ALBERT

Description: Invertebrates in estuaries could be at a greater risk of parasitism as climate change causes sea levels to rise. A new paper published 8 December in Proceedings of the National Academy of Sciences of the United States of America (doi:10.1073/pnas.1416747111) describes how rapid sea level rise in the Holocene affected the population of parasitic flatworms called trematodes.

Description: Spur and groove (SAG) formations are found on the forereefs of many coral reefs worldwide. Modeling results have shown that SAG formations together with shoaling waves induce a nearshore Lagrangian circulation pattern of counter-rotating circulation cells, but these have never been observed in the field. We present results from two separate field studies of SAG formations on Palmyra Atoll which show their effect on waves to be small, but reveal a persistent order 1 cm/s depth-averaged Lagrangian offshore flow over the spur and onshore flow over the grooves. This circulation was stronger for larger, directly-incident waves and low alongshore flow conditions, consistent with predictions from modeling. Favorable forcing conditions must be maintained on the order of one hour to accelerate and develop the SAG circulation cells. The primary cross- and alongshore depth-averaged momentum balances were between the pressure gradient, radiation stress gradient and nonlinear convective terms, and the bottom drag was similar to values found on other reefs. The vertical structure of these circulation cells was previously unknown and the results show a complex horizontal offshore Lagrangian flow over the spurs near the surface driven by alongshore variability in radiation stress gradients. Vertical flow was downward over the spur and upward over the groove, likely driven by alongshore differences in bottom stress and not by vortex forcing. This article is protected by copyright. All rights reserved.

Description: Shipboard current measurements in the equatorial Indian Ocean in October and November of 2011 revealed oscillations in the meridional velocity with amplitude ~ 0.10m/s. These were clearest in a layer extending from ~300 to 600 m depth and had periods near 3 weeks. Phase propagation was upward. Measurements from two sequential time series at the equator, four meridional transects and one zonal transect are used to identify the oscillation as a Yanai wave packet and to establish its dominant frequency and vertical wavelength. The Doppler shift is accounted for, so that measured wave properties are translated into the reference frame of the mean zonal flow. We take advantage of the fact that, in the depth range where the wave signal was clearest, the time-averaged current and buoyancy frequency were nearly uniform with depth, allowing application of the classical theoretical representation of vertically propagating plane waves. Using the theory, we estimate wave properties that are not directly measured, such as the group velocity and the zonal wavelength and phase speed. The theory predicts a vertical energy flux that is comparable to that carried by midlatitude near-inertial waves. We also quantify the wave-driven meridional heat flux and the Stokes drift. This article is protected by copyright. All rights reserved.

Description: Understanding variability in the chlorophyll-specific absorption of marine phytoplankton, a ph * Chl (λ) , is essential for primary production modelling, calculation of underwater light field characteristics, and development of algorithms for remote sensing of chlorophyll concentrations. Previous field and laboratory studies have demonstrated significant apparent variability in a ph * Chl (λ) for natural samples and algal cultures. However, the potential impact of measurement uncertainties on derived values of a ph * Chl (λ) has received insufficient study. This study presents an analysis of measurement uncertainties for a data set collected in the Ligurian Sea in Spring and assesses the impact on estimates of a ph * Chl (λ) . It is found that a large proportion of apparent variability in this set of a ph * Chl (λ) can be attributed to measurement errors. Application of the same analysis to the global NOMAD data set suggests that a significant fraction of variability in a ph * Chl (λ) may also be due to measurement errors. This article is protected by copyright. All rights reserved.

Description: The South Atlantic is an important pathway for the inter-basin exchanges of heat and freshwater with strong influence on the global meridional overturning stability and variability. Along the 34°S parallel, a quarterly, high resolution XBT transect (AX18) samples the temperature structure in the upper ocean. The AX18 transect has been shown to be a useful component of a meridional overturning monitoring system of the region. However, a feasible, cost-effective design for an XBT-based system has not yet been developed. Here we use a high-resolution ocean assimilation product to simulate an XBT-based observational system across the South Atlantic. The sensitivity of the meridional heat transport, meridional overturning circulation, and geostrophic velocities to key observational and methodological assumptions is studied. Key assumptions taken into account are horizontal and temporal sampling of the transect, salinity and deep temperature inference, as well as the level of reference for geostrophic velocities. With the current sampling strategy, the largest errors in the meridional overturning and heat transport estimations are the reference (barotropic) velocity and the western boundary resolution. We show how altimetry can be used along with hydrography to resolve the barotropic component of the flow. We use the results obtained by the state estimation under observational assumptions to make recommendations for potential improvements in the AX18 transect implementation. This article is protected by copyright. All rights reserved.

Description: Herein, we report on the crystal structures of Nb 2 AlC and TiNbAlC—actual composition (Ti 0.45 ,Nb 0.55 ) 2 AlC—compounds determined from Rietveld analysis of neutron diffraction patterns in the 300–1173 K temperature range. The average linear thermal expansion coefficients of a Nb 2 AlC sample in the a and c directions are, respectively, 7.9(5) × 10 −6 and 7.7(5) × 10 −6  K −1 on one neutron diffractometer and 7.3(3) × 10 −6 and 7.0(2) × 10 −6  K −1 on a second diffractometer. The respective values for the (Ti 0.45 ,Nb 0.55 ) 2 AlC composition—only tested on one diffractometer—are 8.5(3) × 10 −6 and 7.5(5) × 10 −6  K −1 . These values are relatively low compared to other MAX phases. Like other MAX phases, however, the atomic displacement parameters (APDs) show that the Al atoms vibrate with higher amplitudes than the Ti and C atoms, and more along the basal planes than normal to them. When the predictions of the APDs obtained from density functional theory are compared to the experimental results, good quantitative agreement is found for the Al atoms. In case of the Nb and C atoms, the agreement was more qualitative.

Description: In this study, lithium disilicate (LS 2 ) glass samples with different particle sizes ranging from less than 105 to 850 μm were prepared. These specimens were inserted in a Pt-Rh DSC crucible and heated to 850°C at different rates (ϕ = 0.5–30 K/min) to identify their crystallization peaks. The activation energies for the overall crystallization ( E ) and the Avrami coefficient ( n ) were evaluated using different nonisothermal models. Specifically, n was evaluated using the Augis–Benett model and the Ozawa method, and E was evaluated using the Kissinger and Ligero methods. As expected, the coarse particles mainly crystallized in the volume, while surface crystallization was predominant in the samples with particle sizes of less than 350 μm. This result was confirmed through SEM analysis of the double stage heat-treated samples. In contrast with previous studies, our results demonstrated that the activation energy decreased as the particle size increased. In addition, no clear correlation between the peak intensity (δ T p ) and the particle size was observed.

Description: Observations of the nearbed velocity field over a rippled sediment bed under asymmetric wave forcing conditions were collected using a submersible particle image velocimetry (PIV) system. To examine the role of bedform-induced dynamics in the total momentum transfer, a double-averaging technique was implemented on the two-dimensional time-dependent velocity field by means of the full momentum equation. This approach allows for direct determination of the bedform-induced stresses, ie. stresses that arise due to the presence of bedforms, which are zero in flat bed conditions. This analysis suggests that bedform-induced stresses are closely related to the presence of coherent motions and may be partitioned from the turbulent stresses. Inferences of stress provided by a bedload transport model suggest that total momentum transfer obtained from the double-averaging technique is capable of reproducing bedform mobilization. Comparisons between the total momentum transfer and stress estimates obtained from local velocity profiles show significant variability across the ripple, and suggest that an array of sensors is necessary to reproduce bedform evolution. The imbalance of momentum obtained by resolving the different terms constituting the near-bed momentum balance (i.e. acceleration deficit, stress gradient, and bedform-induced skin friction) provides an estimate of the bedform-induced pressure that is consistent with flow separation. This analysis reveals three regions in the flow: the free-stream, where all terms are relatively balanced; the near-bed, where momentum imbalance is significant during flow weakening; and below ripple crests, where bedform-induced pressure is the leading order mechanism.

Description: An analysis is presented for the spatial and intensity distributions of North Atlantic extreme atmospheric events crossing the buoyant Amazon-Orinoco freshwater plume. The sea surface cooling amplitude in the wake of an ensemble of storm tracks travelling in that region is estimated from satellite products for the period 1998-2012. For the most intense storms, cooling is systematically reduced by ~50% over the plume area compared to surroundings open ocean waters. Historical salinity and temperature observations from in situ profiles indicate that salt-driven vertical stratification, enhanced oceanic heat content and barrier-layer presence within the plume waters are likely key oceanic factors to explain these results. Satellite SMOS surface salinity data combined with in situ observations are further used to detail the oceanic response to Category 4 hurricane Igor in 2010. Argo and satellite measurements confirm the haline stratification impact on the cooling inhibition as the hurricane crossed the river plume. Over this region, the SSS mapping capability is further tested and demonstrated to monitor the horizontal distribution of the vertical stratification parameter. SMOS SSS data can thus be used to consistently anticipate the cooling inhibition in the wake of TCs travelling over the Amazon-Orinoco plume region.

