bluuebunny/crossref_metadata_2025 huggingface dataset:
Rewet or not – insights on spatiotemporal patterns of greenhouse gas fluxes from soils in a rewetted Danish forested wetland
Authors: Larsen Klaus Steenberg , Christiansen Jesper Riis
Published: March 2020

Previously drained forested wetlands around the world are being restored for biodiversity, but our knowledge on the impact of restored hydrology on the total greenhouse gas (GHG) budget in these systems remains fragmented. Whereas the reduction in the net CO2 emission upon rewetting is well documented, the magnitude of the effect on the microbial production of CH4 and N2O is much more uncertain. This is partly because GHG fluxes, especially for CH4 and N2O, exhibit a highly dynamic spatiotemporal variation tied to the soil hydrological regime. To capture this variation properly a high number of flux measurements in time and space is needed, but many field studies are still highly limited in terms of their spatio-temporal coverage. This hiatus of field data is a primary source of uncertainty in model projections of impacts on the GHG budgets when restoring natural hydrology in drained wetlands.

We use a novel automatic chamber measurement system (SkyLine2D) connected to a Picarro G2508 analyzer for CO2, CH4 and N2O flux measurements in a rewetted Danish forest wetland. With this system, we wish to resolve the little known spatio-temporal patterns of these GHGs and their relationship with environmental drivers such as soil moisture, water table, temperature, and soil carbon content. A total of 30 measurement plots, each measured 5 times per day over a period approaching 1 year (> 40,000 measurements), were placed along a 30 meter transect covering a soil hydrological gradient including well-drained, waterlogged and open water conditions. The gradient also spans a soil carbon gradient increasing from well-drained mineral soils, over gleysols to waterlogged histosols.

Based on the novel, high-frequency flux data of CO2, CH4 and N2O we will present a detailed analysis of the relationship with soil hydrology and temperature over periods spanning from hours to months. The data produced by this gradient approach combined with automated measurements represents an important step towards developing improved ecosystems models that can better predict the GHG effect of rewetting previously drained wetlands.
Clustering dependence structures of environmental extremes
Authors: Vignotto Edoardo , Engelke Sebastian , Zscheischler Jakob
Published: March 2020

Identifying hidden spatial patterns that define sub-regions characterized by a similar behaviour is a central topic in statistical climatology. This task, often called regionalization in hydrology, is helpful for recognizing areas in which the variables under consideration have a similar stochastic distribution and thus, potentially, in reducing the dimensionality of the data. Many examples are available in this context, spanning from hydrology to weather and climate science. However, the majority of regionalization techniques focuses on the spatial clustering of a single variable of interest. Given the often severe impacts of climate extremes at the regional scale, here we develop an algorithm that identifies homogeneous spatial sub-regions that are characterized by a common bivariate dependence structure in the tails of a bivariate distribution.  In particular, we use a novel nonparametric distance able to capture the similarities and differences in the tail behaviour of bivariate distributions as the core of our clustering procedure. We apply the approach to identify homogeneous regions with varying coherence in the co-occurrence of sea level pressure and precipitation extremes in Great Britain and Ireland.
Performance of Modified Temperature-Based Reference Crop Evapotranspiration Models Across Different Agro-Climatic Zones in Karnataka State, India
Authors: Siddalingamurthy Niranjan , Nandagiri Lakshman
Published: March 2020

Reference crop evapotranspiration (ET0) forms an essential forcing variable in hydrological, agricultural, irrigation and climate models. Among several available methods for ET0 estimation using regularly recorded climate data, the Food and Agriculture Organization (FAO) Penman-Monteith (PM) equation is popular among researchers due to its accuracy across different environments. However, routine use of the FAO-PM equation is hampered in data-scarce situations because of the requirement of input data pertaining to a large number of climate variables. Therefore, simpler alternative methods for ET0 estimation such as the Blaney-Criddle (BC) and Hargreaves (HG) have been proposed by previous researchers. However, for routine use of these empirical equations, local calibration of the model parameters may be desirable. Also, a few previous attempts have been made to replace the daily mean temperature with an effective temperature calculated as a weighted average of daily maximum and minimum temperatures.  Therefore, the present study was taken up to evaluate the effect of two aspects on the accuracies of the BC and HG models 1) replacing mean temperature with effective temperature defined using different parameterizations 2) local calibration of parameters. For this purpose, climate records for the historical period 2006-2016 of 67 stations located across ten agro-climatic zones of Karnataka State, India were used and the analysis was carried out using a monthly time step. Since measured ET0 data was unavailable, calibration was performed using PM ET0 estimates and performance was evaluated using various statistical measures. Overall results showed that the BC equation with mean temperature yielded better results than the ones with effective temperature with calibrated parameters. However, the HG method showed an improvement with the use of effective temperature. Information on the spatial distribution of calibrated parameters was derived which will prove useful to practitioners who wish to derive ET0 estimates with only temperature inputs.
Fluid-mediated carbon release by infiltration of serpentinite dehydration fluids during subduction: insights from thermodynamic models of serpentinite-hosted carbonate rocks
Authors: Menzel Manuel , Garrido Carlos J. , López Sánchez Vizcaíno Vicente
Published: March 2020

