bluuebunny/crossref_metadata_2025 huggingface dataset:
Basal Melt of the Greenland Ice Sheet: The Invisible Mass Budget Term
Authors: Karlsson Nanna Bjørnholt , Solgaard Anne Munck , Mankoff Kenneth D. , Box Jason E. , Citterio Michele , Colgan William T. , Kjeldsen Kristian K. , Korsgaard Niels J. , Vandecrux Baptiste , Benn Douglas , Hewitt Ian , Fausto Robert S.
Published: March 2020

The Greenland ice sheet has been one of largest sources of sea-level rise since the early 2000s. The total mass balance of the ice sheet is typically determined using one of the following methods: estimates of ice volume change from satellite altimetry, measurements of changes in gravity, and by considering the difference between solid ice discharge and surface mass balance (often referred to as the input–output method). In spite of an overall agreement between the different methods, uncertainties remain regarding the relative contribution from individual processes, and to date the basal melt has never been explicitly included in total mass balance estimates. Here, we present the first estimate of the contribution from basal melting to the total mass balance. We partition the basal melt into three terms; melt caused by frictional heat, geothermal heat and viscous heat dissipation, respectively. Combined, the three terms contribute approximately 25 Gt per year of basal melt to the total mass loss equivalent to 5% of the average solid ice discharge (average value of 1986-2018 discharge). This is equivalent to the ice discharge from the entire northeastern sector. We find that basal melting also accounts for between 5% and 30% of observed thinning in most major glacier outlets. Over our observation period (winter 2017/18), close to 2/3 of the basal melt is due to frictional heating from fast moving ice. This term is expected to increase in the future, as ice streams are likely to expand and speed up in response to rising temperatures.
Asphalt in trackbed design
Authors: Voulgari Chrysoula
Published: March 2020

Conventional all granular trackbed has been in use around the world for many years, presenting good results although requiring a certain level of ongoing maintenance. Increasing traffic loads and volumes and particularly the introduction of high-speed trains in the last few decades, have resulted in the need for new approaches. To reduce train load-induced stresses in the track subgrade, one approach that has been introduced is the use of a Hot Mix Asphalt (HMA) layer as a partial or full replacement of the granular sub-ballast.

During the past few decades the use of HMA as a sub-ballast layer within the track structure has steadily increased until it has become standard practice in many countries around the world (USA, Japan, Germany, Italy etc.). The HMA mix is designed similarly to the base layer of highway pavements. Specifically, it is designed to be a medium modulus, flexible, low voids, fatigue resistant layer that will accommodate high tensile strains without cracking .

This paper provides a review of the potential use of an asphalt layer to replace the granular sub-ballast during the railway trackbed design.  A literature review of the use of asphalt in trackbed construction and a parametric analysis have been carried out to compare traditional ‘all granular’ and more recent asphalt layer solutions for different subgrade stiffnesses. 

Results indicate various advantages of the use of asphalt in the trackbed; improving trackbed performance and decreasing the overall cost and environmental impact.
An antioxidant function for dimethylsulfonopropionate (DMSP) and dimethylsulfoxide (DMSO) within three different phytoplankton groups
Authors: Gypens Nathalie , Roberty Stéphane , Borges Alberto V. , Cardol Pierre , Royer Colin
Published: March 2020

Dimethylsulfonopropionate (DMSP) and dimethylsulfoxide (DMSO) are two compounds involved in the carbon and sulfur cycle and are the precursors of the climate cooling gas dimethylsulfide (DMS). Despite decades of research, their role as osmoregulator, cryoprotector or antioxidant within the phytoplankton cells remains uncertain in some part. Since the antioxidant cascade system from the DMSP reported by Sunda & al. (2002), more investigation need to be conducted to confirm or accurate these interactions. This study aims to improve the knowledge about DMSP and DMSO and their hypothetic role of antioxidant on three different classes of phytoplankton (Dinophyceae – Prymnesiophyceae – diatom) and one diatom no-DMSP producer Chaetoceros sp. as negative control. Laboratory cultures were submitted to three oxidative stress to produce Reactive Oxygen Species (ROS) with (1) increasing light intensity from 100 to 600 and up to 1200 µmole/m²s for a global and natural oxidative stress; (2) using the menadone bisulfite (MSB) to generate ·O2 and (3) using 3-(3,4-dichlorophenyl)-1,1-dimethylurea (DCMU) to inhibit the photosystem II (PSII). The PSII activity, the Chlorophyll a concentration (Chl a), the lipidic peroxidation (LOP), the ROS production and the pigment variation were analysed after 6h of incubation and related to the evolution of the DMSP and DMSO concentrations to better understand the cellular oxidative stress and its impact on the phytoplankton cell and DMSP and DMSO production.
Hemispheric TOA SW radiation budgets under changed atmospheric radiation conditions
Authors: Crueger Traute , Schmidt Hauke , Stevens Bjorn
Published: March 2020

Under present day conditions the observations approximately show a hemispheric symmetry of the top of atmosphere (TOA)  short wave (SW) reflection despite the asymmetry of surface SW reflection. This has been confirmed by climate models. With models in an aqua planet setup, Voigt et al. (2014) found that tropical clouds largely compensate surface SW hemispheric asymmetries, however to a different degree in dependence on the convection scheme.

