bluuebunny/crossref_metadata_2025 huggingface dataset:
Three methods for observing firn densification velocities with phase-sensitive radar
Authors: Case Elizabeth , Kingslake Jonathan
Published: March 2020

Firn densification operates at the boundary between the atmosphere and ice sheets, impacting estimates of ice thickness change, paleoclimate reconstructions, and near-surface hydrology. Direct measurements of firn densification are scarce and firn densification models, which rely mostly on point measurements of density, disagree on the impact of environmental factors like surface temperature and accumulation rate. Phase-sensitive radar systems (pRES) can observe the movement of isochronal layers in firn and ice by tracking the relative two-way travel times (T) of radio waves. In this work, we demonstrate three methods for extracting measurements of densification velocities from pRES data. Method one uses independently measured firn densities to derive compaction velocities. Method two derives vertical velocities in the firn from an inversion that assumes a steady state and exponential density profile. Method three models changes in T using a semi-physical densification model and compares these changes to the pRES observations. We apply each method to radar data from three ice rises in the Weddell Sea Sector of West Antarctica. Results demonstrate how pRES can be used to explore the accumulation dependence of steady-state densification rates. Average accumulation rate is estimated from pRES measurements in areas that are approximately in steady state. Accumulation gradients can be seen across divides (Korff Ice Rise) and densification-rate differences are observed between relatively high (Fletcher Promontory) and low (Skytrain Ice Rise) accumulation environments. With minimal logistic requirements, new pRES systems like autonomous pRES could be inexpensively deployed to monitor firn densification. Furthermore, existing data may contain densification information even in cases when its deployment primarily targeted other processes.
Using simple RGB Camera to estimate Nitrogen Uptake, Nitrogen Nutrition Index (NNI) and critical Nitrogen: Spring wheat case study.
Authors: Ben-Asher Jiftah
Published: March 2020

The first Nc dilution curve was based on dry matter (DM) power function. This model is limited to  point of singularity near zero. Another disadvantage was that it required meaasurements of DM which is time and labor consuming. Alternatively we proposed a logistic model that starts at zero and on the abscissa assumed a linear relationship between days after emergence (DAE) and DM throughout the relevant stages of wheat growth cycle.  

The Objectives of this study were to: 1) To demonstrate the feasibility of digital camera to replace laboratory tests. 2) To Determine critical N (Nc) and Nitrogen nutrition Index(NNI) of spring wheat and 3) Use N% and dry matter yield in order to calculate N uptake by wheat. This last is expected to be a tool to calculate the required amount of nitrogen to obtain maximum yield.

Wheat experiments were conducted in greenhouse lysimeters. Varied rates of N fertilizer (equivalent to 0–180 kg ha-1) and several  cultivars varying from shortest to longest ripening growth period. Nc reduced gradually from about 6% to 2%  ( =60-20 gr/Kg) when DM increased with DAE  from 0 to 14,000 kg/ha during 80 growing days.  NNI was stable and clearly distinct between   maximal index (1.0  and minimal index (0.2) when (DAE) was about 60;   Photographs succeeded to replicate laboratory measurements and obtained a linear regression curve with a unity  slop and r2=0.93. Nitrogen.  use efficiency (NUE) ranged from 50 to 65 kg  DM/unit N and from 30 to 50 Kg grain /unit N .
Calibration and evaluation of a capacitance probe in agricultural soils in northeast Brazil
Authors: Duarte Guedes Cabral de Almeida Ceres , Barreto Franco Lais , Barbosa dos Santos José Ediclécio , Gomes de Almeida Brivaldo , Provenzano Giuseppe
Published: March 2020

Soil water content is an important parameter for irrigation management. Among the indirect methods to determine soil water content (SWC), there are electronic sensors, that need site-specific calibration to increase the accuracy of the measurements. In this research, a capacitance probe (Diviner 2000®, Sentek Pty Ltda., Australia) was calibrated for two agricultural soils. The experiment was carried out in a protected environment at the Federal Rural University of Pernambuco (UFRPE), Brazil. The textural classes of soils were sandy clay loam (66% sand) and sandy (95% sand). Undisturbed and disturbed soil samples were collected in the soil top layer (0-30 cm). The disturbed soil samples were initially air-dried, passed through a 4.75 mm mesh sieve, and then introduced to fill eight vessels (four replications for each soil). These vessels, equipped with drainage holes, have lower and upper diameters of 15 cm and 25 cm, respectively, and height of 22.5 cm (4.66 L). In each pot, a 5 cm layer of gravel with an average diameter of 2 cm covered with bidim® geotextile was disposed before introducing the soil. During filling, the soil was compacted to reach the same bulk density measured on the undisturbed samples (sandy clay loam: 1.54 g cm-3 and sandy: 1.50 g cm-3). In the center of each pot, a PVC access tube was installed. According to the manufacturer's recommendation, during calibration, the probe normalization was performed. The pots were wetted by capillary rise and, once saturated, they were placed on a bench for drainage. After this process stopped each pot was daily weighed at a fixed time (8 a.m.), and the sensor reading was acquired until when the daily mass variations became negligible. Data were used for regression analysis to fit the site-specific calibration equation and to evaluate the mean error. Linear calibration equations, characterized by R2=0.931 and 0.986, were obtained for the sandy clay loam and the sandy soil, respectively. The mean errors (ME) associated with the manufacturer’s equation resulted in -0.05 and -0.01 for sandy clay loam and for sandy soil and decreased after calibration. The results confirmed the suitability of the manufacturer's equation in sandy soils. On the other hand, the manufacture’s equation slightly underestimated SWC, in sandy clay loam soil, especially in the range above 0.26 m3 m-3. The Diviner 2000 probe can be therefore successfully used to support irrigation management in irrigated areas with soils similar to those investigated because it is easy to operate and allows fairly accurate estimations of soil water content.
Quantifying uncertainty in projections of future European climate: a multi-model multi-method approach
Authors: Brunner Lukas , McSweeney Carol , Befort Daniel , O'Reilly Chris , Booth Ben , Harris Glen , Lowe Jason , Benassi Marianna , Coppola Erika , Nogherotto Rita , Hegerl Gabriele , Knutti Reto , Lendrink Geert , de Vries Hylke , Qasmi Said , Ribes Aurelien , Undorf Sabine
Published: March 2020

