bluuebunny/crossref_metadata_2025_split huggingface dataset:
Spatiotemporal fusion of multiple‐satellite aerosol optical depth (AOD) products using Bayesian maximum entropy method
Authors: Tang Qingxin , Bo Yanchen , Zhu Yuxin 
Published: April 2016

AbstractMerging multisensor aerosol optical depth (AOD) products is an effective way to produce more spatiotemporally complete and accurate AOD products. A spatiotemporal statistical data fusion framework based on a Bayesian maximum entropy (BME) method was developed for merging satellite AOD products in East Asia. The advantages of the presented merging framework are that it not only utilizes the spatiotemporal autocorrelations but also explicitly incorporates the uncertainties of the AOD products being merged. The satellite AOD products used for merging are the Moderate Resolution Imaging Spectroradiometer (MODIS) Collection 5.1 Level‐2 AOD products (MOD04_L2) and the Sea‐viewing Wide Field‐of‐view Sensor (SeaWiFS) Deep Blue Level 2 AOD products (SWDB_L2). The results show that the average completeness of the merged AOD data is 95.2%,which is significantly superior to the completeness of MOD04_L2 (22.9%) and SWDB_L2 (20.2%). By comparing the merged AOD to the Aerosol Robotic Network AOD records, the results show that the correlation coefficient (0.75), root‐mean‐square error (0.29), and mean bias (0.068) of the merged AOD are close to those (the correlation coefficient (0.82), root‐mean‐square error (0.19), and mean bias (0.059)) of the MODIS AOD. In the regions where both MODIS and SeaWiFS have valid observations, the accuracy of the merged AOD is higher than those of MODIS and SeaWiFS AODs. Even in regions where both MODIS and SeaWiFS AODs are missing, the accuracy of the merged AOD is also close to the accuracy of the regions where both MODIS and SeaWiFS have valid observations.
Wet scavenging of soluble gases in DC3 deep convective storms using WRF‐Chem simulations and aircraft observations
Authors: Bela Megan M. , Barth Mary C. , Toon Owen B. , Fried Alan , Homeyer Cameron R. , Morrison Hugh , Cummings Kristin A. , Li Yunyao , Pickering Kenneth E. , Allen Dale J. , Yang Qing , Wennberg Paul O. , Crounse John D. , St. Clair Jason M. , Teng Alex P. , O'Sullivan Daniel , Huey L. Gregory , Chen Dexian , Liu Xiaoxi , Blake Donald R. , Blake Nicola J. , Apel Eric C. , Hornbrook Rebecca S. , Flocke Frank , Campos Teresa , Diskin Glenn 
Published: April 2016

AbstractWe examine wet scavenging of soluble trace gases in storms observed during the Deep Convective Clouds and Chemistry (DC3) field campaign. We conduct high‐resolution simulations with the Weather Research and Forecasting model with Chemistry (WRF‐Chem) of a severe storm in Oklahoma. The model represents well the storm location, size, and structure as compared with Next Generation Weather Radar reflectivity, and simulated CO transport is consistent with aircraft observations. Scavenging efficiencies (SEs) between inflow and outflow of soluble species are calculated from aircraft measurements and model simulations. Using a simple wet scavenging scheme, we simulate the SE of each soluble species within the error bars of the observations. The simulated SEs of all species except nitric acid (HNO3) are highly sensitive to the values specified for the fractions retained in ice when cloud water freezes. To reproduce the observations, we must assume zero ice retention for formaldehyde (CH2O) and hydrogen peroxide (H2O2) and complete retention for methyl hydrogen peroxide (CH3OOH) and sulfur dioxide (SO2), likely to compensate for the lack of aqueous chemistry in the model. We then compare scavenging efficiencies among storms that formed in Alabama and northeast Colorado and the Oklahoma storm. Significant differences in SEs are seen among storms and species. More scavenging of HNO3 and less removal of CH3OOH are seen in storms with higher maximum flash rates, an indication of more graupel mass. Graupel is associated with mixed‐phase scavenging and lightning production of nitrogen oxides (NOx), processes that may explain the observed differences in HNO3 and CH3OOH scavenging.
Connectivity of earthquake‐triggered landslides with the fluvial network: Implications for landslide sediment transport after the 2008 Wenchuan earthquake
Authors: Li Gen , West A. Joshua , Densmore Alexander L. , Hammond Douglas E. , Jin Zhangdong , Zhang Fei , Wang Jin , Hilton Robert G. 
Published: April 2016

