bluuebunny/crossref_metadata_2025_split huggingface dataset:
Historical Trends in pH and Carbonate Biogeochemistry on the Belize Mesoamerican Barrier Reef System
Authors: Fowell S. E. , Foster G. L. , Ries J. B. , Castillo K. D. , de la Vega E. , Tyrrell T. , Donald H. K. , Chalk T. B. 
Published: March 2018

AbstractCoral reefs are important ecosystems that are increasingly negatively impacted by human activities. Understanding which anthropogenic stressors play the most significant role in their decline is vital for the accurate prediction of future trends in coral reef health and for effective mitigation of these threats. Here we present annually resolved boron and carbon isotope measurements of two cores capturing the past 90 years of growth of the tropical reef‐building coral Siderastrea siderea from the Belize Mesoamerican Barrier Reef System. The pairing of these two isotope systems allows us to parse the reconstructed pH change into relative changes in net ecosystem productivity and net ecosystem calcification between the two locations. This approach reveals that the relationship between seawater pH and coral calcification, at both a colony and ecosystem level, is complex and cannot simply be modeled as linear or even positive. This study also underscores both the utility of coupled δ11B‐δ13C measurements in tracing past biogeochemical cycling in coral reefs and the complexity of this cycling relative to the open ocean.
Land Use Change Increases Streamflow Across the Arc of Deforestation in Brazil
Authors: Levy M. C. , Lopes A. V. , Cohn A. , Larsen L. G. , Thompson S. E. 
Published: March 2018

AbstractNearly half of recent decades' global forest loss occurred in the Amazon and Cerrado (tropical savanna) biomes of Brazil, known as the arc of deforestation. Despite prior analysis in individual river basins, a generalizable empirical understanding of the effect of deforestation on streamflow across this region is lacking. We frame land use change in Brazil as a natural experiment and draw on in situ and remote sensing evidence in 324 river basins covering more than 3 × 106 km2 to estimate streamflow changes caused by deforestation and agricultural development between 1950 and 2013. Deforestation increased dry season low flow by between 4 and 10 percentage points (relative to the forested condition), corresponding to a regional‐ and time‐averaged rate of increase in specific streamflow of 1.29 mm/year2, equivalent to a 4.08 km3/year2 increase, assuming a stationary climate. In conjunction with rainfall and temperature variations, the net (observed) average increase in streamflow over the same period was 0.76 mm/year2, or 2.41 km3/year2. Thus, net increases in regional streamflow in the past half century are 58% of those that would have been experienced with deforestation given a stationary climate. This study uses a causal empirical analysis approach novel to the water sciences to verify the regional applicability of prior basin‐scale studies, provides a proof of concept for the use of observational causal identification methods in the water sciences, and demonstrates that deforestation masks the streamflow‐reducing effects of climate change in this region.
The Widespread Influence of Great Lakes Microseisms Across the Midwestern United States Revealed by the 2014 Polar Vortex
Authors: Anthony R. E. , Ringler A. T. , Wilson D. C. 
Published: March 2018

AbstractDuring the winter of 2014, a weak polar vortex brought record cold temperatures to the north‐central (“Midwest”) United States, and the Great Lakes reached the highest extent of ice coverage (92.5%) since 1979. This event shut down the generation of seismic signals caused by wind‐driven wave action within the lakes (termed “lake microseisms”), giving an unprecedented opportunity to isolate and characterize these novel signals through comparison with nonfrozen time periods. Using seismic records at 72 broadband stations, we observe Great Lakes microseism signals at distances >300 km from the lakes. In contrast to conventional oceanic microseisms, there is no clear relationship between the frequency content of the seismic signals (observed from ~0.5–5‐s period) and the dominant swell period or resonance periods of the lakes based on their bathymetric profiles. Thus, the exact generation mechanism is not readily explained by conventional microseism theory and warrants further investigation.
Modulation of Extreme Flood Levels by Impoundment Significantly Offset by Floodplain Loss Downstream of the Three Gorges Dam
Authors: Mei Xuefei , Dai Zhijun , Darby Stephen E. , Gao Shu , Wang Jie , Jiang Weiguo 
Published: March 2018

