bluuebunny/crossref_metadata_2025 huggingface dataset:
A regional view of the linkages between hydro-climatic changes and deforestation in the Southern Amazon
Authors: Wongchuig Sly , Espinoza Jhan Carlo , Condom Thomas , Segura Hans , Ronchail Josyane , Arias Paola , Junquas Clementine , Rabatel Antoine , Lebel Thierry
Published: March 2021

Linking the Amazonian deforestation to changes in the hydrological cycle remains a puzzling question, addressed here through the use of recent global databases analyzing the relations between key hydro-climate variables (Precipitation (P), potential and actual evapotranspiration (PET and AET, respectively)), the surface water-energy balance and indices of forest cover change (regional forest loss ratio -RFL and regional non-forest vegetation ratio -RNF) for Southern Amazon (south of 8°S) and over the 1981-2018 period. The Southern Amazon constitutes a peculiar region due to specific climatic characteristics and shows a higher significant deforestation rate in comparison with the Northern Amazon. We further subdivided the study region into three subregions called Southern Bolivian Amazon (15° S‒21° S, 57° W‒70° W), Southern Peruvian Amazon (8° S‒15° S, 77° W‒65° W) and Southern Brazilian Amazon (8° S‒15° S, 65° W‒50° W). The surface water-energy balance is analyzed using a pixel-based Budyko-like theoretical framework approach, which discriminates energy-limited regions from water-limited regions. Southern Bolivian Amazon is shown to have undergone the strongest forest transition, becoming water-limited in conjunction with high forest loss. In this region, there is a significant relation between RFL values above 40%, P decrease, PET increases and AET decrease. These results suggest that areas with RNF values higher than 40% are prone to shift from an energy-limited to a water-limited state and remain trapped in this new state. Regions further north remain energy-limited due to minor P changes and even though significant increases in PET and decreases in AET are observed, associated with deforestation (high values RFL). This is typically the case in the ‘Arc of Deforestation’. In the Southern Bolivian Amazon, land use transition is associated with much larger changes from closed forest to a low-tree cover state as compared to regions further north - by at least a factor three as a proportion of area. Our findings indicate a clear link between hydro-climatic changes and deforestation, providing a new perspective on their spatial variability on a regional scale.

 

This research is part of the French AMANECER-MOPGA project.
Influence of Climate Variability in King George Island Glacier Retreat – Antarctic Peninsula
Authors: Rojas Macedo Ibeth Celia , Suarez Alayza Wilson Alfredo , Loarte Cadenas Edwin Anibal , Medina Marcos Katy Damacia
Published: March 2021

This research aims to explain the influence of climatic variables (temperature and precipitation) in King George Island (KGI) glacier shrinkage on the Antarctic Peninsula. It employed Landsat satellite images from 1989 to 2020, climatic data and ONI index from 1980 to 2019.

King George Island glaciers have lost 10% of their coverage in the last 31 years. Greater glacier shrinkage was shown until the first mid-period assessed, while the retreat rate slowed down for the second half of the studied period. Furthermore, of 73 KGI glaciers, 37% were marine- and land-terminating, 42% were land-terminating and 21% were sea-terminating. Nonetheless, the decreases in the ice-coverage of marine-contact glaciers (35% of glacier coverage reduced) were higher than land-terminating glaciers (17% of glacier coverage reduced).

There was a perceivable fluctuation in annual average air temperature for the 1980-2006 period. Nevertheless, from around 2007 to 2015/2016 there was a slight continuous cooling period and precipitation was somewhat above the average. Therefore, these patterns could explain the recent KGI glacier-retreat deceleration.

Unlike the 1982/1983 and 1997/1998 El Niño events, the 2015/2016 El Niño was colder with precipitation reduction from the sustained annual amount (since roughly 2007 to 2015/2016) to values below the average. Moreover, during the 2015/2016 El Niño, KGI glacier coverage reduction was the lowest for the 31 year-long evaluated. However, it was revealed that the glacier's height could increase by accumulation in El Niño years, but glacier mass balance could be more negative due to basal melting. Additionally, land-terminating glaciers have lost more glacier coverage than sea-terminating glaciers throughout this ENSO event.

Hence, climate variability might play a significant role in KGI glacier shrinkage, but calving process, glacier features and so on, further a combination of them should be assessed to reach a better understanding of KGI glacier retreat.
Application of dimensional analysis in removal prediction of 2-[4-(dimethylamino) styryl]-1-methylpyridinium iodide dye using humic acid coated magnetic nanoparticle
Authors: Esmaeilian Anahita , O'Shea Kevin E.
Published: March 2021

Numerous factors affect adsorption phenomena in solid–liquid systems. Critical factors are the sorbent dose and initial concentrations of the contaminants in the system. However, the combination of these two factors and their effects on removal prediction are largely unexplored. In this study, batch experiments were conducted to examine such effects on the adsorption of 2-[4-(dimethylamino) styryl]-1-methylpyridinium iodide cationic dye (2-ASP) in contaminated water to humic acid coated magnetic nanoparticles (HA-MNPs). Dimensional analysis and Buckingham’s π theorem were subsequently used to assess the relationship between the sorbent dose, initial concentration, and percent removal. Results of dimensional analysis along with experimental data suggest that sorbent dose and sorbate concentration ratio are the main variables controlling sorption of dye on HA-MNPs. In conventional isothermal studies, the isotherm equations are developed based on experiments of one sorbent dose which cannot be generalized for all sorbent doses.  In this study, a power function (Isotherm-like) model was obtained from the dimensional analysis that can describe precisely the sorption process of dye on HA-MNPs as a function of equilibrium concentration and sorbent dose ratio. Moreover, a relation is deduced for prediction of removal percent as a function of sorbent dose and initial concentration ratio with R2 of 0.98.