Description: The mixed layer salinity (MLS) budget of the tropical Pacific is investigated using results from a model of the Consortium for Estimating the Circulation and Climate of the Ocean (ECCO). The results focusing on the western Pacific freshwater pool indicate that the long-term averaged surface freshwater flux is well balanced by ocean dynamics, in which the subsurface processes account for the major part. The MLS budget shows significant seasonal and interannual variability, as a consequence of interplay among surface freshwater flux, advection, mixing, and vertical entrainment. On seasonal time scale, both the MLS and mixed layer depth are largely controlled by surface freshwater flux. The opposite phase between the subsurface processes and the barrier layer thickness confirms the important influence of the barrier layer on vertical mixing and entrainment from below. On interannual time scale, all the MLS budget terms show significant ENSO signal, which in turn is highly correlated with the salinity front and barrier layer thickness in the equatorial Pacific.

Description: To study the relationship of solar heat input into the Arctic open water and the variations of sea ice extent, improved satellite based estimates of shortwave radiative (SWR) fluxes and most recent observations of ice extent are used. The SWR flux estimates are based on observations from the Moderate Resolution Imaging Spectroradiometer (MODIS) and from the Advanced Very High Resolution Radiometer (AVHRR) for the period of 1984-2009. Ice extent information at 25-km resolution comes from Nimbus-7 SMMR and DMSP SSM/I Passive Microwave Data as generated with the NASA Team algorithm developed by the Oceans and Ice Branch, Laboratory for Hydrospheric Processes, NASA Goddard Space Flight Center. The trends of the solar heat input into the ocean and the open water fraction for 1984-2009 are found to be positive: 0.3%/year and 0.8% / year respectively at a 99% confidence level. There is an obvious transition region separating the 26 years into two periods: one with moderate change: 1984-2002; one with an abrupt growth in both solar heat input and open water fraction: 2003-2009. The impact of the observed changes on the reduction of winter ice growth in 2007 is estimated to be about 44 cm, and a delay in fall freeze-up as about 10~36 days.

Description: Numerous studies have shown the primary importance of wind stress curl in coastal upwelling dynamics. The main goal of this new analysis is to describe the QuikSCAT surface wind stress curl at various scales in the Benguela and Canary upwelling systems. The dominant spatial pattern is characterized by cyclonic curl near continental boundaries and anticyclonic curl offshore, in association with equatorward alongshore (upwelling favorable) wind stress. At a smaller scale, we demonstrate the sensitivity of the QuikSCAT wind stress curl to coastal processes related to sea surface temperature (SST) mesoscale fluctuations by presenting a linear relationship between the curl and crosswind SST gradients. Despite the spatial and temporal sensitivity of the underlying thermal coupling coefficient, a local analysis of the fraction of the curl ascribed to SST variability shows that SST is a main driver of the wind stress curl variability and magnitude over the upwelling extension zone (~100 to 300 km from the coast) in both the Canary and Benguela systems. Closer to the shore, the curl patterns derived from QuikSCAT observations are only loosely related to SST-wind interactions. As a working hypothesis, they can also be associated with the coastline geometry and orographic effects that are likely to play an important role in local cooling processes.

Description: To provide a probable explanation on the field observed rapid sedimentation process near river mouths, we investigate the convective sedimentation in stably stratified saltwater using 3D numerical simulations. Guided by the linear stability analysis (Yu et al. 2013, J. Geophys. Res. Oceans, 118, 256-272), this study focuses on the nonlinear interactions of several mechanisms, which lead to various sediment finger patterns, and the effective settling velocity for sediment ranging from clay (single-particle settling velocity V 0 = 0.0036 and 0.0144 mm/s, or particle diameter d = 2 and 4 μ m) to silt ( V 0 =0.36 mm/s, or d =20 μ m). For very fine sediment with V 0 =0.0036 mm/s, the convective instability is dominated by double diffusion, characterized by millimeter-scale fingers. Gravitational settling slightly increases the growth rate; however, it has notable effect on the downward development of vertical mixing shortly after the sediment interface migrates below the salt interface. For sediment with V 0 = 0.0144 mm/s, Rayleigh-Taylor instabilities become dominant before double-diffusive modes grow sufficiently large. Centimeter-scale and highly asymmetric sediment fingers are obtained due to nonlinear interactions between different modes. For sediment with V 0 = 0.36 mm/s, Rayleigh-Taylor mechanism dominates and the resulting centimeter-scale sediment fingers show a plume-like structure. The flow pattern is similar to that without ambient salt stratification. Rapid sedimentation with effective settling velocity on the order of 1 cm/s is likely driven by convective sedimentation for sediment with V 0 greater than 0.1 mm/s at concentration greater than 10 to 20 g/L.

Description: The surface layer of the southeast Pacific Ocean (SEP) requires an input of cold, fresh water to balance heat gain and evaporation from air-sea fluxes. Models typically fail to reproduce the cool sea surface temperatures (SST) of the SEP, limiting our ability to understand the variability of this climatically important region. We estimate the annual heat budget of the SEP for the period 2004 - 2009, using data from the upper 250 m of the Stratus mooring, located at 85°W 20°S, and from Argo floats. The surface buoy measures meteorological conditions and air-sea fluxes; the mooring line is heavily instrumented, measuring temperature, salinity, and velocity at more than 15 depth levels. We use a new method for estimating the advective component of the heat budget that combines Argo profiles and mooring velocity data, allowing us to calculate monthly profiles of heat advection. Averaged over the 6 year study period, we estimate a cooling advective heat flux of -41 ± 29 W m-2, accomplished by a combination of the mean gyre circulation, Ekman transport, and eddies. This compensates for warming fluxes of 32 ± 4 W m-2 due to air-sea fluxes and 7 ± 9 W m-2 due to vertical mixing and Ekman pumping. A salinity budget exhibits a similar balance, with advection of freshwater (-60 psu m) replenishing the freshwater lost through evaporation (47 psu m) and Ekman pumping (14 psu m).

Description: About an hour and a half before the launch of the Orbital Sciences Corporation's Antares rocket and Cygnus cargo spacecraft at 6:22 p.m. on 28 October, Jeff Goldstein arrived at his vantage point on Arbuckle Neck Road in Assawoman, Va. It was just 1.5 miles from launchpad 0A at NASA's Wallops Flight Facility. Goldstein, director of the National Center for Earth and Space Science Education (NCESSE) had come with about 35 elementary school through college students, as well as some parents, teachers, and school administrators, to watch the liftoff that would deliver the students' microgravity experiments to the International Space Station (ISS).

Description: Americans are very worried about the threat of natural disasters—but don't seem to be prepared for one. This conclusion comes from Chapman University's recent Survey on American Fears, released on 21 October. The survey asked 1500 Americans to rank how worried they were about several types of natural disasters and then how prepared they were for each.

Description: Microbial communities in thawing permafrost contribute a significant amount to atmospheric methane, a greenhouse gas many times more potent than carbon dioxide. A new paper published in Nature on 23 October describes how a newly discovered microbe— Methanoflorens stordalenmirensis —adds another layer to the complicated relationship between the world's permafrost fields and greenhouse gas (GHG) emissions.

Description: Crowdsourcing—“the act of taking a job traditionally performed by a designated agent [expert] and outsourcing it to an undefined, generally large group of people” [ Howe, 2009]—has fundamentally changed and enhanced the collection and dissemination of data. Crowdsourcing has proven effective for rapid data collection, especially where in-depth knowledge of a topic or discipline is not a necessity.

Description: I am a counter by nature. I count things as an effective way to occupy my mind. How many people are in this room? How many are women? How many are wearing glasses? How many people are using a Mac versus a PC?

Description: Ethics education is an increasingly important component of the pre-professional training of geoscientists. Geoethics encompasses the values and professional standards required of geoscientists to work responsibly in any geoscience profession and in service to society. Funding agencies (e.g., the National Science Foundation, the National Institutes of Health) require training of graduate students in the responsible conduct of research; employers are increasingly expecting their workers to have basic training in ethics; and the public demands the highest standards of ethical conduct by scientists. However, there is currently no formal course of instruction in ethics in the geoscience curriculum, and few faculty members have the experience, resources, and sometimes willingness required to teach ethics as a component of their geoscience courses.

Description: U.S. hydrocarbon production is on the rise, meaning that transporting hydrocarbons—whether by pipelines, trucks, or trains—is as well. However, increasing environmental concerns, mixed with other issues such as energy independence and landowner rights, is making this transportation a hot-button issue.

Description: Lava from Iceland's Bardarbunga volcano, which began erupting on 29 August, now covers 60 square kilometers of the Holuhraun lava field. Scientists have arrived in droves to study the ongoing fissure eruptions.

Description: In the early years of the 20th century, physicist Bernard Brunhes, then director of the Geophysical Observatory of Puy de Dôme (now Observatoire de Physique du Globe de Clermont), measured for the first time reverse magnetization in samples from a basaltic lava flow and from the underlying backed argillaceous sediments from the village of Pontfarein (now Pont Farin) in the Cantal volcanic district (Auvergne, France).

Description: During the latter half of the Cenozoic, starting during the Pliocene, the eastern equatorial Pacific (EEP) underwent a change from warm, wet climate conditions—which scientists refer to as “permanent El Niño”—to more moderate conditions like those observed today. Although scientists can track this change using marine proxy records, they are still puzzled as to why the sudden shift occurred.