Serpentinites can significantly modulate the carbon fluxes in subduction zones because they occasionally host substantial concentrations of carbonate formed during the oceanic stage of subducting oceanic lithosphere (ophicalcite; [1]) or during metasomatic reaction with CO2-bearing fluids at the subduction plate interface (e.g. hybrid carbonate–talc rocks; [2]). At subarc depth, fluid-mediated carbon release from lithologies like serpentinite-hosted carbonates is critical to understand the global carbon balance and magnitude of carbon fluxes from the subducting plate into the deep mantle. However, the solubility of carbon and the open-system metasomatic reactions during fluid-rock interactions in carbonated serpentinites at high P are not fully understood. In line with previous studies of prograde devolatilization [3], newer models show that the carbon release during prograde devolatilization reactions of serpentinite-hosted carbonate rocks is limited even if accounting for the higher carbon solubility of electrolytic fluids compared to molecular fluid models [4]. Therefore, devolatilization reactions driven by infiltration of Atg-serpentinite dehydration fluids into serpentinite-hosted meta-carbonate rocks determines how much carbon in the mantle lithosphere subducts deep into the mantle. Here we present the results of thermodynamic modelling – using the implementation of the DEW aqueous database in Perple_X [5] – to explore subduction fluid compositions and metasomatism of serpentinite-hosted carbonate rocks during prograde and infiltration-driven devolatilization reactions. The chemical system of serpentinite + carbonate is ideal to understand the interplay of changes in fluid composition, pH, bulk chemical modification and mineral assemblage during open-system fluid infiltration metamorphism. Our models provide new insights into the interaction of carbon-bearing subduction fluids with the cold hydrated mantle wedge, and the carbon release from serpentinite-hosted carbonates related to infiltration of serpentinite dehydration fluids at subarc depths. Our results further show that even though high fluid fluxes from serpentinite dehydration will transform meta-ophicalcites and talc-carbonate rocks into carbonate-garnet-clinopyroxene-olivine rocks and carbon-bearing orthopyroxenites, these rocks can subduct carbon beyond subarc depths into the deeper mantle where they may be related to the formation of deep diamonds, carbonatites and kimberlites.

REFERENCES

[1] Menzel et al., 2019, JMG 37, 681– 715.

[2] Spandler et al., 2008, CMP 155, 181-198.

[3] Kerrick & Connolly, 1998, Geology 26, 375-378.

[4] Menzel et al., 2020, EPSL 531.

[5] Connolly & Galvez, 2018, EPSL 501, 90-102.
Study of Land Surface feedback in catalysing the intensity and duration of Heatwave over Indian subcontinent
Authors: Kumar Shashi Gaurav , Goswami Ajanta
Published: March 2020

Extreme heat events are rising in nature over the Indian subcontinent under the stressed environmental conditions. Unprecedented event of extreme heat is threatening our socio-economic and ecosystem. April marks the start of summer with a clear sky; agricultural harvesting exposes the large land surface to solar heating, so the drying up of the surface causing loss of soil moisture and vegetations. Temperature anomalies become high during May and June, signifying possible role play local land-surface-atmosphere feedbacks involving dried soils in driving the heat extreme. Thus, the study of extreme heat and surface feedback process is conducted using a combination of ERA5 reanalysis data, GLDAS Noah Land Surface Model data, satellite-based observations (TRMM and MODIS), and in-situ India Metrological Department datasets. To address the bias present in datasets, we make use of IMD Datasets for bias correction. We use 2m air temperature to define the extreme heat events as per the IMD definition for the heatwave from 2001 to 2019. Parameters like surface net solar and thermal radiation and (also, clear sky) heat flux, total precipitation, land surface temperature, land use type and vegetation cover, soil moisture used to study the details of land surface conditions during the heatwave events. The examination of the above datasets in space-time provided the general view of heatwaves and suggest that late April and early May with clear sky increased net solar radiation started drying up the surface. Late May and early June with a clear sky and positive net solar radiation anomaly with positive heat flux anomaly and lack of soil moisture and rainfall developed local forcing on air temperature that catalyzed the heatwave events in terms of intensity and duration. The above conclusion is supported by the satellite-derived land surface temperature and heat flux. The results obtained establish the link between the local surface feedback and extreme heat events during the summer over the Indian subcontinent and can enhance in a dry environment with the large agricultural field with no standing crop barren land or land with dead or no shrubs over India leaving northern Himalayan part.
Magnetic field within magnetosheath jets during northward and southward interplanetary magnetic field conditions
Authors: Vuorinen Laura , Hietala Heli , Plaschke Ferdinand
Published: March 2020