In this study, we question, whether there is also a hemispheric symmetry of TOA SW radiation under changed atmospheric radiation conditions. For that reason, we analyze experiments performed with a set of fully coupled general circulation models. The experiments were performed with either a) hemispheric asymmetric incoming radiation, b) increased atmospheric CO2 concentrations, c) increased atmospheric CO2 concentrations combined with increased stratospheric aerosol burden, or d) increased atmospheric CO2 concentration in conjunction with increased ocean albedo.

We show that generally, a hemispheric symmetry of TOA SW radiation does not occur. Overall, among the group of models, the hemispheric TOA SW radiation budgets are roughly similar for the distinct experiments, although the models utilyze different convection schemes.  We discuss the role of surface and atmospheric feedbacks in the different experiments, especially of tropical and extratropical clouds.

Reference:
Voigt, A., B. Stevens, J. Bader, and T. Mauritsen, 2014: Compensation of Hemispheric Albedo Asymmetries by Shifts of the ITCZ and Tropical Clouds. J. Climate, 27, 1029–1045, https://doi.org/10.1175/JCLI-D-13-00205.1.
New strategies for chemistry-transport modelling of volcanic plumes: application to the case of Mount Etna eruption in March 18, 2012
Authors: Lachatre Mathieu , Mailler Sylvain , Menut Laurent , Turquety Solene , Sellitto Pasquale , Guermaz Henda , Salerno Giuseppe , Carboni Elisa
Published: March 2020

Atmospheric modelling allows to study large spatial scale events such as volcanic eruptions, which can emit large amounts of plume-confined particulate matter and gases, to evaluate their transport in the atmosphere and their subsequent impacts. However, to study more precisely these events, different issues have to be addressed. One notable example of these issues is the well-known excessive numerical diffusion in the atmospheric column in Eulerian models leading to excessive plume dispersion misrepresentation of the plume three-dimensional morphology and subsequent geographical extent of its impacts. Mount Etna volcano’s moderate eruption of March 18, 2012, which released about 3kT of sulphure dioxide in the atmosphere, has been simulated in this study with the CHIMERE chemistry-transport model. The simulated plume has been observed and tracked with satellite instruments (OMI and IASI) for several days during its transport over the Mediterranean Sea in order to compare with model outputs.

Sensitivity tests have been performed to evaluate the impact of injection altitude and profile shape on the subsequent trajectory of the plume. It was shown that altitude is the most sensitive parameter when results remain weakly sensitive to the vertical shape of injection.

In order to effectively address the problem of excessive numerical diffusion, we have included a new antidiffusive transport scheme in the vertical direction and a new strategy to use directly the vertical wind field provided by the forcing meteorological model. We show that both these improvements permit a substantial reduction in numerical diffusion. The use of the new antidiffusive vertical scheme has brought the strongest improvement in our model outputs. To a lesser extent, a more realistic representation of the vertical wind field has also been shown to reduce volcanic plume spreading. In summary, we show that these two improvements bring an improvement in the representation of the plume which is as strong as the improvement brought by increasing the number of vertical levels, but without an additional burden in computational power.

This study has been supported by AID (Agence de l'Innovation de Défense) under grant TROMPET.
Understanding deformation of cratons in presence of mid-lithospheric discontinuity
Authors: Paul Jyotirmoy , Ghosh Attreyee
Published: March 2020

The recent discovery of mid-lithospheric discontinuity (MLD) within most cratons has added a new dimension in the understanding of cratonic survival. The MLD shows up as a seismic discontinuity at ~80-160 km depth. However, there is controversy regarding the strength of this layer. While some studies suggest that this layer is as strong as the craton itself, others advocate that under some special conditions (e.g. metasomatism) MLD can become weak and aid in the delamination of cratons. In this study, we develop 3-D full spherical mantle convection models to understand the effect of MLD in the survival of cratons. In our models, we incorporate MLDs of variable strength, depth and thickness. Along with varying the strength of MLDs, we use different combinations of craton and asthenosphere viscosity to quantitatively estimate how deformation pattern varies. Results obtained from the models suggest that in the presence of a weak MLD stress magnitudes decrease but strain-rates increase  ~2-3 times. This could potentially lead to delamination of cratons. To constrain the present-day strength of MLDs, we predict deviatoric stresses from these different models and compare them to the observed SHmax directions obtained from the World Stress Map. The deviatoric stress pattern changes as the viscosity, depth and thickness of MLD changes.
The use of GPR in Archaeology: the structural detailing of buried roman baths
Authors: Santarelli Roberta , Bianchini Ciampoli Luca , Benedetto Andrea
Published: March 2020