Keywords: Remediation, Dimensional analysis, Isotherm-like model, Magnetic nanoparticle, Styryl pyridinium dyes, Water treatment
Orogenic listening posts along the margins of western Tethys reveal a major tectonic event involving extreme extension at the start of the Eocene–Miocene transition
Authors: Forster Marnie , Lister Gordon
Published: March 2021

Orogenic listening posts have been established along the northern margins of western Tethys: i) in the west and central Alps; ii) in the Cyclades, Aegean Sea, Greece; and iii) along a traverse in the NW Himalaya. We report on modelling and simulation of data from the conjoint inversion of argon geochronology and ultra-high-vacuum (UHV) diffusion experiments, on rocks from these locations. In the Alps, samples come from either side of the Lepontine dome, a metamorphic core complex that resulted from orogen-parallel extension, with a major pulse of stretching coinciding with the onset of the Eocene–Oligocene transition. In the Cyclades, the samples come from Ios, a metamorphic core complex that began its existence at about the same time, related to extreme extension caused by southward rollback of the Hellenic slab, after an immediately preceding accretion event that incorporated Gondwanan slices into the terrane-stack. In the NW Himalaya, samples come from yet another Tethyan metamorphic core complex, the giant schist and gneiss dome that includes the Tso Morari, in Ladakh, India. 

Inversion of data from these locations reveals unprecedented detail in the inferred temperature-time curve, allowing recognition that a rapid cooling event took place in the lower plate of the detachment system at each of these locations, almost at the same time. We discuss the tectonic implications of a synchronised tectonic mode switch at the start of the Eocene–Oligocene transition. In each location there was a preceding period of compressional orogenesis, involving accretion of multiple tectonic slices to the terrane stack after an accretion event, followed by a period during which extreme extension of the continental lithosphere appears to have taken place. This supports our 2001 hypothesis that tectonic mode switches during collisional orogenesis are globally synchronized, in consequence of torque balance being continuously maintained in the planetary assemblages of moving lithospheric plates. Accretion events perturb that torque balance, with tectonic mode switches the result of mechanical adjustment caused by the creation of new subduction systems, with the initiation of rollback offering a potential explanation for the rapid exhumation of core complexes in the over-riding lithosphere.
A landslide-generated tsunami and outburst flood at Elliot Creek, coastal British Columbia  
Authors: Geertsema Marten , Menounos Brian , Shugar Dan , Millard Tom , Ward Brent , Ekstrom Göran , Clague John , Lynett Patrick , Friele Pierre , Schaeffer Andrew , Jackson Jennifer , Higman Bretwood , Dai Chunli , Brillon Camille , Heathfield Derek , Bullard Gemma , Giesbrecht Ian , Hughes Katie
Published: March 2021

On 28 November 2020, about 18 Mm3 of quartz diorite detached from a steep rock face at the head of Elliot Creek in the southern Coast Mountains of British Columbia. The rock mass fragmented as it descended 1000 m and flowed across a debris-covered glacier. The rock avalanche was recorded on local and distant seismometers, with long-period amplitudes equivalent to a M 4.9 earthquake. Local seismic stations detected several earthquakes of magnitude <2.4 over the minutes and hours preceding the slide, though no causative relationship is yet suggested. More than half of the rock debris entered a 0.6 km2 lake, where it generated a huge displacement wave that overtopped the moraine at the far end of the lake. Water that left the lake was channelized along Elliot Creek, deeply scouring the valley fill over a distance of 10 km before depositing debris on a 2 km2 fan in the Southgate River valley. Debris temporarily dammed the river, and turbid water continued down the Southgate River to Bute Inlet, where it produced a 70 km turbidity current and altered turbidity and water chemistry in the inlet for weeks. The landslide followed a century of rapid glacier retreat and thinning that exposed a growing lake basin. The outburst flood extended the damage of the landslide far beyond the limit of the landslide, destroying forest and impacting salmon spawning and rearing habitat. We expect more cascading impacts from landslides in the glacierized mountains of British Columbia as glaciers continue to retreat, exposing water bodies below steep slopes while simultaneously removing buttressing support.
Spatial variability of carbon allocation to soil autotrophic respiration in global forest ecosystems
Authors: Tang Xiaolu , Shi Yuehong , Luo Xinrui , Liu Liang , Jian Jinshi , Bond-Lamberty Ben , Hao Dalei , Olchev Alexander , Zhang Wenjie , Gao Sicong , Li Jingji
Published: March 2021

