bluuebunny/crossref_metadata_2025_split huggingface dataset:
Sources, Load, Vertical Distribution, and Fate of Wintertime Aerosols North of Svalbard From Combined V4 CALIOP Data, Ground‐Based IAOOS Lidar Observations and Trajectory Analysis
Authors: Di Biagio C. , Pelon J. , Ancellet G. , Bazureau A. , Mariage V. 
Published: January 2018

AbstractWe have analyzed aerosol properties at the regional scale over high Arctic north of Svalbard between October 2014 and June 2015 from version 4 (V4) CALIOP (Cloud and Aerosol Lidar with Orthogonal Polarization) spaceborne observations and compared results with surface lidar observations from IAOOS (Ice‐Atmosphere‐Ocean Observing System) platforms. CALIOP data indicate a maximum in aerosol occurrence at the end of winter attributed to low‐level (0–2 km) and midtropospheric (2–5 km) particles identified in CALIOP V4 product as being mostly of dust origin. Another maximum was observed in October–December attributed to clean marine particles below 2 km and smoke and dust above. The 532 nm aerosol extinction was in the range 1–8 Mm−1 (0–2 km), 1–18 Mm−1 (2–5 km), and 0–6 Mm−1 (5–10 km), a factor 2 lower compared to values previously reported using CALIOP V3 data set. Aerosols are identified from trajectory analyses to originate mostly from Russia/Europe at all altitudes, and also North America above 2 km, and it is concluded that dust and clean marine types are most probably overrepresented in the analyzed CALIOP data set. It is proposed that most part of dust types are diamond dust, while part of clean marine are polluted species, as corroborated from colocated polarized lidar IAOOS observations. IAOOS observations allowed confirming the identified sensitivity of CALIOP with a particle backscatter coefficient of ~0.001 km−1 sr−1 at 532 nm. For optically thicker layers CALIOP is shown to be a valuable tool to follow transport of aerosol layers in the Arctic and identify their possible modifications.
Strength, Depth, and Geometry of Magnetic Sources in the Crust of the Moon From Localized Power Spectrum Analysis
Authors: Wieczorek Mark A. 
Published: January 2018

AbstractSpacecraft observations show that weak magnetic fields of crustal origin are ubiquitous across the surface of the Moon. To investigate the origin of these magnetic anomalies, a model was developed for the magnetic power spectrum that consists of ensembles of randomly magnetized sills or prisms. Localized spectrum analyses constrained how the parameters of this model vary with position, including the size of the sources, a quantity proportional to their mean‐squared dipole moment, and the depth to the top and bottom of the magnetized region. The depth to the top of the magnetized region varies from the surface to about 25 km. The magnetic carriers in the deep crust likely formed at the same time as the crust itself, implying that a core‐generated dynamo field must have existed when the crust was cooling during the first 100 Myr of lunar evolution. The parameter related to the strength of magnetization shows the existence of a prominent region on the nearside hemisphere that is largely unmagnetized and that correlates with a region of extremely low surface field strengths. This region lies entirely within a geological province that is highly enriched in heat‐producing elements (the Procellarum KREEP Terrane), suggesting that this region escaped being magnetized because of prolonged high crustal temperatures. The nearside magnetic low may be representative of the size of that portion of the crust that is highly enriched in heat‐producing elements, which is almost one third the size of the Procellarum KREEP Terrane based on surface thorium abundances.
Equatorial Oscillation and Planetary Wave Activity in Saturn's Stratosphere Through the Cassini Epoch
Authors: Guerlet S. , Fouchet T. , Spiga A. , Flasar F. M. , Fletcher L. N. , Hesman B. E. , Gorius N. 
Published: January 2018

