bluuebunny/crossref_metadata_2025 huggingface dataset:
Relationship between salt and crustal tectonics in the Sørvestsnaget Basin, SW Barents Sea
Authors: Travan Gaia , Bellwald Benjamin , Planke Sverre , Gaullier Virginie , Maharjan Dwarika , Vendeville Bruno C.
Published: March 2020

The geology of the Barents Sea has been widely studied because of the interest for hydrocarbon exploration. Our study focuses on the SW Barents Sea, on the western side of the Senja Ridge in the Sørvestsnagets Basin, which is still a less deciphered area. Located at the limit of the continental shelf, this deep Cretaceous basin is characterized by a several-kilometer-thick sequence of Cenozoic sediments locally influenced by salt structures. Because of the peculiar rheological characteristics of salt, the deposition of evaporites during Permo-Carboniferous times still represents a key aspect to deeply understand the geological setting because salt tectonics considerably affects the brittle sedimentary cover.

5,500 km2 of high-quality 3D seismic data, integrated with potential field data and existing wells, led to the interpretation of the main horizons and unconformities in the sedimentary sequence, with focus on the salt structures.

The top of the salt is characterized by a strong positive-amplitude reflection in the seismic data, and has been interpreted with a line spacing of 100 m. Subsequent gridding of the interpreted horizon to a bin size of 12.5 m highlights that the geomorphology for the top of the three salt structures is particularly complex, with presence of salt horns and development of minibasins above the salt. Integration of potential field data shows a strong correlation between salt structures and low values in Bouguer-Gravity anomalies. Different families of faults related to salt and to crustal tectonics have been mapped, and strong seismic anomalies related to faults above the salt structures are identified at multiple stratigraphic levels. Part of these faults have been active until 20 000 years ago, and are rarely active at present day.

The three salt structures interpreted on the western side of the Senja Ridge have a total extent of around 800 km2 and are mainly the consequence of different pulses of reactive diapirism, due to several diachronous rifting events during the opening of the Barents Sea. After the opening of the Sørvestsnagets Basin, salt tectonics continued and was influenced by crustal movements and glacial sedimentation and erosion in this pull-apart basin setting.

The presence of the strong seismic anomalies above the salt structures is interpreted as gas accumulations, which makes this topic of particular interest for the future development of the oil and gas industry of the SW Barents Sea.
Why we believe there is still a model ozone deficit in the upper stratosphere
Authors: Debosscher Jonas , Errera Quentin , Chabrillat Simon , Minganti Daniele , Christophe Yves , Fussen Didier
Published: March 2020

Historically, many photochemical models suffered from an underestimation of the ozone abundance in the upper stratosphere – lower mesosphere, known as the “Ozone deficit problem” (Prather, 1981; Eluszkiewicz et al., 1993, Siskind at al., 2013). Despite improvements in models and increased accuracy of observations, it seems this problem is still present, as evidenced by comparing models participating in the Chemistry-Climate Model Initiative (CCMI) with observations.

The Belgian Assimilation System for Chemical ObsErvations (BASCOE), developed at BIRA-IASB, is used to study and monitor the chemical composition of the stratosphere. It consists of a 3D chemical transport model (CTM) in combination with two data-assimilation methods (4D-Var and EnKF). BASCOE shows an ozone deficit of ~20 % against MLS observations around 1hPa. Since BASCOE will provide operational analysis of ozone based on the assimilation of the future ALTIUS satellite data, and is part of the Integrated Forecasting System of the ECMWF (C-IFS-CB05-BASCOE, Huijnen et al., 2016), the CTM needs to better model the ozone observations in this region of the stratosphere.

We present the results of a sensitivity study using the BASCOE CTM to identify factors that have the largest influence on the ozone budget in the upper stratosphere and can provide clues to solve the ozone deficit. We investigated the effects of solar spectral irradiance, surface albedo, photo-dissociation computation, reaction rate uncertainties and temperature.

Ozone concentrations in the upper stratosphere turned out to be very sensitive to temperatures and to a lesser degree to the solar spectral irradiances used to drive the model. The sensitivity to temperature is compatible with predictions made using a photochemical equilibrium approximation based on pure oxygen chemistry. Given the relatively large temperature uncertainties in the upper stratosphere, we believe temperature biases could substantially contribute to the ozone deficit.
No evidence for climate change in the unprecedented Summer 2018 flow over Europe
Authors: Iles Carley , Vautard Robert
Published: March 2020