Ground Penetrating Radar has widely proven to be an effective tool for archaeological purposes [1-4]. Our contribution concerns a geophysical experimental activity carried out in the Maxentius Complex, an archaeological site located between the second and the third miles of the ancient Appian Way in Rome, Italy. This site is characterized by different phases dated between the end of the 3rd and the beginning of the 4th century AD. The objective of this study is to evaluate the feasibility of GPR, in this case using two different antennas (200 MHz and 600 MHz frequencies), for the structural detailing of buried roman baths structures. As a result, GPR analysis confirmed the literature-based information, i.e. to precisely locate the tanks of the thermal area (2nd century AD). The structure was partially brought to light and reburied during the second half of the last century, providing a partial plan view of the area. In addition, the tomographic results, together with the analysis of B-Scans, highlighted the presence of two further tanks, thereby suggesting the possibility of further rooms which are located close to the known ones. Furthermore, the tomographic analysis revealed a wall pattern that seems to suggest the presence of other rooms in the top-right side of the area. In general terms, GPR demonstrated a great applicability to archaeological purposes, for example to detect buried remains and to interpret the function of buried structures, despite the reliability and productivity of the data interpretation are strongly influenced by the expertise of both the geophysicists and the archaeologists involved.

 

This work falls within the project “ArchaeoTrack”, supported by Regione Lazio, under the Framework “L.R. 13/08, Research Group Project n. 20 prot. 85-2017-14857”.

 

Bianchini Ciampoli, L., Benedetto, A., Tosti, F., {2018} “The ArchaeoTrack Project: Use of Ground-Penetrating Radar for Preventive Conservation of Buried Archaeology Towards the Development of a Virtual Museum”, In. Proc. of MetroArchaeo, Cassino, Italy

Milligan, R., & M., Atkin, {1993}. The use of ground-probing radar within a digital environment on archaeological sites, in Andresen, J., Madsen, T. and Scollar, I., eds., Computing the Past: Computer Application and Quantitative methods in Archaeology: Aarhus, Denmark, Aarhus University Press, pp. 285–291.

Oswin, J., {2018}. The Roman Baths, Bath Archway Project Geophysical Survey, January 2018.

Pisani Sartorio, G., & Calza R., {1976}. “La villa di Massenzio sulla Via Appia: Il Palazzo - Le Opere D'Arte”, in Monumenti romani VI, Roma.
Characterization of volatile organic compounds (VOCs) in megacity Seoul from multiyear observation
Authors: Kang Sunggu , Son Jeewon , Kim Joo-ae , Lee Meehye , Lee Junbok
Published: March 2020

Volatile organic compounds (VOCs) are the key precursors of O­3 and secondary organic aerosols in urban atmosphere. This study investigates the variations and emission sources of 55 VOCs observed in central Seoul between 2013 and 2019. VOCs were continuously measured every hour using an online gas chromatography system by the Seoul Metropolitan Government Research Institute of Public Health and Environment (SIHE). The lower limit of detection was 0.1 ppbC and outliers were removed by applying Chauvenet’s criterion.

Of the 55 VOCs, the most abundant species was ethane, followed by propane and toluene and their average concentrations were 6.6 ppbv, 5.9 ppbv and 4.6 ppbv, respectively. In terms of TVOCs, toluene was the most abundant with the average concentration of 32.1 ppbC and comprises about the half of the aromatic VOCs. Alkane and aromatics showed different seasonal, diurnal and weekly variations, and dependence on meteorological variables. In addition, the toluene to benzene ratio was greater in summer than in winter with the average of 11.0. These results indicate the additional sources for VOCs to traffic related emissions in megacity Seoul. The PSCF (Potential Source Contribution Function) and cluster analysis of backward trajectories of air masses indicate that while alkanes are chiefly emitted from vehicles, aromatic concentrations are greatly influenced by fugitive emission from neighboring cities of Seoul. There is also chance for some VOCs with relatively long lifetime to be transported from nearby countries.
The influence of convective momentum transport and vertical wind shear on the evolution of a cold air outbreak
Authors: Saggiorato Beatrice , Nuijens Louise , Siebesma A. Pier , de Roode Stephan , Sandu Irina , Papritz Lukas
Published: March 2020

To study the influence of convective momentum transport (CMT) on wind, boundary layer and cloud evolution in a marine cold air outbreak (CAO) we use Large-Eddy Simulations subjected to different baroclinicity (wind shear) but similar surface forcing. The simulated domain is large enough ( ≈100 × 100 km2) to develop typical mesoscale cellular convective structures.  We find that a maximum friction induced by momentum transport (MT) locates in the cloud layer for an increase of geostrophic wind with height (forward shear, FW) and near the surface for a decrease of wind with height (backward shear, BW). Although the total MT always acts as a friction, the interaction of friction-induced cross-isobaric flow with the Coriolis force can develop super-geostrophic winds near the surface (FW) or in the cloud layer (BW). The contribution of convection to MT is evaluated by decomposing the momentum flux by column water vapor and eddy size, revealing that CMT acts to accelerate sub-cloud layer winds under FW shear and that mesoscale circulations contribute significantly to MT for this horizontal resolution (250 m), even if small scale eddies are non-negligible and likely more important as resolution increases. Under FW shear, a deeper boundary layer and faster cloud transition are simulated, because MT acts to increase surface fluxes and wind shear enhances turbulent mixing across cloud tops. Our results show that the coupling between winds and convection is crucial for a range of problems, from CAO lifetime and cloud transitions to ocean heat loss and near-surface wind variability.
The 2010 Haiti Earthquake Disaster: The ShakeMap that could have been...
Authors: Shani-Kadmiel Shahar , Averbuch Gil , Smets Pieter , Assink Jelle , Evers Läslo
Published: March 2020

When an earthquake occurs, it is important to rapidly assess the severity of the consequences. The distribution of shaking intensity around the epicenter, known as the ShakeMap, is a key component in this process and is crucial for guiding first responders to the region. Whereas earthquake source characteristics, e.g., location and magnitude, can be rapidly determined using distant seismic stations, ground motion measurements from stations in the near-source region are needed to generate an adequate ShakeMap. When few or no seismometers exist in the region, ground motions are only estimated and the ShakeMap can be grossly inaccurate.