AbstractThermal infrared spectra acquired by Cassini/Composite InfraRed Spectrometer (CIRS) in limb‐viewing geometry in 2015 are used to derive 2‐D latitude‐pressure temperature and thermal wind maps. These maps are used to study the vertical structure and evolution of Saturn's equatorial oscillation (SEO), a dynamical phenomenon presenting similarities with the Earth's quasi‐biennal oscillation (QBO) and semi‐annual oscillation (SAO). We report that a new local wind maximum has appeared in 2015 in the upper stratosphere and derive the descent rates of other wind extrema through time. The phase of the oscillation observed in 2015, as compared to 2005 and 2010, remains consistent with a ∼15 year period. The SEO does not propagate downward at a regular rate but exhibits faster descent rate in the upper stratosphere, combined with a greater vertical wind shear, compared to the lower stratosphere. Within the framework of a QBO‐type oscillation, we estimate the absorbed wave momentum flux in the stratosphere to be on the order of ∼7 × 10−6 N m−2. On Earth, interactions between vertically propagating waves (both planetary and mesoscale) and the mean zonal flow drive the QBO and SAO. To broaden our knowledge on waves potentially driving Saturn's equatorial oscillation, we searched for thermal signatures of planetary waves in the tropical stratosphere using CIRS nadir spectra. Temperature anomalies of amplitude 1–4 K and zonal wave numbers 1 to 9 are frequently observed, and an equatorial Rossby (n = 1) wave of zonal wave number 3 is tentatively identified in November 2009.
Physical Conditions of Fast Glacier Flow: 2. Variable Extent of Anisotropic Ice and Soft Basal Sediment From Seismic Reflection Data Acquired on Store Glacier, West Greenland
Authors: Hofstede C. , Christoffersen P. , Hubbard B. , Doyle S. H. , Young T. J. , Diez A. , Eisen O. , Hubbard A. 
Published: January 2018

Outlet glaciers of the Greenland Ice Sheet transport ice from the interior to the ocean and contribute directly to sea level rise because discharge and ablation often exceed the accumulation. To develop a better understanding of these fast‐flowing glaciers, we investigate the basal conditions of Store Glacier, a large outlet glacier flowing into Uummannaq Fjord in west Greenland. We use two crossing seismic profiles acquired near the centerline, 30 km upstream of the calving front, to interpret the physical nature of the ice and bed. We identify one notably englacial and two notably subglacial seismic reflections on both profiles. The englacial reflection represents a change in crystal orientation fabric, interpreted to be the Holocene‐Wisconsin transition. From Amplitude‐Versus‐Angle (AVA) analysis we infer that the deepest ∼80 m of ice of the parallel‐flow profile below this reflection is anisotropic with an enhancement of simple shear of ∼2. The ice is underlain by ∼45 m of unconsolidated sediments, below which there is a strong reflection caused by the transition to consolidated sediments. In the across‐flow profile subglacial properties vary over small scale and the polarity of the ice‐bed reflection switches from positive to negative. We interpret these as patches of different basal slipperiness associated with variable amounts of water. Our results illustrate variability in basal properties, and hence ice‐bed coupling, at a spatial scale of ∼100 m, highlighting the need for direct observations of the bed to improve the basal boundary conditions in ice‐dynamic models.
Stable Carbon Isotopes Reveal Soil‐Stream DIC Linkages in Contrasting Headwater Catchments
Authors: Campeau A. , Bishop K. , Nilsson M. B. , Klemedtsson L. , Laudon H. , Leith F. I. , Öquist M. , Wallin M. B. 
Published: January 2018

AbstractLarge CO2 evasion to the atmosphere occurs as dissolved inorganic carbon (DIC) is transported from soils to streams. While this physical process has been the focus of multiple studies, less is known about the underlying biogeochemical transformations that accompany this transfer of C from soils to streams. Here we used patterns in stream water and groundwater δ13C‐DIC values within three headwater catchments with contrasting land cover to identify the sources and processes regulating DIC during its transport. We found that although considerable CO2 evasion occurs as DIC is transported from soils to streams, there were also other processes affecting the DIC pool. Methane production and mixing of C sources, associated with different types and spatial distribution of peat‐rich areas within each catchment, had a significant influence on the δ13C‐DIC values in both soils and streams. These processes represent an additional control on δ13C‐DIC values and the catchment‐scale cycling of DIC across different northern landscape types. The results from this study demonstrate that the transport of DIC from soils to streams results in more than just rapid CO2 evasion to the atmosphere but also represents a channel of C transformation, which questions some of our current conceptualizations of C cycling at the landscape scale.
Assessing the Extent and Impact of Online Data Sharing in Eddy Covariance Flux Research
Authors: Dai Sheng‐Qi , Li Hong , Xiong Jun , Ma Jun , Guo Hai‐Qiang , Xiao Xiangming , Zhao Bin 
Published: January 2018