AbstractEvaluating the influence of earthquakes on erosion, landscape evolution, and sediment‐related hazards requires understanding fluvial transport of material liberated in earthquake‐triggered landslides. The location of landslides relative to river channels is expected to play an important role in postearthquake sediment dynamics. In this study, we assess the position of landslides triggered by the Mw 7.9 Wenchuan earthquake, aiming to understand the relationship between landslides and the fluvial network of the steep Longmen Shan mountain range. Combining a landslide inventory map and geomorphic analysis, we quantify landslide‐channel connectivity in terms of the number of landslides, landslide area, and landslide volume estimated from scaling relationships. We observe a strong spatial variability in landslide‐channel connectivity, with volumetric connectivity (ξ) ranging from ~20% to ~90% for different catchments. This variability is linked to topographic effects that set local channel densities, seismic effects (including seismogenic faulting) that regulate landslide size, and substrate effects that may influence both channelization and landslide size. Altogether, we estimate that the volume of landslides connected to channels comprises 43 + 9/−7% of the total coseismic landslide volume. Following the Wenchuan earthquake, fine‐grained (<~0.25 mm) suspended sediment yield across the Longmen Shan catchments is positively correlated to catchment‐wide landslide density, but this correlation is statistically indistinguishable whether or not connectivity is considered. The weaker‐than‐expected influence of connectivity on suspended sediment yield may be related to mobilization of fine‐grained landslide material that resides in hillslope domains, i.e., not directly connected to river channels. In contrast, transport of the coarser fraction (which makes up >90% of the total landslide volume) may be more significantly affected by landslide locations.
The importance of biotic entrainment for base flow fluvial sediment transport
Authors: Rice Stephen P. , Johnson Matthew F. , Mathers Kate , Reeds Jake , Extence Chris 
Published: April 2016

AbstractSediment transport is regarded as an abiotic process driven by geophysical energy, but zoogeomorphological activity indicates that biological energy can also fuel sediment movements. It is therefore prudent to measure the contribution that biota make to sediment transport, but comparisons of abiotic and biotic sediment fluxes are rare. For a stream in the UK, the contribution of crayfish bioturbation to suspended sediment flux was compared with the amount of sediment moved by hydraulic forcing. During base flow periods, biotic fluxes can be isolated because nocturnal crayfish activity drives diel turbidity cycles, such that nighttime increases above daytime lows are attributable to sediment suspension by crayfish. On average, crayfish bioturbation contributed at least 32% (474 kg) to monthly base flow suspended sediment loads; this biotic surcharge added between 5.1 and 16.1 t (0.21 to 0.66 t km−2 yr−1) to the annual sediment yield. As anticipated, most sediment was moved by hydraulic forcing during floods and the biotic contribution from baseflow periods represented between 0.46 and 1.46% of the annual load. Crayfish activity is nonetheless an important impact during baseflow periods and the measured annual contribution may be a conservative estimate because of unusually prolonged flooding during the measurement period. In addition to direct sediment entrainment by bioturbation, crayfish burrowing supplies sediment to the channel for mobilization during floods so that the total biotic effect of crayfish is potentially greater than documented in this study. These results suggest that in rivers, during base flow periods, bioturbation can entrain significant quantities of fine sediment into suspension with implications for the aquatic ecosystem and base flow sediment fluxes. Energy from life rather than from elevation can make significant contributions to sediment fluxes.
Bed load sediment transport inferred from seismic signals near a river
Authors: Roth Danica L. , Brodsky Emily E. , Finnegan Noah J. , Rickenmann Dieter. , Turowski Jens M. , Badoux Alexandre 
Published: April 2016