Political decisions, adaptation planning, and impact assessments need reliable estimates of future climate change and related uncertainties. Different approaches to constrain, filter, or weight climate model simulations into probabilistic projections have been proposed to provide such estimates. Here six methods are applied to European climate projections using a consistent framework in order to allow a quantitative comparison.  Focus is given to summer temperature and precipitation change in three different spatial regimes in Europe in the period 2041-2060 relative to 1995-2014. The analysis draws on projections from several large initial condition ensembles, the CMIP5 multi-model ensemble, and perturbed physics ensembles, all using the high-emission scenario RCP8.5.  
The methods included are diverse in their approach to quantifying uncertainty, and include those which apply weighting schemes based on baseline performance and inter-model relationships, so-called ASK (Allen, Stott and Kettleborough) techniques which use optimal fingerprinting to scale the scale the response to external forcings, to those found in observations and Bayesian approaches to estimating probability distributions. Some of the key differences between methods are the uncertainties covered, the treatment of internal variability, and variables and regions used to inform the methods. In spite of these considerable methodological differences, the median projection from the multi-model methods agree on a statistically significant increase in temperature by mid-century by about 2.5°C in the European average. The estimates of spread, in contrast, differ substantially between methods. Part of this large difference in the spread reflects the fact that different methods attempt to capture different sources of uncertainty, and some are more comprehensive in this respect than others. This study, therefore, highlights the importance of providing clear context about how different methods affect the distribution of projections, particularly the in the upper and lower percentiles that are of interest to 'risk averse' stakeholders. Methods find less agreement in precipitation change with most methods indicating a slight increase in northern Europe and a drying in the central and Mediterranean regions, but with considerably different amplitudes. Further work is needed to understand how the underlying differences between methods lead to such diverse results for precipitation. 
Extreme Value Theory for Observations
Authors: caby Theophile , Faranda Davide , Vaienti Sandro , Yiou Pascal
Published: March 2020

We study the properties of recurrence of a smooth observable computed along a trajectory of a chaotic system near a particular value of interest .  Using the framework of Extreme Value Theory, we are able to derive a limit law which is a Gumbel  distribution whose parameters relate to the dimensions of the image measure. We show that this approach allows to have access to the fine structure of the attractor, by using directly observational data. In particular, we are able to compute local dimensions associated to the underlying attractor whenever the dimensionality of the observable is larger than the dimension of the attractor. 
Substorm Injections as a Source of Relativistic Electrons in Earth’s Outer Radiation Belt
Authors: Turner Drew , Cohen Ian , Sorathia Kareem , Ukhorskiy Sasha , Reeves Geoff , Ripoll Jean-Francois , Gabrielse Christine , Fennell Joseph , Blake J. Bernard
Published: March 2020

Earth’s magnetotail plasma sheet plays a crucial role in the variability of Earth’s outer electron radiation belt. Typically, injections of energetic electrons from Earth’s magnetotail into the outer radiation belt and inner magnetosphere during periods of substorm activity are not observed exceeding ~300 keV.  Consistent with that, phase space density radial distributions of electrons typically indicate that for electrons below ~300 keV, there is a source of electrons in the plasma sheet while for electrons with energies above that, there is a local source within the outer radiation belt itself.  However, here we ask the question: is this always the case or can the plasma sheet provide a direct source of relativistic (> ~500 keV) electrons into Earth’s outer radiation belt via substorm injection? Using phase space density analysis for fixed values of electron first and second adiabatic invariants, we use energetic electron data from NASA’s Van Allen Probes and Magnetospheric Multiscale (MMS) missions during periods in which MMS observed energetic electron injections in the plasma sheet while Van Allen Probes concurrently observed injections into the outer radiation belt. We report on cases that indicate there was a sufficient source of up to >1 MeV electrons in the electron injections in the plasma sheet as observed by MMS, yet Van Allen Probes did not see those energies injected inside of geosynchronous orbit.  From global insight with recent test-particle simulations in global, dynamic magnetospheric fields, we offer an explanation for why the highest-energy electrons might not be able to inject into the outer belt even while the lower energy (< ~300 keV) electrons do. Two other intriguing points that we will discuss concerning these results are: i) what acceleration mechanism is capable of producing such abundance of relativistic electrons at such large radial distances (X-GSE < -10 RE) in Earth’s magnetotail? and ii) during what conditions (if any) might injections of relativistic electrons be able to penetrate into the outer belt?
How uncertain is the hydrological contribution to global sea level based on hydrological modelling compared to observational data?
Authors: Mielke Christian , Engels Olga , Uebbing Bernd , Gerdener Helena , Börger Lara , Schulze Kerstin , Döll Petra , Kusche Jürgen
Published: March 2020