Downstream of the Earth's quasi-parallel shock, transients with higher earthward velocities than the surrounding magnetosheath plasma are often observed. These transients have been named magnetosheath jets. Due to their high dynamic pressure, jets can cause multiple types of effects when colliding into the magnetopause. Recently, jets have been linked to triggering magnetopause reconnection in case studies by Hietala et al. (2018) and Nykyri et al. (2019). Jets have been proposed to affect magnetopause reconnection in multiple ways. Jets can compress the magnetopause and make it thin enough for reconnection to occur. Jets could also affect the magnetic shear either by indenting the magnetopause or via the magnetic field of the jets themselves. Here we want to study whether the magnetic field of jets can statistically affect magnetopause reconnection. In particular, we are interested in whether jets could enhance reconnection during more quiet northward IMF conditions.

We statistically study the magnetic field within jets in the subsolar magnetosheath using measurements from the five Time History of Events and Macroscale Interactions during Substorms (THEMIS) spacecraft and OMNI solar wind data from 2008–2011. We investigate jets next to the magnetopause and find that the magnetic field within jets is statistically different compared to the non-jet magnetosheath. Our results suggest that during southward IMF, the non-jet magnetosheath magnetic field itself has more variation than the jets. This suggests that jets should have no statistical, neither enhancing nor suppressing, effect on reconnection during southward IMF. However, during northward IMF, the magnetic field within jets is statistically favorable for enhancing magnetic reconnection at the subsolar magnetopause as around 70 % of these jets exhibit southward fields close to the magnetopause.
Observations of greenhouse gas and short-lived pollutants in the Baltimore Washington area: Quantification and mitigation
Authors: Dickerson Russell , Canty Tim , Ren Xinrong , Salawitch Ross , Shepson Paul , Lopez Coto Israel , Whetstone James
Published: March 2020

For the past five years, we have been measuring greenhouse gases CO2, and CH4 along with a suite of pollutants related to photochemical smog (O3, NO2, VOCs, CO) and particulate matter (SO2 (sulfate precursor), & aerosol optical properties) from a research aircraft.  These complement a network of tower-based monitors and provide input to a variety of models used to determine emissions.  Initial findings include identification of landfills and leakage from the natural gas delivery system as major local sources of CH4, as well as substantial upwind sources such as oil and gas operations in the Marcellus shale play.  Quantification of emissions and flux is complicated by uncertainties in background concentrations and mesoscale dynamics.  Comparison of short-lived species has shed light on the efficiency of combustion and pollution control as well as the temperature dependence of emissions.  Ratios of CO:CO2, for example, are consistent with emissions inventories and verify the high efficiency catalytic converters. 
Quantifying NOx emissions from a city and a small country with the TROPOMI and OMI satellite instruments
Authors: Boersma Folkert , Zara Marina , Lorente Alba , Eskes Henk , Krol Maarten
Published: March 2020

The TROPOMI and OMI satellite sensors provide an exciting perspective on the sources, dispersion, and fate of air pollution, and in particular on nitrogen dioxide (NO2). Yet it is still difficult to relate satellite observations of tropospheric NO2 columns to the underlying NOx emissions and their trends. Robust interpretation of satellite data relies on a good understanding of the accuracy and representativeness of the satellite data itself, but also on the relationship between NOx emissions and the observable NO2 amount. This relationship is influences by local chemistry, mixing and dispersion, and by the NO2 amount in the free troposphere. We address these issues via two examples:

(1) Direct estimation of NOx emissions from the satellite-observed build-up of pollution over the city of Paris. After validating NO2 measurements from TROPOMI over the heart of Paris, we analyse the observed build-up of NO2 pollution over the city along with the wind. Over the city, recently emitted NOx has been oxidized to limited degree, facilitating the use of TROPOMI data to directly determine the strength and distribution of emissions from the city. From the observed build-up of NO2 pollution, we find highest NOx emissions on cold weekdays in February 2018, and lowest emissions on warm weekend days in spring 2018.