AbstractWe examine broadband (5–480 Hz) seismic data from the Erlenbach stream in the Swiss Prealps, where discharge, precipitation, and bed load transport are independently constrained. A linear inversion of seismic spectra, exploiting isolated discharge or rain events, identifies the signals generated by water turbulence and rainfall. This allows us to remove the contributions of turbulence and rainfall from the seismic spectra, isolating the signal of bed load transport. We calibrate the regression for bed load transport during one storm and then use this regression with precipitation and discharge data to calculate bed load transport rates from 2 months of seismic spectra. Our predicted bed load transport rates correlate reasonably well with transport rates from calibrated geophones embedded in the channel (r2 ~ 0.6, p < 10−10). We find that the seismic response to rainfall is broadband (~16–480 Hz), while water turbulence and sediment transport exhibit seismic power primarily in lower frequencies (<100 Hz), likely due to longer attenuation path lengths. We use the varying attenuation at each seismometer to infer that a downstream waterfall is the primary source of the water turbulence signal. Our results indicate that deconstruction of seismic spectra from rivers can provide insight into the component signals generated by water turbulence, rainfall, and sediment transport. Further, the regression of seismic spectra with precipitation, discharge, and bed load transport data for a single calibration period enables the estimation of transport for subsequent periods with only precipitation, discharge, and seismic data. Hence, in combination with precipitation and discharge data, seismic data can be used to monitor bed load sediment transport.
Seasonal climate signals from multiple tree ring metrics: A case study of Pinus ponderosa in the upper Columbia River Basin
Authors: Dannenberg Matthew P. , Wise Erika K. 
Published: April 2016

AbstractProjected changes in the seasonality of hydroclimatic regimes are likely to have important implications for water resources and terrestrial ecosystems in the U.S. Pacific Northwest. The tree ring record, which has frequently been used to position recent changes in a longer‐term context, typically relies on signals embedded in the total ring width of tree rings. Additional climatic inferences at a subannual temporal scale can be made using alternative tree ring metrics such as earlywood and latewood widths and the density of tree ring latewood. Here we examine seasonal precipitation and temperature signals embedded in total ring width, earlywood width, adjusted latewood width, and blue intensity chronologies from a network of six Pinus ponderosa sites in and surrounding the upper Columbia River Basin of the U.S. Pacific Northwest. We also evaluate the potential for combining multiple tree ring metrics together in reconstructions of past cool‐ and warm‐season precipitation. The common signal among all metrics and sites is related to warm‐season precipitation. Earlywood and latewood widths differ primarily in their sensitivity to conditions in the year prior to growth. Total and earlywood widths from the lowest elevation sites also reflect cool‐season moisture. Effective correlation analyses and composite‐plus‐scale tests suggest that combining multiple tree ring metrics together may improve reconstructions of warm‐season precipitation. For cool‐season precipitation, total ring width alone explains more variance than any other individual metric or combination of metrics. The composite‐plus‐scale tests show that variance‐scaled precipitation reconstructions in the upper Columbia River Basin may be asymmetric in their ability to capture extreme events.
Deposition and fate of organic carbon in floodplains along a tropical semiarid lowland river (Tana River, Kenya)
Authors: Omengo Fred O. , Geeraert Naomi , Bouillon Steven , Govers Gerard 
Published: April 2016

AbstractInland waters organic carbon (OC) burial by sedimentation has recently been shown to be an important component in river catchment carbon (C) budgets. However, data on OC burial by sedimentation are hitherto largely limited to temperate zones. We investigated the deposition and fate of sediment‐associated OC in the floodplains of the tropical lowland Tana River (Kenya), between two main gaging stations (Garissa and Garsen). Freshly deposited surface sediments and sediment cores were sampled and analyzed for OC, total nitrogen content, stable isotope signatures (δ13C) of OC, and grain size distribution. In addition, we incubated sediment cores to quantify CO2 production as a proxy for OC mineralization. While the floodplain receives sediment with a relatively low OC content (1.56 ± 0.42%), sediments are enriched with OC inputs from floodplain vegetation to levels above 3%. Sediment cores show a sharp decrease of OC with depth, from 3 to 12% OC in the (sub) surface to less than 1% OC below approximately 60 cm depth. Relatively elevated OC mineralization rates (0.14 ± 0.07 mol. CO2 kgC−1 d−1) were recorded. We used these data to make a first assessment of the C burial efficiency of the Tana River floodplain. In contrast to what is observed in temperate environments, over 50% of C present in the top layers is lost in less than a century. While significant amounts of OC are buried in the Tana River floodplain, the high rates of postdepositional loss limit the development of a long‐term C sink within this tropical floodplain.
A decadal precession of atmospheric pressures over the North Pacific
Authors: Anderson Bruce T. , Gianotti Daniel J. S. , Furtado Jason C. , Di Lorenzo Emanuele 
Published: April 2016