The summer of 2018 was characterised by prolonged heatwaves over North-Eastern Europe, associated with persistent blocking over Scandinavia, and a jet stream that resided unusually far north on average over this sector. Whilst most event attribution studies tend to focus on the probability or intensity of extreme temperatures themselves, we instead examine whether anthropogenic climate change has affected the likelihood of the circulation pattern that lead to the 2018 hot summer. We examine trends and variability in jet latitude and blocking frequency over the Scandanavian sector in reanalyses, CMIP5 historical simulations, and in two large ensembles of HadGEM3-A simulations with and without anthropogenic forcing. Both the number of blocked days, and the average jet location for last summer were unprecedented in the observational record, and also very rare in climate model simulations. A number of the CMIP5 models examined were able to simulate realistic blocking frequency distributions. Last summer’s circulation did not appear to be part of any systematic increasing trends in blocking frequency or jet latitude in this sector. Instead, this circulation anomaly appears to be explained by a particularly large deviation of natural variability. We will then extend the analysis to examine the western European heatwaves of summer 2019 which were associated with a very different atmospheric circulation pattern –a high pressure ridge which transported warm air northwards from Northern Africa.
High resolution topography and modeling of the Huon coral reef terrace sequence (Papua New Guinea)
Authors: de Gelder Gino , Pastier Anne-Morwenn , Chauveau Denovan , Fernández-Blanco David , Pedoja Kevin , Authemayou Christine , Husson Laurent
Published: March 2020

Coral reef terraces (CRT) are amongst the most important indicators of Quaternary sea level fluctuations, and are therefore relevant to a wide spectrum of climatic and tectonic studies. The Huon Peninsula in Papua New Guinea accomodates one of the first CRT sequences to be mapped, measured and dated in detail through pioneering studies several decades ago. Those studies were limited by the available techniques to assess the large scale terrace sequence morphology, and thus to constrain spatiotemporal uplift rate variations that are key to determine past relative sea-level (RSL). We re-visit the Huon CRTs with the aim of refining tectonic uplift rates and RSL, using digital surface models calculated from 0.5m Pleiades satellite imagery. This allows us to constrain variations in CRT elevation, and assess tectonic deformation wavelengths in detail. We then use a numerical code for coral reef modeling to reconstruct the sequence morphology and constrain the possible range of RSL over the past few glacial-interglacial cycles. We find that large-scale tilting of the terrace sequence is generally N- instead of NW-directed, which is more compatible with the regional tectonic setting. It also implies changes of several meters for RSL highstand estimates compared to previous studies. We compare our results to other terrace sequences, and discuss the potential of combining high-resolution topography with landscape evolution modeling to constrain RSL.
The contribution of earthworms to soil aggregate formation
Authors: Guhra Tom , Stolze Katharina , Ritschel Thomas , Totsche Kai Uwe
Published: March 2020

Anecic and endogeic earthworm species are known as “ecosystem engineers” that significantly contribute to the porosity and coherence of soil as well as soil water infiltration and the turnover rates of organic matter (OM). Additionally, earthworms actively excrete nutrient rich mucus, release bacteria within casts and translocate litter into the subsurface. In this way, earthworms not only shape the structure of soils but also the chemical milieu of the drilosphere where mucus forms a prominent fraction of OM. Furthermore, other biogenic extracellular polymeric substances (EPS) are known to form organo-mineral associations, which suggests that earthworms also facilitate their further attachment into soil aggregates.

With this study, we investigated how earthworms contribute to soil aggregate formation and impact aggregate properties by OM translocation and incorporation in the drilosphere. At vertically sampled burrow walls predominantly formed by Lumbricus terrestris, a patchy and depth dependent distribution of hydrophobic and hydrophilic regions was found with the water drop penetration time (WDPT) test. In the hydrophobic regions, we identified an enrichment of carbon and aggregate surface coatings containing plant residuals, bacteria, OM screenings and enmeshments by scanning electron microscopy (SEM) and elemental analysis. These structures were further investigated by factor analysis of Fourier transform infrared (FTIR) spectra that permitted the FTIR-band extraction of earthworm typical aggregation agents as, e.g., bacterial EPS, earthworm mucus and plant components (leaves, roots and sprout). Furthermore, with sorption experiments to typical minerals of temperate soils (e.g. illite and goethite), we found a mineral-specific adsorption of earthworm cutaneous mucus (of Lumbricus terrestris and Aporrectodea caliginosa) and bacterial EPS (of Bacillus subtilis). Specifically, a preferential adsorption of phosphorus containing constituents of mucus and bacterial EPS to goethite has been observed. The resulting formation of organo-mineral associations characterized by screened mineral surface charges was shown by zeta potential measurements.

We show that besides the active incorporation of particulate OM, as e.g. plant residuals and microorganisms, the mineral specific adsorption of EPS formed by earthworms and bacteria induce the formation of organo-mineral associations and alteration of the physico-chemical properties of earthworm-formed structures and soil aggregates.
Eddy covariance measurements of the forest floor CO2 exchange in two contrasting forest stands in boreal Sweden
Authors: Chi Jinshu , Nilsson Mats , Kljun Natascha , Peichl Matthias
Published: March 2020

Boreal forests cover a large portion of land surface area in the northern hemisphere and greatly affect the global carbon (C) cycle and climate. Since these forests exchange carbon dioxide (CO2) with the atmosphere in different vertical layers, many different CO2 sources and sinks exist within the complex forest stand. The forest floor (soil and understory vegetation) may act as an important component of the C budget in a forest stand, however its contribution may vary from negligible to determining the inter-annual variability of ecosystem C balance. To date, there are a limited number of studies that have directly quantified the CO2 fluxes over a forest floor using the eddy covariance (EC) method primarily due to challenges and potential violation of underlying assumptions when applying this method in the trunk space where turbulence characteristics are complicated, intermittent, and not in accordance with universal theories.

