bluuebunny/crossref_metadata_2025 huggingface dataset:
Activation of hole charge carriers and generation of electromotive force in gabbro blocks subjected to nonuniform loading
Authors: Takeuchi Akihiro , Nagao Toshiyasu
Published: April 2013

This study verifies the activation of hole charge carriers in gabbro under nonuniform loading, which has been proposed as the possible source of the stress‐induced electromotive force in dry rocks without piezoelectric effect. When one end of vacuum‐dried gabbro blocks was subjected to uniaxial loading, the unloaded end became electronically positive (+80 mV at 50 MPa). The Seebeck coefficient of the loaded volume decreased from ~15.8 mV/K to ~14.9 mV/K when loaded, while the Seebeck coefficient of the unloaded end did not change remarkably (~15.6 mV/K). This means that this gabbro originally included a small number of hole charge carriers and the carriers in the loaded volume increased when loaded. From the viewpoint of the fundamental band model of solid state, the most reasonable mechanism of the increment is the decrease of the energy gap between the acceptors and the valence band top. Based on this idea, a generation model of the stress‐induced electromotive force is proposed. Since this model is expected to be universally applicable to various types of rocks, similar electromotive forces in the crustal scale may be induced by seismic, volcanic, and tidal activities.
Source parameter inversion for recent great earthquakes from a decade‐long observation of global gravity fields
Authors: Han Shin‐Chan , Riva Riccardo , Sauber Jeanne , Okal Emile
Published: April 2013

We quantify gravity changes after great earthquakes present within the 10 year long time series of monthly Gravity Recovery and Climate Experiment (GRACE) gravity fields. Using spherical harmonic normal‐mode formulation, the respective source parameters of moment tensor and double‐couple were estimated. For the 2004 Sumatra‐Andaman earthquake, the gravity data indicate a composite moment of 1.2 × 1023 N m with a dip of 10°, in agreement with the estimate obtained at ultralong seismic periods. For the 2010 Maule earthquake, the GRACE solutions range from 2.0 to 2.7 × 1022 N m for dips of 12°–24° and centroid depths within the lower crust. For the 2011 Tohoku‐Oki earthquake, the estimated scalar moments range from 4.1 to 6.1 × 1022 N m, with dips of 9°–19° and centroid depths within the lower crust. For the 2012 Indian Ocean strike‐slip earthquakes, the gravity data delineate a composite moment of 1.9 × 1022 N m regardless of the centroid depth, comparing favorably with the total moment of the main ruptures and aftershocks. The smallest event we successfully analyzed with GRACE was the 2007 Bengkulu earthquake with M0 ~ 5.0 × 1021 N m. We found that the gravity data constrain the focal mechanism with the centroid only within the upper and lower crustal layers for thrust events. Deeper sources (i.e., in the upper mantle) could not reproduce the gravity observation as the larger rigidity and bulk modulus at mantle depths inhibit the interior from changing its volume, thus reducing the negative gravity component. Focal mechanisms and seismic moments obtained in this study represent the behavior of the sources on temporal and spatial scales exceeding the seismic and geodetic spectrum.
High‐temperature deformation and recrystallization: A variational analysis and its application to olivine aggregates
Authors: Hackl Klaus , Renner Jörg
Published: April 2013

We develop a framework for a variational analysis of microstructural evolution during inelastic high‐temperature deformation accommodated by dislocation mechanisms and diffusive mass transport. A polycrystalline aggregate is represented by a distribution function characterizing the state of individual grains by three variables, dislocation density, grain size, and elastic strain. The aggregate's free energy comprises elastic energy and energies of lattice distortions due to dislocations and grain boundaries. The work performed by the external loading is consumed by changes in the number of defects and their migration leading to inelastic deformation. The variational approach minimizes the rate of change of free energy with the evolution of the state variables under constraints on the aggregate volume, on a relation between changes in plastic strain and dislocation density, and on the form of the dissipation functionals for defect processes. The constrained minimization results in four basic evolution equations, one each for the evolution in grain size and dislocation density and flow laws for dislocation and diffusion creep. Analytical steady state scaling relations between stress and dislocation density and grain size (piezometers) are derived for quasi‐homogeneous materials characterized by a unique relation between grain size and dislocation density. Our model matches all currently available experimental observations regarding high‐temperature deformation of olivine aggregates with plausible values for the involved micromechanical model parameters. The relation between strain rate and stress for olivine aggregates maintaining a steady state microstructure is distinctly nonlinear in stark contrast to the majority of geodynamical modeling relying on linear relations, i.e., Newtonian behavior.
Radiography of a normal fault system by 64,000 high‐precision earthquake locations: The 2009 L'Aquila (central Italy) case study
Authors: Valoroso L. , Chiaraluce L. , Piccinini D. , Di Stefano R. , Schaff D. , Waldhauser F.
Published: April 2013