AbstractSustained droughts over the Northwestern U.S. can alter water availability to the region's agricultural, hydroelectric, and ecosystem service sectors. Here we analyze decadal variations in precipitation across this region and reveal their relation to the slow (~10 year) progression of an atmospheric pressure pattern around the North Pacific, which we term the Pacific Decadal Precession (PDP). Observations corroborate that leading patterns of atmospheric pressure variability over the North Pacific evolve in a manner consistent with the PDP and manifest as different phases in its evolution. Further analysis of the data indicates that low‐frequency fluctuations of the tropical Pacific Ocean state energize one phase of the PDP and possibly the other through coupling with the polar stratosphere. Evidence that many recent climate variations influencing the North Pacific/North American sector over the last few years are consistent with the current phase of the PDP confirms the need to enhance our predictive understanding of its behavior.
Influence of ambient water intrusion on coral reef acidification in the Chuuk lagoon, located in the coral‐rich western Pacific Ocean
Authors: Ko Young Ho , Lee Kitack , Noh Jae Hoon , Lee Charity M. , Kleypas Joan A. , Jeong Hae Jin , Kim Kwang Young 
Published: April 2016

AbstractWeekly carbonate chemistry condition data recorded between 2008 and 2014 in the Chuuk lagoon (7.3°N and 151.5°E) of the Federated States of Micronesia, located in the western Pacific Ocean, were analyzed. The results showed that, during periods of weak intrusion of ambient seawater from the surrounding open ocean, two internal biological processes (calcification and respiration) reinforced each other and together lowered the pH of the reef water for extended periods, ranging from a few to several months. The analysis indicated that reduced intrusion of ambient water is associated with periods of low wind speeds. Such conditions increase the residence time of reef water, thus promoting acidification by respiration and calcification. This phenomenon likely affects many other areas of the coral‐rich western Pacific Ocean, which contains 50% of global coral reefs and in which the degree of ambient water intrusion into the atolls has been shown to be closely associated with the El Niño–Southern Oscillation‐induced wind speed change.
Mangrove pore water exchange across a latitudinal gradient
Authors: Tait Douglas R. , Maher Damien T. , Macklin Paul A. , Santos Isaac R. 
Published: April 2016

AbstractWe combined observations of the natural tracer radon (222Rn) with hydrodynamic models across a broad latitudinal gradient covering several climate zones to estimate pore water exchange rates in mangroves. Pore water exchange ranged from 2.1 to 35.5 cm d−1 from temperate to tropical regions and averaged 16.3 ± 5.1 cm d−1. If upscaled to the global weighted mangrove area, pore water exchange in mangroves would recirculate the entire volume of water overlying the continental shelf in less than 153 years. Although pore water exchange (recirculated seawater) and river discharge represent different pathways for water entering the coastal ocean, the estimated global mangrove pore water exchange would be equal to approximately one third of annual global river discharge to the ocean (3.84 × 1013 m3 yr−1). Because biogeochemical processes in mangroves are largely dependent on pore water exchange, these large exchange rates have major implications for coastal nutrient, carbon, and greenhouse gas cycling in tropical marine systems.
Near‐surface salinity and stratification in the north Bay of Bengal from moored observations
Authors: Sengupta Debasis , Bharath Raj G. N. , Ravichandran M. , Sree Lekha J. , Papa Fabrice 
Published: April 2016