AbstractResearch data sharing is appealing for its potential benefits on sharers' scientific impact and is also advocated by various policies. How do scientific benefits and policies correlate with practical ecological data sharing? In this study, we investigated data‐sharing practices in eddy covariance flux research as a typical case. First, we collected researchers' data‐sharing information from major observation networks. Then, we downloaded bibliometric data from the Web of Science and evaluated scientific impact using LeaderRank, a synthetic algorithm that takes both citation and cooperation impacts into consideration. Our results demonstrated the following: (1) specific to eddy covariance flux research, 8% of researchers published information in public data portals, whereas 64% of researchers provided their available data online in a downloadable form; (2) regional differences in data sharing, publications, and observation networks existed; and (3) the data sharers in impact‐ranked ecologists followed a long‐tail distribution, which suggested that, although sharing data is not necessary for researchers to be influential, data sharers are more likely to be high‐impact researchers. Differentiated policies should be proposed to encourage ecologists in the long tail of data sharers, and from regions with little tradition of data sharing, to embrace a more open model of science.
Water Shortage Drives Interactions Between Cushion and Beneficiary Species Along Elevation Gradients in Dry Himalayas
Authors: Ale Rita , Zhang Lin , Li Xiang , Raskoti Bhakta Bahadur , Pugnaire Francisco I. , Luo Tianxiang 
Published: January 2018

AbstractIt is challenging to understand the drivers of plant‐plant interaction patterns in dry mountains. However, such knowledge is important to assess alpine ecosystem resilience to climate change. In water‐limited ecosystems, leaf δ13C and satellite‐derived vegetation index (NDVI) may serve as reliable indicators of environmental severity to address plant responses to water availability. We hypothesized that in dry mountains, interaction intensity between cushion and beneficiary species increases with increasing δ13C and decreasing NDVI regardless of elevation, indicating the importance of water availability in driving plant interactions. We used relative interaction indices (RII) of species and individual numbers within and outside the canopy of three cushion plant species along three elevational transects in dry Himalayas, Nepal. Site‐specific NDVI was calculated from 30 m Landsat images. Thornthwaite moisture index was calculated for each elevation site. We observed nonlinear patterns in RII, δ13C, and NDVI with elevation. Intraspecific variation of δ13C was negatively correlated with moisture index and NDVI, while NDVI across sites was positively correlated with precipitation but not with temperature. RII within a cushion species was positively correlated with δ13C and negatively with NDVI when the effect of elevation was removed. In pooled data across cushion species and sites, RII was negatively correlated with precipitation and NDVI when the effect of temperature was removed. RII was uncorrelated with cushion size under the same environment. Leaf nitrogen showed no correlation with RII or δ13C. Our data show that water shortage is the main driver of plant interactions in the alpine belt of dry Himalayas.
Oceanographic and Climatic Change in the Bering Sea, Last Glacial Maximum to Holocene
Authors: Pelto Ben M. , Caissie Beth E. , Petsch Steven T. , Brigham‐Grette Julie 
Published: January 2018

AbstractPost‐glacial sea level rise led to a direct connection between the Arctic and Pacific Oceans via the Bering Strait. Consequently, the Bering Sea experienced changes in connectivity, size, and sediment sources that were among the most drastic of any ocean basin in the past 30,000 years. However, the sedimentary response to the interplay between climate change and sea level rise in high‐latitude settings such as Beringia remains poorly resolved. To ascertain changes in sediment delivery, productivity, and regional oceanography from the Last Glacial Maximum (LGM) to the Holocene, we analyzed sedimentological, geochemical, and isotopic characteristics of three sediment cores from the Bering Sea. Interpretations of productivity, terrestrial input, nutrient utilization, and circulation are based on organic carbon isotopes (δ13Corg), total organic carbon (TOC), bulk nitrogen isotopes, total organic nitrogen, carbon/nitrogen ratios, elemental X‐ray fluorescence data, grain size, and presence of laminated or dysoxic, green intervals. Principal component analysis of these data captures key climatic intervals. The LGM was characterized by low productivity across the region. In the Bering Sea, deglaciation began around 18–17 ka, with increasing terrestrial sediment and TOC input. Marine productivity increased during the Bølling‐Allerød when laminated sediments revealed dysoxic bottom waters where denitrification was extreme. The Younger Dryas manifested increased terrestrial input and decreased productivity, in contrast with the Pre‐Boreal, when productivity markedly rebounded. The Pre‐Boreal and Bølling‐Allerød were similarly productive, but changes in the source of TOC and a δ13Corg depletion suggest the influence of a gradually flooding Bering Shelf during the Pre‐Boreal and Holocene.
Detrital Zircon Record of a Mesozoic Collisional Forearc Basin in South Central Alaska: The Tectonic Transition From an Oceanic to Continental Arc
Authors: Stevens Goddard Andrea L. , Trop Jeffrey M. , Ridgway Kenneth D. 
Published: January 2018