Besides seismic waves, earthquakes generate infrasound, i.e., inaudible acoustic waves in the atmosphere. Due to the low frequency nature of infrasound, and facilitated by waveguides in the atmosphere, signals propagate over long ranges with limited attenuation and are detected at ground-based stations. Here we show, that acousto-ShakeMaps, indicating the relative shaking intensity, can be rapidly generated using remotely detected infrasound. We illustrate this with infrasound from the 2010 Mw 7.0 Port-au-Prince, Haiti earthquake, detected in Bermuda, over 1700 km away from Haiti.

Such observations are made possible by: (1) An advanced array processing technique that enables the detection of coherent wavefronts, even when amplitudes are below the noise level, and (2) A backprojection technique that maps infrasound detections in time to their origin on the Earth's surface.

Infrasound measurements are conducted globally for the verification of the Comprehensive Nuclear-Test-Ban Treaty and together with regional infrasound networks allow for an unprecedented global coverage. This makes infrasound as an earthquake disaster mitigation technique feasible for the first time.
Spatio-temporal analysis of remotely sensed soil moisture and vegetation patterns during recent European droughts
Authors: van Hateren Theresa C. , Chini Marco , Matgen Patrick , Teuling Adriaan J.
Published: March 2020

Drought occurrence and drought severity are likely to increase in the future due to more extreme weather conditions. Drought preparedness and mitigation can be achieved with the help of skilful drought forecasts and accurate quantifications of both drought severity and drought impact. For that to be possible, we first need to be aware of the spatiotemporal evolution of agricultural droughts and their main effects on vegetation. Therefore, in this study, we evaluated patterns in soil moisture and vegetation during the large scale droughts that occurred in between 2000 and 2018.

Soil moisture data were obtained from the CCI v04.5 dataset. ­­­Vegetation was analysed using (1) the Normalized Difference Vegetation Index (NDVI), a common approach to quantify vegetation cover, and (2) near-infrared reflectance of vegetation (NIRv), which has been shown to strongly correlate to Gross Primary Production (GPP) and canopy development. Both vegetation datasets were derived from MODIS reflectance data. All three datasets were normalized to allow for an in-depth comparison of drought patterns in both space and time.

Correlations were found between soil moisture and vegetation data, and showed the possibility to discern the occurrence of water- and energy- limited vegetation. In both North and South Europe, soil moisture dry anomalies show lower correlation with dry anomalies in vegetation compared to central Europe: the highest correlations were consistently found in between 55-60˚N. In Northern Europe, the lower correlations are likely due to vegetation being energy limited rather than water limited, even during soil moisture drought events. In Southern Europe, on the other hand, it can be argued that the vegetation is better adapted to drought conditions and, as a result, the drought has less impact on vegetation. This analysis shows that drought impacts are not only related to drought severity, but also to latitude and thus climate.

­­In addition, we look at time lags between soil moisture droughts and drought impacts on vegetation, a comparison between the different years in drought over the past two decades and a comparison between drought signatures per precipitation regime. The results of this study will provide insights on the evolution of different droughts and their effects on vegetation. They could be used in future efforts regarding agricultural drought forecasting, because main trends can be predicted.
Palaeo-earthquake magnitudes on the Dzhungarian fault, N. Tien shan, and implications for the rupture processes of intraplate strike-slip faults
Authors: Tsai Chia-Hsin , Walker Richard , Daout Simon , Abdrakhmatov Kanatbek , Mukambayev Aidyn , Grützner Christoph , Rhodes Ed
Published: March 2020

Long-term and present-day crustal deformation in the northern Tien Shan is poorly known, but is a key to understanding the mode of lithospheric deformation deep within the continental interiors, as well as the hazards posed by the slow-moving intraplate faults. Driven by the India-Asia collision, the NW-SE strike-slip faults and the E-W range-front thrust faults in the interior of Tien Shan together accommodate about 15-20 mm/yr of shortening. Here we focus on the NW-SE striking Dzhungarian fault (DZF) and the E-W striking Lepsy fault (LPF), which are large oblique strike-slip faults bounding the Dzhungarian Alatau, northern Tien Shan. Two large historical earthquakes in ~1716 and 1812 (Mw 8) were recorded in this region, and clear fault traces as well as scarps are visible from satellite images along some of the main faults. However, their geometries, slip rates, mode of deformation, expected earthquake magnitudes and recurrence interval have not been studied in details. A previous study suggested that the LPF ruptured in a seismic event around 400 yrBP that might be the 1716 earthquake known from historical records. Offsets of over 15 m were found over a fault length of 120 km, indicating a magnitude in the range Mw 7.5-8.2. The slip to length ratio for the LPF is unusally high, suggesting either that faults in this region are capable of generating very large earthquakes for a given fault length, or that the rupture length is underestimated.

