Planetary and Space science
Planetary and Space science
Kupriyanova E.K.,College Street |
Vinn O.,University of Tartu |
Taylor P.D.,Natural History Museum in London |
Schopf J.W.,Planetary and Space science |
And 8 more authors.
Deep-Sea Research Part I: Oceanographic Research Papers | Year: 2014
Although the carbonate compensation depth (CCD) for calcite, generally located in the depth range 4000-5000m, is often proposed as a physiological barrier to deep-ocean colonization, many organisms with calcareous exoskeletons are found in the deepest oceanic trenches. Serpulid polychaetes inhabiting unprotected calcareous tubes are unlikely deep-sea inhabitants, yet, they are found at all oceanic depths from intertidal to hadal. Here we review and revise the published and unpublished records of Serpulidae from below 5000m depth. We also describe tube ultrastructure and mineralogical content of available deep-sea serpulid tubes to obtain insights into their biomineralisation. Species belonging to the genera Bathyditrupa, Bathyvermilia, Hyalopomatus, Pileolaria (spirorbin) and Protis were found at depths from 5020 to 9735m. However, only specimens of Protis sp. were truly hadal (>6000m) being found at 6200-9700m. Hadal specimens of Protis have irregularly oriented prismatic tube microstructure similar to that found in more shallow-water representatives of the genus. Initial EDX analysis suggested a mostly calcitic composition (i.e., the most stable CaCO3 polymorph) on the basis of high Mg levels. Surprisingly, however, tubes of Bathyditrupa hovei and a species of Protis analysed using the more reliable method of laser Raman spectroscopy were found to be composed of aragonite. The compensation depth for this less stable CaCO3 polymorph in the oceans is usually 2000-3000m. We found no obvious structural adaptations to life at extreme depths in the studied serpulid tubes and how serpulids are able to biomineralise and maintain their tubes below the CCD remains to be explained. © 2014 .
Matteini L.,Imperial College London |
Horbury T.S.,Imperial College London |
Pantellini F.,University Paris Diderot |
Velli M.,Planetary and Space science |
Schwartz S.J.,Imperial College London
Astrophysical Journal | Year: 2015
We investigate the properties of plasma fluid motion in the large-amplitude, low-frequency fluctuations of highly Alfvénic fast solar wind. We show that protons locally conserve total kinetic energy when observed from an effective frame of reference comoving with the fluctuations. For typical properties of the fast wind, this frame can be reasonably identified by alpha particles which, due to their drift with respect to protons at about the Alfvén speed along the magnetic field, do not partake in the fluid low-frequency fluctuations. Using their velocity to transform the proton velocity into the frame of Alfvénic turbulence, we demonstrate that the resulting plasma motion is characterized by a constant absolute value of the velocity, zero electric fields, and aligned velocity and magnetic field vectors as expected for unidirectional Alfvénic fluctuations in equilibrium. We propose that this constraint, via the correlation between velocity and magnetic field in Alfvénic turbulence, is the origin of the observed constancy of the magnetic field; while the constant velocity corresponding to constant energy can only be observed in the frame of the fluctuations, the corresponding constant total magnetic field, invariant for Galilean transformations, remains the observational signature in the spacecraft frame of the constant total energy in the Alfvén turbulence frame. © 2015. The American Astronomical Society. All rights reserved..
