Evolution of fluid flow and carbonate recrystallization rates in deep-sea sediments of the Equatorial Pacific

Fluid flow and carbonate recrystallization rates of deep-sea sediments from eight locations in the Equatorial Eastern Pacific were determined by using δ44/40Ca values of pore water and corresponding sediments. The studied drill sites of IODP Exp. 320/321 are located along a transect of decreasing crustal age and reveal different characteristic pore water depth profiles. The younger sites show an overall isotopic equilibration with the sediment in the upper part of the sedimentary column. In the lower part, the δ44/40Ca of the pore water increases back to seawater-like values at the sediment/basalt interface, forming a bulge-shaped pore water profile. The magnitude of the δ44/40Ca pore water bulge decreases with increasing age of the oceanic crust and sediment cover, resulting in seawater-like δ44/40Ca values throughout the sedimentary column in the oldest Sites U1331 and U1332. These findings indicate a seawater-like fluid input from the underlying crust into the sediment. Thus, after sedimentation, carbonate recrystallization processes start to enrich the pore water in 40Ca, and after a time of carbonate recrystallization and cooling of oceanic crust, a flow of seawater-like fluid starts to move upwards through the sedimentary column, enriching the pore water with 44Ca. We established a carbonate recrystallization and fluid flow model to quantify these processes. Our determined carbonate recrystallization rates between 0.000013e(−t/15.5) and 0.00038e(−t/100.5) and fluid flow rates in the range of 0.42–19 m*Myr−1 indicate that the fluid flow within the investigated sites of IODP Exp. 320/321 depends on the sedimentary composition and location of the specific site, especially the proximity to a recharge or discharge site of a hydrothermal convection cell.

Two-Dimensional Structure of Flow Channels and Associated Upward Field-Aligned Currents: Model and Observations

Flow bursts are a major component of transport within the plasma sheet and auroral oval (where they are referred to as flow channels), and lead to a variety of geomagnetic disturbances as they approach the inner plasma sheet (equatorward portion of the auroral oval). However, their two-dimensional structure as they approach the inner plasma sheet has received only limited attention. We have examined this structure using both the Rice Convection Model (RCM) and ground-based radar and all sky imager observations. As a result of the energy dependent magnetic drift, the low entropy plasma of a flow burst spreads azimuthally within the inner plasma sheet yielding specific predictions of subauroral polarization stream (SAPS) and dawnside auroral polarization stream (DAPS) enhancements that are related to the field-aligned currents associated with the flow channel. Flow channels approximately centered between the dawn and dusk large-scale convection cells are predicted to give significant enhancements of both SAPS and DAPS, whereas flow channel further toward the dusk (dawn) convection cell show a far more significant enhancement of SAPS (DAPS) than for DAPS (SAPS). We present observations for cases having good coverage of flow channels as they approach the equatorward portion of the auroral oval and find very good qualitative agreement with the above RCM predictions, including the predicted differences with respect to flow burst location. Despite there being an infinite variety of flow channels’ plasma parameters and of background plasma sheet and auroral oval conditions, the observations show the general trends predicted by the RCM simulations with the idealized parameters. This supports that RCM predictions of the azimuthal spread of a low-entropy plasma sheet plasma and its associated FAC and flow responses give a realistic physical description of the structure of plasma sheet flow bursts (auroral oval flow channels) as they reach the inner plasma sheet (near the equatorward edge of the auroral oval).

Temperature field around underground power cable for dry and saturated conditions under static and cyclic thermal loads

The safe operation of underground power cables is limited by the temperature of insulation around the conductor which heats up due to joule heating. The insulation temperature depends on the seasonal and diurnal power demand and variations in the surrounding soil’s moisture content. The previous scientific investigations are limited to theoretical and numerical analyses for cyclic loads and experimental studies for only dry conditions with static thermal loads. In this study, a series of large-scale laboratory tests are performed for static and cyclic thermal loads with dry and saturated sand. The cyclic thermal loads with symmetrical and unsymmetrical heating-cooling times are done with dry sand, which is the worst-case scenario for heat dissipation. The cyclic thermal loading on dry sand shows strong thermal charging and is higher with a shorter relaxation time. The static thermal loading results show a significant improvement in the heat dissipation ability with saturated sand due to higher thermal conductivity. However, the heat transfer with saturated sand suggests a strong convection cell formation after three days of heating above the heater. The channelisation of heat with convection cell sand facilitates cooling but is not desirable for power cables below crop fields.