Belowground or ‘soil’ autotrophic respiration (RAsoil) depends on carbohydrates from photosynthesis flowing to roots and rhizospheres, and is one of the most important but uncertain components in forest carbon cycling. Carbon allocation plays an important role in forest carbon cycling and reflects forest adaptation to changing environmental conditions. However, carbon allocation to RAsoil is rarely measured directly and has not been fully examined at the global scale. To fill this knowledge gap, the spatio-temporal patterns of RAsoil with a spatial resolution of half degree from 1981 to 2017 were predicted by Random Forest (RF) algorithm using the most updated Global Soil Respiration Database (v5) with global environmental variables; carbon allocation from photosynthesis to RAsoil (CAsoil), was calculated as the ratio of RAsoil to gross primary production (GPP); and its temporal and spatial patterns were assessed in global forest ecosystems. We found strong temporal and spatial variabilities of RAsoil with an increasing trend from boreal forests to tropical forests. Globally, mean RAsoil from forests was 8.9 ± 0.08 Pg C yr-1 (mean ± standard deviation) from 1981 to 2017 increasing at a rate of 0.0059 Pg C yr-2, paralleling broader soil respiration changes and indicating an increasing carbon loss respired by roots. Mean CAsoil was 0.243 ± 0.016 and showed a decreasing trend over time, although there were interannual variabilities, indicating that CAsoil was sensitive to environmental changes. The temporal trend of CAsoil varied greatly in space, reflecting uneven responses of CAsoil to environmental changes. The spatio-temporal variability of carbon allocation should be considered in global biogeochemical models to accurately predict belowground carbon cycling in an era of ongoing climate change. 
Calibrating SoilGen2 for interglacial soil evolution in the Chinese Loess Plateau considering soil parameters, and the effect of uncertain forcings’
Authors: Ranathunga Keerthika Nirmani , Finke Peter , Yin Qiuzhen , Yu Yanyan
Published: March 2021

To better understand interglacial paleosol formation by quantifying the paleosol formation processes on the Chinese Loess Plateau (CLP), we need a soil genesis model calibrated for long timescales.  Here, we calibrate a process-based soil genesis model, SoilGen2, by confronting simulated and measured soil properties for interglacial soils formed in the CLP for various parameter settings. After the calibration of the intrinsic soil process parameters, the effect of uncertainty of external forcings (e.g. dust deposition) on calibration results was assessed.

This calibration comprises three major soil process formulations, represented by various process parameters. Sequentially : [1]. decalcification by tuning (i) the dissolution constant of calcite (ii) the interception evaporation fraction [2]. clay migration by tuning (iii) the volume of clay in-contact with macropores (iv) the filter coefficient (v) physical weathering (vi) the ectorganic layer thickness [3]. soil organic carbon by tuning the decay rates of (vii) humus and (viii) resistant plant material, and (ix) the ratio of ectorganic/endorganic litter (natural vegetations) (x) the ratio of carbon mineralized (CO2) over that still in the food web (biomass and humus) during decomposition. The order of the tuned parameters was based on sensitivity analyses on parameters for modelling (de-)calcification and clay migration done for West European leaching climates, and on C-cycling parameters done for both West European and Chinese circumstances. These parameters, [1 and 3] and [2] were successfully calibrated to the Holocene and the Marine Isotope Stage (MIS) 13 climate evolution of the CLP, respectively. After calibration, soil properties show a strong response to 10 reconstructed dust deposition scenarios reflecting the propagation of uncertainty in dust deposition.

Our results emphasize the equal importance of calibrating soil process parameters and defining correct external forcings in the future use of soil models. Nevertheless, this calibrated model permits interglacial soil simulation in the CLP over long timescales.
Tephra in the Greenland Ice cores: Insights into Icelandic volcano-climate impacts
Authors: Gabriel Imogen , Plunkett Gill , Abbott Peter , Óladóttir Bergrún , McConnell Joseph , Hörhold Maria , Sigl Michael
Published: March 2021

Volcanic eruptions are considered as one of the primary natural drivers for changes in the global climate system and understanding the impact of past eruptions on the climate is integral to adopt appropriate responses towards future volcanic eruptions.

The Greenland ice core records are dominated by Icelandic eruptions, with several volcanic systems (Katla, Hekla, Bárðarbunga-Veiðivötn and Grimsvötn) being highly active throughout the Holocene. A notable period of increased Icelandic volcanic activity occurred between 500-1250 AD and coincided with climatic changes in the North Atlantic region which may have facilitated the Viking settlement of Greenland and Iceland. However, a number of these volcanic events are poorly constrained (duration and magnitude). Consequently, the Greenland ice cores offer the opportunity to reliably reconstruct past Icelandic volcanism (duration, magnitude and frequency) due to their high-resolution, the proximity of Iceland to Greenland and subsequent increased likelihood of volcanic fallout deposits (tephra particles and sulphur aerosols) being preserved. However, both the high frequency of eruptions between 500-1250 AD and the geochemical similarity of Iceland’s volcanic centres present challenges in making the required robust geochemical correlations between the source volcano and the ice core records and ultimately reliably assessing the climatic-societal impacts of these eruptions.