Description: Scientists who study the physics of inland and coastal water bodies met in Trento, Italy in July for the 17th in a series of workshops that seek to expand cooperation with researchers in related fields. The workshops aim to facilitate the dialogue among physical limnologists, modelers, and colleagues from other disciplines, such as biologists, chemists, and engineers. This year's workshop was attended by 47 participants from 17 different countries.

Description: Saturn's magnetosphere exhibits phenomena with 10.7-hour periodicity that scientists do not fully understand. One proposed explanation is that twin vortices in the upper atmosphere at Saturn's north and south poles generate currents that drive the magnetosphere periodicity.

Description: On 9 December a dynamic, new, broadly inclusive, and freely accessible Earth and space science news website will launch: Eos.org. This new site is inspired by AGU's vision to galvanize our community of Earth and space scientists to collaboratively advance and communicate our science.

Description: The motion of the Earth's mantle is controlled in part by how mantle minerals respond to changes in temperature and pressure. The chemical and physical shifts that minerals undergo as they are heated and squeezed cause some to sink down toward the core and others to rise up toward the surface. This buoyant pressure and gravitational sinking, in turn, affect the convection of the mantle and the large-scale cycling of the Earth.

Description: Because the Earth's population is slated to hit 9 billion in the next century, food scarcity has become an increasingly important topic of study. Food availability is widely examined, but D'Odorico et al. point out that reliance on trade to distribute food has not been sufficiently quantified.

Description: As a glacier slides slowly into the sea, buoyancy eventually trumps gravity, and the sheet of ice floats. The place where the ice starts leaving the ground is called the grounding line, and this line can shift as the mass of the glacier shifts with precipitation or climate. Studying the movement of the grounding line through time helps scientists determine the stability of the glacier and its mass budget—the balance of how much mass the glacier is gaining or losing.

Description: The Edmond M. Dewan Young Scientist Scholarship fund has reached its goal of $25,000. Those who donated to the fund share AGU's mission in taking an active role in educating and nurturing the next generation of scientists and ensuring a sustainable future for society. Thanks to the generosity of more than 100 members of the AGU and science community, a deserving graduate student of atmospheric or space physics will receive financial assistance to further his or her research and advance his or her research and future career.

Description: Throughout the western United States, scientists have noticed that warming has reduced snow accumulation and led to earlier snowmelt, a change that could have dire consequences for the region's ecology and industries. Specifically, previous research has found that the rain-snow transition zone—the area where precipitation is dominated by rain versus snow in the winter—has shifted significantly in the past few decades.

Description: Coastal Oregon is home to a number of slow, recurrent landslides. During bouts of heavy rain, water gets into the soil, reducing friction and causing the ground to slip. Often, these landslides creep along at a barely perceptible rate—less than a centimeter per day. Yet the landslides are a lurking threat, as past events that have damaged infrastructure and cut communities off for months at a time have demonstrated.

Description: Surface ice on oceans and lakes can cause major problems onshore and offshore. Specifically, surface waves interacting with ice can create hazardous conditions for cargo ships, damage coastal structures, and carry important nutrients away from the shore.

Description: Acoustic-gravity waves are compression-type waves propagating with amplitudes governed by the restoring force of gravity. They are generated, among others, by wind-wave interactions, surface waves interactions, and submarine earthquakes. We show that acoustic-gravity waves contribute to deep ocean currents and circulation; they cause chaotic flow trajectories of individual water parcels, which can be transported by a few centimetres per second.

Description: In this letter, 2-μm Pb 0.97 La 0.02 (Zr 0.75 Sn 0.18 Ti 0.07 )O 3 antiferroelectric thick film with tetragonal structure was prepared. The effects of operating electric field, temperature, and frequency on the thermal–electrical energy harvesting capacity of the film were studied by using the Olsen cycle. The results demonstrated that giant energy harvesting effect could be realized in the antiferroelectric thick film. The maximum harvestable energy density per cycle of the film was about 7.8 J/cm 3 at 1 kHz, which was the largest reported value to date. The corresponding energy harvesting efficiency was 0.53%. Moreover, the film had a low leakage current density (about 7.3 × 10 −7 and 3.9 × 10 −5  A/cm 2 at 25 and 200°C, respectively), which was favorable for its application in the devices of the thermal–electrical energy harvesting.

Description: Discharged energy properties of PbO–SrO–Na 2 O–Nb 2 O 5 –SiO 2 glass-ceramics with crystallization time from 1 to 1000 min were investigated by measuring their hysteresis loops (described as quasi-static measuring method) and pulse-discharge current-time curves (described as dynamic measuring method). The results show the same trend for both measuring methods: With the increment of crystallization time, the discharged energy density increases gradually, while the energy efficiency decreases. The highest energy efficiencies were obtained in the sample with crystallization time of 1 min, which are 96.3% and 82.4%, corresponding quasi-static and dynamic measurement, respectively. The reduction of energy efficiency with crystallization time is attributed to combined effect of ferroelectric polarization and interfacial polarization, and part of the corresponding energy could not release in the pulse-discharge process.

Description: The Berau Continental Shelf is located close to the Equator in the Indonesian Archipelago, hosting a complex of coral reefs along its oceanic edge. The Berau coral reefs have a very high biodiversity, but the area is under serious risk due to river-derived nutrients and sediments. The region is characterized by weak winds, moderate tides and almost absent Coriolis forcing. Existing knowledge about river plume behaviour in tropical environments is limited. The aim of this paper is to investigate the influence of the subtle physical forcing on the dynamics of the Berau river plume. A three-dimensional model (ECOMSED) was calibrated with observational data. The model was forced by freshwater input from the Berau river distributaries, tides at the open boundaries and measured hourly wind. The model reproduces the freshwater dynamics on the shelf adequately and highlights that the river plume spreads symmetrically for river forcing only. Tides cause vertical mixing and suppress the cross-shelf spreading of the river plume. However, the spreading of the river plume over the shelf is mainly controlled by the weak monsoonal winds, resulting in a seasonal development. During the Southeast Monsoon, the southerly winds push the plume northeastward and cause a stratified water column in the northern part of the continental shelf. Northerly winds during the Northwest Monsoon disperse the plume to the south, promoting a vertically well-mixed water column. The results can be used to predict the possible impact of land-use changes in the steadily developing Berau region on coral reef health. This article is protected by copyright. All rights reserved.

Description: This study investigates the effect of adaptive (or targeted) observation on improving the mid-range (30 days) forecast skill of ocean state of the South China Sea (SCS). A region associated with the South China Sea Western Boundary Current (SCSWBC) is chosen as the “target” of the adaptive observation. The Conditional Nonlinear Optimal Perturbation (CNOP) approach is applied to a 3-dimensional ocean model and its adjoint model for determining the sensitive region. Results show that the initial errors in the sensitive region determined by the CNOP approach have significant impacts on the forecast of ocean state in the target region; thus, reducing these initial errors through adaptive observation can lead to a better 30-day prediction of ocean state in the target region. Our results suggest that implementing adaptive observation is an effective and cost-saving way to improve an ocean model's forecast skill over the SCS. This article is protected by copyright. All rights reserved.

Description: We present a year-round assessment of the hydrographic variability within the East Greenland Coastal Current on the Greenland shelf from five synoptic crossings and four years of moored hydrographic data. From the five synoptic sections the current is observed as a robust, surface intensified flow with a total volume transport of 0.66 ± 0.18 Sv and a freshwater transport of 42 ± 12 mSv. The moorings showed heretofore unobserved variability in the abundance of Polar and Atlantic water masses in the current on synoptic scales. This is exhibited as large vertical displacement of isotherms (often greater than 100 m). Seasonally, the current is hemmed into the coast during the fall by a full depth Atlantic Water layer that has penetrated onto the inner shelf. The Polar Water layer in the current then thickens through the winter and spring seasons increasing the freshwater content in the current; the timing implies that this is probably driven by the seasonally varying export of freshwater from the Arctic and not the local runoff from Greenland. The measured synoptic variability is enhanced during the winter and spring period due to a lower halocline and a concurrent enhancement in the along-coast wind speed. The local winds force much of the high-frequency variability in a manner consistent with downwelling, but variability distinct from downwelling is also visible. This article is protected by copyright. All rights reserved.

Description: The performance of several numerical ocean models is assessed with respect to their simulation of sea surface height (SSH) in the Arctic Ocean, and the main patterns of SSH variability and their causes over the past 40 years (1970-2009) are analyzed. In comparison to observations, all tested models broadly reproduce the mean SSH in the Arctic and reveal a good correlation with both tide gauge data and SSH anomalies derived from satellite observations. Although the models do not represent the positive Arctic SSH trend observed over the last two decades, their interannual-to-decadal SSH variability is in reasonable agreement with available measurements. Focusing on results from one of the models for a detailed analysis it is shown that the decadal-scale SSH variability over shelf areas and deep parts of the Arctic Ocean have pronounced differences that are determined mostly by salinity variations. A further analysis of the three time periods 1987-1992, 1993-2002 and 2003-2009, corresponding to the transition times between cyclonic and anticyclonic regimes of the atmospheric circulation over the Arctic, revealed an unusual increase of SSH in the Amerasian basin during 2003-2009. Results from this model support the recent finding that the increase is caused mainly by changes in freshwater content brought about by the freshwater export through the Canadian Arctic Archiplago and increased Ekman pumping in the Amerasian basin and partly by lateral freshwater transport changes, leading to a re-distribution of low-salinity shelf water. Overall we show that present day models can be used for investigating the reasons for low-frequency SSH variability in the region. This article is protected by copyright. All rights reserved.