Using a combination of high-resolution digital elevation models (DEMs) and orthophotos from High Mountain Asia (NASA), Pleiades optical imagery (CNES), drone photos and multi-temporal interferometric synthetic-aperture radar (InSAR) from the Sentinel-1 satellites, we identify the geomorphic signatures and quantify the long-term and short-term strain accumulation along the faults. The ~400 km DZF shows evidence for relatively ‘fresh’ rupturing along much of its length. We calculate an average lateral slip per event of 9.9 m from offset stacking analysis, which underlines the potential future large earthquakes on this fault. The proximity of the DZF and LPF ruptures and equivalent level of preservation opens the possibility that they were formed in a single earthquake event, with a moment-magnitude greater than 8. We also present estimates of long-term and short-term rates of slip across the DZF in order to estimate average recurrence intervals and to build a kinematic model of the faulting in the Northern Tien Shan.
Regenerating ecosystems with Nature-Based Solutions: demonstrator study Inn River Basin, Austria
Authors: Molenaar Roy , Kohl Bernhard , Stepanek Leopold , Kleidorfer Manfred , Achleitner Stefan
Published: March 2020

Nature-Based Solutions (NBS) could be effective measures to respond to land degradation processes and events such as floods. This study demonstrates how to evaluate the benefits of afforestation being a long-term NBS utilizing a combination of an innovative monitoring technology and modelling approaches. The catchment Geroldsbach-Götzens is used as a lead catchment, being typical for numerous Alpine catchments with interacting urban and torrential features. The catchment comprises NBS such as afforestation being installed in the torrent since the early 1950ies.

We use an artificial rainfall runoff test site to test different scenarios and analyse runoff behaviour. Besides artificial rainfall simulations, the site is equipped for continuous monitoring of natural occurring rainfall runoff events. In that course, precipitation, snowfall, snow cover, air and soil parameters are assessed. The development and effects of measures over time are modelled utilizing as well the monitoring data. For generalizing and upscaling of the findings, especially with regard to (a) land use in torrents and (b) land use at the urban scale, models are realized as well for other catchments. Beyond realizing historic and current situations exclusively, land use scenarios for assessing the change over time and potential future scenarios are to be modelled.

Results can provide a quantification of the benefits and co-benefits of NBS such as: reduction of flood risks, improvement of the recreational qualities, and enhancement of biodiversity. Experience from the field can show the best practices and how to develop innovative ways that can be used for upscaling. Land use and climate scenarios give an indication of changes that can be expected over time and potential future scenarios. Overall findings lead to a better understanding of long-term implementation of NBS and support decision making of stakeholders in other catchments.
Time sequence of TGFs and optical pulses detected by ASIM
Authors: Bjørge-Engeland Ingrid , Østgaard Nikolai , Skeie Chris Alexander , Mezentsev Andrey , Neubert Torsten , Reglero Victor , Marisaldi Martino , Kochkin Pavlo , Lehtinen Nikolai , Sarria David , Maiorana Carolina , Lindanger Anders , Ullaland Kjetil , Genov Georgi , Christiansen Freddy , Chanrion Olivier , Heumesser Matthias
Published: March 2020

In 2018, the Atmospheric Space Interactions Monitor (ASIM) was launched and mounted onboard the Columbus module of the International Space Station (ISS). Using data from the Modular X- and Gamma-Ray Sensor (MXGS) and the Modular Multispectral Imaging Array (MMIA), we investigate the time sequence of the TGFs detected by MXGS and the optical pulses detected by the MMIA. The optical pulses are observed in the 337 nm and 777.4 nm, and the X- and gamma-rays are detected by the High Energy Detector of MXGS, which is sensitive to energies from 300 keV to more than 30 MeV. We will also look into the TGF duration and any correlation with the time between the TGFs and the main optical signals. The data used is from June 2018 (shortly after mounting on the Columbus module) until the end of March 2019, when the relative timing uncertainty between the two instruments was +/- 80 us. The data after this is presented in Skeie et al.
Impacts of Greenland freshwater discharge on fjord productivity: a long-term perspective
Authors: Oksman Mimmi , Bang Kvorning Anna , Ribeiro Sofia
Published: March 2020

In the past few decades, warming of the Arctic region has resulted in an abrupt increase of freshwater discharge from the Greenland Ice Sheet into its surrounding ocean. Greenland fjords are modulated by ice-ocean interactions and are very productive ecosystems that sustain important fisheries and other societal ecosystem services. While many studies are ongoing to understand seasonal and inter-annual changes, very little is known about the long-term impacts of freshwater discharge on primary producers and overall Arctic marine ecosystem functioning and structure. This long-term perspective is particularly important because freshwater runoff is expected to increase in the future along with rising atmospheric temperatures. Here, we present records from three marine sediment cores from the Godthåbsfjord that were used to reconstruct past marine productivity and freshwater discharge. The results based on diatom assemblages, BSi and TOC indicate marked fluctuations in past fjord productivity since the end of the Medieval Climate Anomaly, and periodical bursts of freshwater into the fjord resulting in a lowered productivity.
The dawn of Molecular Genetics in Paleoceanography: tracing Arctic change during the Holocene with marine sedaDNA records from Greenland
Authors: Ribeiro Sofia , Hardardottir Sara , Ray Jessica Louise , De Schepper Stijn , Limoges Audrey , Lovejoy Connie , Seidenkrantz Marit-Solveig
Published: March 2020