AbstractRiver flooding—the world's most significant natural hazard—is likely to increase under anthropogenic climate change. Most large rivers have been regulated by damming, but the extent to which these impoundments can mitigate extreme flooding remains uncertain. Here the catastrophic 2016 flood on the Changjiang River is first analyzed to assess the effects of both the Changjiang's reservoir cascade and the Three Gorges Dam (TGD), the world's largest hydraulic engineering project on downstream flood discharge and water levels. We show that the Changjiang's reservoir cascade impounded over 30.0 × 103 m3/s of flow at the peak of the flood on 25 July 2016, preventing the occurrence of what would otherwise have been the second largest flood ever recorded in the reach downstream of the TGD. Half of this flood water storage was retained by the TGD alone, meaning that impoundment by the TGD reduced peak water levels at the Datong hydrometric station (on 25 July) by 1.47 m, compared to pre‐TGD conditions. However, downstream morphological changes, in particular, extensive erosion of the natural floodplain, offset this reduction in water level by 0.22 m, so that the full beneficial impact of floodwater retention by the TGD was not fully realized. Our results highlight how morphological adjustments downstream of large dams may inhibit their full potential to mitigate extreme flood risk.
Composition of 1–128 keV Magnetospheric ENAs
Authors: Valek P. W. , Delmonico E. , McComas D. J. , Goldstein J. , Allegrini F. , Livi S. 
Published: March 2018

AbstractThe Two Wide‐angle Imaging Neutral‐atom Spectrometers (TWINS) mission has observed the inner magnetosphere since 2008. TWINS flies energetic neutral atom (ENA) cameras aboard two spacecraft in separate Molniya orbits. TWINS images the ENA emissions from the inner magnetosphere across a broad range of energies (1 to 128 keV for H, 16 to 128 keV for O, and higher energies for total ENAs). This allows TWINS to observe the evolution, on minute timescales, of the trapped and precipitating particles that dominate storm time dynamics. Presented here are ENA observations over this broad energy range of the large storm of 17 March 2015 (Dst < −223)—the St. Patrick's Day storm. The ENA observations are presented with a 15‐min cadence for improved counting statistics. During the St. Patrick's Day storm the flux of ENAs and the concentration of O+/H+ increased significantly during the main phase. The concentration increased to a value of 1.0 for the 16 keV ions, and the temperature in the inner magnetosphere dropped during the time between the prestorm phase and the main phase. Comparing the results from this storm to a moderate storm on 22 July 2009, and a collection of nine other large storms, we find that the most energetic O+ ions in the ring current occur before the peak of the storm.
Measurements of Ion‐Neutral Coupling in the Auroral F Region in Response to Increases in Particle Precipitation
Authors: Kiene A. , Bristow W. A. , Conde M. G. , Hampton D. L. 
Published: March 2018

AbstractNeutral winds are a key factor in the dynamics of the ionosphere‐thermosphere system. Previous observations have shown that neutral and ion flows are strongly coupled during periods of auroral activity when ion drag forcing can become the dominant force driving neutral wind flow. This is primarily due to increases in ion density due to enhanced particle precipitation as well as associated increases the strength of the electric fields that drive ion motions. Due to this strong coupling, numerical simulations of neutral dynamics have difficulty reproducing neutral wind observations when they are driven by modeled precipitation and modeled convection. It is therefore desirable whenever possible to have concurrent coincident measurements of auroral precipitation and ion convection. Recent advancements in high‐resolution fitting of Super Dual Auroral Radar Network ion convection data have enabled the generation of steady maps of ion drifts over Alaska, coinciding with several optics sites. The Super Dual Auroral Radar Network measurements are compared with scanning Doppler imager neutral wind measurements at similar altitude, providing direct comparisons of ion and neutral velocities over a wide field and for long periods throughout the night. Also present are a digital all‐sky imager and a meridian spectrograph, both of which provide measurements of auroral intensity on several wavelengths. In this study, we combine these data sets to present three case studies that show significant correlation between increases in F region precipitation and enhancements in ion‐neutral coupling in the evening sector. We investigate the time scales over which the coupling takes place and compare our findings to previous measurements.
Combining Multiphase Groundwater Flow and Slope Stability Models to Assess Stratovolcano Flank Collapse in the Cascade Range
Authors: Ball J. L. , Taron J. , Reid M. E. , Hurwitz S. , Finn C. , Bedrosian P. 
Published: March 2018