We studied the anatomy of the fault system where the 2009 L'Aquila earthquake (MW 6.1) nucleated by means of ~64 k high‐precision earthquake locations spanning 1 year. Data were analyzed by combining an automatic picking procedure for P and S waves, together with cross‐correlation and double‐difference location methods reaching a completeness magnitude for the catalogue equal to 0.7 including 425 clusters of similar earthquakes. The fault system is composed by two major faults: the high‐angle L'Aquila fault and the listric Campotosto fault, both located in the first 10 km of the upper crust. We detect an extraordinary degree of detail in the anatomy of the single fault segments resembling the degree of complexity observed by field geologists on fault outcrops. We observe multiple antithetic and synthetic fault segments tens of meters long in both the hanging wall and footwall along with bends and cross fault intersections along the main fault and fault splays. The width of the L'Aquila fault zone varies along strike from 0.3 km where the fault exhibits the simplest geometry and experienced peaks in the slip distribution, up to 1.5 km at the fault tips with an increase in the geometrical complexity. These characteristics, similar to damage zone properties of natural faults, underline the key role of aftershocks in fault growth and co‐seismic rupture propagation processes. Additionally, we interpret the persistent nucleation of similar events at the seismicity cutoff depth as the presence of a rheological (i.e., creeping) discontinuity explaining how normal faults detach at depth.
Environmental magnetic record of paleoclimate, unroofing of the Transantarctic Mountains, and volcanism in late Eocene to early Miocene glaci‐marine sediments from the Victoria Land Basin, Ross Sea, Antarctica
Authors: Roberts Andrew P. , Sagnotti Leonardo , Florindo Fabio , Bohaty Steven M. , Verosub Kenneth L. , Wilson Gary S. , Zachos James C.
Published: April 2013

We synthesize environmental magnetic results for sediments from the Victoria Land Basin (VLB), which span a total stratigraphic thickness of 2.6 km and a ~17 Myr age range. We assess how magnetic properties record paleoclimatic, tectonic, and provenance variations or mixtures of signals resulting from these processes. The magnetic properties are dominated by large‐scale magnetite concentration variations. In the late Eocene and early Oligocene, magnetite concentration variations coincide with detrital smectite concentration and crystallinity variations, which reflect paleoclimatic control on magnetic properties through influence on weathering regime; high magnetite and smectite concentrations indicate warmer and wetter climates and vice versa. During the early Oligocene, accelerated uplift of the Transantarctic Mountains gave rise to magnetic signatures that reflect progressive erosion of the Precambrian‐Mesozoic metamorphic, intrusive, and sedimentary stratigraphic cover succession associated with unroofing of the adjacent Transantarctic Mountains. From the early Oligocene to the early Miocene, a consistent fining upward of magnetite particles through the recovered composite record likely reflects increased physical weathering with glacial grinding contributing to progressively finer grained Ferrar Dolerite‐sourced magnetite. After 24 Ma, the magnetic properties of VLB sediments are primarily controlled by the weathering and erosion of McMurdo Volcanic Group rocks; increased volcanic glass contents contribute to the fining upward of magnetite grain size. Overall, long‐term magnetic property variations record the first‐order geological processes that controlled sedimentation in the VLB, including paleoclimatic, tectonic, provenance, and volcanic influences.
Seismic anisotropy in the Sumatra subduction zone
Authors: Collings R. , Rietbrock A. , Lange D. , Tilmann F. , Nippress S. , Natawidjaja D.
Published: April 2013

An important tool for understanding deformation occurring within a subduction zone is the measurement of seismic anisotropy through observations of shear wave splitting (SWS). In Sumatra, two temporary seismic networks were deployed between December 2007 and February 2009, covering the fore arc between the fore‐arc islands to the back arc. We use SKS and local SWS measurements to determine the type, amount, and location of anisotropy. Local SWS measurements from the fore‐arc islands exhibit trench‐parallel fast directions which can be attributed to shape preferred orientation of cracks/fractures in the overriding sediments. In the Sumatran Fault region, the predominant fast direction is fault/trench parallel, while in the back‐arc region it is trench perpendicular. The trench‐perpendicular measurements exhibit a positive correlation between delay time and raypath length in the mantle wedge, while the fault‐parallel measurements are similar to the fault‐parallel fast directions observed for two crustal events at the Sumatran Fault. This suggests that there are two layers of anisotropy: one due to entrained flow within the mantle wedge and a second layer within the overriding crust due to the shear strain caused by the Sumatran Fault. SKS splitting results show a NNW‐SSE fast direction with delay times of 0.8–3.0 s. The fast directions are approximately parallel to the absolute plate motion of the subducting Indo‐Australian Plate. The small delay times exhibited by the local SWS (0.05–0.45 s), in combination with the large SKS delay times, suggest that the anisotropy generating the teleseismic SWS is dominated by entrained flow in the asthenosphere below the slab.
The dynamics of two‐phase hydrothermal systems at a seafloor pressure of 25 MPa
Authors: Han Liang , Lowell Robert P. , Lewis Kayla C.
Published: April 2013