To address this, we use two Greenland ice core records (TUNU2013 and B19) and undertake geochemical analysis on tephra from the volcanic events in the selected time window which have been detected and sampled using novel techniques (insoluble particle peaks and sulphur acidity peaks). Further geochemical analysis of proximal material enables robust correlations to be made between the events in the ice core records and their volcanic centres. The high-resolution of these polar archives provides a precise age for the event and when utilised alongside other proxies (i.e. sulphur aerosols), both the duration and magnitude of these eruptions can be constrained, and the climatic-societal impacts of these eruptions reliably assessed.
Using high-resolution UAV spectral images to disentangle soil, shade, and tree contributions to satellite vegetation indices in sparse dry forests
Authors: Wang Huanhuan , Muller Jonathan , Tatarinov Fedor , Rotenberg Eyal , Yakir Dan
Published: March 2021

Remote sensing (RS) techniques have great potentials for earth surface monitoring. Nevertheless, for most low to moderate resolution satellites, the problem of mixed pixels with information from the vegetation of interest and the background surfaces can cause large biases in signals and also in their interpretations. This is especially so in low-density forests and semi-arid ecosystems. Ground-level multispectral instruments reduce these effects by measuring at close range to the canopy. However, little work has been published on partitioning the contributions from vegetation and the background elements for both approaches.

This work was motivated by the observed mismatch between data for the same ecosystem from Landsat 8 satellite and Skye radiometer installed on a flux tower in a low-density semi-arid pine forest from 2013-2019. Data from both sources showed similar seasonal patterns in NDVI, but large differences in the reflectance bands. This was most prominent in the NIR reflectance, which showed an opposite seasonal cycle in the two sensors. Thus, similar changes in NDVI were produced by different signals. We hypothesized that the different contributions of the surface components (canopy, shaded areas, and exposed soil) in the footprint areas of the two sensors can explain, and can help correct, these differences.  

Multispectral images with a spatial resolution of 5 cm were captured monthly using an Unmanned Aerial Vehicle (UAV) from April 2018 to November 2019. Reflectance-based algorithms were developed to identify and estimate the fraction and reflectance from the canopy, shaded areas, and open soil. This information was, in turn, applied in the equivalent nadir-viewing satellite pixel. For the tower-based Skye footprint, the same quantities were calculated from its 90° angle of view and the 3D canopy data.

The results showed a canopy fraction of 45% and 95% in the Landsat 8 and Skye footprints. The remaining soil fraction showed a similar seasonal cycle in NDVI as the canopy, but different in the NIR reflectance. The partition between exposed and shaded soil was related to the sun angle, with the exposed soil having a NIR seasonal cycle opposite to that of the vegetation (correlating with soil moisture), and shaded soil having a weak NIR signal variably diluting the overall pixel NIR signal. Differences in the red reflectance were smaller with less effects on the seasonal NDVI cycles.

The results demonstrated firstly, that accounting for the fractional contributions of the surface components can reconcile differences between satellite and ground-based RS. Secondly, vegetation indices such as NDVI obtained by satellite RS in low-density forests can provide misleading information, despite its apparent correlation with certain vegetation variables.
The place for agency in social collapse: the case of the Eastern Roman Empire in the 7th c. AD
Authors: Izdebski Adam
Published: March 2021

The breakdowns of big empires have attracted the attention of historians for generations. Massive processes of social and political change, taking place over several generations and often several continents, they constantly invite new questions and ideas, and thus have often been studied in incredible detail. If we already know so much about them, is there potentially a lesson to be learnt for our times? Can we look at the historical examples to understand how the process of social collapse takes place, what are its key determinants and how – if at all – human agency can steer this process, with different human actors achieving their goals despite the overall unpredictability and decomposition of the existing structures.

In my talk, I will look at one of the best-studied instances of social collapse – that of the Roman Empire, or, more precisely, the Eastern part of it, which took place in the 7th c. AD – in order to look at the moments when human agency was able to steer the process of disintegration/collapse. I will focus on the different interventions of the imperial government (the emperor and the central administrative and military apparatus), the ideological innovations, elite transformation and other processes, which created a smaller, yet surprisingly resilient, social-economic system. Moreover, while environmental factors, such as climate or disease – as things stand now – do not seem to have been the primary causes of the collapse, a profound environmental change was taking place in parallel to the social transformation, underpinning the new emerging system in terms of its resource base. Overall, the seventh-century collapse of the Eastern Roman Empire could be seen as a successful transformation, largely due to human agency, or, more specifically, thanks to fortunate interventions and innovations of different human actors.
Putting humans in the loop: coupling behavioral modeling with natural systems' models
Authors: Giuliani Matteo
Published: March 2021

Natural systems’ models have done tremendous progress in accurately reproducing a large variety of physical processes both in space and time. Conversely, despite human footprint is increasingly recognized as a major driver of undergoing global change, human behaviors and their interactions with natural processes still remain oversimplified in many models supporting strategic policy design. Recent years have seen an increasing interest and effort by scientists in quantitatively characterizing the co-evolution of nature and society. Nevertheless, state-of-the-art models often relies on behavioral rules empirically defined or derived by general social science or economic studies, which lack proper formalization for the specific case study as well as validation against observational data.