Description: In this study, a neural network-based four-band model (NNFM) for the global oceanic and coastal waters has been developed in order to retrieve the total absorption coefficients a ( λ ). The applicability of the quasi-analytical algorithm (QAA) and NNFM models is evaluated by five independent datasets. Based on the comparison of a ( λ ) predicted by these two models with the field measurements taken from the global oceanic and coastal waters, it was found that both the QAA and NNFM models had good performances in deriving a ( λ ), but that the NNFM model works better than the QAA model. The results of the QAA model-derived a ( λ ), especially in highly turbid waters with strong backscattering properties of optical activity, was found to be lower than the field measurements. The QAA and NNFM models-derived a ( λ ) could be obtained from the MODIS data after atmospheric corrections. When compared with the field measurements, the NNFM model decreased by a 0.86 to 24.15% uncertainty (root mean square relative error) of the estimation from the QAA model in deriving a ( λ ) from the Bohai, Yellow, and East China seas. Finally, the NNFM model was applied to map the global climatological seasonal mean a (443) for the time range of July, 2002 to May, 2014. As expected, the a (443) value around the coastal regions was always larger than the open ocean around the equator. Viewed on a global scale, the oceans at a high latitude exhibited higher a (443) values than those at a low latitude. This article is protected by copyright. All rights reserved.

Description: In this study, we investigate the interannual variability of the sea surface temperature (SST) in the South China Sea (SCS) associated with two types of El Niño, namely, the eastern Pacific (EP) El Niño and the central Pacific (CP) El Niño. First, double warm peaks can occur during both types of El Niño events in the SCS. However, the strong warm basin mode can only develop in the EP El Niño, while the warm semi-basin mode exists during the CP El Niño. Associated with an anomalous positive (negative) net surface heat flux in the EP (CP) El Niño, along with a shallower thermocline with weaker (stronger) northeasterly wind anomalies, the SST anomalies become warmer (cooler) in the developing autumn. Over the background of cooling SST in autumn of CP El Niño, therefore, only a weak warming can occur in the subsequent years, which is limited in the western boundary area under the forcing of warm ocean advection. Second, the SST oscillation periods are different in these two types of El Niño. The SST evolution in the EP El Niño is negative-positive with a quasi-biennial oscillation, but that in the CP El Niño is positive-negative-positive-negative with an annual oscillation. It seems that the double cooling in the CP El Niño is phase-locked to the late autumn season. This article is protected by copyright. All rights reserved.

Description: Following the idea that analysis of in-situ information in the salt budget could be used as a surrogate for global “ocean rain gauge”, the annual mean oceanic net freshwater flux (E-P) was estimated from the Argo profiles and the wind stress data on a global scale. The comparison between the independent E-P estimation from Argo and the E-P product sets, including the combination of precipitation from TRMM, GPCP, CMAP and evaporation from OAFlux, GSSTF3 and IFREMER and E-P set from NEWS formed from satellite, generally show similar spatial patterns, particularly on the larg scale. However, there are differences among the different satellite-based E-P estimates and between satellite estimates and independent in-situ estimates. Based on the pattern correlation and the RMSD, the evaporation and precipitation from OAFlux and TRMM agrees best with the E-P estimated from the independent Argo-based estimates.

Description: The rapidly changing East Siberian Arctic Shelf (ESAS) receives large amounts of terrestrial organic carbon (OC) from coastal erosion and Russian-Arctic rivers. Climate warming increases thawing of coastal Ice Complex Deposits (ICD) and can change both the amount of released OC, as well as its propensity to be converted to greenhouse gases (fueling further global warming) or to be buried in coastal sediments. This study aimed to unravel the susceptibility to degradation, and transport and dispersal patterns of OC delivered to the ESAS. Bulk and molecular radiocarbon analyses on surface particulate matter (PM), sinking PM and underlying surface sediments illustrate the active release of old OC from coastal permafrost. Molecular tracers for recalcitrant soil OC showed ages of 3.4-13 14 C-ky in surface PM and 5.5-18 14 C-ky in surface sediments. The age difference of these markers between surface PM and surface sediments is larger (i) in regions with low OC accumulation rates, suggesting a weaker exchange between water column and sediments, and (ii) with increasing distance from the Lena River, suggesting preferential settling of fluvially-derived old OC nearshore. A dual-carbon end-member mixing model showed that (i) contemporary terrestrial OC is dispersed mainly by horizontal transport while being subject to active degradation, (ii) marine OC is most affected by vertical transport and also actively degraded in the water column, and (iii) OC from ICD settles rapidly and dominates surface sediments. Preferential burial of ICD-OC released into ESAS coastal waters might therefore lower the suggested carbon cycle climate feedback from thawing ICD permafrost. This article is protected by copyright. All rights reserved.

Description: The Arctic sea ice cover undergoes large changes over an annual cycle. In winter and spring the ice cover consists of large, snow-covered plate-like ice floes, with very little open water. By the end of summer the snow cover is gone and the large floes have broken into a complex mosaic of smaller, rounded floes surrounded by a lace of open water. This evolution strongly affects the distribution and fate of the solar radiation deposited in the ice-ocean system and consequently the heat budget of the ice cover. In particular, increased floe perimeter can result in enhanced lateral melting. We attempt to quantify the floe evolution process through the concept of a floe size distribution that is modified by lateral melting and floe breaking. A time series of aerial photographic surveys made during the SHEBA field experiment is analyzed to determine evolution of the floe size distribution from spring through summer. Based on earlier studies, we assume the floe size cumulative distribution could be represented by a power law D -α where D is the floe diameter. The exponent α as well as the number density of floes N tot are estimated from measurements of total ice area and perimeter. As summer progressed, there was an increase in α as the size distribution shifted towards smaller floes and the number of floes increased. Lateral melting causes the distribution to deviate from a power law for small floe sizes. This article is protected by copyright. All rights reserved.

Description: The responses of the ocean planktonic ecosystem to finite-amplitude perturbations are investigated using an ocean planktonic ecosystem model. Through changing the higher predation rate on zooplankton, multiple equilibria of the model, namely “high-nutrient” and “low-nutrient” states, are obtained under certain parameter values. Based on these states, the perturbations with maximum nonlinear growth are determined using the conditional nonlinear optimal perturbation (CNOP) method. The linear and nonlinear evolutions of the CNOP perturbation are compared. The results show that the nonlinear evolution of the perturbation leads to predator–prey oscillations with larger amplitude than the linear evolution. Besides, after the perturbation amplitude exceeds a critical value, the nonlinear evolution of the perturbation will induce the linearly stable ecosystem state to lose the stability and become nonlinearly unstable. This implies that nonlinear processes have important impacts on the stability of the ecosystem. Specifically, we identify the nonlinear processes related to zooplankton grazing to impact the stability most for the high-nutrient state, while for the low-nutrient state the main nonlinear process affecting the stability is the uptake process. These results help to improve our understanding of the sensitivity of the oceanic ecosystem model to finite-amplitude perturbations and the underlying nonlinear stability properties. This article is protected by copyright. All rights reserved.

Description: We evaluated the impacts of summertime mesoscale convective systems (MCS) on the heat balance and diel surface mixed layer (SML) dynamics of the Brazilian Amazon's Tucuruí Hydroelectric Reservoir (THR). We used a synergistic approach that combines in situ data, remote sensing data and three-dimensional (3D) modeling to investigate the typical behavior of the components of the heat balance and the SML dynamics. During the study period (the austral summer of 2012-2013), 22 days with MCS activity were identified. These events occurred approximately every 4 days, and they were most frequent during January (50% of the observations). An analysis of local meteorological data showed that when MCS occur, the environmental conditions at THR change significantly ( p-value 〈 0.01). The net longwave flux, which was the heat balance component most strongly impacted by MCS, increased more than 32% on days with MCS activity. The daily integrated heat balance became negative (-54 W m -2 ) on MCS days, while the balance was positive (19 W m -2 ) on non MCS days. In response to the changes in the heat balance, the SML dynamics changed when a MCS was over the THR. The SML depth was typically 28% higher on the days with MCS (~1.6 m) compared with the days without MCS (~1.3 m). The results indicate that MCS are one of the main meteorological disturbances driving the heat balance and the mixing dynamics of Amazonian hydroelectric reservoirs during the summer. These events may have implications for the water quality and greenhouse gas emissions of Amazonian reservoirs. This article is protected by copyright. All rights reserved.

Description: As part of the Amazon Web Services Hack-A-Thon, this year's AGU Fall Meeting attendees will be challenged to create an idea for a Web product based on climate change data for individual cities.

Description: The rate of ocean acidification in coral reefs outpaces the rise in carbon dioxide (CO 2 ) in Earth's atmosphere, indicating that anthropogenic carbon emissions alone are not to blame for the threat to coral reefs, a new study shows.