AbstractHydrothermal alteration can create low‐permeability zones, potentially resulting in elevated pore‐fluid pressures, within a volcanic edifice. Strength reduction by rock alteration and high pore‐fluid pressures have been suggested as a mechanism for edifice flank instability. Here we combine numerical models of multiphase heat transport and groundwater flow with a slope‐stability code that incorporates three‐dimensional distributions of strength and pore‐water pressure to address the following questions: (1) What permeability distributions and contrasts produce elevated pore‐fluid pressures in a stratovolcano? (2) What are the effects of these elevated pressures on flank stability? (3) Finally, what are the effects of magma intrusion on potential flank failure in an edifice? Simulation results show that under a range of plausible parameters, water tables in a stratovolcano can be elevated or perched. These elevated water tables result in universally lower stability (lower factor of safety) compared with equivalent dry edifices, indicating a higher likelihood of flank collapse. Low‐permeability (<1 × 10−17 m2) layers such as altered pyroclastic deposits or breccias can result in locally saturated regions (perched water) and lower factors of safety near the ground surface but may actually reduce liquid water saturation and pore pressures in the core of the edifice and thus may favor small, shallow collapses over larger, deeper collapses. Magma intrusion into the base of the edifice increases pore‐fluid pressures and decreases the factor of safety. However, the shear strength of edifice rocks also exerts a significant control on stability, so both mechanical properties and pore‐fluid pressures are important for stability assessments.
Bomb‐14C Peak in the North Pacific Recorded in Long‐Lived Bivalve Shells (Mercenaria stimpsoni)
Authors: Kubota Kaoru , Shirai Kotaro , Murakami‐Sugihara Naoko , Seike Koji , Minami Masayo , Nakamura Toshio , Tanabe Kazushige 
Published: March 2018

AbstractThe excess radiocarbon produced by nuclear bomb testing in the atmosphere in the 1950s–1960s (bomb‐14C) is used as a tracer in the surface ocean, extending our understanding of geophysics and biogeochemical cycles. However, there is no bomb‐14C record for the high‐latitude western North Pacific Ocean because of the paucity of long‐lived marine calcifying organisms equivalent to reef‐building corals. The shells of Stimpson's hard clam, Mercenaria stimpsoni, potentially provide such a record because the clam's lifespan is very long (>100 years). We analyzed 14C in six live‐caught M. stimpsoni shells from the western North Pacific (39.4°N, 142°E) and report, for the first time, the bomb‐14C record with robust calendar ages based on annual growth increments. The value was constant in 1934–1952 (Δ14C = −66‰), with a sudden increase in 1959, a peak in 1974 (107‰), which was 60‰ lower than that of the Kuroshio Current, a gradual decline after 1974, and a current value of 16–18‰, which is ∼10‰ higher than the atmospheric value. The bomb‐14C values are between the Kuroshio Current (the northwestern subtropical gyre) and Oyashio Current (the Western Subarctic Gyre) values, suggesting that the Tsugaru Current, downstream from the Kuroshio Current, mixes with the Oyashio Current after passing through Tsugaru Strait.
Quantifying Growth of Pancake Sea Ice Floes Using Images From Drifting Buoys
Authors: Roach Lettie A. , Smith Madison M. , Dean Samuel M. 
Published: March 2018