Quantifying individual contributors to global and regional mean sea level along with corresponding uncertainties is crucial for future projections. However, the contribution of terrestrial hydrology seems to be the least known, but is particularly important, since in addition to the climate-driven changes human activities (such as groundwater pumping, irrigation, deforestation) have a large impact on global sea level changes. Under the common assumption that atmospheric water storage change is negligible, (total) terrestrial water storage anomalies (TWSA) represents a proxy for the hydrologic contribution. Generally, TWSA can be derived using models, observations or a combination of both. Each of the methods has its pros and cons.

In this study, we estimate the contribution of terrestrial hydrological cycle changes to global mean sea level along with corresponding uncertainties for 2003 - 2016 based on land TWSA time series derived (i) from WaterGAP Global Hydrological Model WGHM that also simulates anthropogenic effects and provides a partitioning of TWSA into global river discharge and evapotranspiration minus precipitation, (ii) satellite gravimetry data from GRACE, and (iii) from a joint inversion using GRACE and altimetry data. To realistically describe uncertainties in forcing data, model parameters, initial water states, and errors in the model structure, an ensemble of 30 runs is generated and analyzed. Because of well-known large inter-annual and decadal hydrological variations, we estimate time-varying trends using a Kalman filter framework in addition to the usually estimated linear trends. This approach provides more reliable trend and corresponding uncertainty estimates. Moreover, it naturally enables detecting any changes in rates, which is acceleration.
Formation of stable aggregates by fluid-assembled solid bridges
Authors: Jerolmack Douglas , Seiphoori Ali
Published: March 2020

Earh's surface is covered with soil; particulate mixtures subject to cycles of wetting and drying. The role of this transient hydrodynamic forcing in creating and destroying aggregates is virtually unexplored. We examine this process at the grain scale. When a colloidal suspension is dried, capillary pressure may overwhelm repulsive electrostatic forces, assembling aggregates that are out of thermal equilibrium. This poorly understood process confers cohesive strength to many geological and industrial materials. Here we observe evaporation-driven aggregation of natural and synthesized particulates, and then probe their stability under rewetting using a microfluidics channel as a flume to determine the entrainment threshold. We also directly measure bonding strength of aggregates using an atomic force microscope. Cohesion arises at a common length scale (~5 microns), where interparticle attractive forces exceed particle weight. In polydisperse mixtures, smaller particles condense within shrinking capillary bridges to build stabilizing “solid bridges” among larger grains. This dynamic repeats across scales forming remarkably strong, hierarchical clusters, whose cohesion derives from grain size rather than mineralogy. Transient capillary pressures are even sufficiently large to sinter the smallest particles together. These results may help to understand the strength and erodibility of natural soils, and other polydisperse particulates that experience transient hydrodynamic forces.
Modeling the geometry of melt ponds on Arctic sea ice
Authors: Golden Kenneth , Bowen Brady , Ma Yiping , Moore Ryleigh , Strong Court , Sudakov Ivan
Published: March 2020

In late spring small pools of melt water on the surface of Arctic sea ice begin to grow and coalesce to form large connected labyrinthine ponds. The fractal geometry of these iconic blue patterns is both beautiful to the eye and important to the evolution of sea ice albedo and its role in the climate system. Here we report on recent results in modeling the geometry of Arctic melt ponds. We consider two models, first where pond boundaries are the level curves of random surfaces representing snow topography, and then an Ising model, originally developed a century ago to understand ferromagnetic materials, adapted to describe melt ponds. Our melt pond Ising model requires only one measured input - a length scale from snow topography data. Then energy minimization produces realistic ponds whose sizes and transition in fractal dimension with increasing area agree closely with observations. Finally we examine how the random snow topography influences the evolution of pond fractal geometry and find that the saddle points of the surface play the critical role in transitional behavior.
The climates of Earth's next supercontinent: effects of tectonics, rotation rate, and insolation
Authors: Way Michael , Davies Hannah , Duarte Joao , Green Mattias
Published: March 2020

We investigate two possible deep future Earth climate scenarios using a 3-D GCM [1], 200 and 250 million years into the future when the next supercontinent phase is expect to take place. We use knowledge of the evolution of plate tectonics, solar luminosity, and rotation rate over this time period.  In one scenario, a supercontinent forms at low latitudes. In the other scenario it forms at high northerly latitudes with an Antarctic subcontinent remaining at the south pole.  The climates differences between these two scenarios are dramatic, with differences in mean surface temperatures approaching 4 degrees. The fractional habitability (where mean surface temperatures are between 0<T<100C year round) on land surfaces (as opposed to the ocean) is shown to differ up to 40% between the two simulations. We believe these demonstrate that the community needs to consider alternative boundary conditions when simulating Earth-like exoplanetary climates.