We present 2‐D numerical simulations of two‐phase flow in seafloor hydrothermal systems using the NaCl‐H2O numerical code Fully Implicit Seafloor Hydrothermal Event Simulator to better understand phase separation and the evolution of the temperature and salinity of vent fluids in seafloor hydrothermal systems. We consider a fixed seafloor pressure of 25 MPa, a range of homogeneous and isotropic permeabilities, and various constant bottom temperatures to represent a subaxial magma chamber. The goal is to investigate how permeability and maximum bottom temperature affect vent fluid temperature and salinity. The simulations show that hydrothermal heat output increases nearly linearly with permeability, or Rayleigh number, but maximum bottom temperature has a greater effect on vent fluid temperature and salinity than the permeability. Although plume structures are relatively stable, the high Rayleigh numbers considered here result in temporal and spatial variations in temperature and salinity of vent fluids. The frequency of the fluctuations in the temperature and salinity of vent fluids increases with Rayleigh number. Vapor‐ and brine‐derived fluids can vent simultaneously in close proximity and at different times and locations throughout a simulation. The simulations also show that vent fluids are complex mixtures between phase separated fluids formed near the base of the system and seawater. Consequently, neither the spatial and temporal variability, nor the temperature and salinity of vent fluids can be used to uniquely determine P‐T conditions or indicate temporal changes in such conditions at depth.
Structural controls on localized intraplate deformation and seismicity in Southern Australia: Insights from local earthquake tomography of the Flinders Ranges
Authors: Pilia S. , Rawlinson N. , Direen N. G. , Cummins P. R. , Balfour N.
Published: April 2013

Data from an array of 24 seismometers are used to image the crust beneath the Flinders Ranges, southeast Australia, with the goal of improving our understanding of crustal structure, rheology, and the mechanism responsible for the localized intraplate deformation that characterizes this region. A subset of P‐ and S‐wave traveltimes is inverted to jointly recover earthquake hypocenters, P‐wave velocity structure and vp/vs anomalies. The P‐wave velocity model reveals a spatial correlation between major negative velocity perturbations and concentrations of seismicity. In particular, a cluster of seismicity is observed within a distinct low velocity region between the Archean‐Mesoproterozoic Gawler Craton and the Palaeo‐Mesoproterozoic Curnamona Province, from 7 to 20 km depth. We postulate that this may be associated with a pre‐existing structural weakness in the crust that arises primarily from rifting between the Curnamona Province and the Gawler Craton. Another area characterized by a high level of seismicity overlies a major sequence of N‐S trending Ross‐Delamerian thrust faults, which correspond to a band of low vp and particularly vp/vs. The lack of evidence for elevated heat flows in both of these seismogenic regions suggests that thermally induced weakness is unlikely to play a dominant role. Instead, the dynamic behavior of this intraplate region appears to be caused by a serendipitously oriented regional stress field, provided by far field forces that originate from the boundary between the Pacific and Australian plates, which acts upon preexisting structural weaknesses in the lithosphere.
Bayesian inversion of data from effusive volcanic eruptions using physics‐based models: Application to Mount St. Helens 2004–2008
Authors: Anderson Kyle , Segall Paul
Published: April 2013

Physics‐based models of volcanic eruptions can directly link magmatic processes with diverse, time‐varying geophysical observations, and when used in an inverse procedure make it possible to bring all available information to bear on estimating properties of the volcanic system. We develop a technique for inverting geodetic, extrusive flux, and other types of data using a physics‐based model of an effusive silicic volcanic eruption to estimate the geometry, pressure, depth, and volatile content of a magma chamber, and properties of the conduit linking the chamber to the surface. A Bayesian inverse formulation makes it possible to easily incorporate independent information into the inversion, such as petrologic estimates of melt water content, and yields probabilistic estimates for model parameters and other properties of the volcano. Probability distributions are sampled using a Markov‐Chain Monte Carlo algorithm. We apply the technique using GPS and extrusion data from the 2004–2008 eruption of Mount St. Helens. In contrast to more traditional inversions such as those involving geodetic data alone in combination with kinematic forward models, this technique is able to provide constraint on properties of the magma, including its volatile content, and on the absolute volume and pressure of the magma chamber. Results suggest a large chamber of >40 km3 with a centroid depth of 11–18 km and a dissolved water content at the top of the chamber of 2.6–4.9 wt%.
A new driving mechanism for backarc extension and backarc shortening through slab sinking induced toroidal and poloidal mantle flow: Results from dynamic subduction models with an overriding plate
Authors: Schellart W. P. , Moresi L.
Published: April 2013

We present numerical subduction models to investigate overriding plate deformation at subduction zones. All models show forearc shortening, resulting predominantly from shear stresses at the subduction zone interface and opposite‐sense mantle shear stresses at the base of the forearc lithosphere. Models dominated by backarc extension show that it results from trench‐normal positive velocity gradients in the mantle below the overriding plate. Such gradients result from toroidal mantle flow induced by slab rollback, with velocities below the leading part of the backarc faster than the overriding plate velocity. The velocity gradients induce basal shear stresses that increase trenchward and cause trenchward overriding plate motion at a velocity (vOP⊥) whose spatial average is below the trench retreat velocity (vT⊥). The combination of basal shear stresses and average vOP⊥ < vT⊥ causes trench‐normal deviatoric tension in the backarc and backarc extension. Models dominated by backarc shortening show that it results from a relatively immobile subduction hinge and trenchward overriding plate motion driven by poloidal mantle flow. The poloidal mantle flow is induced by downdip slab sinking and causes the average vOP⊥ > vT⊥. This results in trench‐normal deviatoric compression and shortening in the leading part of the overriding plate as it collides with the subduction hinge. Ultimately, the geodynamic models demonstrate that backarc extension is favored for narrow slabs and near lateral slab edges and is driven by rollback induced toroidal mantle flow, while backarc shortening is favored for the center of wide slabs and is driven by poloidal mantle flow resulting from downdip slab motion.
Annual modulation of non‐volcanic tremor in northern Cascadia
Authors: Pollitz Fred F. , Wech Aaron , Kao Honn , Bürgmann Roland
Published: April 2013

