Trough Sites Research Articles

Potassium-isotope variations of marine sediments adjacent to the Izu-Bonin Trench and Nankai Trough

Characterizing the K-isotope compositions of marine sediments is a necessary step to using this novel isotope system to investigate K cycling both in the ocean system and in subduction zones. Here we report data for 70+ samples in order to characterize the K-isotope compositions of deep-sea sediments for two drill sites in the western Pacific: (1) IODP Site C0011 adjacent to the Nankai Trough and Southwest Japan arc and (2) Site 1149 adjacent to the Izu-Bonin trench and arc. Variation in δ41K at both sites is mostly subtle, reflecting a consistently strong contribution of K from sources that have δ41K similar to the upper continental crust (UCC). Yet, in detail, the mean δ41K at both sites is about 0.05–0.10 ‰ lower than a recently proposed best estimate for UCC (δ41K = −0.44 ‰). We infer that the slightly low mean δ41K values relative to UCC are likely caused by secondary processes acting on the volcanogenic component of the sediments, though chemical weathering of (non-volcanogenic) terrigenous materials may also play a role. We measured a very low δ41K value (−1.33 ± 0.04 ‰) for one discrete ash layer at Site C0011, so volcanoclastic materials may lower the δ41K values of the bulk sediments, despite only accounting for a small fraction of the K in the sediments. Correlations between δ41K, Cr/Al, and K/Al in the upper sediments of Site 1149 were used to investigate mixing between volcanic ash and terrigenous materials. This approach indicates that mixing of isotopically light volcanic ash (with δ41K about −0.75 ‰) and terrigenous materials (about −0.46 ‰) can account for the observed variation in δ41K values in these sediments. In addition, we observe that at Site C0011 K isotopes exhibit a shift (by ~0.08 ‰) at ~250 m below the seafloor from UCC-like compositions in the upper sediments to slightly lighter compositions in the lower sediments. This shift in δ41K coincides with an abrupt change in certain physical properties (porosity and cementation) of the sediments that may relate to the extent of weathering/degradation of the dispersed volcaniclastics, with more extensively weathered materials present in the lower sediments. Finally, we find evidence for variable admixture of a high δ41K silicic volcanic ash in the lowermost sediments at Site C0011, supporting the view that heterogeneous volcaniclastics can give rise to significant δ41K variations in marine sediments.

Biostratigraphically constrained chronologies for Quaternary sequences from the Hikurangi margin of north-eastern Zealandia

ABSTRACT New biostratigraphically constrained chronologies have been developed to help elucidate the sedimentary and tectonic history of Quaternary sequences on the Hikurangi margin of north-eastern Zealandia. Three sites on the mid to lower slope of the accretionary prism (IODP Site 372-U1517, 375-U1519, 375-U1518) and two sites east of the deformation front (Hikurangi Trough Site 375-U1520 and Tūranganui Seamount Site 375-U1526) are dated using a detailed biostratigraphic framework based on planktic foraminiferal records from ODP Site 181-1123. The dating indicates sedimentation rates are very high and variable on the accretionary prism (0.2–9.6 m/kyr), especially during the Last Glacial Maximum (LGM) when downslope redeposition from the continental shelf and upper slope is common. Sedimentation rates at Hikurangi Trough Site 375-U1520 are also variable (0.01–3.0 m/kyr) and they increase markedly as the incoming site approached the deformation front, especially during the LGM, due to an abundance of downslope redeposition from the inner to mid shelf. The incoming Quaternary section at Tūranganui Seamount Site 375-U1526, is punctuated by hiatuses that shorten in duration as the site approached the deformation front, whilst sedimentation rates remain relatively low (0.04–0.4 m/kyr).