In this talk I will discuss my experiences in modeling human behaviors by taking advantage of the unprecedented amount of information and data nowadays available and of the improvements in machine learning and optimization algorithms. The resulting decision-analytic behavioral models flexibly blend descriptive models, which derive if-then behavioral rules specifying human actions in response to external stimuli, and normative models, which assume fully rational behaviors and provide optimal decisions maximizing a given utility function, where the ultimate goal is not to support optimal decisions but, rather, to understand and model human decisions and behaviors at different spatial and temporal scales.

A number of real world examples in the water domain will be used to provide a synthesis of recent advances in behavioral modeling and to stimulate discussion on key challenges, such as the role of individual behavioral factors in modeling decisions under uncertainty, the scalability of the models for capturing heterogenous behaviors, the definition of model’s boundaries, the identification of behavioral preferences in terms of tradeoff among multiple competing objectives and the dynamic evolution of this tradeoff driven by extreme hydroclimatic events.
Realistic Electromagnetic Modeling of SAR’s Capability for Oil Spill Thickness Measurement
Authors: Jaruwatanadilok Sermsak , Duan Xueyang , Holt Benjamin , Jones Cathleen
Published: March 2021

A layer of oil on the sea surface reduces the components of ocean wave spectra corresponding to the capillary and gravity-capillary waves leading to significantly reduced radar backscatter and making slicks appear dark in synthetic aperture radar (SAR) images.  The ratio of the backscatter between clean and slicked ocean surfaces is known as the ‘damping ratio,’ and has been shown to be sensitive to variations within slicks that correlate with the oil layer’s thickness and fractional water volume.  Although the relative thickness relationship is well established and can be used to identify areas of ‘thicker’ oil within a slick, quantifying the thickness from SAR alone remains to be shown.  There is considerable uncertainty regarding the potential capability of SAR to quantitatively determine the oil layer thickness for slicks in open water given the dependence on bulk and interfacial oil layer properties and the variation of the properties typical in this setting and for different types of oil.  Here, we report the results of a study modeling radar backscatter from slicked and unslicked ocean surfaces based on electromagnetic scattering theory and accounting for oil properties and meteorological conditions.  The electromagnetic scattering model is used to evaluate whether the oil thickness can be quantified with reasonable accuracy based upon SAR backscatter intensities alone, and how information about metocean conditions, oil properties and ocean temperature and salinity can be used to calibrate the model to obtain more accurate thickness estimates.

The research was carried out at the Jet Propulsion Laboratory, California Institute of Technology, under contract with the National Aeronautics and Space Administration.
A scalable hybrid model to predict riverine nitrous oxide emissions from the reach to the global scale
Authors: Marzadri Alessandra , Amatulli Giuseppe , Tonina Daniele , Bellin Alberto , Shen Longzhu Q. , Allen George H. , Raymond Peter A.
Published: March 2021

Nitrous oxide, N2O, is the leading cause for stratospheric ozone depletion and one of the most potent greenhouse gases. Its emissions from riverine systems have been poorly constrained. Thus, we present a novel conceptual framework that leverages the strength of a data driven machine learning technique and physically based model to predict global nitrous oxide emissions (N2O) from streams and rivers worldwide at the reach-scale resolution (about 1-km length). The model accounts for reactant loads, mainly dissolved inorganic nitrogen, biochemical transformation rates, and riverine hydro-morphology. Its high resolution and ability to account for hyporheic, benthic and water column N2O contributions identify small streams (those with widths less than 10 m) as a primary source of riverine N2O emissions to the atmosphere. These streams contribute nearly 36 GgN2O−N/yr, almost 50% of the entire N2O emissions from riverine systems, although they account for only 13% of the total riverine surface area worldwide. Large rivers (widths wider than 100 m), such as the main stems of the Mississippi (∼2 GgN2O−N/yr) and Amazon River (∼7 GgN2O−N/yr), only contribute 30% of global N2O emissions, which primarily originate from their water column. Our approach introduces a dimensionless Emission Factor that varies spatially and temporally and can be quantified from standard hydromorphological and water quality data routinely measured in streams and rivers or can be predicted with good accuracy from interpolation methods such as machine learning. This approach can improve the accuracy of climate change models which can account for a better prediction of N2O spatial and temporal distribution.
Nordic Seas Heat Loss, Atlantic Inflow, and Arctic Sea Ice cover over the last century
Authors: Smedsrud Lars H. , Muilwijk Morven , Brakstad Ailin , Madonna Erica ,   Nordic Seas Synthesis Team
Published: March 2021