Description: New lead-free perovskite solid solution ceramics of (1  − x )( Bi 1/2 Na 1/2 ) TiO 3 – x Ba ( Ni 1/2 Nb 1/2 ) O 3 [(1− x )BNT– x BNN, x  =   0.02–0.06) were prepared and their dielectric, ferroelectric, piezoelectric, and electromechanical properties were investigated as a function of the BNN content. The X-ray diffraction results indicated that the addition of BNN has induced a morphotropic phase transformation from rhombohedral to pseudocubic symmetry approximately at x  =   0.045, accompanying an evolution of dielectric relaxor behavior as characterized by enhanced dielectric diffuseness and frequency dispersion. In the proximity of the ferroelectric rhombohedral and pseudocubic phase coexistence zone, the x  =   0.045 ceramics exhibited optimal piezoelectric and electromechanical coupling properties of d 33 ~121 pC/N and k p ~0.27 owing to decreased energy barriers for polarization switching. However, further addition of BNN could cause a decrease in freezing temperatures of polar nanoregions till the coexistence of nonergodic and ergodic relaxor phases occurred near room temperature, especially for the x  =   0.05 sample which has negligible negative strains and thus show the maximum electrostrain of 0.3% under an external electric field of 7 kV/mm, but almost vanished piezoelectric properties. This was attributed to the fact that the induced long-range ferroelectric order could reversibly switch back to its original ergodic state upon removal of external electric fields.

Description: Light transmission in polycrystalline magnesium fluoride was studied as a function of the mean grain size at different wavelengths. The mean grain size was varied by annealing hot-pressed billets in argon atmosphere at temperatures ranging from 600°C to 800°C for 1 h. The grain-size and grain-orientation distributions were characterized by electron back scatter diffraction. The scattering coefficients were calculated from the in-line transmittance measured at various wavelengths. The scattering coefficient of polycrystalline magnesium fluoride increased linearly with the mean grain size and inversely with the square of the wavelength of light. It is shown that these trends are consistent with theoretical models based on both a limiting form of the Raleigh–Gans–Debye (RGD) theory of particle scattering and light retardation theories that take refractive index variations along the light path. Quantitative predictions of the theories are, however, subject to uncertainly due to the restrictive assumptions made in the theories and difficulties in representing the microstructure in the theoretical models. In particular, grain-size distribution has a significant influence on the scattering coefficient calculated using particle scattering models.

Description: Determining the absolute chronology of ceramic artifacts has significant implications for archeological and historical research. Wilson, Hall et al . recently suggested a new technique for direct absolute dating of archeological ceramics based on a moisture-induced chemical reaction, called rehydroxylation (RHX) dating. RHX dating proceeds by measuring the mass of chemically combined water in the ceramics in the form of OH hydroxyls, and the mass gain rate at the Effective Lifetime Temperature (ELT) that the ceramics experienced over its lifetime. To date, ELT determinations have been based on estimates of the ceramic's lifetime temperature history; taking into account weather and climate data and the depth at which the artifact was found. The uncertainty in determining the ELT can be a major component of the overall dating uncertainty. Here, we propose an alternative method which relies minimally on weather and climate data, and provides more precise determinations of the ELT and the ceramic age . The proposed method (SAS: Same Age Samples) involves a minimum of four measurements of the RHX mass gain rate constant for two ceramic samples of the same age at two temperatures. We show via simulations that the proposed SAS method can determine the ELT with a precision of 0.2 K which is comparable to the best ELT determination based on lifetime temperature history, and also comparable to available microbalance temperature resolutions of around 0.1 K. The corresponding percent age error is then 1.4%, or 43 yr for a 3000-yr-old ceramic. The proposed SAS method should be tested with ceramic samples of different ages, whose ELT are well-known.

Description: Glasses in the Na 2 O–CaO–SrO–ZnO–SiO 2 system have previously been investigated for suitability as a reagent in Al-free glass polyalkenoate cements (GPCs). These materials have many properties that offer potential in orthopedics. However, their applicability has been limited, to date, because of their poor strength. This study was undertaken with the aim of increasing the mechanical properties of a series of these Zn-based GPC glasses by doping with nitrogen to give overall compositions of: 10Na 2 O–10CaO–20SrO–20ZnO–(40−3 x )SiO 2 – x Si 3 N 4 ( x is the no. of moles of Si 3 N 4 ). The density, glass-transition temperature, hardness, and elastic modulus of each glass were found to increase fairly linearly with nitrogen content. Indentation fracture resistance also increases with nitrogen content according to a power law relationship. These increases are consistent with the incorporation of N into the glass structure in threefold coordination with silicon resulting in extra cross-linking of the glass network. This was confirmed using 29 Si MAS-NMR which showed that an increasing number of Q 2 units and some Q 3 units with extra bridging anions are formed as nitrogen content increases at the expense of Q 1 units. A small proportion of Zn ions are found to be in tetrahedral coordination in the base oxide glass and the proportion of these increases with the presence of nitrogen.

Description: Deep water circulation in the Luzon Strait, which connects the Pacific deep circulation with the South China Sea throughflow, is investigated using a set of oceanographic observations combined with results from three numerical experiments. Both the in situ observations and the model show a deep water overflow in the Luzon Strait. Their results suggest that the deep Pacific water first flows into the Luzon Strait through the Bashi Channel (1.2 Sv, 1 Sv = 1×10 6 m 3 s -1 ) and the Taltung Canyon (0.4 Sv), then turns southward along the Luzon Trough, and finally enters the South China Sea primarily through two gaps in the Heng-Chun Ridge. Overall, the mean transport of the Luzon Strait overflow is about 1.5 Sv. Results from numerical experiments suggest that strong diapycnal mixing in the South China Sea and Luzon Strait, which sustains the baroclinic pressure gradient across the Luzon Strait, is the primary driving mechanism of the deep circulation in the Luzon Strait.

Description: Earlier studies indicate that during El Niño events the iceberg concentration increases in the east of the Pacific sector and in the west of the Atlantic sector of Southern Ocean, but decreases in the center of the Pacific sector. During La Niña the pattern of the iceberg concentration anomalies in these regions reverses. This iceberg redistribution is explained by anomalous winds and currents around an extensive positive atmospheric pressure anomaly that typically develops in the South-East Pacific during the warm El Niño-Southern Oscillation (ENSO) phase. In this study the results of iceberg observations during two cruises of the r/v “Akademik Fedorov” in Antarctica in January-February of 2008 (La Niña) and 2010 (El Niño) have been used to examine the consistency of changes in the iceberg distribution in the Southern Ocean related to El Niño events. The analysis of these observations has shown that in the Pacific Sector of Antarctica changes in the iceberg distribution between 2008 and 2010 followed the scenario outlined above and thus could be associated with the ENSO phase change. Contrary to earlier observations, the iceberg concentration in the Atlantic sector of Antarctica did not increase during 2010 El Niño. The latter is explained by a non-canonical type of 2010 El Niño, El Niño Modoki and associated atmospheric circulation pattern different from the canonical El Niño. Further analysis has shown that a more frequent occurrence of El Niño Modoki in recent years have resulted in weaker links between El Niño events and the Antarctic iceberg distribution.

Description: Although it is not possible to predict when an earthquake will occur, many earthquakes have been found to have had some precursor activity. To study precursors of stick-slip behavior, Johnson et al . conducted laboratory experiments on a sheared granular material under normal stress ranging from 2 to 8 megapascals as an analog for a fault under tectonic stress. They found that acoustic emissions and microslips are a precursor to larger movements. Very similar results were obtained in a discrete element simulation of sheared beads. These types of experiments could help scientists better understand when earthquakes are more likely to occur. As shown by a number of researchers, very similar activity preceding faulting can occur in the Earth.

Description: In Arctic seafloor sediments, methane, a potent greenhouse gas, is trapped in chemical structures called hydrates. Methane hydrates form at low-temperature, high-pressure conditions, and methane can be released if the temperature rises. Previous studies have raised concern that global climate change could lead to release of significant amounts of methane from Arctic hydrates.

Description: A 308-year ice core record provides new data on climate variability in coastal West Antarctica and shows that a clear warming trend has occurred in recent decades. To study climate over the past 3 centuries, Thomas et al . analyzed stable isotopes in the ice core, which provide a record of past temperatures. They observed that climate variability in coastal West Antarctica is strongly driven by sea surface temperatures and atmospheric pressure in the tropical Pacific.

Description: When tectonic plates collide, the less buoyant plate will, in some cases, be forced beneath the other. At such subduction zones the sinking tectonic plate, known as a slab, does not follow a simple path from the surface to the deeper mantle. Instead, new research by Fukao and Obayashi suggests that subducting slabs pass through four largely distinct stages as they penetrate toward the core. To systematically catalog the stages of slab subduction, the authors analyzed roughly 10 million observations of the subsurface that were part of a tomographic study that used primary seismic waves to detect the structure of slabs in subduction zones around the Pacific.

Description: It is an honor and privilege to accept the David Perlman Award. Though I have never met Dave, he is a legend, and I can only hope to have a reporting career half as distinguished and a third as long as his own.

Description: It's my pleasure to nominate Paul Voosen, the former science reporter for Greenwire , for the David Perlman award. Last November, as Superstorm Sandy pounded the East Coast of the United States, Paul found himself stranded for several days in Miami, mourning a recently deceased family member.