Two catalogs of episodic tremor events in northern Cascadia, one from 2006 to 2012 and the other from 1997 to 2011, reveal two systematic patterns of tremor occurrence in southern Vancouver Island: (1) most individual events tend to occur in the third quarter of the year; (2) the number of events in prolonged episodes (i.e., episodic tremor and slip events), which generally propagate to Vancouver Island from elsewhere along the Cascadia subduction zone, is inversely correlated with the amount of precipitation that occurred in the preceding 2 months. We rationalize these patterns as the product of hydrologic loading of the crust of southern Vancouver Island and the surrounding continental region, superimposed with annual variations from oceanic tidal loading. Loading of the Vancouver Island crust in the winter (when the land surface receives ample precipitation) and unloading in the summer tends to inhibit and enhance downdip shear stress, respectively. Quantitatively, for an annually variable surface load, the predicted stress perturbation depends on mantle viscoelastic rheology. A mechanical model of downdip shear stress on the transition zone beneath Vancouver Island—driven predominantly by the annual hydrologic cycle—is consistent with the 1997–2012 tremor observations, with peak‐to‐peak downdip shear stress of about 0.4 kPa. This seasonal dependence of tremor occurrence appears to be restricted to southern Vancouver Island because of its unique situation as an elongated narrow‐width land mass surrounded by ocean, which permits seasonal perturbations in shear stress at depth.
Direct observations of the Antarctic circumpolar current transport on the northern flank of the Kerguelen Plateau
Authors: Damerell G. M. , Heywood K. J. , Stevens D. P.
Published: April 2013

The standing meander in the Antarctic Circumpolar Current (ACC) found on the northern flank of the Kerguelen Plateau was investigated during the Southern Ocean Finestructure cruise in November–December 2008. An 18 year time series of surface geostrophic currents from satellite altimetry shows that the meander as observed during this survey is typical of the region. Hydrographic stations were occupied between 65–75°E and 43–48°S on the shelf (~200 m depth) and slope into the deep ocean to the north of Kerguelen (~4700 m), providing the most detailed survey of this region to date. Geostrophic shears are referenced to lowered acoustic Doppler current profiler velocities to give the first estimate of the total volume transport in this region, and the transport budget is closed around the survey box. The Subtropical Front, Subantarctic Front, and a northern branch of the Polar Front together have an associated transport of 174 ± 22 Sv eastward. While 174 Sv is large compared with typical Drake Passage transports, it is reconciled with other estimates of the total transport with the additional 15 Sv of the Indonesian Throughflow. Baroclinic transport referenced to the deepest common level between station pairs is 119 Sv, consistent with other estimates of the baroclinic transport in this area. At this longitude, the fronts of the ACC are exceptionally close together. We discuss the exchange of properties across the fronts.
Revisit the interannual variability of the North Equatorial Current transport with ECMWF ORA‐S3
Authors: Zhai Fangguo , Hu Dunxin
Published: April 2013

The interannual variability of the North Equatorial Current (NEC) transport in the tropical northwestern Pacific Ocean is investigated with the output from ECMWF Ocean Analysis/Reanalysis System 3 (ORA‐S3). The results show that the amplitude and root mean square (RMS) of interannual NEC transport anomalies increase from about 3.0–4.0 Sv and 2.0 Sv at 170°E to above 5.0 and 3.4 Sv at 135°E, respectively. The NEC transport variation agrees well with the variation of the sea surface height (SSH) anomaly difference between the southern and northern boundaries of the NEC region. Further analysis near the Philippine coast suggests that their good agreement mainly comes from the agreement of the NEC transport and SSH variations south of the gyre boundary. Around the bifurcation point off the Philippine coast, the southern branch of the NEC transport is highly related to El Niño–Southern Oscillation (ENSO) events. During El Niño/La Niña years, westerly/easterly wind anomalies and positive/negative wind stress curl anomalies develop in the tropical northwestern Pacific Ocean south of 20°N before the mature phase. The wind forcing center moves eastward with time and reaches the easternmost position around 170°E several months before the mature phase. This wind forcing generates upwelling/downwelling Rossby waves, which propagate westward to result in negative/positive SSH anomalies, hence inducing a cyclonic/anticyclonic gyre anomaly, which is responsible for the increase/decrease of the NEC transport. The northern branch of the NEC transport near the Philippine coast has no significant simultaneous relation with ENSO events.
Dynamics of the summer shelf circulation and transient upwelling off Ningaloo Reef, Western Australia
Authors: Xu Jiangtao , Lowe Ryan J. , Ivey Gregory N. , Pattiaratchi Charitha , Jones Nicole L. , Brinkman Richard
Published: April 2013