In this study, we installed two identical EC flux systems at two contrasting boreal forests (sparse pine stand vs. a dense mixed pine-spruce stand) in Sweden to measure the forest floor CO2 exchange. We developed site-specific ideal cospectral models for the below-canopy fluxes in the trunk space under the well-mixed condition as defined by the standard deviation of the vertical wind speed. Spectral correction to the half-hourly fluxes was performed based on the newly fitted cospectral models at each site. Chamber measurements of CO2 fluxes during the growing season were conducted to compare with the estimates from the below-canopy EC data.

Our below-canopy cospectral models show that more high-frequency signals (small eddies) occurred in the forest trunk space compared to the ideal above-canopy cospectral model. The high-frequency contribution was greater in the dense pine-spruce forest compared to the open pine stand. The spectral corrected CO2 fluxes measured by the EC method agreed well with the concurrent chamber measurements. The EC results revealed that the forest floor of the two contrasting stands acted as net CO2 sources during the 3-year period (2017-2019). This study highlights that by applying a data correction based on site-specific below-canopy cospectral models, the EC method can be used in the trunk space to accurately measure the net CO2 exchange between the forest floor and the atmosphere and thus to improve our understanding of the role of the forest floor in the ecosystem-scale C budget in the boreal forest region.
Impact of 3D cloud structures on tropospheric NO2 column measurements from UV-VIS sounders
Authors: Yu Huan , Kylling Arve , Emde Claudia , Mayer Bernhard , Stebel Kerstin , Van Roozendael Michel , Veihelmann Ben
Published: March 2020

Operational retrievals of tropospheric trace gases from space-borne spectrometers are made using 1D radiative transfer models. To minimize cloud effects generally only partially cloudy pixels are analysed using simplified cloud contamination treatments based on radiometric cloud fraction estimates and photon path length corrections based on oxygen collision pair (O2-O2) or O2A-absorption band measurements. In reality, however, the impact of clouds can be much more complex, involving scattering of clouds in neighbouring pixels and cloud shadow effects. Therefore, to go one step further, other correction methods may be envisaged that use sub-pixel cloud information from co-located imagers. Such methods require an understanding of the impact of clouds on the real 3D radiative transfer. We quantify this impact using the MYSTIC 3D radiative transfer model. The generation of realistic 3D input cloud fields, needed by MYSTIC (or any other 3D radiative transfer model), is non-trivial. We use cloud data generated by the ICOsahedral Non-hydrostatic (ICON) atmosphere model for a region including Germany, the Netherlands and parts of other surrounding countries. The model simulates realistic liquid and ice clouds with a horizontal spatial resolution of 156 m and it has been validated against ground-based and satellite-based observational data.

As a trace gas example, we study NO2, a key tropospheric trace gas measured by the atmospheric Sentinels. The MYSTIC 3D model simulates visible spectra, which are ingested in standard DOAS retrieval algorithms to retrieve the NO2 column amount. Spectra are simulated for a number of realistic cloud scenarios, snow free surface albedos, and solar and satellite geometries typical of low-earth and geostationary orbits. The retrieved NO2 vertical column densities (VCD) are compared with the true values to identify conditions where 3D cloud effects lead to significant biases on the NO2 VCDs. A variety of possible mitigation strategies for such pixels are then explored.
Agro-climatic observations in Huaraz, Peru – first insights from water, energy and carbon dioxide flux measurements
Authors: Hänchen Lorenz , Wohlfahrt Georg , Gurgiser Wolfgang , Maussion Fabien , Calanca Pierluigi , Cochachín Rapre Alejo , Cruz Encarnación Rolando , Quiñonez Collas Fiorella
Published: March 2020

Small-scale farming in the Tropical Andes has been increasingly challenged by recent economic growth due to globalization of agriculture and increasing mining activities. Furthermore, in Ancash and its capital Huaraz decreasing water availability and higher water demand are a great concern for sustainable development. Recent studies have investigated the situation of small-scale farmers in hydrological sub-catchments of the Rio Santa Basin around Huaraz between the Coordillera Negra and Blanca using interdisciplinary methods. Their results show a clear disagreement between the perception of climate (or precipitation) change by local farmers and the statistical analysis of meteorological data collected at nearby weather stations. In the framework of the project AgroClim Huaraz (www.agroclim-huaraz.info), our team tries to investigate the reasons of this disparity and to assess the potential vulnerabilities and risks in local small-scale agriculture in rural areas close to Huaraz.

Recently, we installed two automatic weather stations (AWS) and a network of rain gauges (5) representing a broad range of ecosystems and altitudes along a precipitation transect (East to West). In addition, one field site has been equipped with an eddy covariance system (EC) providing continuous energy (latent and sensible heat) and carbon dioxide fluxes, while in other locations, covering the most important crop types in the region, our mobile EcoBot system has been used for periodic observations of latent and sensible heat fluxes and crop development (biomass, vegetation height) since November 2019. To date, these measurements of climate-vegetation interaction are still regularly carried out by local partners in Huaraz.