Trench floor depositional response to glacio-eustatic changes over the last 45 ka, northern Hikurangi subduction margin, New Zealand

ABSTRACT Glacio-eustatic cycles lead to changes in sedimentation on all types of continental margins. There is, however, a paucity of sedimentation rate data over eustatic sea-level cycles in active subduction zones. During International Ocean Discovery Program Expedition 375, coring of the upper ∼110 m of the northern Hikurangi Trough Site U1520 recovered a turbidite-dominated succession deposited during the last ∼45 kyrs (Marine Isotope Stages (MIS) 1–3). We present an age model integrating radiocarbon dates, tephrochronology, and δ18O stratigraphy, to evaluate the bed recurrence interval (RI) and sediment accumulation rate (SAR). Our analyses indicate mean bed RI varies from ∼322 yrs in MIS1, ∼49 yrs in MIS2, and ∼231 yrs in MIS3. Large (6-fold) and abrupt variations in SAR are recorded across MIS transitions, with rates of up to ∼10 m/kyr occurring during the Last Glacial Maximum (LGM), and <1 m/kyr during MIS1 and 3. The pronounced variability in SAR, with extremely high rates during the LGM, even for a subduction zone, are the result of changes in regional sediment supply associated with climate-driven changes in terrestrial catchment erosion, and critical thresholds of eustatic sea-level change altering the degree of sediment bypassing the continental shelf and slope via submarine canyon systems.

Kondo effect in a two-dimensional topological insulator: Exact results for adatom impurities

The Lanczos transformation [Phys. Rev. B 91, 085101 (2015)] combined with density matrix renormalization group calculations is used to obtain exact real space properties of a model for a magnetic adatom impurity coupled to the edge of a zigzag stanene ribbon, which, given stanene's sizable spin-orbit interaction, has non-trivial topological properties. We consider an impurity coupled to a site from either sublattice A or B (where a zigzag edge can be pictured as ⋯/∖/∖⋯, or ⋯ABABA⋯, where a B-site, dubbed a crest site, is an outermost one, while an A-site is dubbed a trough site). Our real space resolution allows us to conclude that the two possible ground states are qualitatively very different: in both cases, the introduction of spin-orbit interaction greatly increases the range of the spin correlations between the impurity and the electron spins in the metallic edge-state; however, for the trough-site-coupled impurity the spin correlations show very strong anisotropy (〈Simp,zsz〉≠〈Simp,xsx〉, where Simp denotes the impurity spin and s denotes the spin of an electron in the lattice), while the spin correlations for the crest-coupled impurity are almost isotropic. These results suggest that for either type of site (crest or through) the problem can be mapped onto an Anderson impurity problem, with the adatom side-coupled to a one-dimensional channel. For the crest-coupled case this channel has practically trivial character, while for a trough site the spin-orbit interaction introduces a strong Dzyaloshinskii-Moriya interaction.

Spatial structure of correlations around a quantum impurity at the edge of a two-dimensional topological insulator

We calculate exact zero-temperature real space properties of a substitutional magnetic impurity coupled to the edge of a zigzag silicene-like nanoribbon. Using a Lanczos transformation [Phys. Rev. B 91, 085101 (2015)] and the density matrix renormalization group method, we obtain a realistic description of stanene and germanene that includes the bulk and the edges as boundary one-dimensional helical metallic states. Our results for substitutional impurities indicate that the development of a Kondo state and the structure of the spin correlations between the impurity and the electron spins in the metallic edge state depend considerably on the location of the impurity. More specifically, our real space resolution allows us to conclude that there is a sharp distinction between the impurity being located at a crest or a trough site at the zigzag edge. We also observe, as expected, that the spin correlations are anisotropic due to an emerging Dzyaloshinskii-Moriya interaction with the conduction electrons, and that the edges scatter from the impurity and "snake" or circle around it. Our estimates for the Kondo temperature indicate that there is a very weak enhancement due to the presence of spin-orbit coupling.