(2) Trends in NO2 over The Netherlands. We use the QA4ECV OMI NO2 record to investigate trends in tropospheric NO2 columns over Europe, and in particular over The Netherlands between 2005 and 2018. In spite of the differences in metrics and sampling techniques, the NO2 measured in the Dutch atmosphere from space and from the ground follows a trend that is consistent with predictions by emission inventories. Surface NO2 is reduced by 32% in 2018 relative to 2005, OMI NO2 by 35%, and NOx emissions by 32%-38% depending on the inventory. Interestingly, the Dutch surface concentrations reveal an upward trend in the NO2:NO ratio in line with O3 increases. This suggests that the NO2 makes up an increasing share of the NOx in the lower atmosphere as NOx emissions decline. This needs to be accounted for when interpreting NO2 trends as proxy for NOx trends.
Relative timing of mountain glacial maxima and pluvial lake highstands in the Great Basin, western United States
Authors: Laabs Benjamin , Munroe Jeffrey
Published: March 2020

During the last Pleistocene glaciation, dozens of mountain ranges in the Great Basin of the western United States were glaciated and numerous valleys were occupied by pluvial lakes. This unique setting provides an opportunity to reconstruct regional-scale climate change during the last glacial-interglacial transition based on a well-documented record of lacustrine deposits and moraines. Chronologies of water-level changes in pluvial lakes throughout the Great Basin have been developed through decades of effort chiefly involving radiocarbon dating of fossil material recovered from paleoshorelines and sediment cores. Glacial chronologies have been developed more recently through cosmogenic nuclide exposure dating of glacial features in mountains of the northern Great Basin. Here, we resolve the relative timing of mountain glacial maxima and pluvial lake highstands based on an analysis of these chronologies. The moraine record displays evidence of two intervals of near-maximum glacier length, one represented by terminal moraines with cosmogenic nuclide exposure ages 22-19 ka, and another represented by downvalley recessional moraines with exposure ages 18-16 ka. The earlier maximum corresponds to the latter part of the global Last Glacial Maximum, during which lake highstands occurred in the southern Great Basin, whereas many lakes in the northern Great Basin were below their highstand levels. The climate in the northern Great Basin during this interval was apparently cold enough to drive glaciers to their maximum extents but too dry for the expansion of lakes, in contrast to the southern Great Basin where conditions were wetter. The latter glacial maximum was synchronous with lake highstands across much of the Great Basin and to the early part of Heinrich Stadial 1, which featured persistent cooling and shifting precipitation patterns in western North America. Most lake highstands occurred at this time, although some lakes in the extreme northwestern Great Basin reached highstands somewhat later. Widespread lake highstands during the interval 18-16 ka combined with near-maximum glacier lengths suggests a cool and wet climate favoring both glacial and lacustrine maxima, despite rising atmospheric greenhouse gases and summer insolation. Nearly all downvalley moraines in the Great Basin were abandoned by 16 ka, whereas many lakes persisted until 15 ka or later. This pattern suggests a climatic shift at ca. 16 ka to conditions favoring lakes but not glaciers. By the time of the last lake highstands, glaciers had diminished greatly in length and were generally confined to cirques.
Radiative impacts of convective anvil outflow in the Asian monsoon region
Authors: Sullivan Sylvia , Voigt Aiko , Krämer Martina , Miltenberger Annette , Khaykin Sergey , Rolf Christian
Published: March 2020

We investigate the radiative impacts of convectively detrained and in-situ formed ice crystals at uppermost altitudes with high-resolution ICON model runs in the Asian monsoon region. Radiatively, this area should be characterized by persistent longwave warming from thin and ubiquitous anvils and intermittent shortwave cooling from deep but infrequent convective systems. But how do different degrees of sophistication in the ice microphysics schemes modulate this picture? Three days coinciding with the StratoClim field campaign are simulated (6-9 August 2017), using two-moment microphysics, and in-situ ice water content (IWC) values and specific humidity profiles are used for validation. We calculate the shortwave and longwave radiative fluxes associated with IWC between 14 and 17 km over different timescales and examine the role of ambient dryness in anvil base radiative heating. We compare our results with the cloud-resolving Meso-NH simulation of Lee et al. ACP 2019 in which moist and ice layers were identified and tracked through the uppermost troposphere.
Comparison of different regularization schemes for the 1D laterally constrained inversion of seismic surface wave data
Authors: Guillemoteau Julien , Vignoli Giulio , Barreto Jennifer
Published: March 2020

The 1D layered inversion of surface wave dispersion data is a powerful tool to characterize the vertical distribution of S-wave velocity. Its applications span from seismology to geotechnical engineering, going through exploration geophysics. As many others, also this non-linear inverse problem is considerably ill-posed. Thus, in the Tikhonov’s regularization framework, the associated non-uniqueness and instability of the solution with respect to the data and their uncertainty can be tackled by including prior information in the inversion process. However, for the case of the gradient-based deterministic inversion problem, only constraints enforcing smooth spatial variations of the S-velocities have been used, even when blocky targets were expected. This, clearly, generates results that might fit the observed data, but that are often not compatible with other sources of information. On the other hand, probabilistic approaches can be used to properly map the model space; however, they are still very computationally expensive to be used routinely, or to be easily integrated in a multi-physical inversion procedure involving other geophysical methods.