In this contribution we will (i) report for the first time the EC data, (ii) validate the EcoBot against the EC measurements and (iii) analyse the variability in crop phenology and evapotranspiration (driven by spatial differences in rainfall).

In the future, we aim to use our novel in-situ data to 1) validate remote sensing and reanalysis data, 2) run and calibrate FAOs AquaCrop model and 3) add an open-source (OS) module to AquaCrop OS integrating NDVI data (acquired by EcoBot) to drive it on larger scales with remote sensing data.
A Paleomagnetic Study of the Tectonic Deformation in Circum-Marmara Region, NW Anatolia, during the Late Cretaceous and Cenozoic Period
Authors: Cabuk Burak Semih , Cengiz Mualla
Published: March 2020

The Marmara region is located on the Alpine Himalayan orogenic belt which experienced a active tectonic deformation. The region consists of tectonic units such as the Istanbul Zone, the Strandja Zone and the Sakarya Continent. It is reported in the previous geological studies that the Istanbul Zone began to move southwards appart from the Moesia Platform with the effect of West Blacksea Fault in the west and West Crimea Fault in the east after the the opening of the Black Sea in the Cretaceous. It is known that the Intra Pontide suture is formed after the closure of the Intra-Pontide ocean during the Early Eocene due to the collision between İstanbulzone and the Sakarya continent which moved northwards. As a result of the continental collision, the region has completed its evolution under the influence of basin formation and the emplacement of North Anatolian Fault Zone from Miocene to the present.

 

In this study, Upper Cretaceous-Oligocene sedimentary and volcanic rocks were sampled at 103 sites to investigate the tectonic deformation of the area. As a result of rock magnetism studies, it was shown that magnetic minerals in sedimentary and volcanic rocks are defined by titanium-rich titanomagnetite showing low coercivity, while in limestone samples, magnetization is defined by hematite showing high coercivity. As a result of anisotropy of magnetic susceptibility (AMS) measurements, it was observed that most of the samples show magnetic foliation and a deformation ellipsoid which is oblate. Paleomagnetic results show counterclockwise rotation of 19.9°±10.9° for the Sakarya continent, 27.4°±11.6°for the Pontides and 15.6°±11.8°for the Strandja Zone from Eocene to present. The results indicate that the region has completed the collision in Eocene and rotated counterclockwise as a large block. Deformation due to basin development or fault bounded block rotations which developed after Miocene could not been detected in this study. Miocene paleomagnetic data from previous studies in the study area are compatible with counterclockwise rotations in Upper Cretaceous-Oligocene which shows that different blocks emplaced in the study area moved together as a single plate during Eocene-Miocene time.
Response of benthic species to post-glacial sea-level rise on the northern Adriatic shelf revealed by stratigraphic unmixing of fossil assemblages
Authors: Nawrot Rafał , Scarponi Daniele , Tomašových Adam , Kowalewski Michał
Published: March 2020

Late Quaternary fossil record offers a window into ecosystem dynamics during episodes of abrupt climate warming and sea-level rise following the Last Glacial Maximum, but in marine settings ecological inferences might be hindered by high time-averaging affecting transgressive deposits. However, the signature of temporal shifts in local skeletal production rates may be preserved in the age-frequency distributions (AFDs) of death assemblages. We use carbonate-target radiocarbon ages of 191 shells to examined variation in AFDs among four bivalves species collected from a 2.3-meter-long core recording the post-glacial transgression on the northern Adriatic shelf over the last the last ~14,500 yr.

The scale of time-averaging within species (interquartile age range) varied from 200 to 7,400 yrs, while the between-species age offsets (differences between the median ages of species) ranged from ~2 to 6,400 yrs within 5-cm-thick core intervals. Although the median ages of Varicorbula, Timoclea and Parvicardium increased with increasing burial depth, shells of Lentidium appeared age-homogeneous throughout the core. Age unmixing revealed a single massive peaks in the abundance of this opportunistic, shoreface species around 14 cal ka BP, coincident with the initial marine flooding of this shelf area during the melt-water pulse 1A. Moreover, a prominent gap in the AFDs between 11 and 12.5 cal ka BP corresponds to a minor sea-level fall associated with the Younger Dryas cold spell. Importantly, the reconstructed onsets and durations of shell production pulses across the four species are consistent with independently-derived relative sea-level history at the site. The species gradually replaced each other through time as the dominant component of the assemblage in accordance with their bathymetric preferences estimated from surveys of the modern Adriatic benthic fauna.