δ 18Osw estimate for Globigerinoides ruber from core-top sediments in the East China Sea

The paired analyses of the Mg/Ca ratio and oxygen isotopic composition (δ 18Oc) of surface-dwelling planktonic foraminifera have become a widely used method for reconstructing the oxygen isotopic composition of ambient seawater (δ 18Osw) as a robust proxy for surface salinity. Globigerinoides ruber (G. ruber) is a mixed-layer dweller, and its fossil shell is an ideal archive for recording past sea surface water conditions, such as those caused by variability in the East Asian summer monsoon (EASM). Here, we investigate the validity of shell-derived δ 18Osw estimates for G. ruber using core-top sediments from the East China Sea (ECS). First, we determined a local δ 18Osw–salinity equation for the eastern part of the ECS in July [δ 18Osw = −7.74 + 0.23 × salinity]. Then, we calculated δ 18Osw from core-top δ 18Oc and Mg/Ca values in G. ruber using the δ 18Oc–temperature equation of Bemis et al. (Paleoceanography 13(2):150–160, 1998) and the Mg/Ca–temperature equation of Hastings et al. (EOS 82:PP12B-10, 2001). The core-top δ 18Osw and salinity were estimated to be in the ranges of −0.2 to +0.39 ‰ and 33.7 to 34.5, respectively, which fall close to the local δ 18Osw–salinity regression line. The core-top data showed that the Mg/Ca–temperature calibration by Hastings et al. (EOS 82:PP12B-10, 2001) and the δ 18Oc–temperature equation by Bemis et al. (Paleoceanography 13(2):150–160, 1998) are appropriate for calculating δ 18Osw in the ECS. Furthermore, we measured core-top Ba/Ca ratios of G. ruber (Ba/Ca G. ruber ), which ranged from 0.66 to 2.82 μmol mol−1. There was not a significant relationship between the salinity and Ba/Ca G. ruber ratios due to the highly variable Ba/Ca G. ruber data. Given the seawater Ba/Ca data and the published partition coefficient for Ba (D Ba = 0.15–0.22), pristine Ba/Ca G. ruber ratios at northern Okinawa Trough sites should be less than 0.84 μmol mol−1. Anomalously high Ba/Ca G. ruber ratios (>0.84 μmol mol−1) might be attributable to contamination by sedimentary barite adherent on fossil shells. Therefore, further evaluation of the Ba/Ca G. ruber ratio as a paleo-salinity proxy requires diethylene triamine pentaacetic acid (DTPA)-cleaned Ba/Ca data that can minimize the influence of barite contamination.

Faulting and hydration of the upper crust of the SW Okinawa Trough during continental rifting: Evidence from seafloor compliance inversion

AbstractThe elastic response of seafloor to ocean gravity wave loading, or seafloor compliance, provides a constraint on the elastic properties of the crust. We measured seafloor compliance at three ocean bottom seismometer (OBS) sites around Taiwan—two in the southwestern (SW) Okinawa Trough and one on the Ryukyu arc—and performed inversion for crustal structures beneath them. Models best fitting the data demonstrate a decrease in upper crustal shear velocity and an increase in the compressional/shear velocity ratio from the arc site to the trough sites with increasing amount of back‐arc extension. This variation suggests that the upper continental crust is highly faulted and hydrated during rifting of the Eurasian lithosphere.

Understanding the mechanism of H atom absorption in the Pd(1 1 0) surface

The underlying mechanism of H atom absorption in the Pd(110) (1×2) missing-row reconstructed surface is investigated by performing density functional theory based calculations. The stronger binding energy of H on ridge than on trough site of the missing-row surface is due to the more pronounced creation of derived bonding state as had been depicted from the electronic structure of the system. Hydrogen absorption takes place with the involvement of other incoming H atoms through an assisted absorption process that is facilitated by the repulsion between the incoming H and the absorbing H. The geometry of the missing-row surface enables the Pd atoms to accommodate the H atoms efficiently leading to H absorption as well as H2 dissociation.