[1] Way et al. 2017, ApJS, 231, 21.
A predictive and invertible model of fluvial sediment geochemistry
Authors: Roberts Gareth , Lipp Alex , Whittaker Alexander , Gowing Charles , Fernandes Victoria
Published: March 2020

The composition of sediments in large rivers and the rocks they form in sedimentary basins record provenance, weathering and surface processes. We predict the geochemical evolution of the Earth’s eroding surface from source regions through fluvial systems, and into the sedimentary record using a simple deterministic model. Using a stream power formulation of fluvial erosion we predict the incision rate at any point in an eroding landscape. Combining these predictions with information about the geochemistry of the eroding substrate we predict the composition of the eroded sediment as it is routed through the landscape. This simple approach is tested in a case study of Scottish rivers by comparing predictions with fine-grained sediment composition measurements. The high-density GBASE stream sediment geochemical survey was utilised to predict fine-grained sediment geochemistry along major regional rivers (Spey, Dee, Don, Tay, Deveron). Sediment samples were gathered from river heads to mouths and their bulk geochemical composition was determined by ICP-MS following mixed acid digestion. Predicted geochemistry of major rivers was tested using the new independent geochemical dataset. Using this data we discuss down-system trends in fluvial sediment geochemsitry, and evaluate the success of our model. Finally, we discuss how bulk geochemical data from river sediments can be formally inverted to reconstruct the geochemistry of their source regions.
Processes, Products & Policy: Investigating how drought events are perceived differently across spatial scales
Authors: Baulch Josie , Sheffield Justin , Dash Jadu
Published: March 2020

Traditionally, availability of consistent, high quality, high-resolution data for Sub-Saharan Africa (SSA) has been limited, with political barriers, poverty and slow technological advancement all contributing to this issue. Over the past 30 years, a rapid increase in the advancement of satellite technology has led to the new era of ‘big data’, which includes a number of high-resolution, global remote sensing datasets. With an overwhelming amount of data now being downloaded and processed, we need to be sure that the best products are being used, in the most appropriate way, to determine the onset and evolution of extreme hydrological events and to influence policy implementation. This study uses scaling analysis of a number of hydrological and agricultural variables to investigate how spatial resolution influences monitoring of drought events. By studying the 2016/17 drought in Kenya, and assessing the drought footprint at various resolutions, it is evident that the data and its scale largely influences the apparent drought signal. Across all the variables, coarser data showed a significantly reduced drought extent than finer data, with a number of regions appearing to not fall below the drought threshold, when in reality, that area was experiencing drought. The implications of these scale issues could be significant, as drought policies in Kenya are implemented on a county level basis. By understanding the importance of effective scaling between the decision-making scale (policy), the data used for drought assessment (products) and the impacts of drought on the ground (processes), updated drought management and mitigation techniques can be used, with potential to reduce vulnerability to future drought events.
Basin- and global-scale environment alternately drive diatom community structure in ancient Lake Ohrid
Authors: Cvetkoska Aleksandra , B. Van de Waal Dedmer , H. Donders Timme , Jovanovska Elena , Levkov Zlatko , Hauffe Torsten , M. Reed Jane , Francke Alexander , Vogel Hendrik , Wilke Thomas , Wagner Bernd , Wagner-Cremer Friederike
Published: March 2020

Evidence for global environmental and climate change-related loss of biodiversity is accumulating. Understanding the causes of species community change is thus essential for effective management and conservation policies. Nonetheless, disentangling the relative influence of the individual or multiple drivers determining the species communities is challenging, as ecosystems are simultaneously affected by variable drivers acting on different spatial and temporal scales. To this end, paleolimnological data may provide critical information on long-term community changes, species dominance shifts, and their underlying drivers. Natural forced changes in the aquatic environments can be used to study the response of biota to repeated fluctuations in essential key variables. In this study, we investigated the planktonic diatom communities in a continuous, 1.36 Ma sedimentary succession from ancient Lake Ohrid (North Macedonia/Albania). This is the oldest, continuously existing freshwater lake in Europe, acknowledged as a site of exceptional biodiversity and endemic species richness. An extended biogeochemical dataset from the DEEP site sedimentary record and previously-published variables representing global climate variability was used to: i) quantify the relative influence of individual environmental variables in governing species communities, and ii) disentangle the contribution of basin-scale environmental processes and global-scale climate variability in driving community patterns over time. The results show that the structure of planktonic communities was primarily determined by the basin-scale environment, particularly, nutrient availability, water temperature and water column mixing, but also local tectonic processes, since lake ontogeny. However, since the onset of the penultimate glacial period 0.185 Ma ago, global-scale climate variability became the principal drivers of the diatom community structure. Our proxy time-series illustrates how various factors at different spatial scales may determine the freshwater planktonic communities over geological time-scales. Extended periods of stable communities can be terminated by changes in climate, environmental conditions and/or lake ontogeny, leading to species extinctions and community turnovers. Thereby lake ecosystem structure and functioning are affected and effective management and conservation policies are required to minimize additional anthropogenic change-related loss of biodiversity. 
Iron and manganese colimitation in the Southern Ocean examined with a proteomic allocation model
Authors: McCain J. Scott P. , Achterberg Eric P. , Tagliabue Alessandro , Bertrand Erin M.
Published: March 2020