The diachronous production histories of four bivalve species coupled with subsequent exhumation of old shells and burial of younger shells through bioturbation and sediment reworking resulted in the ecologically mixed fossil assemblages. These assemblages are thus characterized by multi-modal age distribution and millennial-scale age offsets between species co-occurring in the same stratigraphic increments. Although this stratigraphic homogenization and disorder greatly limits the resolution of the raw stratigraphic record, our results demonstrate the power of AFDs to capture shifts in abundance of benthic species during recent episodes of rapid sea-level rise. Fossil assemblages from transgressive deposits preserved on continental shelves represent a rich and underutilized source of data on long-term biotic responses to global climate change and associated shifts in sea level.
Simulated last deglaciation of the Barents Sea Ice Sheet primarily driven by oceanic conditions
Authors: Petrini Michele , Florence Colleoni , Nina Kirchner , Anna L. C. Hughes , Angelo Camerlenghi , Michele Rebesco , Renata G. Lucchi , Emanuele Forte , Renato R. Colucci , Riko Noormets , Jan Mangerud
Published: March 2020

An interconnected complex of ice sheets, collectively referred to as the Eurasian ice sheets, covered north-westernmost Europe, Russia and the Barents Sea during the Last Glacial Maximum (around 21 ky BP), connecting to the Scandinavian Ice Sheet to the south. Due to common geological features, the Barents Sea component of this ice complex is seen as a paleo-analogue for the present-day West Antarctic Ice Sheet. Investigating key processes driving the last deglaciation of the Barents Sea Ice Sheet represents an important tool to interpret recent observations in Antarctica over the multi-millennial temporal scale of glaciological changes. We present results from a statistical ensemble of ice sheet model simulations of the last deglaciation of the Barents Sea Ice Sheet, all forced with transient atmospheric and oceanic conditions derived from AOGCM simulations. The ensemble of transient simulations is evaluated against the data-based DATED-1 reconstruction. We find that the simulated deglaciation of the Barents Sea Ice Sheet is primarily driven by the oceanic forcing, with sea level rise and surface melting amplifying the ice sheet sensitivity to ocean warming over relatively short intervals. Despite a large model/data mismatch at the western and eastern ice sheet margins, the simulated and DATED-1 deglaciation scenarios agree well on the timing of the deglaciation of the central and northern Barents Sea. The primary role played by ocean forcing in our simulations suggests that the long-term stability of the West Antarctic Ice Sheet could be at stake if the current trend in ocean warming will continue.
Deriving tillage-controlled runoff patterns for agricultural fields
Authors: Brunner Thomas , Zeiser Anna , Klik Andreas , Strauss Peter
Published: March 2020

On agricultural fields, management (especially tillage) operations with a distinct orientation often lead to a corresponding preferred orientation of surface runoff and associated sediment transport. When deriving surface properties like flow directions and slope for runoff modelling from digital elevation model (DEM) data with grid sizes larger than 1m, these features of the surface will usually remain undetected and by default predict runoff and sediment transport patterns based on the topographic slope and flow directions alone.

A methodology proposed by (Takken et al., 2001) involves calculating 1) topographic slope and flow directions and 2) slope and flow directions assuming that surface runoff takes place exclusively along the tillage orientation. A decision algorithm then decides for each grid cell, whether 1) or 2) is to be used, based on cell slope, oriented roughness and the angle between topographic and tillage-controlled flow directions. An exception is made for distinct thalweg situations, where 1) is always used.

For larger areas, where the manual assignment of the management direction of individual fields (e.g. based on orthophotos) is not feasible, automatic estimation of a field’s tillage orientation is done using field geometry parameters and assuming tillage taking place in the direction of the longest field extent.

The output of the methodology is to be used subsequently in grid-based soil erosion modelling and is expected to provide more realistic results of surface runoff and soil loss patterns. Initial tests using the output flow directions and slope of the method as input for an MMF (Morgan-Morgan-Finney) based soil erosion model in a small experimental catchment (0.7 km²) show surface runoff and soil loss concentrating on the field borders (headlands) for some fields, potentially leading to a shift of priority for protection of either whole individual fields or particularly affected portions of fields.

The improved modelling results can in some situations be significant for decisions on the placement of best management practices (BMP) that intend to limit either soil loss from the field or sediment input into adjacent surface water bodies (e.g. vegetated filter strips, grassed waterways or the feasibility of contouring), since these measures might be rendered useless, when their placement is based on topographic flow directions alone, as is the default practice.
The distribution and trends in Chinese methane emissions, 2010-2017
Authors: Zhu Sihong , Feng Liang , Palmer Paul , Liu Yi
Published: March 2020

We use satellite observations of methane (CH4) from the Japanese Greenhouse gases Observing SATellite (GOSAT) to study the temporal and spatial changes in Chinese CH4 emissions from 2010 to 2017. We use v12.5.0 of the GEOS-Chem model of atmospheric chemistry and transport, driven by prior emission inventories, to describe observed variations of atmospheric CH4. To infer fluxes from North, central, South, East, northeast, northwest and southwest China we use an established ensemble Kalman filter method in conjunction with the GEOS-Chem model. We find that annual nationwide CH4 emissions decreased from 53 Tg in 2010 to 49 Tg in 2012, but then increased to 54 Tg in 2017. Emissions from eastern China represent the largest regional contribution to the nationwide total, accounting for 22%, while southern and northeast China each represent the smallest regional contributions of 7%. We find that emission trends of various regions are very different. Generally, regional CH4 emissions are smallest during January and peak in July. We report a downward trend during Spring over southwest and southern regions but find no significant trend in northern and northwest China.  By analyzing the seasonal maximum and minimum values over each region, we find that annual mean trends are driven by changes in seasonal peak values, with no obvious trend in the seasonal minimum. We will discuss how changes in coal mine emissions may have impacted nationwide trends after 2013.
Lateral transport of SOC induced by water erosion in a Spanish agroecosystem
Authors: Gaspar Leticia , Mabit Lionel , Lizaga Ivan , Navas Ana
Published: March 2020