Assessing the Potential of the Mesohellenic Trough and Other Sites, in Greece, for CO2 Storage

The Greek CO2 storage potential is composed mainly of aquifers as well as a few hydrocarbon fields. The potential for CO2 storage capacity in oil and gas fields in Greece lies offshore, in the Prinos-Kavala basin, in NE Greece, whereas the biggest share of the point source CO2 emissions come from NW Greece. There is also potential for storage in lignite fields, which have been extensively mined for power generation. This paper presents an overview of the potential CO2 storage of the Mesohellenic Trough (MT), in north-western Greece. Geological modelling assessed the CO2 storage potential in the (MT) and provided an estimation for the Pentalofos reservoir. According to the geological model, characterized by horizontal maximum dimensions of 47km by 100km and covering a surface area of 3813 km2, the deepest point where we can store CO2 corresponds to the base of the Tsarnos member, at -2544 m depth. We estimate that we can store up to 1435 Gt of CO2 in the Pentalofos Fm (Tsarnos and Kalloni Members) in the MT. The location of the potential storage sites, relative to emission points, forms interesting combinations, which are briefly presented in this paper. The results presented here will serve as a basis for pursuing this worthwhile piece of research in order to determine the most reliable and most cost efficient ways of transporting and storing CO2 in Greece and developing the right legal framework for achieving these goals.

Hydrogen atom absorption in hydrogen-covered Pd(110) (1 × 2) missing-row surface

The absorption of H atom in H-covered Pd(110) (1 × 2) missing-row surface is investigated using density functional theory based calculations. For 1.5 monolayer H coverage, interaction among the adsorbed H atoms is found to be negligible and was verified by analyzing the electronic structure of the system and by comparing the calculated binding energies with low H coverage case. Neither the monoatomic absorption of H nor the assistance from the initially adsorbed H atom explains the experimentally observed presence of subsurface H in Pd(110) at high H coverage. Instead, H absorption is realized through the assistance of incoming H atoms from vacuum. The absorption of H in the H-covered surface is non-activated while the dissociation of H2 is the rate-limiting process. Dissociation on ridge site is energetically more preferred than on trough site and the difference in the activation barrier is elucidated by investigating the electronic structures of the system.

Self-Assembly of Cysteine Dimers at the Gold Surface: A Computational Study of Competing Interactions

The only proteinogenic acid with a mercapto group, cysteine is the main participant in the binding of proteins and peptides to the surfaces of noble metals. A chiral molecule, it becomes a major player in surface patterning for chiral amplification, biosensing, and chiral catalysis. Here, we examine the interplay of molecule–surface and molecule–molecule interactions in the self-assembly process of monomers, dimers, and trimers of l-cysteine on a (1 × 2)-reconstructed Au(110) surface, and the implications for chiral recognition. Multiple adsorbed configurations of l-cysteine and l-cysteinate in neutral and zwitterionic forms were generated using molecular dynamics simulations, serving as starting points for further density functional theory (DFT)-based optimizations. We found that binding for both monomers and dimers was stronger at kink sites formed on the surface during the chemisorption process, and was unlikely to occur along the highly coordinated trough sites. In this, DFT calculations disagreed wit...

Unique water-water coordination tailored by a metal surface

At low coverage of water on Cu(110), substrate-mediated electrostatics lead to zigzagging chains along [001] as observed with STM [T. Yamada, S. Tamamori, H. Okuyama, and T. Aruga, "Anisotropic water chain growth on Cu(110) observed with scanning tunneling microscopy" Phys. Rev. Lett. 96, 036105 (2006)]. Using x-ray absorption spectroscopy we find an anomalous low-energy resonance at ~533.1 eV which, based on density functional theory spectrum simulations, we assign to an unexpected configuration of water units whose uncoordinated O-H bonds directly face those of their neighbors; this interaction repeats over trough sites with enhanced electron density and is analogous to the case of a hydrated electron.