Poleward ocean heat transport is a key process in the earth system. Here we detail the changing northward Atlantic Water (AW) flow in the Nordic Seas and the associated Arctic Ocean heat transport and heat loss to the atmosphere since 1900, in relation to the sea ice cover. Our synthesis is largely based on a sea ice-ocean model forced by a reanalysis atmosphere (1900-2018) corroborated by a comprehensive hydrographic database (1950-), measurements of AW inflow (1996-), and other key long-term regional time series. Since the 1970s, ocean temperatures have increased in the Nordic, Barents and Polar Seas, in particular on the shelves. The AW loses heat to the atmosphere as it travels poleward, mostly in  the Nordic Seas, where ~60% of the Arctic Ocean total heat loss resides. Nordic Seas heat loss variability is large, but the long-term positive trend is small. The Barents Sea heat loss is ~30% of the total, but has larger consistently positive trends, related to AW heat transport and sea ice loss. The Arctic seas farther north see only ~10% of the  total heat loss, but show a consistently large increase in heat loss as well as decrease in sea ice since 1900. The AW inflow, the cooling of this water mass as it travels poleward, and the dense outflow have thus all increased since 1900, and they are consistently related through theoretical scaling. Some of the increased AW inflow is wind-driven, and much of the heat loss variability is linked to Cold Air Outbreaks and cyclones in the Nordic and Barents Seas. The oceanic warming is congruent with increased ocean heat transport and a loss of sea ice, and has contributed to the retreat of marine terminating glaciers on Greenland. After 2000, the warming has accelerated, creating a “new normal” that appears to also affect deep water volumes and temperature. The 20th century average Nordic, Barents and Polar Seas CO2 uptake constitutes ~8% of the global ocean, and is almost entirely driven by heat loss to the atmosphere as the AW transforms from inflow to overflow water. The total Arctic Ocean CO2 uptake has increased by ~30% since 1900, which is closely linked to the loss of sea ice in the Barents and Polar Seas.
Reconstructing atmospheric circulation and sea-ice extent in the West Antarctic over the past 200 years using data assimilation 
Authors: Dalaiden Quentin , Goosse Hugues , Rezsohazy Jeanne , Thomas Elizabeth R.
Published: March 2021

Ocean and ice sheet in the West Antarctic sector have witnessed large climate changes during the second half of the 20th century including a strong and widespread continental warming, important regional changes in sea-ice extent and snow accumulation, as well as a major mass loss from the melting of some ice shelves. However, the potential links between those observed changes are still unclear and instrumental data do not allow determining if they are part of a long-term evolution or specific to the recent decades. In this study, we analyze the climate variability of the past two centuries in the West Antarctic sector by reconstructing the key atmospheric variables (atmospheric circulation, near-surface air temperature and snow accumulation) as well as the sea-ice extent at the annual timescale using a data assimilation approach. To this end, information from Antarctic ice core records (snow accumulation and δ18O) and tree-ring width sites located in the mid-latitudes of the Southern Hemisphere are combined with the physics of climate models using a data assimilation method. This ultimately provides a complete spatial reconstruction over the west Antarctic region. Our reconstruction reproduces well the main characteristics of the observed changes over the instrumental period. We show that the observed sea-ice reduction in the Bellingshausen-Amundsen Sea sector over the satellite era is part of a long-term trend, starting at around 1850 CE, while the sea-ice expansion in the Ross Sea sector has only started around 1950 CE. Furthermore, according to our reconstruction, the Amundsen Sea Low pressure (ASL) displays no significant linear trend in its strength or position over 1850-1950 CE but becomes stronger and shifts eastward afterwards. The year-to-year sea-ice variations in the Ross Sea sector are strongly related to the ASL variability over the past two centuries, including the recent trends. By contrast, the link between ASL and sea ice the Bellingshausen-Amundsen Sea sector changes with time, being stronger in recent decades than before, Our reconstruction also suggests that the continental response to the variability of the ASL may not be stationary over time, being significantly affected by modification of the mean circulation. Finally, we show that the widespread warming since 1958 CE in West Antarctica is unusual in the context of past 200 years and is explained by both the deeper ASL and the positive phase of the Southern Annular Mode.
Quantifying vertical streambed fluxes around woody structures using high-resolution streambed temperature measurements.
Authors: Schneidewind Uwe , Folegot Silvia , van Berkel Matthijs , Bertagnoli Andrea , van Kampen Ricky , Luce Charles , Tonina Daniele , Krause Stefan
Published: March 2021

The quantification of water fluxes across streambeds is an important aspect in the study of groundwater-surface water interactions. One way to deduce fluxes is to use heat as an environmental tracer and measure streambed temperatures. In this study we quantified vertical streambed fluxes over a small reach of the Hammer Stream (West Sussex, UK) that is characterized by a heterogeneous streambed morphology and large woody debris. The Hammer Stream is a meandering lowland stream draining a catchment of 24.6 km2 with mixed agricultural and forest areas.