The main route for the lateral movement of soil organic carbon (SOC) is water erosion. Awareness of the distribution and magnitude of land carbon mobilization is important both for improving models of the carbon cycle and for management practices aimed to preserve carbon stocks and enhance carbon sinks. There is a need to consider the global significance of soil erosion from soil organic carbon cycling schemes and for this reason, the movement of SOC during erosion processes should be elucidated.

Our study aims to estimate the SOC redistribution induced by water erosion during a 40 years period in an agroforestry mountain ecosystem located in northern Spain. To this purpose, topographically driven transects were selected with mixed land uses to i) assess what factors modify the runoff patterns with impact on soil and carbon redistribution and ii) evaluate the mobilization of topsoil organic carbon along the transects.

The lateral movement of SOC shows similar spatial patterns with that of soil erosion. To identify whether erosional or depositional processes have been predominant in the sampling sites we used 137Cs inventories and the characterization of terrain attributes of the study with a detailed analysis of the main runoff pathways. Results indicate that SOC losses were related to an increase in water flow accumulation, while the highest SOC gains were recorded at concave positions. Soil erosion processes and the content of SOC in soils are the two main factors controlling carbon budgets. The topographical and geomorphological characteristics of the transects, the spatial distribution of land uses and the presence of landscape linear elements such as terraces or paths, affect runoff and determine the sediment connectivity and carbon dynamics along the slopes.

The interactions between topography and land use produce significant positive or negative effects on SOC accumulation, particularly in areas with complex topography, as the results obtained in our study sustain. Even though the effect of topography and land use/land cover and their interactions on the horizontal distributions of carbon remains largely unknown, our approach contributes to better understand the pattern of gains and losses of soil organic and inorganic carbon induced by water erosion.
The effect of vertical distribution functions on CO2 efflux and production calculated with the flux gradient approach
Authors: Jochheim Hubert , Wirth Stephan , Paulus Sinikka , Maier Martin , Haas Christoph , Gerke Horst H.
Published: March 2020

Soil respiration is one of the most significant carbon fluxes in terrestrial ecosystems. The analyses and quantification of soil CO2 production and its influencing factors play a crucial role in the understanding of the global carbon budget.

To investigate CO2 efflux from terrestrial soils under field conditions, manual or automated soil chambers are the most common methods. The flux-gradient approach (FGA) as an alternative method applies Fick’s law to vertical profiles of soil CO2. The FGA uses the soil gas diffusivity to calculate vertical fluxes of soil CO2 and the CO2 efflux from soil. The vertical partitioning the production of CO2 in different soil layers can be regarded as an option and an advantage of FGA as compared to chamber methods.

This investigation aims at clarifying whether a spline or an exponential function is more suitable for fitting vertical distributions of measured CO2 concentrations. We compared simulation results on the CO2 efflux and the vertical distribution of CO2 production within the soil when applying an exponential function or a spline function, respectively. Soil CO2 concentrations were measured at the soil surface and at 0, 0.1, 0.2, 0.3 and 1.0 m soil depth of a Scots pine and a European beech forest stand of the Northeast German Lowlands. Additionally, the CO2 efflux was estimated by applying the manual chamber method. The results suggest that vertical distribution function of soil CO2 affects both the calculated CO2 efflux and the production of soil CO2. The CO2 efflux from the chamber method fits best with the CO2 efflux from spline function. We discus some effects with the application of the spline function on the calculated vertical distribution of CO2 production.
Identifying key predictors for the susceptibility of Himalayan glacial lakes to sudden outburst floods
Authors: Fischer Melanie , Veh Georg , Korup Oliver , Walz Ariane
Published: March 2020