Iron (Fe) limits primary productivity in a large part of the ocean; but recent geochemical profiles and bottle incubation assays indicate that manganese (Mn) can also limit primary productivity in the Southern Ocean. Fe and Mn can interact to influence primary productivity, but the extent to which these elements colimit phytoplankton in the Southern Ocean is uncertain. In addition, current models are insufficient to assess colimitation as they assume a single, most scarce, resource. In order to examine Fe and Mn colimitation in phytoplankton, we developed a modeling framework to predict proteomic profiles under varying Fe, Mn, and light conditions. In our model, proteins are optimally allocated to various coarse-grained cellular pools, governed by environmental conditions. We predict that Fe controls cellular Mn quotas, largely because of paired stoichiometry within photosynthetic machinery. Our model suggests that the diffusion-limitation paradigm of Fe should be revisited, as diffusive flux of Fe does not appear to be limiting. We then use our model to explore various cellular mechanisms leading to phytoplankton Fe limitation. Lastly, using Fe and Mn biogeochemical model output, we predict regions in the Southern Ocean where Fe/Mn colimitation is most likely to occur.
Impacts of Ice Cloud Particle Size Uncertainty on Radiation, and Precipitation and Climate Sensitivity and the Significance of Future Satellite-Based Constraints
Authors: Su Hui , Wang Yuan , Jiang Jonathan , Xu Feng , Yung Yuk
Published: March 2020

Ice cloud particle size is important to determining ice cloud radiative effect and precipitating rate. However, there is a lack of accurate ice particle effective radius (Rei) observation on the global scale and the parameterization of Rei in climate models is poorly constrained. We conduct a modeling study to assess the sensitivity of climate simulations to Rei. Perturbations to Rei are represented in ice fall speed parameterization and radiation scheme, respectively, in NCAR CESM1 model with a slab ocean configuration. We show that an increase in ice fall speed due to a larger Rei results in a longwave cooling dominating over a shortwave warming, a global mean surface temperature decrease, and precipitation suppression. Similar longwave and shortwave cloud radiative effect changes occur when Rei is perturbed in the radiation scheme. Perturbing falling snow particle size (Res) results in much smaller changes in the climate responses. We further show that varying Rei and Res by 50% to 200% relative to the control experiment can cause climate sensitivity to differ by +12.3% to −6.2%. A future mission under design with combined multi-frequency microwave radiometers and cloud radar can reduce the uncertainty ranges of Rei and Res from a factor of 2 to ±25%, which would help reducing the climate sensitivity uncertainty pertaining to ice cloud particle size by approximately 60%.

 
Interactions and implications of halogens and VOCs on tropospheric oxidant cycles in the remote atmosphere
Authors: Apel Eric C.
Published: March 2020

Reactive halogens have wide-ranging consequences on tropospheric chemistry including ozone destruction, HOx and NOx partitioning, oxidization of volatile organic compounds (VOCs) and initiation of new particle formation. Of particular note and importance, the tropospheric Ox loss due to halogens is estimated to be between 10-20% globally, and up to 50% in some local marine environments. In this work, we include a state-of-the-art coupled halogen and VOCs chemical mechanism into the CAM-Chem global model. Complementing the model development and providing the opportunity to test the model are recent results from the NASA Atmospheric Tomography (ATom) experiment.  ATom was conducted with a heavily instrumented NASA DC-8 aircraft over the course of two and a half years, transecting the lengths of the Pacific and Atlantic Oceans during four seasons, constantly profiling from the surface (200 m) to the upper troposphere/lower stratosphere (12000 m). The ATom payload included instruments that measured both inorganic halogens and organic halogen-containing very short-lived substances (VSLS), as well as those that measured additional volatile organic compounds (VOCs), including hydrocarbons and oxygenated VOCs (OVOCs), both of which react with halogens. Modeled BrO is sensitive to the inclusion of reactions between Br and OVOCs, particularly the aldehydes, which rapidly convert Br to HBr, a far less reactive form of Bry. These reactions can have large implications in the remote troposphere where the ATom measurements have revealed significant emissions and chemical production of low molecular weight aldehydes over the remote marine environment. A version of CAM-chem, updated to include aldehyde emissions from the ocean to close the gap between models and measurements, is used in these analyses. Comparisons between measured and modeled halogen containing species, both organic and inorganic, is presented along with a summary of the implications of our findings on the overall budgets of tropospheric halogens and ozone.
Reconstructing the intensity and location of Northern Hemisphere westerlies during the Plio-Pleistocene using marine sediments
Authors: Abell Jordan T. , Winckler Gisela , Anderson Robert F. , Herbert Timothy
Published: March 2020