AbstractNew sea ice in the polar regions often begins as small pancake floes in autumn and winter that grow laterally and weld together into larger floes. However, conditions in polar oceans during freezeup are harsh, rendering in situ observations of small‐scale sea ice growth processes difficult and infrequent. Here we apply image processing techniques to images obtained by drifting wave buoys (SWIFTs) deployed in the autumn Arctic Ocean to quantify these processes in situ for the first time. Small pancake ice floes were observed to form and grow gradually in freezing, low‐wave conditions. We find that pancake floe diameters are limited by the wave field, such that floe diameter is proportional to wavelength and amplitude over time. Floe welding correlates well with sea ice concentration, and the observations can be used to estimate a key model parameter for floe size evolution. There is some agreement between observed lateral growth rates and those predicted using a theoretical model based on heat flux balance, but the model lateral growth rates are too conservative in these conditions. These results will be used to inform description of lateral floe growth and floe welding in new models that evolve sea ice floe size distribution.
A New Approach to Estimating Coccolithophore Calcification Rates From Space
Authors: Hopkins Jason , Balch William M. 
Published: March 2018

AbstractThe production and ultimate fate of calcium carbonate in the global ocean has implications for the efficiency of the biological carbon and alkalinity pumps. Historically, sediment trap flux data and/or mass balance equations have been used to estimate the rate of particulate inorganic carbon production in the ocean. More recently, satellite data have been used to provide a more comprehensive global overview of this important biogeochemical process based on relationships determined from multilinear regression of measured calcification rates against a number of measurable variables. Here we describe a simple model to estimate calcification rate based around elements of coccolithophore physiology that can be easily parametrized with satellite ocean color data. The model output conforms to our understanding of the spatial and temporal distribution of coccolithophores and performs relatively well at reproducing global rates that are of the correct order of magnitude, while capturing the variability in such a complex, natural process when compared to field calcification rate measurements (slope = 0.98; R2 = 0.28; p < 0.05; RMSE = 0.53 mg C · m−3 · day−1). Average, global, euphotic zone depth‐integrated calcification rate is estimated to be 1.42 ± 1.69 Pg particulate inorganic carbon/year with the oceanic gyres contributing the greatest influence.
Modeled Influence of Land Ice and CO2on Polar Amplification and Paleoclimate Sensitivity During the Past 5 Million Years
Authors: Stap L. B. , van de Wal R. S. W. , de Boer B. , Köhler P. , Hoencamp J. H. , Lohmann G. , Tuenter E. , Lourens L. J. 
Published: March 2018

AbstractPolar amplification and paleoclimate sensitivity (S) have been the subject of many paleoclimate studies. While earlier studies inferred them as single constant parameters of the climate system, there are now indications that both are conditioned by the type of forcing. Moreover, they might be affected by fast feedback mechanisms that have different strengths depending on the background climate. Here we use the intermediate complexity climate model CLIMBER‐2 to study the influence of land ice and CO2on polar amplification andS. We perform transient 5‐Myr simulations, forced by different combinations of insolation, land ice, and CO2. Our results provide evidence that land ice and CO2changes have different effects on temperature, both on the global mean and the meridional distribution. Land ice changes are mainly manifested in the high latitudes of the Northern Hemisphere. They lead to higher northern polar amplification, lower southern polar amplification, and lowerSthan more homogeneously distributed CO2forcing in CLIMBER‐2. Furthermore, toward colder climates northern polar amplification increases and consequently southern polar amplification decreases, due to the albedo‐temperature feedback. As an effect, a global average temperature change calculated from high‐latitude temperatures by using a constant polar amplification would lead to substantial errors in our model setup. We conclude that to constrain feedback strengths and climate sensitivity by paleoclimate data, the underlying forcing mechanisms and background climate states have to be taken into consideration.
Regional Extreme Precipitation Events: Robust Inference From Credibly Simulated GCM Variables
Authors: Farnham David J. , Doss‐Gollin James , Lall Upmanu 
Published: March 2018