Description: Some of the most dramatic effects of climate change have been observed in the Earth's polar regions. In Greenland, ice loss from the Greenland ice sheet has accelerated in recent years [ Shepherd et al ., 2012]. Outlet glaciers are changing their behavior rapidly, with many thinning, retreating, and accelerating [ Joughin et al ., 2004]. The loss of ice weighing on the crust and mantle below has allowed both to rebound, resulting in high rock uplift rates [ Bevis et al ., 2012]. Changes in ice cover and meltwater production influence sea level and climate feedbacks; they are expected to contribute to increasing vulnerability to geohazards such as landslides, flooding, and extreme weather.

Description: A numerical model of the northern California Current System along the coasts of Washington and British Columbia is used to quantify the impact of submarine canyons on upwelling from the continental slope onto the shelf. Comparisons with an extensive set of observations show that the model adequately represents the seasonal development of near-bottom density, as well as along-shelf currents that are critical in governing shelf-slope exchange. Additional model runs with simplified coastlines and bathymetry are used to isolate the effects of submarine canyons. Near submarine canyons, equatorward flow over the outer shelf is correlated with dense water at canyon heads and subsequent formation of closed cyclonic eddies, which are both associated with cross-shelf ageostrophic forces. Lagrangian particles tracked from the slope to mid shelf show that canyons are associated with upwelling from depths of ~140-260 m. Source depths for upwelling are shallower than 150 m at locations away from canyons and in a model run with bathymetry that is uniform in the along-shelf direction. Water upwelled through canyons is more likely to be found near the bottom over the shelf. Onshore fluxes of relatively saline water through submarine canyons are large enough to increase volume-averaged salinity over the shelf by 0.1--0.2 psu during the early part of the upwelling season. The nitrate input from the slope to the Washington shelf associated with canyons is estimated to be 30–60% of that upwelled to the euphotic zone by local wind-driven upwelling.

Description: The flow north of warm subtropical water though the northeastern Atlantic is known to have many pathways that vary over time. Here we use a combination of upper ocean current measurements between Greenland and Scotland near 60°N and satellite altimetry to examine the space-time variability of poleward transport. The high-resolution scans of currents in the top 400 m show that the Reykjanes Ridge serves as a very effective separator of flow towards the Nordic and Labrador Seas, respectively. Whereas the Labrador Sea branch exhibits two mean flows to the north on the western slope of the Reykjanes Ridge, the eastern branch flows north in roughly equal amounts over the deep Maury channel and east of Hatton Bank including the Slope Current. There is also a well-defined southward flow along the eastern slope of the Reykjanes Ridge. The satellite altimetric sea surface height (SSH) data show good overall agreement with geostrophically determined sea level difference from the repeat ADCP sections (1999-2002), but are unable to resolve the fine structure of the topographically defined mean circulation. The altimetric data show that variations in poleward flow west and east of the Reykjanes Ridge are strongly anticorrelated. They further reveal that the two eastern sub-branches also exhibit anticorrelated variability, but offset in time with respect to the Labrador Sea branch. Remarkably, all these variations cancel out for the entire Greenland-Scotland section leaving a gradual decrease in sea level difference of about 0.06 m over the 1993 to the end of 2010 observation period.

Description: Suzette Kimball, who has served as acting director of the U.S. Geological Survey (USGS) since February 2013, will be nominated to be director of the agency, U.S. president Barack Obama announced on 9 January. If Kimball's nomination is confirmed by the U.S. Senate, she will lead the science agency, which has more than 8000 employees and an annual budget of more than $1.1 billion.

Description: With titles like “Correlates of avian building strikes at a glass façade museum surrounded by avian habitat” and “Electrospray ionization FT-ICR/MS investigation of zinc sulfate clusters,” a series of posters presented at AGU's Fall Meeting on 12 December 2013 might seem like a session covering general contributions from AGU members. However, something was unique about the posters: Most were created and presented by high school students.

Description: Bubble size distributions ranging from 0.5 to 125 μm radius were measured optically during high winds of 13 m s -1 and large-scale wave breaking as part of the Southern Ocean Gas Exchange Experiment. Very small bubbles with radii less than 60 µm were measured at 6-9 m depth using optical measurements of the near forward volume scattering function and critical scattering angle for bubbles (˜80°). The bubble size distributions generally followed a power law distribution with mean slope values ranging from 3.6 to 4.6. The steeper slopes measured here were consistent with what would be expected near the base of the bubble plume. Bubbles, likely stabilized with organic coatings, were present for time periods on the order of 10-100 s at depths of 6-9 m. Here, relatively young seas, with an inverse wave age of approximately 0.88 and shorter characteristic wave scales, produced lower bubble concentrations, shallower bubble penetration depths, and steep bubble size distribution slopes. Conversely, older seas, with an inverse wave age of 0.70 and longer characteristic wave scales, produced relatively higher bubble concentrations penetrating to 15 m depth, larger bubble sizes and shallower bubble size distribution slopes. When extrapolated to 4 m depth using a previously published bubble size distribution, our estimates suggest that the deeply-penetrating small bubbles measured in the Southern Ocean supplied ˜36% of the total void fraction and likely contributed to the transfer and supersaturation of low solubility gases.

Description: This study presents a thermodynamic analysis to predict the type of initial, amorphous oxide overgrowth (i.e., am - Al 2 O 3 or am - SiO 2 ) on bare Al – Si alloy substrates. This analysis have taken into account the energies associated with both its interfaces (interface between the Al – Si alloy substrate and the thin oxide film and interface between the thin oxide film and vacuum) along with the bulk Gibbs free energy of oxide formation. This developed analysis is then applied for various parameters, such as, Si alloying element content at the substrate/oxide interface, the growth temperature, the oxide film thickness (up to 1 nm), and various low-index crystallographic surfaces of the substrate. It is found that am - SiO 2 overgrowth is thermodynamically preferred for a combination of lower oxide film thickness, lower growth temperature, and lower Si alloying content at the alloy/oxide interface. This is because of the overcompensation of the lower energies of both the interfaces over the bulk Gibbs free energy. Furthermore, it is found that for all cases, am - Al 2 O 3 forms a more stable interface with Al – Si alloy than am - SiO 2.

Description: A writer needs two distinct qualities to produce an article like “The Calm Before the Wave,” the piece on tsunamis for which Tim Folger is being honored with the 2013 Walter Sullivan Award. Like any good science writer, he needs the ability to sort through a large mass of scientific information and transform it into a clear, compelling narrative. But he also needs an empathic eye and ear—the ability to feel his way into the lives of people whose stories are utterly different from his own and to see and hear the telling details that will make those people come alive on the page.

Description: Wave interferometry is a remote sensing technique, which is increasingly employed in helioseismology, seismology, and acoustics to retrieve parameters of the propagation medium from two-point cross-correlation functions of random wave fields. Here, we apply interferometry to yearlong records of seafloor pressure at 28 locations off New Zealand's South Island to investigate propagation and directivity properties of infragravity waves away from shore. A compressed cross-correlation function technique is proposed to make the interferometry of dispersive waves more robust, decrease the necessary noise averaging time, and simplify retrieval of quantitative information from noise cross-correlations. The emergence of deterministic wave arrivals from cross-correlations of random wave fields is observed up to the maximum range of 692 km between the pressure sensors in the array. Free, linear waves with a strongly anisotropic distribution of power flux density are found to be dominant in the infragravity wave field. Lowest-frequency components of the infragravity wave field are largely isotropic. The anisotropy has its maximum in the middle of the spectral band and decreases at the high-frequency end of the spectrum. Highest anisotropy peaks correspond to waves coming from portions of the New Zealand's shoreline. Significant contributions are also observed from waves propagating along the coastline and probably coming from powerful sources in the northeast Pacific. Infragravity wave directivity is markedly different to the east and to the west of the South Island. The northwest coast of the South Island is found to be a net source of the infragravity wave energy.

Description: The Indonesian Throughflow (ITF) is the only open pathway for inter-ocean exchange between the Pacific and Indian Ocean basins at tropical latitudes. A proxy time series of ITF transport variability is developed using remotely-sensed altimeter data. The focus is on the three outflow passages of Lombok, Ombai and Timor that collectively transport the entire ITF into the Indian Ocean, and where direct velocity measurements are available to help ground-truth the transport algorithm. The resulting 18-year proxy time series shows strong interannual ITF variability. Significant trends of increased transport are found in the upper layer of Lombok Strait, and over the full depth in Timor Passage that are likely related to enhanced Pacific trade winds since the early 1990s. The partitioning of the total ITF transport through each of the major outflow passage varies according to the phase of the Indian Ocean Dipole (IOD) or El Niño-Southern Oscillation (ENSO). In general, Pacific ENSO variability is strongest in Timor Passage, most likely through the influence of planetary waves transmitted from the Pacific along the Northwest Australian shelf pathway. Somewhat surprisingly, concurrent El Niño and positive IOD episodes consistently show contradictory results from those composites constructed for purely El Niño episodes. This is particularly evident in Lombok and Ombai Straits, but also at depth in Timor Passage. This suggests that Indian Ocean dynamics likely win out over Pacific Ocean dynamics in gating the transport through the outflow passages during concurrent ENSO and IOD events.