As we move towards a “blue” Arctic Ocean in the summer within the next decades, predicting the full range of effects of climate change on the marine arctic environment remains a challenge. This is partly due to the paucity of long-term data on ocean-biosphere-cryosphere interactions over time and partly because, today, much of our knowledge on past ocean variability derives from microfossil and biogeochemical tracers that all have considerable limitations such as preservation biases and low taxonomic resolution or coverage.

Recent studies have revealed sedaDNA as a potential “game-changer” in our ability to reconstruct past ocean conditions, due to the preservation of DNA at low temperatures, and the possibility to capture a much larger fraction of the Arctic marine biome diversity than with classical approaches. However, while sedaDNA has been used in terrestrial, archeological, and lake studies for some years, its application to marine sediment records is still in its infancy.

Here, we will present new results from material recently collected along the two Arctic Ocean outflow shelves off Greenland (Greenland Sea/Fram Strait and Northern Baffin Bay/Nares Strait). We have used a combination of modern and ancient DNA methods applied to seawater, surface sediments, and sediment cores covering the past ca. 12 000 years with the objectives of: 1) characterizing the vertical export of sea ice-associated genetic material through the water column and into the sediments following sea ice melt and 2) exploring the potential of sedaDNA from the circum-polar sea ice dinoflagellate Polarella glacialis as a new sea ice proxy. For the first objective, we followed a comparative metabarcoding approach while the second objective included designing species-specific primers followed by gene copy number quantification by a droplet digital PCR assay. 

We argue that sedaDNA will have a critical role in expanding the Paleoceanography “toolbox” and lead to the establishment of a new cross-disciplinary field.

 
Growing multicentennial-scale precipitation variability in Eastern Brazil during the late Holocene
Authors: Bahr André , Kaboth-Bahr Stefanie , Jaeschke Andrea , Chiessi Christiano , Cruz Francisco , Rethemeyer Janet , Schefuß Enno , Geppert Philipp , Spadano Albuquerque Ana Luiza , Pross Jörg , Friedrich Oliver
Published: March 2020

Eastern Brazil belongs to the ecologically most vulnerable regions on Earth due to its extreme intra- and inter-annual variability in precipitation amount. In order to constrain the driving forces behind this strong natural fluctuations we investigated a high-resolution sediment core taken off the Jequitinhonha river mouth in central E Brazil to reconstruct Holocene river run-off and moisture availability in the river’s catchment. Modern day climate in the hinterland of the Jequitinhonha is influenced by the South American Summer Monsoon (SASM), in particular by the manifestation of the South Atlantic Convergence Zone (SACZ) during austral summer. Variations in the position and strength of the SACZ will have immediate impact on the moisture balance over the continent and hence influence sediment and water delivery. Our multi-proxy records, comprising XRF core-scanning, grain size, mineralogical (XRD), as well as organic biomarker analyses indicate abrupt centennial scale variations between dry and wet conditions throughout the past ~5 kyrs. Our results document a gradual weakening of the SASM over the past ~2,7 kyrs driven by changes in the intertropical heat distribution. This long-term trend is superposed by centennial to millennial-scale spatial shifts in moisture distribution that result from migrations of the SACZ. The combination of both processes caused increasingly pronounced aridity spells in eastern South America over the past 2 kyrs. As the spatial fluctuations were triggered by freshwater anomalies in the North Atlantic, we surmise that enhanced meltwater input into the North Atlantic due to future global warming might severely increase the risk for mega-droughts in tropical South America.
Reflections on drought phenomenon from western Romania based on station-observed climatological data
Authors: Halbac-Cotoara-Zamfir Rares , Halbac-Cotoara-Zamfir Cristina
Published: March 2020

Droughts are one of the costlier natural hazards on a year-to-year basis considering their impacts which are generally significant and widespread. Monitoring these events is a vital process in the efforts of predicting, analyzing and recovering after. A clear understanding of droughts and their behavior will improve the resilience of the affected regions and their capacity to recover after such events. It is important to note that the impacts of droughts can be as varied as the causes of droughts. Drought represents the effects of water demands unmet by the available resources. Regional characteristics of a drought, such as covered area, total water deficit, or return time, are very important in determining the phenomenon’s severity.  Worldwide, over 100 drought indices were developed, each of them with specific features and approaching different aspects of drought.

In this article, several drought indices (SPI (Standardized Precipitation Index), RAI (Rainfall Anomaly Index), RDI (Reconnaissance Drought Index) and SPEI (standard index of rainfall drought)) will be used for a critical analysis of drought in the last 50 years (1968 - 2018) in western Romania (Timisoara area). These indices will be calculated using several programs (DRINC, RDIT, CLIC-MD) recently introduced in Romanian research institutions for drought estimation and monitoring. We compared the results for SPI indicating the correlations among drought indices calculated with these programs and emphasized the pros and cons for each of these tools.