The shelf circulation off Ningaloo Reef near the North West Cape of Western Australia is driven by complex interactions between the southward flowing Leeuwin Current and wind‐driven currents that episodically reverse the coastal flow toward the north. The presence of these northward (equatorward) wind‐driven currents is thought to make this section of coast one of the few locations along Western Australia to experience periodic coastal upwelling. We used a combination of field observations and numerical modeling to investigate the summer circulation and upwelling dynamics along Ningaloo Reef. We analyzed current and temperature profiles from moorings at four sites across the shelf and used two Regional Ocean Modeling System (ROMS) sub‐models: (1) a coarser model of northwestern Australia forced by a global ocean model and (2) a nested fine‐scale model of the Ningaloo region. This nesting significantly improved model skill as it included the offshore mesoscale dynamics that strongly influenced the shelf circulation off Ningaloo. The field observations revealed several northward flow reversals, accompanied by cooling of the coastal waters adjacent to Ningaloo, which were associated with strong northward wind events. Analysis of the coastal heat budget revealed that cooling events were primarily driven by upwelling, whereas warming of coastal waters during relaxation events resulted mostly from along‐shelf advection of warm water from the north. Due to the combined effects of its relatively steep (~1/50 slope) shelf and strong summer stratification, upwelled water was sourced from the interior of the water column, likely influencing the sources and fluxes of nutrients to Ningaloo Reef.
Canadian Basin freshwater sources and changes: Results from the 2005 Arctic Ocean Section
Authors: Newton Robert , Schlosser Peter , Mortlock Richard , Swift James , MacDonald Robie
Published: April 2013

We present measurements of oxygen isotope ratios and nutrient concentrations along the 2005 Arctic Ocean Section aboard the icebreaker Oden. The data are used to estimate freshwater contributions from meteoric water (mainly river runoff), sea‐ice meltwater, and Chukchi Sea shelf water, itself a combination of Pacific and indigenous Arctic water types. Nutrients ratios are combined to form quasi‐conservative water‐mass tracers (phosphate‐star, N‐star, and the empirical Arctic N‐P relationship) and used along with salinity and δ18O, which are conservative in the ocean interior. Disagreements between two different freshwater analyses in the Western Arctic are largely resolved using a salinity‐dependent Redfield ratio, a new estimate of the Pacific end‐member, and an analysis of the Bering Strait inflow contribution to detraining shelf waters. Freshwater components from 2005 are placed into the context of the overlapping 1994 Arctic Ocean Section (aboard the Louis St. Laurent) and a time series of hydrographic/tracer casts between 1987 and 1992 in the Canada Basin. Compared to 1987–1994; the 2005 transect exhibits increased meteoric water concentrations in the northern part of the Canadian Basin and a decrease in the southern part. This pattern is related to changes in the distribution of wind‐stress curl during the several years prior to each sampling campaign. In addition, a previously observed correlation between sea‐ice formation and river runoff disappears over the Central Arctic in 2005, a change that we attribute to a northward shift of sea‐ice formation. Resampling approximately every 3 years should resolve the dynamics driving changes in freshwater and nutrient distributions.
Physical controls on hypoxia in Chesapeake Bay: A numerical modeling study
Authors: Scully Malcolm E.
Published: April 2013

A three‐dimensional circulation model with a relatively simple dissolved oxygen model is used to examine the role that physical forcing has on controlling hypoxia and anoxia in Chesapeake Bay. The model assumes that the biological utilization of dissolved oxygen is constant in both time and space, isolating the role that physical forces play in modulating oxygen dynamics. Despite the simplicity of the model, it demonstrates skill in reproducing the observed variability of dissolved oxygen in the bay, highlighting the important role that variations in physical forcing have on the seasonal cycle of hypoxia. Model runs demonstrate significant changes in the annual integrated hypoxic volume as a function of river discharge, water temperature, and wind speed and direction. Variations in wind speed and direction had the greatest impact on the observed seasonal cycle of hypoxia and large impacts on the annually integrated hypoxic volume. The seasonal cycle of hypoxia was relatively insensitive to synoptic variability in river discharge, but integrated hypoxic volumes were sensitive to the overall magnitude of river discharge at annual time scales. Increases in river discharge were shown to increase hypoxic volumes, independent from the associated biological response to higher nutrient delivery. However, increases in hypoxic volume were limited at very high river discharge because increased advective fluxes limited the overall length of the hypoxic region. Changes in water temperature and its control on dissolved oxygen saturation were important to both the seasonal cycle of hypoxia and the overall magnitude of hypoxia in a given year.
Seasonal variability of submarine melt rate and circulation in an East Greenland fjord
Authors: Sciascia R. , Straneo F. , Cenedese C. , Heimbach P.
Published: April 2013