Hydrogen adsorption and desorption at the Pt(110)-(1×2) surface: experimental and theoretical study

The interaction of hydrogen with the Pt(110)-(1×2) surface is studied using temperature programmed desorption (TPD) measurements and density functional theory (DFT) calculations. The ridges in this surface resemble edges between micro-facets of Pt nano-particle catalysts used for hydrogen evolution (HER) and hydrogen oxidation reactions (HOR). The binding energy and activation energy for desorption are found to depend strongly on hydrogen coverage. At low coverage, the strongest binding sites are found to be the low coordination bridge sites at the edge and this is shown to agree well with the He-atom interaction and work function change which have been reported previously. At higher hydrogen coverage, the higher coordination sites on the micro-facet and in the trough get populated. The simulated TPD spectra based on the DFT results are in close agreement with our experimental spectra and provide microscopic interpretation of the three measured peaks. The lowest temperature peak obtained from the surface with highest hydrogen coverage does not correspond to desorption directly from the weakest binding sites, the trough sites, but is due to desorption from the ridge sites, followed by subsequent, thermally activated rearrangement of the H-adatoms. The reason is low catalytic activity of the Pt-atoms at the trough sites and large reduction in the binding energy at the ridge sites at high coverage. The intermediate temperature peak corresponds to desorption from the micro-facet. The highest temperature peak again corresponds to desorption from the ridge sites, giving rise to a re-entrant mechanism for the thermal desorption.

Distribution of glycerol dialkyl glycerol tetraethers, alkenones and polyunsaturated fatty acids in suspended particulate organic matter in the East China Sea

We investigated the spatial distribution of glycerol dialkyl glycerol tetraethers (GDGTs), alkenones, and polyunsaturated fatty acids in particulate organic matter collected at four sites along a depth transect from the continental shelf to the Okinawa Trough in the East China Sea during the spring bloom in 2008. The maximum alkenone concentration appeared in the top 25 m at all sites and the $$ U_{37}^{{{\text{K}}'}} $$ values were consistent with in situ water temperatures in the depth interval, suggesting that the alkenones were produced mainly in surface water. At the slope and shelf sites, GDGTs in the water column showed a concentration maximum at 74–99 m depth, and the $$ {\text{TEX}}_{86}^{\text{H}} $$ agreed with in situ water temperatures, suggesting the in situ production of GDGTs in the depth interval. The low-salinity surface water above 20 m depth was characterized by low GDGT concentrations and low $$ {\text{TEX}}_{86}^{\text{L}} $$ -based temperatures, suggesting either the production of GDGTs in winter season or the lateral advection of GDGTs by an eastward current. At the slope and Okinawa Trough sites, TEX86-based temperatures were nearly constant in the water column deeper than 300 m and corresponded to temperatures at the surface and near-surface waters rather than in situ temperatures. This observation is consistent with a hypothesis that Thaumarchaeota cells produced in surface waters are delivered to deeper water and also indicates that the residence time of suspended GDGTs in the deep-water column is large enough to mix the GDGTs produced in different seasons.

Reentrant Mechanism for Associative Desorption:H2/Pt(110)−(1×2)

Calculations of the desorption of hydrogen from Pt(110)-(1×2), a surface used to model nanoparticle edge sites, show the activation energy varying strongly with hydrogen coverage, from 0.8 to 0.3eV. The predicted temperature programed desorption spectra agree well with experiments, but the formation of the hydrogen molecules occurs only at two types of sites on the surface even though three peaks are observed. The lowest and highest temperature peaks result from desorption from the same strong binding sites at the ridge, while desorption from the weakest binding trough sites is insignificant.

The effect of Bi adsorption on CO oxidation inside 1.8 nm Pt pores

Modification of the surface of H(1)-e Pt with Bi causes significant changes in the CO stripping voltammetry; the pre-wave disappears and CO and Bi oxidation peaks appear. The absence of the pre-wave suggests that Bi preferentially adsorbs on the trough sites of the concave 1.8 nm diameter pore walls preventing oxygenated species from nucleating there.

First-principles study of GaAs(001)-β2(2×4) surface oxidation and passivation with H, Cl, S, F, and GaO

The interactions of oxygen atoms on the GaAs(001)-β2(2×4) surface and the passivation of oxidized GaAs(001)-β2(2×4) surface were studied by density functional theory. The results indicate that oxygen atoms adsorbed at back-bond sites satisfy the bond saturation conditions and do not induce surface gap states. However, due to the oxygen replacement of an As dimer atom at a trough site or row site, the As–As bond is broken, and gap states are produced leading to the Fermi level pinning because of unsaturated As dangling bonds. Atomic H, Cl, S, F, and the molecular species GaO were examined to passivate the unsaturated As dangling bond. The results show that H, Cl, F, and GaO can remove such gap states. It is also found that the interaction of S with the unsaturated As dangling bond does not remove the gap states, and new gap states are generated upon single S adsorption. A higher S coverage forms S–S dimer pairs which passivate two unsaturated As atoms, and removes the As-induced gap states.