Our goal is to combine computer efficiency, capability of integration with other geophysical methods, and some exhaustiveness regarding the non-uniqueness of the inverse problem. For this, we developed a coherent set of tools for the deterministic inversion of dispersion curves that is capable of applying a quite large spectrum of constraints. This includes, for example, vertically and laterally constrained inversions with different levels and kinds of regularization (sharpness and/or smoothness). In this study, we evaluate the capabilities and the possible limitations of the different regularization approaches on various datasets.
Uncertainties in breakup markers along the Iberian Newfoundland margin: The need for a new North Atlantic plate model
Authors: Causer Annabel , Pérez-Díaz Lucía , Eagles Graeme , Adam Jürgen
Published: March 2020

The Iberian-Newfoundland conjugate margins are one of the most extensively studied non-volcanic rifted margins in the world. In recent years, researchers have focused their efforts at better understanding the earliest stages of continental rifting, often relying heavily on the identification of so-called “break-up features” imaged in seismic profiles or interpreted from potential field data. Along the Iberian-Newfoundland margins, widely used break-up markers include interpretations of old magnetic anomalies from the M-Series, as well as the J-anomaly, believed to mark the occurrence and spatial extent of first oceanic lithosphere. However, uncertainties in the location and interpretation of these features have led to discrepancies between modelled depictions of the palaeopositions of Iberia and Newfoundland during the early Cretaceous as well as the timing of first seafloor spreading between the two. 

Using new seismic data from the Southern Newfoundland Basin (SNB) we are able to illustrate the unsuitability of “break-up” features along the Iberian – Newfoundland Margin for plate kinematic reconstructions. Our data shows that basement associated with the younger M-Series magnetic anomalies is comprised of exhumed mantle and magmatic additions, and most likely represents transitional domains and not true oceanic lithosphere. Magmatic activity in the SNB as early as M4 times (128 Ma), and the presence of SDR packages onlapping onto basement faults suggest that, at this time, plate divergence was still being accommodated by tectonic faulting. Therefore, young M-series anomalies (including the J-anomaly) are not suitable basis on which to reconstruct plate positions during the early stages of continental separation.

We instead follow an alternative modelling approach, not reliant on the identification of extended continental margin features, to robustly constrain North Atlantic tectonics pre-M0 (~121 Ma) times. We do this by using seafloor spreading data and a statistically robust inversion method as the basis for a number of purpose built two-plate models for Africa, Iberia, Eurasia, Greenland and North America, with quantified uncertainties. Together, these models will provide an invaluable framework within to study the evolution of the extended continental margins immediately prior to and during continental separation.

 

 

 

 

 
The Effect of Variable Solar Wind Conditions on the Bow Shock Structure and its Ability to Generate Energetic Ions
Authors: Kucharek Harald , Young Matthew , Lugaz Noe , Farrugia Charles , Schwartz Steven , Trattner Karlheinz
Published: March 2020

Turbulent fluctuations in the magnetic field and in the bulk plasma parameters of the solar wind have important effects on the propagation and evolution of energetic particles throughout the heliosphere and on the coupling of the solar wind to the Earth's magnetosphere. At the shock the solar wind kinetic energy is converted into downstream plasma heating, ion reflection and acceleration. Changes in upstream plasma conditions can result in changes in the dynamics of the shock, its structure, and the suprathermal ion population it generates. These upstream variations can be due to transients, interplanetary shocks, and other discontinuities. They can also result from nonlinear interactions, causing an intermittent energy dissipation and leading to possible currents sheet structures. A number of these events can be found in observations from STEREO (for interplanetary traveling shocks) and CLUSTER/MMS (for the Earth’s bow shock) in the magnetosheath. 

