From serpentinization to carbonation : new insights from a CO2 injection experiment

Author Posting. © The Author(s), 2013. This is the author's version of the work. It is posted here by permission of Elsevier for personal use, not for redistribution. The definitive version was published in Earth and Planetary Science Letters 379 (2013): 137-145, doi:10.1016/j.epsl.2013.08.017.We injected a CO2-rich hydrous fluid of seawater chlorinity into an ongoing, mildly reducing (H2(aq) ≈ 3 mmol/kg) serpentinization experiment at 230°C and 35 MPa to examine the changes in fluid chemistry and mineralogy during mineral carbonation. The chemistry of 11 fluid samples was measured, speciated, and compared with MgO-SiO2-H2O-CO2 (MSHC) phase equilibria to approximate the reaction pathway from serpentinization to carbonation. Although the overall system was in apparent disequilibrium, the speciated activities of dissolved silica (aSiO2(aq)) and carbon dioxide (aCO2(aq)) evolved roughly along MSHC equilibrium phase boundaries, indicative of 4 distinct mineral assemblages over time: 1) serpentine22 brucite (± magnesite) before the injection, to 2) serpentine-talc-magnesite 2 hours after the injection, to 3) quartz-magnesite (48h after injection), and 4) metastable olivine – magnesite (623h after injection) until the experiment was terminated. Inspection of the solid reaction products revealed the presence of serpentine, magnesite, minor talc, and magnetite, in addition to relict olivine. Although quartz was saturated over a short segment of the experiment, it was not found in the solid reaction products. A marked and rapid change in fluid chemistry suggests that serpentinization ceased and precipitation of magnesite initiated immediately after the injection. A sharp decrease in pH after the injection promoted the dissolution of brucite and olivine, which liberated SiO2(aq) and dissolved Mg. Dissolved Mg was efficiently removed from the solution via magnesite precipitation, whereas the formation of talc was relatively sluggish. This process accounts for an increase in aSiO2(aq) to quartz saturation shortly after the injection of the CO2-rich fluid. Molecular dihydrogen (H2(aq)) was generated during serpentinization of olivine by oxidation of ferrous iron before the injection; however, no additional H2(aq) was generated after the injection. Speciation calculations suggest a strong affinity for the formation of methane (CH4(aq)) at the expense of CO2(aq) and H2(aq) after the injection, but increased CH4(aq) formation was not observed. These findings suggest that kinetically fast mineral carbonation dominates over sluggish CH4(aq) formation in mildly reducing serpentinization systems affected by injection of CO2-rich fluids.This work was supported by an Ocean Ridge Initiative Research Award at WHOI (to FK) and NSF Marine Geology and Geophysics award OCE-0927744 (TMM)

A second anniversary operational review of the OmniTRACS(R): The first two-way mobile Ku-band satellite communications system

A novel two-way mobile satellite communications and vehicle position reporting system that is currently operational in the United States and Europe is described. The system characteristics and service operations are described in detail. Technical descriptions of the equipment and signal processing techniques are provided

Aftereffects of Saccades Explored in a Dynamic Neural Field Model of the Superior Colliculus

When viewing a scene or searching for a target, an observer usually makes a series of saccades that quickly shift the orientation of the eyes. The present study explored how one saccade affects subsequent saccades within a dynamic neural field model of the superior colliculus (SC). The SC contains an oculocentric motor map that encodes the vector of saccades and remaps to the new fixation location after each saccade. Our simulations demonstrated that the observation that saccades which reverse their vectors are slower to initiate than those which repeat vectors can be explained by the afore-mentioned remapping process and the internal dynamics of the SC. How this finding connects to the study of inhibition of return is discussed and suggestions for future studies are presented

High phenotypic plasticity at the dawn of the eosauropterygian radiation

The initial radiation of Eosauropterygia during the Triassic biotic recovery represents a key event in the dominance of reptiles secondarily adapted to marine environments. Recent studies on Mesozoic marine reptile disparity highlighted that eosauropterygians had their greatest morphological diversity during the Middle Triassic, with the co-occurrence of Pachypleurosauroidea, Nothosauroidea and Pistosauroidea, mostly along the margins of the Tethys Ocean. However, these previous studies quantitatively analysed the disparity of Eosauropterygia as a whole without focussing on Triassic taxa, thus limiting our understanding of their diversification and morphospace occupation during the Middle Triassic. Our multivariate morphometric analyses highlight a clearly distinct colonization of the ecomorphospace by the three clades, with no evidence of whole-body convergent evolution with the exception of the peculiar pistosauroid Wangosaurus brevirostris, which appears phenotypically much more similar to nothosauroids. This global pattern is mostly driven by craniodental differences and inferred feeding specializations. We also reveal noticeable regional differences among nothosauroids and pachypleurosauroids of which the latter likely experienced a remarkable diversification in the eastern Tethys during the Pelsonian. Our results demonstrate that the high phenotypic plasticity characterizing the evolution of the pelagic plesiosaurians was already present in their Triassic ancestors, casting eosauropterygians as particularly adaptable animals

Higher and Lower Order Factor Analyses of the Temperament in Middle Childhood Questionnaire.

The Temperament in Middle Childhood Questionnaire (TMCQ) is a widely used parent-report measure of temperament. However, neither its lower nor higher order structures has been tested via a bottom-up, empirically based approach. We conducted higher and lower order exploratory factor analyses (EFAs) of the TMCQ in a large ( N = 654) sample of 9-year-olds. Item-level EFAs identified 92 items as suitable (i.e., with loadings ≥.40) for constructing lower order factors, only half of which resembled a TMCQ scale posited by the measure\u27s authors. Higher order EFAs of the lower order factors showed that a three-factor structure (Impulsivity/Negative Affectivity, Negative Affectivity, and Openness/Assertiveness) was the only admissible solution. Overall, many TMCQ items did not load well onto a lower order factor. In addition, only three factors, which did not show a clear resemblance to Rothbart\u27s four-factor model of temperament in middle childhood, were needed to account for the higher order structure of the TMCQ