We also present the effects of drought in relation with land management from western Romania as well as the main key recommendations from the national strategy on mitigation of drought effects.
ESA’s Wind Lidar Mission Aeolus – Instrument Performance and Stability
Authors: Kanitz Thomas , Witschas Benjamin , Marksteiner Uwe , Flament Thomas , Rennie Michael , Schillinger Marc , Parrinello Tommaso , Wernham Denny , Reitebuch Oliver
Published: March 2020

The European Space Agency, ESA deployed the first Doppler wind lidar in space within its Earth Explorer Mission Aeolus in August 2018. After the initial commissioning of the satellite and the single payload ALADIN, the mission has started to demonstrate the capability of Doppler lidar to measure wind from space. In order to provide the best Aeolus wind product possible, detailed monitoring of the instrument is crucial for analysis of system health, but also for the assessment of measurement performance and data product calibration. Within the last 1.2 years the different instrument modes to assess instrument and laser health, as well as the nominal wind processing indicated longterm instrument drifts. The laser beam profile has been monitored and showed an energy redistribution within the beam. The line of sight has slowly drifted, resulting in a change of incidence angle at spectrometer level. The impact of these observed drifts on the wind product are compensated on demand by updates of dedicated ground processing calibration files. This contribution will provide an overview about the Aeolus instrument modes and the observed stability that are needed to provide the Aeolus wind product. The current Aeolus performance has been assessed by various Numerical Weather Prediction centers. The positive outcome is represented by ECMWF’s decision to start using Aeolus data operationally on 9th January 2020.
Microphysics of the air-sea coupling at high winds and its role in the dynamics and thermodynamics of severe sea storms
Authors: Troitskaya Yuliya , Kandaurov Alexander , Sergeev Daniil , Ermakova Olga , Kozlov Dmitrii , Vdovin Maxim , Druzhinin Oleg
Published: March 2020

Showing the record strengths and growth-rates, a number of recent hurricanes have highlighted needs for improving forecasts of tropical cyclone intensities most sensitive to models of the air-sea coupling. Especially challenging is the nature and effect of the very small-scale phenomena, the sea-spray and foam, supposed to strongly affecting the momentum- and heat- air-sea fluxes at strong winds. This talk will focus on our progress in understanding and describing these "micro-scale" processes, their physical properties, the spray and foam mediated air-sea fluxes and the impact on the development of marine storms.

The starting points for this study were two laboratory experiments. The first one was designed for investigation of the spray generation mechanisms at high winds. We found out 3 dominant spray generating mechanisms: stretching liquid ligaments, bursting bubbles, splashing of the falling droplets and "bag-breakup". We investigated the efficiency spray-production mechanisms and developed the empirical statistics of the numbers of the spray generating events of each type. Basing on the "white-cap method" we found out the dependence of the spray-generating events on the wind fetch. The main attention was paid to the "bag-breakup" mechanism. Here we studied in detail the statistics of spray produced from one "bag-breakup" event. Basing on these developments, we estimated heat and momentum fluxes from the spray-generating events of different types and found out the dominant role of the "bag-breakup" mechanism.

To estimate the direct heat and momentum fluxes from the ocean surface to the atmosphere, we studied in the special experiment the foam impact on the short-wave part of the surface waves and the heat momentum exchange in the atmospheric boundary layer at high winds. Based on these results, we suggest a simple model for the aerodynamic and temperature roughness and the eddy viscosity in the turbulent boundary layer over a fractionally foam-covered water surface.

The synergetic effect of foam at the water surface and spray in the marine atmospheric boundary layer on ocean surface resistance at high winds is estimated so as to be able to explain the observed peculiarities of the air-sea fluxes at stormy conditions. Calculations within the nonhydrostatic axisymmetric model show, that the "microphysics" of the air-sea coupling significantly accelerate development of the ocean storm.

This work was supported by RFBR grant 19-05-00249 and RSF grant 19-17-00209.
Tephra anchored floating varve chronology covering ca. 19.0-11.0 ka BP in new core from Lake Lago Grande di Monticchio: preliminary results
Authors: Zhao Xueru , Wulf Sabine , Schwab Markus J. , Tjallingii Rik , Brauer Achim
Published: March 2020

The high-resolution Monticchio (MON) sediment record has been demonstrated to be a key archive for reconstructing climate and environmental changes in the central Mediterranean for the last glacial-interglacial cycle. New sediment cores have been retrieved in April 2016 to investigate particularly the transition from the Last Glacial Maximum into the Holocene with a new high-resolution methodological approach. A floating varve chronology spanning ca. 8,000 years has been established by varve counting on thin sections using a petrographic microscope and layer thickness based sedimentation rate estimates for non- or poorly varved intervals. Varve counting is based on detailed seasonal deposition models of five different varve types. The resulting floating chronology consist of 66.6% individually counted varves and 33.4% interpolated years. The uncertainty estimate of the floating chronology has been determined by double counting and amounts to ±5.8%.