We performed 3D-hybrid simulations to study the effects of spatially confined disturbances, such as density enhancements, depletions, and current layers/sheets and studied the shock dynamics, and the energetic particle release at various distances from the bow shock. The results of these simulations are then discussed in terms of multi-spacecraft observations in the magnetosheath at various scales.  The results show that shock reformation is highly impacted by density depressions/enhancements and so is the generation of waves and suprathermal ions. Also, upstream solar wind variations can alter the shock properties considerably at the various virtual spacecraft in the simulations.
Spatio-temporal variations of surface creep along the Hazar-Palu Segment of the East Anatolian Fault, Turkey
Authors: Dogan Ugur , Ergintav Semih , Ozarpaci Seda , Ozdemir Alpay , Erkoç M. Hilmi , Yigitoglu Alper , Ayruk Efe T. , Çakir Ziyadin , Karabulut Hayrullah , Bayram Bulent , Zabci Cengiz , Bilham Roger
Published: March 2020

Aseismic creep is detected and started to be monitored along the 100 km-long Palu-Hazar Segment of the Eastern Anatolian Fault (EAF) in Turkey, a major plate boundary between Anatolia and Arabia. We used creepmeters, InSAR, GPS, and seismic observations to document the extent and magnitude of this motion in order to increase our knowledge on the spatiotemporal variation of creep along the EAF, its relationship with the lithology and tectonic structures, and the stress change on the neighboring fault segments. Until now, we observed the region with continuous GPS and survey GPS measurements with near (~ 0.1- 4 km to the fault) and far-field (~25 – 225 km from the fault) stations to determine the depth of the creep zone and its velocity along the EAF. We processed 6 years (2014 – 2019) of continuous and 7 campaign (2015 – 2019) GPS data with GAMIT/GLOBK software. With elastic models, we determined a creep rate that reaches about 5 ± 0.3 mm/yr from GPS observations (50% of secular velocity). In addition to surface control of the creeping zone, we analyzed the deformations, by using three Terrestrial Laser Scanner (TLS) survey, in the Palu railway tunnel that crosses the fault where the walls of the tunnel have been offset by 15 ± 2 mm since the construction in the middle of the last century. Also, two creepmeters were installed inside the tunnel and transient creep anomalies are detected. These results are correlated with seismic and InSAR data (This study is supported by TUBITAK 1001 projects 114Y250 and 118Y450).

Keywords: Hazar-Palu, Creep, East Anatolian Fault, Earthquake, GPS, InSAR, TLS
Impacts of technically modified plant pits on water balance dynamics and tree vitality in urban environments
Authors: Nofz Ines A. , Kleinschmidt Volker , Becker Joscha N. , Eschenbach Annette
Published: March 2020

Trees as essential components of green urban structures are of crucial importance for the regulation of the urban climate and human wellbeing. Despite this, the currently rising demand for living space and infrastructure causes an increase in the share of sealed and compacted soils. These trends directly affect soil-plant interactions in urban environments. The synergy of the increasing land use pressure and changing climatic conditions worsen the site and growth conditions and thus the vitality for young and mature trees. A possible adaptation strategy is the transformation of plant pits into water reservoirs combining the discharge of excess water with impermeable sole materials and substrates that optimise the water conductivity and storage capacity. The corresponding aim of this study is the quantification of the effects of the water balance dynamic in the rooting zone on the vitality of young trees at highly sealed sites in the city of Hamburg. The two main questions are 1) Do technically modified plant pits reduce summerly drought stress inside the rooting zone and thus improve the root water uptake and tree vitality?, and 2) Does excess water after high rainfall limit the gas exchange and thus the root growth? To answer these questions, we selected two different sites, one residential area and one pedestrian zone, which differ regarding the type of excess water discharge. Overall, two technically modified plant pit variants will be compared with generally constructed variants. Each site will be characterized by soil physical and chemical parameters. Additionally, each plant pit is equipped with TDR- and water tension probes for a continuous monitoring of the soil water balance and O2 as well as CO2 probes for monitoring the gas household. Rhizotrones and dendrometers in combination with Δ13C isotope analysis and stomatal resistance will help to investigate the tree vitality. The data will be used for modelling local water balance dynamics under expected climatic scenarios and for evaluating the different plant pit variants. Development as well as dimensioning recommendations for prospective plant pit constructions, improving the soil-plant interaction, will be derived.
North Atlantic deep water sources and export since MIS3: implications from Nd isotopes
Authors: Blaser Patrick , Pöppelmeier Frerk , Frank Martin , Gutjahr Marcus , Lippold Jörg
Published: March 2020

Deep water formation in the North Atlantic represents an integral link between the atmosphere, cryosphere, and the deep ocean: heat loss from warm surface waters supplies moisture to the high latitudes and their subsequent sinking ventilates the deep ocean and sequesters greenhouse gases from the atmosphere. This moisture supply supported the formation of immense ice sheets in the region during the last glacial, which in turn affected climate. While many studies have improved our understanding of these processes for past glacials, a comprehensive picture including the significance and variation of deep water export from the Nordic Seas is still missing. Furthermore, recent observations suggested the export of a previously unknown bottom water mass from the glacial subpolar North Atlantic.