Despite being a rather rare phenomenon when compared to the occurrence rates of other alpine hazards (e.g. landslides, avalanches), glacial lake outburst floods (GLOFs) pose a significant threat to downvalley communities in glaciated mountain areas. Characteristically high peak discharge rates and flood volumes, documented to have reached 30,000 m³/s and > 50 million m³ in the past century, not only provide GLOFs with a landscape-forming potential but also killed a reported global total of > 12,000 people and caused severe damage to infrastructures. Extensive glacial covers and steep topographic gradients, coupled with rapidly changing socio-economical implications, make the Hindu-Kush-Himalaya (HKH) a high priority region for GLOF research, even though recent studies suggest an annual occurrence rate of 1.3 GLOFs per year across this range during the past three decades. So far, GLOF research in the greater HKH region has been predominantly focused on the classification of potentially dangerous glacial lakes derived from analysing a limited number of glacial lakes and even fewer reportedly GLOF-generating glacial lakes. Moreover, subjectively set thresholds are commonly used to produce GLOF hazard classification matrices. Contrastingly, our study is aimed at an unbiased, statistical robust and reproducible assessment of GLOF susceptibility. It is based on the currently most complete inventory of GLOFs in the HKH since the 1980’s, which comprises 38 events. In order to identify key predictors for GLOF susceptibility, a total of 104 potential predictors are tested in logistic regression models. These parameters cover four predictor categories, which describe each glacial lake’s a) topography, b) catchment glaciers, c) geology and seismicity in its surroundings, and c) local climatic variables. Both classical binary logistic regression as well as hierarchical logistic regression approaches are implemented in order to assess which factors drive susceptibility of HKH glacial lakes to sudden outbursts and whether these are regionally distinct.
IDC Infrasound technology path to continuous improvement
Authors: Mialle Pierrick
Published: March 2020

The IDC advances its methods and continuously improves its automatic system for the infrasound technology. The IDC focuses on enhancing the automatic system for the identification of valid signals and the optimization of the network detection threshold by identifying ways to refine signal characterization methodology and association criteria. Alongside these efforts, the IDC and its partners also focuses on expanding the capabilities in NDC-in-a-Box (NiaB), which is a software package specifically aimed at the CTBTO user community, the National Data Centres (NDC).

An objective of this study is to illustrate the latest efforts by IDC to increase trust in its products, while continuing its infrasound specific effort on reducing the number of associated infrasound arrivals that are rejected from the automatic bulletins when generating the reviewed event bulletins. A number of ongoing projects at the IDC will be presented, such as: - improving the detection accuracy at the station processing stage by introducing the infrasound signal detection and interactive review software DTK-(G)PMCC (Progressive Multi-Channel Correlation) and by evaluating the performances of detection software; - development of the new generation of automatic waveform network processing software NET-VISA to pursue a lower ratio of false alarms over GA (Global Association) and a path for revisiting the historical IRED. The IDC identified a number of areas for improvement of its infrasound system, those will be shortly introduced.
Flow regime variation in Arctic rivers
Authors: Fazel Nasim , Torabi Haghighi Ali , Rasouli Kabir , Kløve Bjørn
Published: March 2020

Arctic rivers’ flow regime has changed under climate change and its consequences on melting glaciers, thawing permafrost, and precipitation patterns. Reservoirs, hydro-power sites, and water diversions have also changed flow regimes in the Arctic. The flow regime alteration in the Arctic rivers has a strong influence on the conservation and sustainability of the native biodiversity of the riverine ecosystem. The main objective of this paper is to evaluate changes in the (1) magnitude of monthly stream flows, (2) magnitude and duration of annual maxima and minima flows, (3) timing of annual maxima and minima, (4) frequency and duration of high and low pulses, and (5) rate and frequency of daily flows in seven major Arctic Rivers. The analyses provide an important basis to characterize and understand the influence of climate change and anthropogenic activities on the flow regimes in the Arctic. Streamflow observations were obtained from the outlet of the Lena, Yenisei, Kolyma, Ob (Russia), Yukon (USA and Canada), Mackenzie (Canada), and Tana (Norway and Finland) rivers in this study. These rivers are main freshwater suppliers for Arctic Ocean. Of these, five have been regulated and two are considered pristine rivers. In addition, the impact of 16 reservoirs on flow regime in the headwaters and tributaries of Lena, Yenisei, Mackenzie, and Kolyma were evaluated. The annual flow showed an increasing trend in all rivers and with a statistically significant level in Yenisei, Lena, and Mackenzie. Our results also indicated that changes in the observed flow regimes at the outlet stations vary from low to incipient level. Out of 16 reservoirs that were analyzed for flow regimes changes, construction of Krasnoyarsk and Shushenskaya dams on the Yenisei River showed the highest impact on flow regime and flow regime alteration was classified as severe in this river.
Phenology-induced energy and carbon fluxes in land surface models
Authors: De Pue Jan , Barrios José Miguel , Maignan Fabienne , Liu Liyang , Ciais Philippe , Arboleda Alirio , Hamdi Rafiq , Balzarolo Manuela , Gellens-Meulenberghs Françoise
Published: March 2020