The circulation in a glacial fjord driven by a large tidewater glacier is investigated using a nonhydrostatic ocean general circulation model with a melt rate parameterization at the vertical glacier front. The model configuration and water properties are based on data collected in Sermilik Fjord near Helheim Glacier, a major Greenland outlet glacier. The approximately two‐layer stratification of the fjord's ambient waters causes the meltwater plume at the glacier front to drive a “double cell” circulation with two distinct outflows, one at the free surface and one at the layers' interface. In summer, the discharge of surface runoff at the base of the glacier (subglacial discharge) causes the circulation to be much more vigorous and associated with a larger melt rate than in winter. The simulated “double cell” circulation is consistent, in both seasons, with observations from Sermilik Fjord. Seasonal differences are also present in the vertical structure of the melt rate, which is maximum at the base of the glacier in summer and at the layers' interface in winter. Simulated submarine melt rates are strongly sensitive to the amount of subglacial discharge, to changes in water temperature, and to the height of the layers. They are also consistent with those inferred from simplified one‐dimensional models based on the theory of buoyant plumes. Our results also indicate that to correctly represent the dynamics of the meltwater plume, care must be taken in the choice of viscosity and diffusivity values in the model.
Dynamic response of surface water‐groundwater exchange to currents, tides, and waves in a shallow estuary
Authors: Sawyer Audrey H. , Shi Fengyan , Kirby James T. , Michael Holly A.
Published: April 2013

In shallow, fetch‐limited estuaries, variations in current and wave energy promote heterogeneous surface water‐groundwater mixing (benthic exchange), which influences biogeochemical activity. Here, we characterize heterogeneity in benthic exchange within the subtidal zone of the Delaware Inland Bays by linking hydrodynamic circulation models with mathematical solutions for benthic exchange forced by current‐bedform interactions, tides, and waves. Benthic fluxes oscillate over tidal cycles as fluctuating water depths alter fluid interactions with the bed. Maximum current‐driven fluxes (~1–10 cm/d) occur in channels with strong tidal currents. Maximum wave‐driven fluxes (~1–10 cm/d) occur in downwind shoals. During high‐energy storms, simulated wave pumping rates increase by orders of magnitude, demonstrating the importance of storms in solute transfer through the benthic layer. Under moderate wind conditions (~5 m/s), integrated benthic exchange rates due to wave, current, and tidal pumping are each ~1–10 m3/s, on the order of fluid contributions from runoff and fresh groundwater discharge to the estuary. Benthic exchange is thus a significant and dynamic component of an estuary's fluid budget that may influence estuarine geochemistry and ecology.
A three‐dimensional eddy census of a high‐resolution global ocean simulation
Authors: Petersen Mark R. , Williams Sean J. , Maltrud Mathew E. , Hecht Matthew W. , Hamann Bernd
Published: April 2013

A three‐dimensional eddy census data set was obtained from a global ocean simulation with one‐tenth degree resolution and a duration of 7 years. The census includes 6.7 million eddies in daily data, which comprise 152,000 eddies tracked over their lifetimes, using a minimum lifetime cutoff of 28 days. Variables of interest include eddy diameter, thickness (vertical extent), minimum and maximum depth, location, rotational direction, lifetime, and translational speed. Distributions of these traits show a predominance of small, thin, short‐lived, and slow eddies. Still, a significant number of eddies possess traits at the opposite extreme; thousands of eddies larger than 200 km in diameter appeared in daily data each year. A tracking algorithm found hundreds of eddies with lifetimes longer than 200 days. A third of the eddies are at least 1000 m tall and many penetrate the full depth of the water column. The Antarctic Circumpolar Current contains the thickest and highest density of eddies. Thick eddies are also common in the Gulf Stream, Kuroshio Current, and Agulhas ring pathway. The great majority of eddies extend all the way to the surface, confirming that eddy censuses from surface observations are a good proxy for the full‐depth ocean. Correlations between variables show that larger‐diameter eddies tend to be thicker and longer lived than small eddies.
The Eastern Mediterranean Sea biogeochemical dynamics in the 1990s: A numerical study
Authors: Mattia Gelsomina , Zavatarelli Marco , Vichi Marcello , Oddo Paolo
Published: April 2013

The coupled physical‐biogeochemical dynamics of the Mediterranean Sea have been hindcasted for the decade 1990–2000 with the Nucleus for European Modeling of the Ocean‐Biogeochemical Flux Model coupled modeling system. This work describes and discusses the simulated changes in the Eastern Mediterranean Sea physical and biogeochemical dynamics occurring in the 1990s, contemporary to the establishment of the Eastern Mediterranean Transient. The physical component of the modeling system reproduces several changes in the Eastern Mediterranean physical dynamics and thermohaline structure that are consistent with observations pertinent to the transient period. The simulated change in the atmospheric forcing during the early 1990s is considered sufficient to develop upwelling favorable conditions that determine an overall upward displacement of the simulated deep Eastern Mediterranean nutrient pool. Model results indicate that in the post transient period, the displaced nutrients were advected westward along with the reestablishment of the Levantine Intermediate Water pathway, and together with the occurrence of strong winter mixing events in the Ionian Sea, they determined an increase of the primary production processes in the euphotic layer along the eastern coast of Ionian Sea and northern Levantine basin. The biogeochemical model suggests that such an increase in productivity apparently impacted mostly the microbial branch of the marine trophic web.
Modeling how surface nitrogen fixation influences subsurface nutrient patterns in the North Atlantic
Authors: Yoshikawa Chisato , Coles Victoria J. , Hood Raleigh R. , Capone Douglas G. , Yoshida Naohiro
Published: April 2013