In this study we investigate the distribution and sourcing of water masses in the subpolar North Atlantic since MIS3 with the help of authigenic Nd isotopes. This method benefits from the large heterogeneity in Nd isotopic compositions of source rocks in this region, but the post-depositional dissolution of detritus within the sediments can also impede interpretations of individual records. We thus compare several Nd isotope records from the subpolar North Atlantic and Nordic Seas in order to define distinct deep water mass end members and estimate their prevalence and mixing in the subpolar North Atlantic during the last 30 ka. Our observations suggest that Nordic Seas deep water overflowing the Greenland-Scotland Ridge during MIS2 reached into the deep subpolar North Atlantic. Furthermore, its spatial distribution implies that overflow across Denmark Strait into the Irminger Basin was more pronounced than overflow into the Iceland Basin further south. The hydrographic configuration during the Last Glacial Maximum thus appears to have been more complex and more similar to today than previously thought.
Millennial solar irradiance forcing (Hallstatt’s cycle) in the terrestrial temperature variations
Authors: Zharkova Valentina , Shepherd Simon , Popova Elena
Published: March 2020

In this paper we explore the millennial oscillations (or Hallstatt cycle) of the baseline solar magnetic field, total solar irradiance and baseline terrestrial temperature detected from Principal Component Analysis of the observed solar background magnetic field. We confirm the existence of these oscillations with a period of 2100-2200 years with the similar oscillations detected in carbon 14C isotope abundances and with wavelet analysis of solar irradiance in the past 12 millennia indicating the presence of this  millennial period among a few others. We also test again the idea expressed in our paper Zharkova et al, 2019 that solar inertial motion (SIM) can cause these millennial variations because of a change of the distance between the Sun and Earth. In this paper we use the S-E distance derived from the current JPL ephemeris, finding that currently starting from the Maunder minimum the Sun-Earth  distance is reducing by 0.00025 au per 100 years, or by 0.0025 au per 1000 years.. We present the estimation of variations of solar irradiance caused by this variation of the S-E distance caused by solar inertial motion (SIM) demonstrating these variations to be closely comparable with the observed variations of the solar irradiance measured by the SATIRE payload. We also estimate the baseline temperature variations since Maunder Minimum caused by the increase of solar irradiance caused by the recovery from grand solar minimum and by reduction of the S-E distance caused by  SIM. These estimations show that the Sun will still continue moving towards the Earth in the next 700 years that will result in the increase of the baseline terrestrial temperature by up to 2.5◦C in 2700. These variations of solar irradiance will be over-imposed by the variations of solar activity of 11 cycles and the two grand solar minima occurring in 2020-2053 and 2370-2415 caused by the double dynamo actions inside the Sun.
Time-Domain Reflectometry Observations of Meltwater Percolation and Retention in the Firn Layer of the Greenland Ice Sheet
Authors: Samimi Samira , Marshall Shawn , McFerrin Michael
Published: March 2020

Mass loss from the Greenland Ice Sheet has increased in recent decades due to significant increases in surface melt and runoff. The fraction of summer melt retains as a liquid water or refreezes as it percolates into the underlying cold firn, acting as a buffer to the summer runoff. There are challenges to quantifying both infiltration and refreezing of meltwater in this complex heterogeneous cold firn and to understand the spatial variability of these processes. In this study we present continuous in situ measurements of near-surface temperature and dielectric permittivity, a proxy for volumetric water content, using TDR (Time Domain Reflectometry) methods in the percolation zone of the southern Greenland Ice Sheet. We established two observation sites near Dye 2 in April, 2016, excavating firn pits to depths of 2.2 and 5.3 m. The two sites are 650 m apart to quantify the percolation and refreezing of meltwater and to observe the spatial variability of these processes through summer 2016. Thermistor arrays were used to track the thermal signature of meltwater penetration in firn, through the effects of latent heat release when meltwater refreezes. Through the addition of TDR probes, we attempt to directly quantify meltwater volume as well as hydraulic conductivity of the near-surface snow and firn. An automatic weather station (AWS) configured for surface energy balance monitoring was also installed. AWS data were used to calculate the surface energy balance and model meltwater production. The melting front, characterized by 0°C conditions and direct evidence of liquid water, penetrated to a depth of between 1.8 and 2.1 m in summer 2016; at depths of 2.1 m and greater, temperatures remained below 0°C, there was no evidence of abrupt warming (i.e. latent heat release), and dielectric permittivities remained at their background levels. Meltwater penetrated several thick ice layers, but not until temperatures reached the melting point at these depths, implying that ice layers may transition to a permeable ‘slush’ layer, given enough conductive and latent heating, permitting progressive penetration of meltwater to depth. Firn temperatures (sub-zero conditions below ~2 m) appear to have been the main barrier to deep penetration of meltwater during summer 2016.
Bringing light into the darkness  – Chernozem evolution in Central Germany clarified by single-grain luminescence data
Authors: Reimann Tony , van Meer Mike , von Suchodoletz Hans
Published: March 2020