AbstractThe collision of oceanic arcs with continental margins is an important mechanism for the growth of continents. Ancient forearc basin strata in collisional orogens provide a record of the upper crustal response to this tectonic process. In south central Alaska, Mesozoic forearc basin strata are exposed in a complete crustal section. U‐Pb detrital zircon geochronology from the forearc basin strata was analyzed within a ~107 Ma stratigraphic framework. The Jurassic strata contain unimodal detrital zircon populations that become progressively younger upsection and range from 175 to 151 Ma. These strata are derived from the active oceanic Talkeetna arc. The Cretaceous strata were deposited above multiple unconformities that collectively represent as much as ~30 Ma of nondeposition and/or erosion in the forearc basin. Erosion in the forearc basin and a general absence of detrital zircon ages between 140 and 120 Ma are interpreted as a hiatus of magmatism triggered by collision of the oceanic arc with the former continental margin. The Cretaceous strata have two main detrital zircon populations: a Cretaceous population ranging from 90 to 68 Ma that becomes progressively younger upsection and a Jurassic population with a broad range of peak ages from 194 to 144 Ma. The Cretaceous population marks the establishment of an active Cretaceous continental arc following the collisional event, and the older population reflects continued erosion of the remnant Jurassic oceanic arc plutons. Our results show that detrital zircon geochronology provides a powerful approach for delineating stages of forearc basin collision and the erosion of multiple magmatic arcs.
High‐Elevation Evapotranspiration Estimates During Drought: Using Streamflow and NASA Airborne Snow Observatory SWE Observations to Close the Upper Tuolumne River Basin Water Balance
Authors: Henn Brian , Painter Thomas H. , Bormann Kat J. , McGurk Bruce , Flint Alan L. , Flint Lorraine E. , White Vince , Lundquist Jessica D. 
Published: January 2018

AbstractHydrologic variables such as evapotranspiration (ET) and soil water storage are difficult to observe across spatial scales in complex terrain. Streamflow and lidar‐derived snow observations provide information about distributed hydrologic processes such as snowmelt, infiltration, and storage. We use a distributed streamflow data set across eight basins in the upper Tuolumne River region of Yosemite National Park in the Sierra Nevada mountain range, and the NASA Airborne Snow Observatory (ASO) lidar‐derived snow data set over 3 years (2013–2015) during a prolonged drought in California, to estimate basin‐scale water balance components. We compare snowmelt and cumulative precipitation over periods from the ASO flight to the end of the water year against cumulative streamflow observations. The basin water balance residual term (snow melt plus precipitation minus streamflow) is calculated for each basin and year. Using soil moisture observations and hydrologic model simulations, we show that the residual term represents short‐term changes in basin water storage over the snowmelt season, but that over the period from peak snow water equivalent (SWE) to the end of summer, it represents cumulative basin‐mean ET. Warm‐season ET estimated from this approach is 168 (85–252 at 95% confidence), 162 (0–326) and 191 (48–334) mm averaged across the basins in 2013, 2014, and 2015, respectively. These values are lower than previous full‐year and point ET estimates in the Sierra Nevada, potentially reflecting reduced ET during drought, the effects of spatial variability, and the part‐year time period. Using streamflow and ASO snow observations, we quantify spatially‐distributed hydrologic processes otherwise difficult to observe.
Flow Resistance Interactions on Hillslopes With Heterogeneous Attributes: Effects on Runoff Hydrograph Characteristics
Authors: Papanicolaou Athanasios N. , Abban Benjamin K. B. , Dermisis Dimitrios C. , Giannopoulos Christos P. , Flanagan Dennis C. , Frankenberger James R. , Wacha Kenneth M. 
Published: January 2018

