine ecosystems in the face of global climate change. In ecological climate change research full-factorial experiments across seasons in multi-species, cross-trophic level set-ups are essential as they allow making realistic estimations about direct and indirect effects and the relative importance of both major environmental stressors on ecosystems. In benthic mesocosm experiments we tested the responses of coastal Baltic Sea Fucus vesiculosus communities to elevated seawater temperature and CO2 concentrations across four seasons of one year. While increasing [CO2] levels only had minor effects, warming had strong and persistent effects on grazers which affected the Fucus community differently depending on season. In late summer a temperature-driven collapse of grazers caused a cascading effect from the consumers to the foundation species resulting in overgrowth of Fucus thalli by epiphytes. In fall/ winter, outside the growing season of epiphytes, intensified grazing under warming resulted in a significant reduction of Fucus biomass. Thus, we confirm the prediction that future increasing water temperatures influence marine food-web processes by altering top-down control, but we also show that specific consequences for food-web structure depend on season. Since Fucus vesiculosus is the dominant habitat-forming brown algal system in the Baltic Sea, its potential decline under global warming implicates the loss of key functions and services such as provision of nutrient storage, substrate, food, shelter and nursery grounds for a diverse community of marine invertebrates and fish in Baltic Sea coastal waters.