We represented mechanistically the process of nitrogen (N) fixation and associated N* anomalies in the Atlantic Ocean using a three‐dimensional coupled physical/biogeochemical model. Available direct measurements of N fixation rates in the Atlantic Ocean are compiled, and these, along with observed N* anomalies, constrain the model. The model N fixation rate for the whole Atlantic domain is 2.1 × 1012 molN yr–1. The model‐generated N* anomaly shows the observed feature of a subsurface maximum. When plotted on isopycnal surfaces, the model‐generated N* anomaly bears little relation to the pattern of N fixation at the surface. However, the highest N fixation rates should be spatially related to N* distribution if particulate export is remineralized at depths in the same region where the N fixation occurred. We performed case studies varying remineralization and advection to clarify the genesis of the N* anomaly and to determine the reasons underlying differences between N* anomalies and N fixation rate patterns. These studies indicated that the difference between these two patterns was created by both horizontal advection of excess N compared to phosphorus (P) and preferential remineralization of P compared to N. N fixation and preferential P remineralization create high N* anomalies both at the surface and in subsurface waters in the tropical Atlantic, which are transported into the northwestern North Atlantic by western boundary currents and subsequently subducted. As a result, the highest N* anomalies are located not in the tropics but in the northwestern North Atlantic.
Multiple jets in the Malvinas Current
Authors: Piola Alberto R. , Franco Bárbara C. , Palma Elbio D. , Saraceno Martín
Published: April 2013

The velocity structure of the Malvinas Current is described based on the analysis of high‐resolution hydrographic data and direct current observations. The data show that though the current width exceeds 150 km, the flow is concentrated in two relatively narrow (~10–20 km) jets. Within these cores, the direct observations indicate surface velocities exceeding 0.5 m.s−1. Surface drifter, satellite‐derived mean dynamic topography, and sea surface temperature data suggest that the high‐velocity jets are also ubiquitous features of the time mean circulation. Both jets appear to be continuous features extending more than 900 km along the western slope of the Argentine Basin. These jets closely follow the 200 and 1400 m isobaths. Additional high‐velocity cores are apparent in direct current measurements and hydrographic observations, but these features are weaker and not continuous along the slope. Though the Malvinas Current transport is mostly barotropic, baroclinic jets are also identified in relative geostrophic velocity sections. The baroclinic jets are colocated with the barotropic jets. Our results suggest that the main Malvinas Current core is located over a relatively flat portion of the bottom, referred to as the Perito Moreno terrace. This observation is in agreement with recent seismic and geological evidence suggesting that in geological time scales the Malvinas Current played a key role in the configuration of the bottom sediments over the western slope of the Argentine Basin.
Spatio‐temporal distribution, along‐channel transport, and post‐riverflood recovery of salinity in the Guadalquivir estuary (SW Spain)
Authors: Díez‐Minguito M. , Contreras E. , Polo M. J. , Losada M. A.
Published: April 2013

This paper presents an experimental analysis of the salinity distribution, the salt balance, and the variation of the saline intrusion in comparison to the freshwater discharge in the Guadalquivir estuary, which is a mesotidal system regulated and normally subjected to extremely low river flows. In such low‐flow conditions, it is positive, well‐mixed, and tidally dominated. The estuary is also characterized by a nonstationary, effective longitudinal dispersion coefficient, whose probability density becomes increasingly narrower and whose mean value is higher further upstream. The tidal‐averaged salt flux is controlled by the following mechanisms (in order of importance): the nontidal transport, the Stokes transport, and the tidal pumping induced by the covariance between the current and salinity. These three factors account for more than 98% of the flux variation. In high river‐flow conditions, the subtidal response and recovery of the estuary to changes in the river flow is analyzed. The increase in the tidal‐averaged salinity during the first 2 weeks of the post‐riverflood recovery in the middle and upper sections of the estuary is found to be linear in time. During that time, the celerity of the salt intrusion front was 4cm/s. The 2 psu isohaline salt intrusion X2 exhibits a complex dependence on the river flow Qd, including the effects of human interventions in the estuary. Three regimes are identified for the intrusion: X2=57.0± 2.1km for discharges of less than 20m 3/s, X2 proportional to between 20 and 1000m 3/s, and X2proportional to for larger discharges.
Toward representing wave‐induced sediment suspension over sand ripples in RANS models
Authors: Amoudry Laurent O. , Bell Paul S. , Thorne Peter D. , Souza Alejandro J.
Published: April 2013