Geodynamics, diamondiferous system tectonics and minerageny

The paper presents a unique geodynamic evolution concept of all processes and structures ensuring carbon source formation and movement for diamond crystals growth in the mantle, and diamondiferous medium supply to the surface. Geodynamic basis for diamond formation is exogenetic source sinking in old subduction zones evolving along convection cell edges. The supply is ongoing in an advection system, with transtension combined with convection playing a key role. The paper shows periods of spatial pipe cluster location and tectonophysical pattern of this phenomenon. Based on geodynamics, the authors suggest improving a taxonomical scheme of the diamondiferous system due to its fractal structure, from a mineragenic province to a pipe cluster. Specific examples are presented to highlight major structural elements of diamondiferous taxons (systems) and their formation patterns. Debatable issues of kimberlite nature are discussed.

Geothermal energy and ore-forming potential of 600 °C mid-ocean-ridge hydrothermal fluids

The ∼4500-m-deep Iceland Deep Drilling Project (IDDP) borehole IDDP-2 in Iceland penetrated the root of an active seawater-recharged hydrothermal system below the Mid-Atlantic Ridge. As direct sampling of pristine free fluid was impossible, we used fluid inclusions to constrain the in situ conditions and fluid composition at the bottom of the hydrothermal convection cell. The fluid temperature is ∼600 °C, and its pressure is near-hydrostatic (∼45 MPa). The fluid exists as two separate phases: an H2O-rich vapor (with an enthalpy of ∼59.4 kJ/mol) and an Fe-K–rich brine containing 2000 µg/g Cu, 3.5 µg/g Ag, 1.4 µg/g U, and 0.14 µg/g Au. Occasionally, the fluid inclusions coexist with rhyolite melt inclusions. These findings indicate that the borehole intersected high-energy steam, which is valuable for energy production, and discovered a potentially ore-forming brine. We suggest that similar fluids circulate deep beneath mid-ocean ridges worldwide and form volcanogenic massive sulfide Cu-Zn-Au-Ag ore deposits.

Vibration-induced boundary-layer destabilization achieves massive heat-transport enhancement

Thermal turbulence is well known as a potent means to convey heat across space by a moving fluid. The existence of the boundary layers near the plates, however, bottlenecks its heat-exchange capability. Here, we conceptualize a mechanism of thermal vibrational turbulence that breaks through the boundary-layer limitation and achieves massive heat-transport enhancement. When horizontal vibration is applied to the convection cell, a strong shear is induced to the body of fluid near the conducting plates, which destabilizes thermal boundary layers, vigorously triggers the eruptions of thermal plumes, and leads to a heat-transport enhancement by up to 600%. We further reveal that such a vibration-induced shear can very efficiently disrupt the boundary layers. The present findings open a new avenue for research into heat transport and will also bring profound changes in many industrial applications where thermal flux through a fluid is involved and the mechanical vibration is usually inevitable.

Experimental investigation on turbulent rotating thermal convection at large Rayleigh numbers

<p>Thermal convection is of major importance in various astro- and geophysical systems, exemplary are buoyancy driven flows in the atmosphere or in the stellar interior. It has been studied for decades in an idealized model system - the Rayleigh-Bénard convection (RBC) - which consists of a horizontal fluid layer heated at the bottom and cooled at the top. Within the Oberbeck-Boussinesq approximation this system is controlled by two parameters only. These are the Rayleigh number (Ra), which represents the thermal driving and the Prandtl number (Pr) that relates the momentum and thermal diffusivities of the fluid. Convection flows in geo- and astrophysics are often influenced by Coriolis forces due to the rotation of the planet or the star. In RBC-system, Coriolis forces are introduced by rotating the convection cell around its vertical axis. The rotation is expressed by an additional dimensionless control parameter, i.e., the inverse Rossby number 1/Ro. We study experimentally the influence of rotation on the heat transport and the temperature field at very large Ra in the High Pressure Convection Facility (HPCF) in Göttingen. The facility consists of a cylindrical cell of 1.10m diameter and 2.20m height that is filled with pressurized sulfur hexafluoride (SF<sub>6</sub>) at up to 19bar. The height of the cell and the large density of SF<sub>6</sub> enable us to reach very large Ra (up to 8×10<sup>14</sup>) at 0.74<Pr<0.96. The cell is mounted on a rotating table and connected to the non-rotating world via water feed-throughs and slip rings. With these, the signals of more than 100 thermistors close to the sidewalls are collected.<br>We find a monotonic decrease of the heat transport with increasing rotation rate. Furthermore, we measure quantities of the flow close to the lateral side walls of the convection cylinder. For large rotation rates we analyze this as part of the recently proposed “Boundary Zonal Flow” (BZF), where the vertical heat transport is enhanced and warm (cold) up (down) flow self-organizes in a periodic manner. In the experiment we observe the BZF most notably in the probability density function of the temperature, which develops a bimodal Gaussian distribution. We also find that the periodic warm-cold structure drifts in anti-cyclonic direction and thus form traveling waves of the temperature field.</p>