State-resolved reactivity of CH4 on Pt(110)-(1×2): The role of surface orientation and impact site

The reactivity of methane (CH(4)) on Pt(110)-(1 x 2) has been studied by quantum state-resolved surface reactivity measurements. Ground state reaction probabilities, S(0)(v=0) congruent with S(0)(laser-off), as well as state-resolved reaction probabilities S(0)(2nu(3)), for CH(4) excited to the first overtone of the antisymmetric C-H stretch (2nu(3)) have been measured at incident translational energies in the range of 4-64 kJ/mol. We observe S(0)(2nu(3)) to be up to three orders of magnitude higher than S(0)(v=0), demonstrating significant vibrational activation of CH(4) dissociation on Pt(110)-(1 x 2) by 2nu(3) excitation. Furthermore, we explored the azimuthal and polar incident angle dependence of S(0)(2nu(3)) and S(0)(v=0) for a fixed incident translational energy E(t)=32 kJ/mol. For incidence perpendicular to the missing row direction on Pt(110)-(1 x 2) and polar angles theta>40 degrees, shadowing effects prevent the incident CH(4) molecules from impinging into the trough sites. Comparison of this polar angle dependence with reactivity data for incidence parallel to the missing rows yields state-resolved site specific reactivity information consistent with a Pt(110)-(1 x 2) reactivity that is dominated by top layer Pt atoms located at the ridge sites. A comparison of S(0)(v=0) measured on Pt(110)-(1 x 2) and Pt(111) yields a lower average barrier for Pt(110)-(1 x 2) by 13.7+/-2.0 kJ/mol.

Ambient Noise and Teleseismic Signals Recorded by Ocean-Bottom Seismometers Offshore Eastern Taiwan

Broadband records from ocean-bottom seismometers deployed in the Okinawa trough and the Huatung basin were analyzed to provide seafloor noise characteristics and the detection thresholds for teleseismic body and surface waves. Ambient noise levels on the horizontal components are 10-40 dB higher than on the vertical component, with the sensor seated on the surface of the sediment. On the vertical components, infragravity waves are 10-30 dB more energetic at the shallower Okinawa trough sites (≤2000 m depth) than at the deeper Huatung basin site (~4700 m). From 0.03 to 0.2 Hz, the Huatung basin noise levels are comparable to that of the broadband stations in Taiwan on a quiet day. The microseism peaks (~0.2-0.5 Hz) of OBSs reach or exceed the high noise model of continental stations. At regional distances M(subscript w) 6.5 is required for recording prominent Rayleigh waves if the source radiation is unfavorable, but 6.2 is sufficient for a favorable focal mechanism. Several tens to over one hundred high-fidelity P, P(subscript diff) and PKP waveforms have been recorded per year by OBSs at high corner frequency of 0.1 Hz with a minimum M(subscript w) 5.3-6.0. The number of recording drops to less than 5 per year at 1 Hz with M(subscript w)≥6.4 and distances less than 90°.

First-principles study of GaAs(0 0 1)-β2(2 × 4) surface oxidation

Oxygen atom adsorption on GaAs(0 0 1)-β2(2 × 4) during initial surface oxidation is studied by density functional theory (DFT). The results show that one or two oxygen atom adsorption at back-bond sites satisfy the bond saturation conditions leading to no effect on the surface gap states. However, for an oxygen replacement of an As dimer atom at trough site or row site As dimer atoms, an As–As bond is broken. Mid gap states are produced leading to the Fermi level pining due to the unsaturated As dangling bonds.