The warm Pliocene serves as an analogue for predicted warming over the next century. However, large uncertainties exist for atmospheric circulation and land surface conditions during the Pliocene. Dust transported by wind to locations of accumulation (terrestrial or marine) can provide a record of wind intensity and/or direction. Few dust flux records spanning the Plio-Pleistocene exist. As such, there is ample opportunity to use marine sediments to reconstruct changes in atmospheric conditions during a warmer-than-present world, as well as across the onset/intensification of Northern Hemisphere Glaciation (NHG). During this time, East Asia’s interior, the second largest source of mineral dust today, experienced aridification, occurring alongside a major reorganization of the subarctic North Pacific circulation which led to stratification of the surface ocean. Here, we present two North Pacific marine sediment records of extraterrestrial (ET) 3He-derived terrigenous dust flux proxies (4HeTerr and Th), along with a record of multiple paleoproductivity proxies (Baxs, Opal, and C37Total) for the period spanning ~2.5-4.5 Ma. Our results show that dust flux to the western North Pacific was relatively low and constant through the Pliocene up until ~2.7 Ma, with minor peaks during cooler phases from ~2.9-3.1 Ma. At ~2.7 Ma, concurrent with the intensification of NHG and formation of a permanent halocline cap in the subarctic North Pacific, dust fluxes increase dramatically. The central North Pacific record shows a less drastic shift in dust, but generally displays higher fluxes after ~3 Ma. Dust fluxes in East Asia and the North Pacific are consistent during this time interval, as are global dust fluxes from the North Atlantic, South Atlantic and North Pacific. Western North Pacific dust, SST, and paleoproductivity records point to northward-shifted and weakened Northern Hemisphere westerlies during the warm Pliocene, with evidence for strengthening and southward movement of the westerlies during glacials after ~2.7 Ma. Changes in both winds and dust production mechanisms are likely working in tandem to produce the coherent global dust signals.
Hydrological conditions and peat constitution effect on DOC leaching from permafrost-affected soils: model experiment (Western Siberia, Russia)
Authors: Timofeeva Maria , Goncharova Olga , Matyshak Georgy
Published: March 2020

In the northern ecosystems’ soils, the carbon stock is preserved in peat soils which includes frozen peat. It is vulnerable to any climate changes. The permafrost degradation can affect both the quantity and the composition of dissolved organic carbon of permafrost-affected soils, especially peat soils.

The main aim of our study was to determine the relationship among peat type, water regime and the quantity and composition of water borne carbon export. The research site was located in the discontinuous permafrost zone (N65º18’, E72º52’). Monoliths of various peat soils were collected in summer 2019 for a laboratory experiment.

The experiments were carried out with 6 types of monoliths (oligotrophic fibric peat; oligotrophic hemic peat with lichen debris; eutrophic hemic peat with reindeer moss debris; eutrophic sapric peat; eutrophic sapric peat with a burnt horizon; oligotrophic fibric peat, underlied with sand). We try to understand how organic matter is leached from peat soils with different constitution and different degree of decomposition. In the model experiment, we simulated 3 types of hydrological conditions. Soil monoliths were watered, and the contents of DOC and POC were determined in the collected soil waters.

Simulation of the moderate rainfall (70 mm) by adding distilled water during the week. DOC in this case ranged from 44,2±3.0 mg/l in oligotrophic peat to 80,6±28,7 mg/l in eutrophic peat.

The simultaneous flow of large quantities of water, simulating prolonged rainfall or spring snowmelt. In this case DOC content leaching from fibric oligotrophic peat didn`t change much while DOC leaching from sapric eutrophic peat decreased in comparison with moderate rainfall.

During modeling short stagnant regimen (spring conditions) we observed increase DOC, especially in sapric eutrophic peat (up to 291,0±11,3 mg/l). The mineral horizon under the peat layer reduced the rate of leaching of organic substances from the soil.

Our results indicate the significant role of both the peat constitution and hydrological regime of soils on the rate and amount of organic matter entering the hydrological basin from peat permafrost-affected soils. The data can be used to simulate the dynamics of permafrost ecosystems with changing climatic parameters or with the activation of anthropogenic load.