Parameterizations of near‐bed sediment processes are commonly associated with the poor predictive skill of coastal sediment transport models. We implement a two‐dimensional Reynolds‐averaged Navier‐Stokes model to directly assess these parameterizations by reproducing measurements obtained in large‐scale wave flume experiments. A sediment transport model has been coupled to wave hydrodynamics and turbulence, and numerical experiments provide temporal and spatial variations of free surface, flow velocity, sediment concentration, and turbulence quantities. Model‐data comparisons enable the direct assessment of how key suspension processes are represented and of the inherent variability of the sediment transport model. We focus on the different processes occurring above rippled beds versus dynamically flat beds. Numerical results show that increasing roughness alone is not sufficient to have good predictive capability above steep ripples. Some parameterization of the vortex entrainment process is necessary and a simple modification, which leads to constant sediment diffusivity above steep‐rippled beds, is sufficient to obtain good predictions of wave‐averaged suspended concentrations. Model‐data comparisons for the turbulent kinetic energy are also presented and highlight the need to account for the effect of vortex entrainment on near‐bed turbulence and transfer of momentum.
Global carbon budgets simulated by the Beijing Climate Center Climate System Model for the last century
Authors: Wu Tongwen , Li Weiping , Ji Jinjun , Xin Xiaoge , Li Laurent , Wang Zaizhi , Zhang Yanwu , Li Jianglong , Zhang Fang , Wei Min , Shi Xueli , Wu Fanghua , Zhang Li , Chu Min , Jie Weihua , Liu Yiming , Wang Fang , Liu Xiangwen , Li Qiaoping , Dong Min , Liang Xiaoyun , Gao Yang , Zhang Jie
Published: April 2013

The paper examines terrestrial and oceanic carbon budgets from preindustrial time to present day in the version of Beijing Climate Center Climate System Model (BCC_CSM1.1) which is a global fully coupled climate‐carbon cycle model. Atmospheric CO2 concentration is calculated from a prognostic equation taking into account global anthropogenic CO2 emissions and the interactive CO2 exchanges of land‐atmosphere and ocean‐atmosphere. When forced by prescribed historical emissions of CO2 from combustion of fossil fuels and land use change, BCC_CSM1.1 can reproduce the trends of observed atmospheric CO2 concentration and global surface air temperature from 1850 to 2005. Simulated interannual variability and long‐term trend of global carbon sources and sinks and their spatial patterns generally agree with other model estimates and observations, which shows the following: (1) Both land and ocean in the last century act as net carbon sinks. The ability of carbon uptake by land and ocean is enhanced at the end of last century. (2) Interannual variability of the global atmospheric CO2 concentration is closely correlated with the El Niño‐Southern Oscillation cycle, in agreement with observations. (3) Interannual variation of the land‐to‐atmosphere net carbon flux is positively correlated with surface air temperature while negatively correlated with soil moisture over low and midlatitudes. The relative contribution of soil moisture to the interannual variation of land‐atmosphere CO2 exchange is more important than that of air temperature over tropical regions, while surface air temperature is more important than soil moisture over other regions of the globe.
The 2010 California Research at the Nexus of Air Quality and Climate Change (CalNex) field study
Authors: Ryerson T. B. , Andrews A. E. , Angevine W. M. , Bates T. S. , Brock C. A. , Cairns B. , Cohen R. C. , Cooper O. R. , de Gouw J. A. , Fehsenfeld F. C. , Ferrare R. A. , Fischer M. L. , Flagan R. C. , Goldstein A. H. , Hair J. W. , Hardesty R. M. , Hostetler C. A. , Jimenez J. L. , Langford A. O. , McCauley E. , McKeen S. A. , Molina L. T. , Nenes A. , Oltmans S. J. , Parrish D. D. , Pederson J. R. , Pierce R. B. , Prather K. , Quinn P. K. , Seinfeld J. H. , Senff C. J. , Sorooshian A. , Stutz J. , Surratt J. D. , Trainer M. , Volkamer R. , Williams E. J. , Wofsy S. C.
Published: April 2013

The California Research at the Nexus of Air Quality and Climate Change (CalNex) field study was conducted throughout California in May, June, and July of 2010. The study was organized to address issues simultaneously relevant to atmospheric pollution and climate change, including (1) emission inventory assessment, (2) atmospheric transport and dispersion, (3) atmospheric chemical processing, and (4) cloud‐aerosol interactions and aerosol radiative effects. Measurements from networks of ground sites, a research ship, tall towers, balloon‐borne ozonesondes, multiple aircraft, and satellites provided in situ and remotely sensed data on trace pollutant and greenhouse gas concentrations, aerosol chemical composition and microphysical properties, cloud microphysics, and meteorological parameters. This overview report provides operational information for the variety of sites, platforms, and measurements, their joint deployment strategy, and summarizes findings that have resulted from the collaborative analyses of the CalNex field study. Climate‐relevant findings from CalNex include that leakage from natural gas infrastructure may account for the excess of observed methane over emission estimates in Los Angeles. Air‐quality relevant findings include the following: mobile fleet VOC significantly declines, and NOx emissions continue to have an impact on ozone in the Los Angeles basin; the relative contributions of diesel and gasoline emission to secondary organic aerosol are not fully understood; and nighttime NO3 chemistry contributes significantly to secondary organic aerosol mass in the San Joaquin Valley. Findings simultaneously relevant to climate and air quality include the following: marine vessel emissions changes due to fuel sulfur and speed controls result in a net warming effect but have substantial positive impacts on local air quality.