The annual phenological cycle is of key importance for the carbon and energy fluxes in terrestrial ecosystems. Although the processes controlling budburst and leaf senescence are fairly well known, the connection between plant phenology and the carbon fluxes remains a challenging aspect in land surface modelling (LSM). In this study, the modelling strategies of three well stablished LSM are compared. The LSM considered in this study were: ORCHIDEE, ISBA-A-gs and the model driving the LSA-SAF evapotranspiration product (https://landsaf.ipma.pt). The latter model does not simulate the carbon fluxes but focuses on the computation of evapotranspiration and energy fluxes.
The phenological cycle is simulated explicitly in the ORCHIDEE model, using empirical relations based on temperature sum, water availability, and other variables. In the ISBA-A-gs model, phenology and LAI development is fully photosynthesis-driven. The phenology in the LSA-SAF model is driven by remote sensing forcing variables, such as LAI observations. Alternatively, the assimilation of remote sensing LAI products is a convenient method to improve the simulated phenological cycle in land surface models. A dedicated module for this operation is available in ISBA-A-gs.
Simulations were performed over a wide range of climatological conditions and plant functional types. The results were then validated with in-situ measurements conducted at Fluxnet stations. In addition to the comparison between measured and modelled carbon fluxes, the validation in this study included the intra-annual variation in the simulated phenological cycle.
Quantifying contemporary debris supply in a debris-covered glacier catchment using high-resolution repeat terrestrial LiDAR
Authors: Stewart Rebecca , Westoby Matthew , Dunning Stuart , Pellicciotti Francesca , Woodward John
Published: March 2020

Glacial debris cover is increasing at a global scale in response to increasing temperatures and negative glacier mass balance. The last decade or so has seen an abundance of research which focuses on debris-covered glacier dynamics and supraglacial processes, such as ice-cliff back wasting and the development of supraglacial ponds. However, far fewer studies have focussed on improving understanding of debris supply to these systems over short- (months-years) or long (centennial-millennial) timescales. Existing work has attempted to quantify headwall erosion by calculating the ratio of supraglacial debris flux (the product of debris thickness and supraglacial velocity) to the headwall catchment area. Whilst these studies provide estimates of headwall erosion rates over long timescales, they are unable to capture subtle (or extreme) spatial and temporal variations in debris supply that operate over shorter timescales. Capturing this variation is important because it will allow predictions of the spatial distribution and volume of debris layers on debris-covered glaciers, which in turn will increase the accuracy of ablation modelling and future melt predictions for these systems. To quantify such variability, we conducted terrestrial LiDAR surveys of potential debris slopes at Miage Glacier, Italy, between July – September 2019. We acquired > 1.8 billion 3D points per catchment survey covering an approximate slope area of 7.7 km2, which supplies debris to ~33% of the glacierised area. Sequential 3D point clouds were co-registered using iterative closest point adjustment. Vegetated surfaces were automatically detected using the CloudCompare plugin CANUPO and removed from further analysis. The M3C2 change detection algorithm was used to calculate 3D change normal to the surface plane, and a 95th percentile confidence interval was applied to eliminate non-significant change. Connected components analysis was used to identify discrete rockfall events, estimate their dimensions, explore their magnitude-frequency and quantify their spatial distribution. We find at least one large failure which developed over a period of two weeks (validated by in situ time-lapse footage) and comprised an estimated volume of around 1 x 106 m3. This particular failure occurred from a recently (<10 years) deglaciated slope, lending support to the theory that large-scale slope response to glacial erosion can be rapid.
Application of hyperspectral imaging of peat profiles to the case of fen-bog transition in aapa mires
Authors: Granlund Lars , Tahvanainen Teemu , Keinänen Markku
Published: March 2020

Hyperspectral imaging (HSI) is a promising precision tool for analysing chronological peat strata from vegetation transitions in peatlands. We explored the potential of HSI in identifying transitions in peat-forming vegetation and degree of peat humification. The changes in aapa mire complexes during recent decades have been assessed by various remote sensing methods (aerial image time series, satellite data and high-resolution UAV multispectral imaging) and HSI methods have been developed to support the data from other sources. Rapid growth of Sphagnum mosses over string-patterned aapa mires in the north-boreal zone has immense significance, since it can alter ecosystem structure and functions such as carbon sequestration. HSI is well suited for analysis of recent ecosystem changes, since it can be applied for large sample sets with extremely fine spatial detail. Additionally, peat layers have complex 3D structures that can be overlooked by other sampling methods.

The HSI data was collected in laboratory conditions with two spectral imaging cameras, covering the visible to near-infrared range (VNIR 400-1000 nm), short-wave infrared range (SWIR, 1000-2500 nm). We used various methods such as PCA, k-means clustering and support vector machines for both quantitative and qualitative analysis of peat.  Our analyses revealed detailed spectral changes that matched with transitions in peat quality and composition. Methodological issues unique to peat samples, such as the effect of oxidation and water content, were assessed for method development. We also used HSI to estimate quality changes that would easily be overlooked or only found by most laborious conventional techniques, like high-frequency microscopic counting of plant remains. Here, the spectral results can be used to guide sampling for microscopic routines, for example.

Results with Carex and Sphagnum peat proved that efficient image-based classification methods for identifying peat transitions can be developed. Our SVM models in the VNIR and SWIR regions were able to distinguish Sphagnum and Carex peat with overall accuracy of validation 80 % and 81 %, respectively. We also developed simple NDI indices for the estimation of von Post humification index that worked with accuracy of 86 % and 59 % for VNIR and SWIR, respectively. In combination with data collected from other sources (remote sensing, ground-truthing, conventional laboratory analysis), peat spectral analyses give strong inference of changes. In our study system, results indicate high sensitivity of northern aapa mires to ecosystem-scale changes.