Gabrielse C.,Planetary and Space science |
Angelopoulos V.,Planetary and Space science |
Runov A.,Planetary and Space science |
Turner D.L.,Planetary and Space science
Journal of Geophysical Research: Space Physics | Year: 2014
Energetic particle injections are critical for supplying particles and energy to the inner magnetosphere. Recent case studies have demonstrated a good correlation between injections and transient, narrow, fast flow channels as well as earthward reconnection (dipolarization) fronts in the magnetotail, but statistical observations beyond geosynchronous orbit (GEO) to verify the findings were lacking. By surveying trans-geosynchronous injections using Time History of Events and Macroscale Interactions during Substorms (THEMIS), we show that their likely origin is the earthward traveling, dipolarizing flux bundles following near-Earth reconnection. The good correlation between injections and fast flows, reconnection fronts and impulsive, dawn-dusk electric field increases is not limited to within 12 RE but extends out to 30 R E. Like near-Earth reconnection, both ion and electron injections are most probable in the premidnight sector. Similar to bursty bulk flows (BBFs), injection-time flow speeds are faster farther from Earth. With faster flows, injection intensity generally increases and extends to higher energy channels. With increased geomagnetic activity, injection occurrence rate increases (akin to that of BBFs) and spectral hardening occurs (κ decreases). The occurrence rate increase within the inner magnetosphere suggests that injections populate the radiation belts more effectively under enhanced activity. Our results are inconsistent with the classical concept of an azimuthally wide injection boundary moving earthward from ~9 to 12 RE to GEO under an enhanced cross-tail electric field. Rather, particle injection and transport occur along a large range of radial distances due to effects from earthward penetrating, azimuthally localized, transient, strong electric fields of recently reconnected, dipolarizing flux bundles. Key Points Injections are correlated to reconnection-related phenomena like fast flows Injection occurrence rates increase with geomagnetic activity Injection occurrence rate has dawn-dusk asymmetry preferring premidnight ©2014. American Geophysical Union. All Rights Reserved.
Young E.D.,Planetary and Space science |
Manning C.E.,Planetary and Space science |
Schauble E.A.,Planetary and Space science |
Shahar A.,Carnegie Institution of Washington |
And 3 more authors.
Chemical Geology | Year: 2015
High-temperature partitioning of the stable isotopes of rock-forming elements like Mg, Si, Fe, Ni and others are useful new tools in geochemistry and cosmochemistry. Understanding the fundamental driving forces for equilibrium inter-mineral fractionation comes from basic crystal chemistry and is invaluable for interpreting data from natural systems. Both charge and coordination number are key factors affecting bond length and bond stiffness and therefore the relative proclivity of a mineral phase for concentrating heavy or light isotopes. Quantitative interpretation of the plethora of new data relies on refinements of equilibrium fractionation factors through a feedback between crystal chemical reasoning, ab initio predictions, experiments, and analyses of well-characterized natural samples. This multifaceted approach is leading to a rapid rate of discovery using non-traditional stable isotopes in high temperature systems. For example, open-system mass transfer in the mantle is becoming increasingly evident from departures from equilibrium Mg and Fe isotope ratio partitioning between minerals, and differences in isotope ratios between bulk silicate Earth and meteorites are elucidating the conditions for Earth's core formation quantitatively. These applications rely critically on accurate equilibrium fractionation factors. © 2014 Elsevier B.V.
Davis P.M.,Planetary and Space science
Journal of Volcanology and Geothermal Research | Year: 2015
Self-potential (SP) and VLF measurements were made in 1973, 1975, 1995, 1997 and 2012 across a basaltic dike that intruded into the Koae fault zone of Kilauea volcano, Hawaii in May 1973. The SP anomaly remained strong throughout. In 2012 it was at about 60% of the strength it had in 1973. In contrast, the VLF anomaly, though diminished, was still observable in 1995/1997, but by 2012 it had disappeared. A hydrothermal dike model, with parameters calibrated by modeling the solidification of Kilauea Iki lava lake, is used to calculate temperatures and conductivity variation. Following Jaeger's (1957) method, we find that the time in years for a dike of width W (m) to solidify is 0.0075W2. Thus, a 1m dike solidifies within the first few days, and after 39years is only tens of degrees above ambient. Given the orders of magnitude difference between the conductivities of wet and dry basalt, we infer, that after solidification, the VLF anomalies were caused by induction in a localized veil of wet, hot basalt enveloping the dike, that was generated initially by condensation of steam, and subsequently by condensation of evaporated water as temperatures reduced. The conductivity anomaly persisted until the mid-nineties. By 2012, temperatures and condensation were too small for a VLF signal. The persistent SP anomaly is attributed to localized fluid disruption, with evaporation mainly at the water table and in the vadose zone. Streaming potentials are associated with evaporative circulation in the vadose zone. Next to the dike a positive potential is generated by upward flow of moisture-laden air, with a smaller negative potential on its flanks from downward infiltrating rainwater. The analysis indicates that the combination of SP and VLF measurements can characterize the evolving geothermal regime of intrusions above the water table. © 2015 Elsevier B.V.