Our 40 m-long study reach is situated in a deciduous forested valley, characterized by sand-dominated streambed sediments and several large-scale instream woody structures. Previous geophysical measurements identified extensive clay lenses at 1-2 m depth within the streambed, in parts disconnecting the upper streambed from the connected aquifer. Nine high-resolution-temperature sensors (HRTS) were deployed in the upper streambed along the investigated reach to monitor streambed temperatures over several days in different seasons (summer, autumn, winter) and to cover the diverse stream morphology. Each HRTS comprised a fiberoptic cable wrapped around a PVC tube and connected to a XT-DTS (Silixa, single-ended mode with alternating measurement directions) system. This setup allowed us to measure streambed temperatures at an effective vertical resolution of less than 0.5 cm about every 2 min. HRTS measurements were accompanied by surface water and air temperature measurements while previous studies provided information on streambed grain size and hydraulic conductivity.

For analyzing the temperature time-series data we made use of the LPMLEn method, embedded in a newly developed GUI that allows for easy-to-use model setup and estimation of vertical exchange fluxes and thermal streambed parameters. By solving the heat transport equation in the frequency domain for a finite model domain, the LPMLEn method is a continuation of the LPMLE3 method but unlike the latter can make use of temperature information from multiple (n) vertically deployed sensors while optimally taking into account measurement uncertainty during flux estimation.

Results show that streambed temperatures are variable in space and time, with warming/cooling patterns primarily driven by seasonal hydrometeorological conditions. High-flow conditions in winter led to increased hyporheic exchange around the large woody structures.
3D active seismic tomography of the Barents Sea.
Authors: Shulgin Alexey , Lie Jan Erik , Planke Sverre
Published: March 2021

The Barents Sea shelf has been coverded by a numerous wide-angle seismic profiles, aiming to resolve the crustal structure of the shelf. However, the overall structural arcitecture of the crystaline crust is still not fully understood, due to limited and sparse distribution of deep-sampling seismic profiles. 

The petroleum related seismic exploration in Norwegian waters has been ongoing for decades. The recent increase of the seismic broadband stations onshore (including temporal deployments) provokes the idea to use these stations and the active seismic sources from the regional seismic reflection surveys, including academic and industry seismic projects, to reveal the crustal scale structure of the western Barents Sea.

We have analyzed seismic records from 8 permanent seismic stations from Norway, Sweden and Finland, and 12 temporally deployed broadband seismic stations from the ScanArray seismic network, which recorded more than 100’000 marine airgun shots from academic and oil industry campaigns in the south-western quarter of the Barents Sea.

The overall quality of the seismic records is exceptionally good. We clearly identify phases recorded from the offsets reaching 750 km. The identified phases include refracted crustal and mantle arrivals as well as Moho reflections, including both P and S waves. The overall quantity, quality, and the geometry of the seismic data makes it perfect for the application of the 3D joint refraction/reflection travel time seismic tomography to study the crustal structure of the Barents Sea.

The preliminary results show very complex and laterally inhomogeneous crustal structure of the Barents Sea, which has been known before. However, with the help of 3D seismic tomography we are able to cover the gaps in between isolated deep-sampling seismic profiles and cross-correlate structures identified on them. In this work we would like to present our up-to-date results from the 3D seismic tomography.
Extreme wave statistics of random waves propagating over a 3D varying bathymetry
Authors: Lawrence Christopher , Trulsen Karsten , Gramstad Odin
Published: March 2021

Non-uniform bathymetry may modify the wave statistics for both surface elevation and velocity field.
Laboratory evidence reported by Trulsen et al. (2012) shows that for a relatively long unidirectional
waves propagating over a sloping bottom, from deep to shallower water, there can be a local maximum
of kurtosis and skewness in surface elevation near the edge of the shallower side of the slope. Recent
laboratory experiments of long-crested irregular waves propagating over a shoal by Trulsen et al. (2020)
reported that the kurtosis of horizontal velocity field have different behaviour from the kurtosis of surface
elevation where the local maximum of kurtosis in surface elevation and horizontal velocity occur at
different location.
In present work, we utilize numerical simulation to study the evolution of skewness and kurtosis for
irregular waves propagating over a three-dimensional varying bathymetry. Numerical simulations are
based on High Order Spectral Method (HOSM) for variable depth as described in Gouin et al. (2017)
for wave evolution and Variational Boussinesq model (VBM) as described in Lawrence et al. (2021) for
velocity field calculation.

 

References

GOUIN, M., DUCROZET, G. & FERRANT, P. 2017 Propagation of 3D nonlinear waves over an elliptical
mound with a High-Order Spectral method. Eur. J. Mech. B Fluids 63, 9–24.
LAWRENCE, C., GRAMSTAD, O. & TRULSEN, K. 2021 Variational Boussinesq model for kinematics
calculation of surface gravity waves over bathymetry. Wave Motion 100, 102665.
TRULSEN, K., RAUSTØL, A., JORDE, S. & RYE, L. 2020 Extreme wave statistics of long-crested
irregular waves over a shoal. J. Fluid Mech. 882, R2.
TRULSEN, K., ZENG, H. & GRAMSTAD, O. 2012 Laboratory evidence of freak waves provoked by
non-uniform bathymetry. Phys. Fluids 24, 097101.
Effect of soil organic carbon loss on the stability and structure of microaggregates: First insights from an organic carbon depletion field trial in a loess soil
Authors: Roosch Svenja , Felde Vincent , Uteau Daniel , Peth Stephan
Published: March 2021

Soil microaggregates are considered to play an important role in soil functioning and soil organic carbon (SOC) is of great importance for the formation and stabilization of these aggregates. The loss of SOC can occur, for example, after a change in land use and may lead to a decreased aggregate stability, which makes soils vulnerable to various threats, such as erosion or compaction. It is therefore important to shed light on the effect of SOC loss on aggregate stability in order to better understand and preserve the functioning of healthy soils.