The floating chronology is anchored to an absolute chronology using the Agnano Pomici Principali tephra, dated at 11,999±52 cal yrs BP from paleosols overlying proximal tephra (Bronk Ramsey et al. 2015), is a suitable anchoring point to cross correlation. The resulting varve-based chronology has been compared with several other marker tephras dated elsewhere including the Soccavo 4 tephra (11,700±150 cal yrs BP), the Neapolitan Yellow Tuff (NYT; 14,194±172 cal yrs BP) and the Greenish tephra (19226±104 cal yrs BP). Further comparison with published (Hajdas et al. 1997) and new radiocarbon dates from different terrestrial macro remains are discussed in this paper. This study presents an independent chronology for the last glacial/interglacial transition for a comparison of MON data with high-resolution lake records western and central Europe.

References

Bronk Ramsey, C., P. G. Albert, S. P. E. Blockley, M. Hardiman, R. A. Housley, C. S. Lane, S. Lee, I. P. Matthews, V. C. Smith & J. J. Lowe (2015) Improved age estimates for key Late Quaternary European tephra horizons in the RESET lattice. Quaternary Science Reviews, 118, 18-32.

Hajdas, I., G. Bonani, B. Zolitschka, A. Brauer & J. Negendank (1997) 14C Ages of Terrestrial Macrofossils from Lago Grande Di Monticchio (Italy). Radiocarbon, 40, 803-807.
Components of past cold mega-droughts and modern warm dry events in central Europe could interfere constructively in the future
Authors: Ionita-Scholz Monica , Dima Mihai , Nagavciuc Viorica , Scholz Patrick , Lohmann Gerrit
Published: March 2020

Mega-droughts are notable manifestations of the American Southwest, but not so much of the European climate. By using long-term hydrological and meteorological observations, as well as paleoclimate reconstructions, we show that central Europe has experienced much longer and severe droughts during the Spörer Minimum (~AD 1400 – 1500) and Dalton Minimum (~AD 1770 – 1850), than the ones observed during the 21st century. These two mega-droughts appear to be linked with a weak state of the Atlantic Meridional Overturning Circulation (AMOC) and enhanced winter atmospheric blocking activity over the British islands and western part of Europe, associated with reduced solar forcing and explosive volcanism. In contrast with these mega-droughts, present-day extreme dry events in Europe are mainly related to high temperature levels. Since numerical simulations indicate a future slowdown of AMOC in a globally warming world, we argue that these two forcing factors for droughts, weakening ocean circulation and temperature increase, could interfere constructively in the future. Consequently, this will potentially lead to an increase in the frequency of hot and dry summers, especially over the central part of Europe, posing enormous challenges to governments and society.
Climate change impacts on water resources in North African basins
Authors: Tramblay Yves , Ruelland Denis , Hanich Lahoucine , Bargaoui Zoubeida , Dakhlaoui Hammouda
Published: March 2020

Countries in North Africa are facing water scarcity and a high inter-annual variability of precipitation. In this context, many dams have been built to collect surface water and improve the management of existing water resources. We present the main results of a recent MISTRALS-ENVIMED research project about the potential climate change impacts on water resources at the regional and basin scales. The project notably focuses on the uncertainties linked to the different components of the modelling chain required to produce hydrological scenarios. Climate change impacts on surface water resources are investigated using an ensemble of regional climate model simulations from the CORDEX experiment under different emission scenarios and different hydrological models, adapted to the context of data scarcity. Climate scenarios under RCP4.5 and RCP8.5 over North Africa indicate a future decrease in precipitation together with an increase in temperature that could have significant impacts on water resources. Indeed, a future decrease of surface water availability is expected in all major dam catchments, with a stronger decline over Morocco.
Exploring Driving Forces of Avian Diversity in a Subtropical Asian City.
Authors: Huang Chun-Wei , Hsu Yi-Lei , Lau Hui Xian , Ko Jerome Chie-Jen
Published: March 2020

Global urbanization has led to biodiversity decline. Although some case studies reveal rich biodiversity in cities, we still know little about the underlying factors that shape biodiversity at different levels of urbanization. This study statistically analyzes the relationships between environmental, socio-economic and landscape-ecological factors with avian diversity along the rural-urban gradient of Taipei, Taiwan. We use stepwise regression to explore factors that are correlated to variation of bird diversity. First, based on a citizen-science based breeding bird survey in Taiwan (BBS Taiwan), we identify avian richness at different levels of urbanization, using population density as a proxy. Then we correct median income, proportion of tertiary education attainment, precipitation and temperature data from open government data of Taiwan. Finally, we quantify landscape structures using landscape metrics. The results indicate that landscape-ecological factors, such as cohesion of forest, the edge length between building and wetland and area size of building, etc. are correlated with avian richness. On the other hand, socio-economic factors, such as median income and education level are not correlated with avian diversity. Our results reveal that the luxury effect, which describes the positive influence of wealth on urban biodiversity, may not be influential at a subtropical compact city in Asia. On the contrary, we suggest an eco-friendly landscape design that creates a landscape mosaic with scattered trees or wetlands can lead to a network of ecological stepping stones through urban areas for improving bird diversity.