AbstractAn improved modeling framework for capturing the effects of space and time‐variant resistance to overland flow is developed for intensively managed landscapes. The framework builds on the WEPP model but it removes the limitations of the “equivalent” plane and time‐invariant roughness assumption. The enhanced model therefore accounts for spatiotemporal changes in flow resistance along a hillslope due to changes in roughness, in profile curvature, and downslope variability. The model is used to quantify the degree of influence—from individual soil grains to aggregates, “isolated roughness elements,” and vegetation—on overland flow characteristics under different storm magnitudes, downslope gradients, and profile curvatures. It was found that the net effects of land use change from vegetation to a bare surface resulted in hydrograph peaks that were up to 133% larger. Changes in hillslope profile curvature instead resulted in peak runoff rate changes that were only up to 16%. The stream power concept is utilized to develop a taxonomy that relates the influence of grains, isolated roughness elements, and vegetation, on overland flow under different storm magnitudes and hillslope gradients. Critical storm magnitudes and hillslope gradients were found beyond which the effects of these landscape attributes on the peak stream power were negligible. The results also highlight weaknesses of the space/time‐invariant flow resistance assumption and demonstrate that assumptions on landscape terrain characteristics exert a strong control both on the shape and magnitude of hydrographs, with deviations reaching 65% in the peak runoff when space/time‐variant resistance effects are ignored in some cases.
Three‐Dimensional Effects of Artificial Mixing in a Shallow Drinking‐Water Reservoir
Authors: Chen Shengyang , Little John C. , Carey Cayelan C. , McClure Ryan P. , Lofton Mary E. , Lei Chengwang 
Published: January 2018

AbstractStudies that examine the effects of artificial mixing for water‐quality mitigation in lakes and reservoirs often view a water column with a one‐dimensional (1‐D) perspective (e.g., homogenized epilimnetic and hypolimnetic layers). Artificial mixing in natural water bodies, however, is inherently three dimensional (3‐D). Using a 3‐D approach experimentally and numerically, the present study visualizes thermal structure and analyzes constituent transport under the influence of artificial mixing in a shallow drinking‐water reservoir. The purpose is to improve the understanding of artificial mixing, which may help to better design and operate mixing systems. In this reservoir, a side‐stream supersaturation (SSS) hypolimnetic oxygenation system and an epilimnetic bubble‐plume mixing (EM) system were concurrently deployed in the deep region. The present study found that, while the mixing induced by the SSS system does not have a distinct 3‐D effect on the thermal structure, epilimnetic mixing by the EM system causes 3‐D heterogeneity. In the experiments, epilimnetic mixing deepened the lower metalimnetic boundary near the diffuser by about 1 m, with 55% reduction of the deepening rate at 120 m upstream of the diffuser. In a tracer study using a 3‐D hydrodynamic model, the operational flow rate of the EM system is found to be an important short‐term driver of constituent transport in the reservoir, whereas the duration of the EM system operation is the dominant long‐term driver. The results suggest that artificial mixing substantially alters both 3‐D thermal structure and constituent transport, and thus needs to be taken into account for reservoir management.
Socio‐Hydrology of Channel Flows in Complex River Basins: Rivers, Canals, and Distributaries in Punjab, Pakistan
Authors: Wescoat James L. , Siddiqi Afreen , Muhammad Abubakr 
Published: January 2018

AbstractThis paper presents a socio‐hydrologic analysis of channel flows in Punjab province of the Indus River basin in Pakistan. The Indus has undergone profound transformations, from large‐scale canal irrigation in the mid‐nineteenth century to partition and development of the international river basin in the mid‐twentieth century, systems modeling in the late‐twentieth century, and new technologies for discharge measurement and data analytics in the early twenty‐first century. We address these processes through a socio‐hydrologic framework that couples historical geographic and analytical methods at three levels of flow in the Punjab. The first level assesses Indus River inflows analysis from its origins in 1922 to the present. The second level shows how river inflows translate into 10‐daily canal command deliveries that vary widely in their conformity with canal entitlements. The third level of analysis shows how new flow measurement technologies raise questions about the performance of established methods of water scheduling (warabandi) on local distributaries. We show how near real‐time measurement sheds light on the efficiency and transparency of surface water management. These local socio‐hydrologic changes have implications in turn for the larger scales of canal and river inflow management in complex river basins.