This research was supported by the Russian Foundation for Basic Research (Grant 18-04-00952)
The Sensitivity of Regional Climate Projections to SSP-Based Land Use Changes in the North American CORDEX Domain
Authors: Bukovsky Melissa , Mearns Linda , Gao Jing , O'Neill Brian
Published: March 2020

In order to assess the combined effects of green-house-gas-induced climate change and land-use land-cover change (LULCC), we have produced regional climate model (RCM) simulations that are complementary to the North-American Coordinated Regional Downscaling Experiment (NA-CORDEX) simulations, but with future LULCCs that are consistent with particular Shared Socioeconomic Pathways (SSPs).  In standard, existing NA-CORDEX simulations, land surface characteristics are held constant at present day conditions.  These new simulations, in conjunction with the NA-CORDEX simulations, will help us assess the magnitude of the changes in regional climate forced by LULCC relative to those produced by increasing greenhouse gas concentrations.     

Understanding the magnitude of the regional climate effects of LULCC is important to the SSP-RCP scenarios framework.  Whether or not the pattern of climate change resulting from a given SSP-RCP pairing is sensitive to the pattern of LULCC is an understudied problem.  This work helps address this question, and will inform thinking about possible needed modifications to the scenarios framework to better account for climate-land use interactions.

Accordingly, in this presentation, we will examine the state of the climate at the end of the 21st century with and without SSP-driven LULCCs in RCM simulations produced using WRF under the RCP8.5 concentration scenario.  The included LULCC change effects have been created following the SSP3 and SSP5 narratives using an existing agricultural land model linked with a new long-term spatial urban land model. 
Community Engagement in Permafrost Research at the Western Arctic Research Centre, Inuvik, Northwest Territories, Canada
Authors: Hille Erika , McAlister Joel , Wilson Alice , Kokelj Steve
Published: March 2020

The Arctic is experiencing climate warming at a more pronounced rate than other regions. This has significant implications for the thermal stability of permafrost, which strongly depends on the long, cold winters typical of the region. Canada’s western Arctic is typically more sensitive to permafrost thaw than other Arctic regions in Canada, because it is underlain by large regions of ice-rich permafrost that are only protected by a thin layer of organic and mineral soil. As a result, disturbances (i.e. fire, shallow landslides, thermal and mechanical erosion, construction) often lead to the exposure and thaw of the underlying permafrost. Climate-induced permafrost thaw has led to dramatic changes to the landscape, impacting communities, infrastructure, and traditional ways of being. In this region, northern stakeholders have invested in research infrastructure that enables them to actively participate in research, research design and implementation, and lead their own research programs. Since permafrost is intrinsically linked to the social, cultural, and economic fabric of the region, it is critical that local stakeholders be engaged in permafrost research.

The Western Arctic Research Centre (WARC) is located in Inuvik, Northwest Territories, Canada. Inuvik is situated in the Beaufort Delta Region of Northwestern Canada, approximately 120km from the Arctic Ocean. A key goal of WARC is to support and conduct research that fosters the social, cultural, and economic prosperity of the people of the Northwest Territories. In response to local concerns, WARC has developed a suite of research programs that focus on the impacts of permafrost thaw on terrestrial, freshwater, and marine systems. To ensure that these research programs are responsive to the concerns of northern and Indigenous residents, WARC works in partnership with researchers, communities, government bodies, and Indigenous and co-management organizations. Project partners provide critical feedback on research design, study site selection, and how to communicate research to a northern audience. Furthermore, the Permafrost Information Hub at WARC is working with local organizations to establish community-based permafrost research and monitoring in the Beaufort Delta Region. This includes the development and delivery of training programs for local environmental monitors, increasing capacity in the region to support permafrost research. Northerners need to be involved in permafrost research. How Northerners want to be involved will differ depending on the location within the region and the nature of the research. This emphasizes the need for consistent, open lines of communication between researchers and local partners.

This oral presentation will outline the steps WARC has taken to engage northern and Indigenous residents in its permafrost research programs, lessons learned, and successes.
Global coupled climate - ice sheet model simulations for the penultimate deglaciation and the last interglacial
Authors: de Boer Bas , Quiquet Aurélien , Bakker Pepijn , Roche Didier
Published: March 2020