AbstractGeneral circulation models (GCMs) have been demonstrated to produce estimates of precipitation, including the frequency of extreme precipitation, with substantial bias and uncertainty relative to their representation of other fields. Thus, while theory predicts changes in the hydrologic cycle under anthropogenic warming, there is generally low confidence in future projections of extreme precipitation frequency for specific river basins. In this paper, we explore whether a GCM simulates large‐scale atmospheric circulation indices that are associated with regional extreme precipitation (REP) days more accurately than it simulates REP days themselves, and thus whether conditional simulation of the precipitation events based on the circulation indices may improve the simulation of REP events. We show that a coupled Geophysical Fluid Dynamics Laboratory GCM simulates too many springtime REP days in the Ohio River Basin in historical (1950–2005) simulations. The GCM, however, does credibly simulate the distributional and persistence properties of several indices (which represent the large‐scale atmospheric pressure features, local atmospheric moisture content, and local vertical velocity) that are shown to modulate the likelihood of REP occurrence in the reanalysis/observational record. We show that simulation of REP events based on the GCM‐based atmospheric indices greatly reduces the bias of GCM REP frequency relative to the observed record. The simulation is conducted via a Bayesian regression model by imposing the empirical relationship between observed REP occurrence and the reanalysis‐based atmospheric indices. Application of this model to future (2006–2100) representative concentration pathway 8.5 scenario suggests an increasing trend in springtime REP incidence in the study region. The proposed approach of simulating precipitation events of interest, particularly those poorly represented in GCMs, with a statistical model based on climate indices that are reasonably simulated by GCMs could be applied to subseasonal to seasonal forecasts as well as future projections.
Intercomparison and Uncertainty Assessment of Nine Evapotranspiration Estimates Over South America
Authors: Sörensson Anna A. , Ruscica Romina C. 
Published: March 2018

AbstractThis study examines the uncertainties and the representations of anomalies of a set of evapotranspiration products over climatologically distinct regions of South America. The products, coming from land surface models, reanalysis, and remote sensing, are chosen from sources that are readily available to the community of users. The results show that the spatial patterns of maximum uncertainty differ among metrics, with dry regions showing maximum relative uncertainties of annual mean evapotranspiration, while energy‐limited regions present maximum uncertainties in the representation of the annual cycle and monsoon regions in the representation of anomalous conditions. Furthermore, it is found that land surface models driven by observed atmospheric fields detect meteorological and agricultural droughts in dry regions unequivocally. The remote sensing products employed do not distinguish all agricultural droughts and this could be attributed to the forcing net radiation. The study also highlights important characteristics of individual data sets and recommends users to include assessments of sensitivity to evapotranspiration data sets in their studies, depending on region and nature of study to be conducted.
Magnetic Reconnection, Turbulence, and Particle Acceleration: Observations in the Earth's Magnetotail
Authors: Ergun R. E. , Goodrich K. A. , Wilder F. D. , Ahmadi N. , Holmes J. C. , Eriksson S. , Stawarz J. E. , Nakamura R. , Genestreti K. J. , Hesse M. , Burch J. L. , Torbert R. B. , Phan T. D. , Schwartz S. J. , Eastwood J. P. , Strangeway R. J. , Le Contel O. , Russell C. T. , Argall M. R. , Lindqvist P.‐A. , Chen L. J. , Cassak P. A. , Giles B. L. , Dorelli J. C. , Gershman D. , Leonard T. W. , Lavraud B. , Retino A. , Matthaeus W. , Vaivads A. 
Published: March 2018

AbstractWe report observations of turbulent dissipation and particle acceleration from large‐amplitude electric fields (E) associated with strong magnetic field (B) fluctuations in the Earth's plasma sheet. The turbulence occurs in a region of depleted density with anti‐earthward flows followed by earthward flows suggesting ongoing magnetic reconnection. In the turbulent region, ions and electrons have a significant increase in energy, occasionally >100 keV, and strong variation. There are numerous occurrences of |E| >100 mV/m including occurrences of large potentials (>1 kV) parallel to B and occurrences with extraordinarily large J · E (J is current density). In this event, we find that the perpendicular contribution of J · E with frequencies near or below the ion cyclotron frequency (fci) provide the majority net positive J · E. Large‐amplitude parallel E events with frequencies above fci to several times the lower hybrid frequency provide significant dissipation and can result in energetic electron acceleration.