We sampled two adjacent plots from a loess soil in Selhausen (Germany) and measured aggregate stability and architecture of soil microaggregates. One plot was kept free from vegetation by the application of herbicides and by tillage (to a depth of 5 cm) from 2005 on (organic matter depletion, OMD), while the other plot was used for agriculture using conventional tillage (control). Over the course of 14 years, the SOC concentration in the bulk soil has been reduced from 12.2 to 10.1 g SOC kg-1 soil. It was, however, unclear whether a loss of SOC had also taken place in microaggregates (since they are known to have very long turnover times). We took 10 undisturbed soil cores from two depths of each plot (Ap and Bt horizons).

The stability of aggregates against hydraulic and mechanical stresses was tested using wet sieving  (mesh sizes of 0.25 to 8 mm) and a crushing test in a load frame adapted to the microaggregate scale. For the latter test, microaggregates were isolated from the bulk soil using a newly developed dry crushing approach. To shed light on the effect of a decreased SOC content on microaggregate structure, we scanned several microaggregates with a computed tomography scanner at sub-micron resolution and analysed the features of their pore systems. SOC losses had also occurred in large  microaggregates (250-53 µm) in the Ap horizon: SOC contents in this fraction were 16.3 g SOC kg⁻¹ (control) and 12.8 g SOC kg⁻¹ (OMD). While wet sieving indicated a lower stability of macroaggregates from the Ap horizon in the OMD plot (geometric mean diameter: 1.54 mm (control) vs 0.43 mm (OMD)), an effect on the tensile strength of large microaggregates could not be found. Total porosity and pore connectivity, derived from Euler characteristic, as well as several pore skeleton traits (number of branches, junctions, etc.) were lower in aggregates from the OMD treatment. However, the difference was also present or even stronger in the Bt horizon than in the Ap horizon, so the supposed treatment effect might have been due to other effects like spatial heterogeneity of texture. Thus, the observed SOC losses may not have been large enough to substantially influence struture or stability of large microaggregates.
Passive ring laser gyroscopes to access fast variations in EOPs
Authors: Stellmer Simon , Heckl Oliver
Published: March 2021

Quite generally, the Earth Orientation Parameters (EOPs) as obtained via VLBI and GNSS lack short-term sensitivity on (sub-)diurnal timescales. To access these fast dynamics, large active ring laser gyroscopes have been devised and are currently operated in geodesy and seismology. Here, we propose a novel type of gyroscope, namely passive ring lasers. By placing the gain medium outside of the optical resonator, the passive variant may remove many of the systematic limitations of active gyroscopes, and holds the potential to increase sensitivites by two orders of magnitude. Interfacing the gyroscopes with our optical clock technology will improve long-term stability as well. We will report on preliminary work and on the design and anticipated performance parameters of two demonstrators, as put forward by a recently established European collaboration.
Water sources for apple trees in Alpine orchards: where does irrigation water go?
Authors: Penna Daniele , Frentress Jason , Zanotelli Damiano , Scandellari Francesca , Aguzzoni Agnese , Engel Michael , Tagliavini Massimo , Comiti Francesco
Published: March 2021

Understanding the dynamics and sources of root water uptake in agricultural systems is becoming increasingly important for implementing efficient and sustainable water resources management and, at the same time, for optimizing crop yield and quality under changing climatic conditions. In this work, we adopted the stable isotope approach to investigate the water sources accessed by apple trees in two orchards growing in the upper Etsch/Adige valley (South Tyrol, Eastern Italian Alps). We tested the general hypothesis that soil water, composed of a mixture of rain and irrigation water, was the main source for tree transpiration but that river water and groundwater mixed with soil water and contributed to root uptake for trees growing close to the river and with higher water table. Our results revealed that apple trees during the 2015 and 2016 growing seasons relied mostly on soil water present in the upper 20-40 cm of soils, with an apparently negligible contribution of groundwater and river water, irrespective of the field position across the valley bottom. The isotopic composition of xylem water did not reflect the one of irrigation water (and neither that of groundwater) but rather of rainfall and throughfall, as well as that of soil water. We related this “hidden” tracer signature of irrigation water to the effect of soil evaporation that strongly modified its original isotopic composition: irrigation and rain water infiltrated into the soil and mixed with isotopically fractionated soil water, and trees took up a mixture of water with different isotopic composition compared to the one of the original irrigation source. This work contributes to improve the understanding of water uptake strategies in Alpine apple orchards and paves the way for further analysis on the proportion of irrigation and rain water used by apple trees in mountain agroecosystems.