Glacial-interglacial changes of the Earth's climate are largely controlled by internal mechanisms that drive changes in greenhouse gases and ice sheets. In this study, we present model experiments of the penultimate deglaciation into the the last interglacial period, obtained with the Earth system model of intermediate complexity iLOVECLIM (v. 1.1.4). We show experiments with an imposed ice-sheet scenario together with initial results with both North and South interactive ice sheets using the GRISLI (v. 2.0) 3-D ice-sheet model. To this aim, we use a recently developed dynamical downscaling procedure to compute temperature and precipitation fields from the relative low resolution atmospheric model grid (T21, ~5.6º) to the GRISLI spherical grids of both the Northern Hemisphere and Antarctica (both 40 x 40 km). We investigate the separate impact of variations of greenhouse gases (GHG), orbital parameters and ice sheets on glacial-interglacial climate change over the past 240 kyr. Using prescribed greenhouse gases or ice sheets induce comparable changes in global mean temperature. Greenhouse gases, predominantly CO2, mainly have a global impact through radiative forcing on atmospheric temperatures. On the other hand, ice sheets have a more regional impact over the Northern Hemispheric (NH) continents and Antarctica during glacial times. Henceforth, polar amplification is more pronounced during glacial periods following large ice-sheet induced changes. Overall these results are comparable to other studies using a similar experimental design. In order to initiate the coupling between the ice sheets and climate model, we perform a large ensemble of experiments to calibrate ice-sheet model parameters for the present day. We will present how the optimal settings for the two ice-sheet regions are selected, based on a comparison with the present-day ice sheets on Antarctica and Greenland. For the coupling, iLOVECLIM generates downscaled SMB, surface temperatures, ocean temperature and salinity, and GRISLI provides surface elevation and ice extent, the coupling interval is 5 years. These experiments are started during the penultimate glacial maximum. We initialize the coupled iLOVECLIM - GRISLI experiments from a climatic forcing experiment using prescribed greenhouse gases and ice sheets, and generate a spin-up simulation of GRISLI using the optimal settings for three different time points at 136, 135 and 134 kyr ago. Initial experiments show a clear linkage between changes in ice sheets, sea ice and ocean circulation. Following the forced rise in atmospheric GHGs, the magnitude of retreat varries between ice sheets, related to location and insolation change (which increases for the NH but decreased for Antarctica). Moreover, sea ice both decrease following GHGs increase, and vary more in phase with global mean temperature.
Paleogene Polar Plankton and export productivity changes between the Eocene and Oligocene
Authors: Rodrigues de Faria Gabrielle , Lazarus David , Struck Ulrich , Asatryan Gayane , Renaudie Johan , Ozen Volkan
Published: March 2020

Aiming to support the prediction of future climate developments, this project investigates the role on geological timescale of the ocean plankton in reducing atmospheric carbon concentration by exporting carbon to the deep-sea. While it is well-known that the transition from the Eocene to the Oligocene brought significant climate changes and, in connection, also a change of the oceans’ carbon export production, the important role of phytoplankton and the links to changing ocean circulation are still poorly understood, as is, similarly, the impact on those changes on the diversity of the plankton contributing to the carbon pump. Investigating the nature of this interaction will provide significant insight into the functions of the oceans as climate regulators.

To address those question, we are generating diversity and absolute abundance data for diatoms and radiolarians, biogeographic data for radiolarians, as well as oxygen and carbon isotope data on planktic and benthic foraminifera, and on the fine fraction (<45µm, i. e. coccoliths), as well as other proxies to estimate surface and deep ocean temperatures and export productivity. These will be generated as paired data from individual samples in various deep-sea drilling sites in and around the Southern Ocean (as it is the focal point of the climatic/oceanographic changes at that period). These data will then be compiled and confronted to an ocean circulation model.

Here we will present our results so far (oxygen and carbon isotope on the bulk fine fraction, as well as radiolarian and diatom diversity estimates), based on two main localities from the antarctic (ODP Site 689B from the Weddell Sea) and the subantarctic (ODP Site 1090B on the southern flank of the Agulhas ridge) South Atlantic. A comparison with a newly generated, database-driven diversity analysis of the same groups in the same region, using the Neptune (NSB) database, will also be shown. While the exhaustive taxonomical compilation made on these two sites for the diatoms records three times more species than what was recorded in the literature for the Southern Ocean biome, it still shows an evolutionary turnover at the Eocene-Oligocene, just as the classic, NSB-driven analysis does. The fine fraction oxygen isotope at both sites 689B and 1090B show a pattern similar to that recorded in planktonic foraminifera in neighbour sites, indicating a significant drop in SST close to the Eocene-Oligocene boundary, while the fine fraction carbon isotope signal in the antarctic site shows a subsequent decrease indicating changes in exported productivity 2Myr after the global cooling.
Mapping Antarctic Grounding Lines from ICESat-2 Laser Altimetry
Authors: Li Tian , Dawson Geoffrey , Chuter Stephen , Bamber Jonathan
Published: March 2020

The grounding line is the point where the grounded ice sheet detaches from the bed and begins to float. Knowledge of its position and dynamics are critical in mass budget assessments, ice sheet instability monitoring and ice sheet numerical modelling. The grounding line is typically mapped from the landward limit of tidal flexural using different satellite techniques, such as differential synthetic aperture radar interferometry (DInSAR) and ICESat-1 laser altimetry repeat track analysis. However, these methods have, to date, been limited by either spatial or temporal coverage. Launched on 15 September 2018, ICESat-2 satellite offers the potential to address both spatial and temporal coverage issues. Its six-beam pattern as well as the small footprint (~17 m in diameter) and high pulse repetition frequency (10 KHz) of laser altimeter instrument, can achieve a higher accuracy and an order of magnitude denser spatial coverage than ICESat-1. Here we present the results of mapping the grounding line position in Antarctica by detecting the landward limit of tidal flexure from a combination of ICESat-2 repeat track data with a crossover analysis of ascending and descending tracks. Grounding line positions mapped from this method are compared with previous estimates from DInSAR, ICESat-1 altimetry and the break-in-slope mapped from optical imagery. The results show an overall good agreement and highlight the improvements with the new satellite to provide high accuracy and density observations of grounding line in both space and time. 