Description: Time series of ice draft from 2003-2012 from moored sonar data are used to investigate variability and describe the reduction of the perennial sea ice cover in the Beaufort Gyre (BG), culminating in the extreme minimum in 2012. Negative trends in median ice drafts and most ice fractions are observed, while open water and thinnest ice fractions (〈0.3 m) have increased, attesting to the ablation or removal of the older sea ice from the BG over the nine year period. Monthly anomalies indicate a shift occurred toward thinner ice after 2007, in which the thicker ice evident at the northern stations was reduced. Differences in the ice characteristics between all of the stations also diminished, so that the ice cover throughout the region became statistically homogenous. The moored data are used in a relationship with satellite radiometer data to estimate ice volume changes throughout the BG. Summer solid fresh water content decreased drastically in consecutive years from 730 km 3 in 2006 to 570 km 3 in 2007, and to 240 km 3 in 2008. After a short rebound, solid fresh water fell below 220 km 3 in 2012. Meanwhile hydrographic data indicate that liquid fresh water in the BG in summer increased 5410 km 3 from 2003 to 2010 and decreased at least 210 km 3 by 2012. The reduction of both solid and liquid fresh water components indicates a net export of approximately 320 km 3 of fresh water from the region occurred between 2010 and 2012, suggesting that the anticyclonic atmosphere-ocean circulation has weakened.

Description: The effects of water level variations on breaking wave setup over fringing reefs are assessed using field measurements obtained at three study sites in the Republic of the Marshall Islands and the Mariana Islands in the western tropical Pacific Ocean. At each site, reef flat setup varies over the tidal range with weaker setup at high tide and stronger setup at low tide for a given incident wave height. The observed water level dependence is interpreted in the context of radiation stress gradients specified by an idealized point break model generalized for non-normally incident waves. The tidally varying setup is due in part to depth-limited wave heights on the reef flat, as anticipated from previous reef studies, but also to tidally dependent breaking on the reef face. The tidal dependence of the breaking is interpreted in the context of the point break model in terms of a tidally varying wave height to water depth ratio at breaking. Implications for predictions of wave-driven setup at reef-fringed island shorelines are discussed.

Description: The distribution and thickness of sea ice in the Arctic is changing rapidly, resulting in changes to Arctic marine ecosystems. Seabirds are widely regarded as indicators of marine environmental change, and understanding their distribution patterns can serve as a tool to monitor and elucidate biological changes in the Arctic seas. We examined the at-sea distribution of seabirds in the North American Arctic in July and August, 2007-2012, and marine areas of high density were identified based on bird densities for four foraging guilds. Short-tailed shearwaters ( Puffinus tenuirostris ) were the most abundant species observed. Northern fulmars ( Fulmarus glacialis ), thick-billed murres ( Uria lomvia ) and dovekies ( Alle alle ) were also sighted in large numbers. Few birds were sighted between Dolphin and Union Strait and King William Island. Areas of high density over multiple years were found throughout the entire western portion of the study area (Bering Sea, Bering Strait, Chukchi Sea), Lancaster Sound, Baffin Bay, Davis Strait and the low-arctic waters off Newfoundland. These waters are characterized by high primary productivity. This study is the first to document the marine distribution of seabirds across the entire North American Arctic within the same time period, providing a critical baseline for monitoring the distribution and abundance of Arctic seabirds in a changing Arctic seascape.

Description: Deformation processes involve systems of tens to hundreds of kilometers moving at highly variable rates. Because direct kinematic observations have proven difficult, geoscientists are sometimes found in the lab creating analogs, or laboratory models of the Earth. The main scope—and a key challenge—of laboratory modeling of Earth systems is to provide a quantitative approach for understanding geological processes. Since the last decade, various image analysis techniques in laboratory modeling have been designed and used to constrain the kinematics of the simulated processes at an unprecedented resolution. These techniques prove to be the key quantification tools in experimental modeling, not only allowing mechanical analysis of the experiments but also producing experimental data sets that are directly comparable to geophysical and geodetic data in nature and numerical models.

Description: Continental scientific drilling is an important tool for exploring natural and anthropogenic processes on Earth. In past decades the results obtained from lake drilling projects contributed significantly to a better understanding of short-term and long-term climate change and natural hazards.

Description: Radiative transfer in sea ice is subject to anisotropic, multiple scattering. The impact of anisotropy on the light field under sea ice was found to be substantial and has been quantified. In this study, a large dataset of irradiance and radiance measurements under sea ice has been acquired with a Remotely Operated Vehicle (ROV) in the central Arctic. Measurements are interpreted in the context of numerical radiative transfer calculations, laboratory experiments, and microstructure analysis. The ratio of synchronous measurements of transmitted irradiance to radiance shows a clear deviation from an isotropic under-ice light field. We find that the angular radiance distribution under sea-ice is more downward directed than expected for an isotropic light field. This effect can be attributed to the anisotropic scattering coefficient within sea ice. Assuming an isotropic radiance distribution under sea ice leads to significant errors in light-field modeling and the interpretation of radiation measurements. Quantification of the light field geometry is crucial for correct conversion of radiance data acquired by Autonomous Underwater Vehicles (AUVs) and ROVs.

Description: In comparison to the deep ocean, the upper mixed layer is a region typically characterized by substantial vertical gradients in water properties. Within the Tropics, the rich variability in the vertical shapes and forms that these structures can assume through variation in the atmospheric forcing results in a differential effect in terms of the temperature and salinity stratification. Rather than focusing on the strong halocline above the thermocline, commonly referred to as the salinity barrier layer, the present study takes into account the respective thermal and saline dependencies in the Brunt-Väisälä frequency (N 2 ) in order to isolate the specific role of the salinity stratification in the layers above the main pycnocline. We examine daily vertical profiles of temperature and salinity from an ocean reanalysis over the period 2001-2007. We find significant seasonal variations in the Brunt-Väisälä frequency profiles are limited to the upper 300 m depth. Based on this we determine the ocean salinity stratification (OSS) to be defined as the stabilizing effect (positive values) due to the haline part of N 2 averaged over the upper 300m. In many regions of the tropics the OSS contributes 40 to 50% to N 2 as compared to the thermal stratification and, in some specific regions, exceeds it for a few months of the seasonal cycle. Away from the tropics, for example near the centers of action of the subtropical gyres, there are regions characterized by the permanent absence of OSS. In other regions previously characterized with salinity barrier layers the OSS obviously shares some common variations: however, we show that where temperature and salinity are mixed over the same depth, the salinity stratification can be significant. In addition, relationships between the OSS and the sea surface salinity are shown to be well defined and quasi-linear in the tropics, providing some indication that in the future, analyses that consider both satellite surface salinity measurements at the surface and vertical profiles at depth will result in a better determination of the role of the salinity stratification in climate prediction systems.

Description: Impacts of extreme Barents Sea air-sea exchanges are examined using the HadCM3 coupled ocean-atmosphere model. Variability in the Barents Sea winter air-sea density flux is found to be a potentially significant factor in determining changes in the southward transport of dense water through Fram Strait. The density flux variability is primarily driven by the thermal term, F T , due to heat loss to the atmosphere. The other two terms (haline flux and ice formation) play a relatively minor role. The difference in ocean circulation between winters with extreme strong and weak Barents Sea surface density flux anomalies is analysed. This reveals an increase in strong winters of both the north-westwards intermediate depth flow out of the basin and the east-west deep flows north of Spitsbergen and south through the Fram Strait. A linear fit yields a Fram Strait southward transport increase of 1.22 Sv for an increase in F T of 1x10 -6 kg m -2 s -1 . For the ten strongest Barents Sea surface density flux winters, the Fram Strait winter southward transport increases by 2.4 Sv. This compares with a reduction of 1.0 Sv for the corresponding weakest winters. Furthermore, the properties of the southwards flowing water are modified in strong density flux winters. In such winters, the Fram Strait water below 250 m is colder by up to 0.5 ° C and fresher by 0.05 than the climatological winter mean.

Description: In viscous-plastic (VP) sea-ice models, small deformations are approximated by irreversible viscous deformations, introducing a non-physical energy sink. As the spatial resolution and the degree of numerical convergence of the models increase, linear kinematic features (LKFs) are better resolved and more states of stress lie in the viscous regime. Energy dissipation in this non-physical viscous regime therefore increases. We derive a complete kinetic energy (KE) balance for sea ice, including plastic and viscous energy sinks to study energy dissipation. The main KE balance is between the energy input by the wind and the dissipation by the water drag and the internal stresses (dissipating respectively 87% and 13% of the energy input on an annual average). The internal stress term is mostly important in winter when ice-ice interactions are dominant. The energy input that is not dissipated locally is redistributed laterally by the internal stresses in regions of dissipation by small scale deformations (LKFs). Of the 13% dissipated annually by the internal stress term, 93% is dissipated in friction along LKFs (14% in ridging, 79% in shearing) and 7% is stored as potential energy in ridges. For all time and spatial scales tested, the frictional viscous dissipation is negligible in the KE balance. This conclusion remains valid when the spatial resolution and the numerical convergence of the simulations are increased. Overall, the results confirm the validity, from an energetical point of view, of the VP approximation.