AbstractA thin layer of fresh water from summer monsoon rain and river runoff in the Bay of Bengal (BoB) has profound influence on air‐sea interaction across the south Asian region, but the mechanisms that sustain the low‐salinity layer are as yet unknown. Using the first long time series of high‐frequency observations from a mooring in the north BoB and satellite salinity data, we show that fresh water from major rivers is transported by large‐scale flow and eddies, and shallow salinity stratification persists from summer through the following winter. The moored observations show frequent 0.2–1.2 psu salinity jumps with time scales of 10 min to days, due to O(1–10) km submesoscale salinity fronts moving past the mooring. In winter, satellite sea surface temperature shows 10 km wide filaments of cool water, in line with moored data. Rapid salinity and temperature changes at the mooring are highly coherent, suggesting slumping of salinity‐dominated fronts. Based on these observations, we propose that submesoscale fronts may be one of the important drivers for the persistent fresh layer in the north BoB.
Ephemerality of discrete methane vents in lake sediments
Authors: Scandella Benjamin P. , Pillsbury Liam , Weber Thomas , Ruppel Carolyn , Hemond Harold F. , Juanes Ruben 
Published: April 2016

AbstractMethane is a potent greenhouse gas whose emission from sediments in inland waters and shallow oceans may both contribute to global warming and be exacerbated by it. The fraction of methane emitted by sediments that bypasses dissolution in the water column and reaches the atmosphere as bubbles depends on the mode and spatiotemporal characteristics of venting from the sediments. Earlier studies have concluded that hot spots—persistent, high‐flux vents—dominate the regional ebullitive flux from submerged sediments. Here the spatial structure, persistence, and variability in the intensity of methane venting are analyzed using a high‐resolution multibeam sonar record acquired at the bottom of a lake during multiple deployments over a 9 month period. We confirm that ebullition is strongly episodic, with distinct regimes of high flux and low flux largely controlled by changes in hydrostatic pressure. Our analysis shows that the spatial pattern of ebullition becomes homogeneous at the sonar's resolution over time scales of hours (for high‐flux periods) or days (for low‐flux periods), demonstrating that vents are ephemeral rather than persistent, and suggesting that long‐term, lake‐wide ebullition dynamics may be modeled without resolving the fine‐scale spatial structure of venting.
Influence of current velocity and wind speed on air‐water gas exchange in a mangrove estuary
Authors: Ho David T. , Coffineau Nathalie , Hickman Benjamin , Chow Nicholas , Koffman Tobias , Schlosser Peter 
Published: April 2016

AbstractKnowledge of air‐water gas transfer velocities and water residence times is necessary to study the fate of mangrove derived carbon exported into surrounding estuaries and ultimately to determine carbon balances in mangrove ecosystems. For the first time, the 3He/SF6 dual tracer technique, which has been proven to be a powerful tool to determine gas transfer velocities in the ocean, is applied to Shark River, an estuary situated in the largest contiguous mangrove forest in North America. The mean gas transfer velocity was 3.3 ± 0.2 cm h−1 during the experiment, with a water residence time of 16.5 ± 2.0 days. We propose a gas exchange parameterization that takes into account the major sources of turbulence in the estuary (i.e., bottom generated shear and wind stress).
Direct measurements of air‐sea CO2 exchange over a coral reef
Authors: McGowan Hamish A. , MacKellar Mellissa C. , Gray Michael A. 
Published: April 2016

AbstractQuantification of CO2 exchange with the atmosphere over coral reefs has relied on microscale measurements of pCO2 gradients across the air‐sea interfacial boundary; shipboard measurements of air‐sea CO2 exchange over adjacent ocean inferred to represent over reef processes or ecosystem productivity modeling. Here we present by way of case study the first direct measurements of air‐sea CO2 exchange over a coral reef made using the eddy covariance method. Research was conducted during the summer monsoon over a lagoonal platform reef in the southern Great Barrier Reef, Australia. Results show the reef flat to be a net source of CO2 to the atmosphere of similar magnitude as coastal lakes, while adjacent shallow and deep lagoons were net sinks as was the surrounding ocean. This heterogeneity in CO2 exchange with the atmosphere confirms need for spatially representative direct measurements of CO2 over coral reefs to accurately quantify their role in atmospheric carbon budgets.