Description: Sintered nanoceramics of Pr -doped lanthanum hafnate, La 2 Hf 2 O 7 : Pr , were prepared by means of a high-pressure sintering technique using nanopowders made by Pechini method. Structure, morphology, and spectroscopic properties of the ceramics compared to the starting powder are presented and discussed. Emission and excitation spectra recorded at room temperature as well as at 7 K using synchrotron radiation are presented together with results of luminescence kinetics measurements. In ceramics, at 7 K, the Pr 3+ luminescence from 3 P 0 (blue-green, green, and red region) and 1 D 2 (red) levels is accompanied by a broad-band emission located in the 380–530 nm range of wavelengths, whereas powders gives only the Pr 3+ -related luminescence. Depending on the excitation wavelength, the broad-band emission maximum moves between 430 and 470 nm indicating superposition of at least two components. In sintered nanoceramics, the lifetimes of Pr 3+ emissions from 3 P 0 and 1 D 2 levels were by 10%–20% shorter compared to the powder. The existence of different luminescence centers was proved by the selective emission decays examination. The fast 5 d → 4 f luminescence of Pr 3+ was not observed from either of the two types of La 2 Hf 2 O 7 :Pr materials.

Description: We, Kevin's friends and colleagues, are pleased to have prepared his nomination package. Across the broad and expansive climate science community, there are very few people who have a history of sustained engagement like Kevin. Whereas many people have worked to convey the importance of climate change, Kevin has tirelessly done so for decades. In addition, the breadth of his activities is astonishing. It includes innumerable interviews on radio, on television, and in printed media over the past 30 years. He has also taken on many leadership communication roles within the scientific community, including the Intergovernmental Panel on Climate Change to name just one.

Description: Ted Flinn and John LaBrecque followed remarkably, perhaps eerily, similar career paths. Ted started as a seismologist, John as a tectonician and sea-going geophysicist. Both decided to rededicate their efforts toward supporting the geophysical community, recognizing that it depends ever more critically on global, space-based measurements and observations. Ted did that a decade after the 1968 Williamstown conference, and John did it a decade after the 1988 Coolfont conference. Both of these history-making conferences focused on the geophysical uses of space assets to study the planet.

Description: Chapman conferences are intended for deeper discussions of specific topical areas of scientific interest. This Chapman conference was organized to review and discuss new strategies to observe and understand processes and drivers in the biogeosphere, particularly those related to coupled biogeochemical and hydrological processes in terrestrial systems. The topics presented at the meeting included transport and exchange processes of organic and gaseous compounds across the soil-water and soil-plant interfaces, monitoring strategies of soil-mediated processes and drivers from the local to the catchment scale, and the impact of soil formation and functions on ecosystem services. These topics were addressed and intensively discussed by participants covering the fields of soil systems sciences, hydrology, and biogeosciences.

Description: It is a great pleasure and an honor to give the citation for the 2013 Athelstan Spilhaus awardee, Iain Stewart, professor of geoscience communication at the University of Plymouth, recognizing his truly exceptional work over the last decade in communicating geoscience to the general public. Iain has been making documentaries for the BBC, National Geographic, and Discovery for nearly a decade. These programs have huge international audiences and wide-reaching impact.

Description: I am delighted to be recognized with this prize. I want to first thank AGU and the prize committee and, especially, Nature's Own for establishing this prize in a field that has become contentious and highly political. It did not used to be this way. Following the media frenzy with the 2007 Intergovernmental Panel on Climate Change (IPCC) report, there was hope at the 2009 Conference of Parties meeting in Copenhagen that an international framework agreement on climate change might be achieved. It was not to be. Planned actions to address issues of climate change were undermined by huge funding of misinformation by vested interests. It was not helped by so-called “climategate” in which many emails illegally hacked from a computer server at the University of East Anglia in the United Kingdom were released, cherry picked, distorted, and misused by climate change deniers. Minor errors in the IPCC report were blown out of all proportion and ineffectively addressed. I was caught up in all this, and one of my many emails went viral: the “travesty” quote in which I bemoaned the inability to close the global energy balance associated with short-term climate variability but which was misinterpreted as saying there was no global warming. These examples highlight failures of communication.

Description: Solomon Hsiang is representative of a new generation in the geosciences community, whose work spans several disciplines, drawing on methods and concepts from far outside the traditional physical science domain in order to make progress on difficult questions at the intersection of natural science, social science, and public policy. Broadly speaking, by examining how humanity has responded to climate variability and change in the distant and recent past, Sol's research elucidates the question of how humanity may respond to a changing climate in the future. Combining large, independent sets of social science, meteorological, and climatological data and analyzing them with tools more common in microeconomics than natural science, Sol, still at an early stage of his career, has made critical contributions to an incipient revolution in our understanding of the sensitivity and adaptability of humans and their social arrangements to climate variability and change. Such insights will greatly improve the information base from which effective public policy is developed.

Description: Thanks to AGU and our citationist, Richard Alley, for this joint award to Erna and myself. While it is, of course, personally gratifying, we also consider it an acknowledgement that “science journalism” has broadened out from print to include video in all forms—from PBS primetime to YouTube anytime—and also social media and spoken-word presentations. We're pleased that this is one more way in which AGU is validating the participation of its members in all forms of public outreach. We're gratified that our efforts in this regard have been supported by NSF, NASA, and NOAA, among other government agencies, and are happy to acknowledge their “priceless” role as funders. As one of our current collaborators, former NASA chief scientist Waleed Abdalati, likes to say, “The science isn't done until it's shared”…and there are more and more ways in which that sharing can be done.

Description: On 24 August 2013 a sudden burst of gas erupted from the ground near Rome's airport, about 15 kilometers southwest of the city. The eruption produced a crater that was initially about half a meter wide but that gradually increased in size and eventually reached a diameter of about 3 meters.

Description: Dr. Chelle Gentemann is a worthy recipient of the Charles S. Falkenberg Award. Through her leadership at both national and international levels, Chelle has contributed significantly to improving the accuracy, accessibility, and utility of satellite-derived fields of sea surface temperature (SST) for a wide range of applications, including numerical weather forecasting, operational oceanography, and climate research.

Description: Thank you, Cinna, for your kind and generous citation and for your friendship. It is a great recognition having been selected for the 2013 International Award. I feel honored, especially considering the international breadth of AGU, fostering scientific excellence and promoting research in Earth and space sciences worldwide. AGU has evolved over the years, becoming increasingly international and multidisciplinary, providing the intellectual framework and networking for research collaboration. I have been privileged to serve as International Secretary of the Union, which together with work in the committees permitted me to better appreciate the range of activities and the programs AGU does to serve its membership and the geophysics community.

Description: The meaning of “interdisciplinary” has evolved over my career. When I started my science research career, it meant bridging atmospheric and ocean science and embracing the science of the Earth system and its interacting components. Thus, I found a home at AGU submitting science abstracts to atmospheric science, oceanography, or hydrology sessions. In fact, my first research paper appeared in Journal of Geophysical Research (JGR)-Atmospheres , and a letter to the editor and response appeared in JGR-Oceans . It also meant getting scientists in these disciplines talking to each other. I organized a seminar series at Rice University under the umbrella of an Earth Systems Institute that included the Departments of Space Physics and Astronomy, Geology and Geophysics, Biology, and Hydrology. I also began working with Dr. Patricia Reiff, a space physicist with a passion for science education.

Description: It is really wonderful to receive this award and the recognition of AGU for my work. I've been a member of the Union since my Ph.D. days, 25 years or so ago, when I was working on earthquake faulting in Greece and Turkey. Its meetings were always the place that showcased geoscience at its most novel and exciting. It was the breadth of what was on offer that was so exhilarating. My doctoral studies had already opened up fairly wide vistas for me since my interest in Holocene earthquake activity also required an understanding of the Mediterranean's rich cultural history and the vagaries of millennial-scale climate fluctuations. Later, my research would distract me into farther-flung realms, such as volcanic faulting on Mount Etna, paleotsunamis along Aegean shores, even postglacial earthquakes in northern Scotland! Kindly colleagues would occasionally advise me to focus my efforts on a single substantive area of research, cautioning that my flighty research forays weren't conducive to climbing the academic ladder. I'm sure they were correct. Or would have been proved so if I hadn't been rescued by television.

Description: I am honored to receive this award, created by Peter Schlosser, nominated by my postdoc advisor Michael Oppenheimer, and alongside my thesis advisor Mark Cane, recipient of this year's Maurice Ewing Medal—all role models and original pioneers in “the application and use of Earth and space sciences to solve societal problems.”

Description: A question about how to predict the runoff from a basin where there is no history of flow measurements is probably featured in almost every hydrology graduate student's oral examinations. It has certainly been one of the longest-standing problems for the profession. The International Association of Hydrological Sciences Prediction in Ungauged Basins initiative [ Wagener et al ., 2004] has focused researchers and meetings on the topic, culminating in this book, which assembles the thoughts gathered over the last decade.

Description: From Cosmos to Mars and Pluto and back home, Geoffrey Haines-Stiles and Erna Akuginow have invested their careers reporting the best modern science in novel, compelling, and accessible ways through documentaries, live events, print, and new media. They are outstanding recipients of the AGU Robert C. Cowen Award for Sustained Achievement in Science Journalism.