Chernozems are among the most productive soils in the world, as they unite several favorable factors such as high fertility, favorable pH, a granular structure and high moisture retention capacity. Because of that they are typically characterized by a high agrarian value and often provide long records of intensive human land-use that reach back several millennia. However, despite their high relevance for soil sciences and geoarchaeology, many important aspects regarding chernozem formation – e.g. the question whether natural or human factors were more important - are still poorly understood (Eckmeier et al., 2007). One important drawback in this context is the lack of powerful methods to get grip on timing and rates of chernozem evolution.

Recently it has been suggested that the nexus of soil mixing and soil evolution can be clarified through single-grain luminescence analyses (Reimann et al., 2017). In this study we apply the suggested protocol for the first time to two chernozem profiles in Central Germany that were buried by the Late Bronze Age burial mound Bornhöck ca. 3.8 ka ago. Our goals are (i) to test the newly developed luminescence methodology, and if successful, (ii) to date the start of chernozem formation and degradation and (iii) to quantify soil formation rates through time.

First results suggest that chernozem formation of the two profiles started most likely in the early Holocene and ceased between ca. 5.5 and 5.0 ka ago. Furthermore, our data demonstrate that chernozem formation was characterized by very intensive vertical soil mixing, most likely related to intensive bioturbation. In a next step we will calculate corresponding biological soil mixing rates to further detail chernozem evolution. Already at this stage of research, however, we can confidently conclude that we are able to trace key processes of chernozem formation through the analyses of single-grain luminescence data.

 

References:

- Eckmeier, E., Gerlach, R., Gehrt, E. & Schmidt, M.W.I.  (2007). Pedogenesis of Chernozems in Central Europe - A review. Geoderma 139, 288-299.

- Reimann, T., Román-Sánchez, A., Vanwalleghem, T. & Wallinga, J. (2017). Getting a grip on soil reworking–Single-grain feldspar luminescence as a novel tool to quantify soil reworking rates. Quaternary Geochronology 42, 1-14.

 
Geobites: Down-to-earth summaries of new geoscience research for a broad audience
Authors: Shobe Charles M. , Vrouwenvelder Kristina T. , Moerchen Margaret , Giampoala Matthew
Published: March 2020

The academic literature is the primary source for current developments in science. But limited access to journals as well as the widespread use of technical jargon can inhibit the dissemination of new knowledge to scientists from other fields and to non-scientists. These serve as major barriers to interdisciplinary collaboration with non-geoscientists and to efforts to further public understanding of geoscience research. Meanwhile, traditional science news focuses on topics of obvious interest to the public, such as geohazards or climate change. While engaging with non-geoscientists on these topics is important, the majority of geoscience research lacks a mechanism for generating public interest.

“Bites” sites, originally introduced in the astronomy community, are blogs dedicated to communicating new developments in science to a broad audience. Each bite is an engaging, short (400-700 word) summary that explains an exciting new scientific paper and discusses its importance in the field. Bites are typically written by graduate students and other early career scientists about recently published articles that have not been picked up by more traditional science news outlets. These sites serve three key purposes: 1) to keep the interested public – especially university students who may consider careers in geoscience – up to date with recent developments in the field, 2) to generate attention for new work that traditional science media outlets may miss, and 3) to give early career scientists practice with public-facing writing and editing, which are critical skills both within and beyond academia.

Here we present the new site Geobites, targeted at communicating new geoscience (broadly defined) research to the public. We show examples of articles on Geobites, diagram the structure of a good article, present initial site analytics, and solicit feedback from the geoscience communication community.
A mechanism to explain the timing of glaciations related to orogenic episodes
Authors: Joshi Manoj , Mills Benjamin
Published: March 2020

Over very long timescales, mountain building or orogenesis is associated with increased weathering, the drawdown of atmospheric CO2, and global cooling. Considering the Phanerozoic glaciation in particular, a multimillion‐year delay appears to exist between peaks in low‐latitude mountain uplift and the maximum extent of glaciation, implying a complex causal relationship between them. We show, using a combination of physical climate/circulation modelling and geochemical modelling approaches, that global silicate weathering can be modulated by orogeny in three distinct phases. High, young mountain ranges experience preferential precipitation and the highest erosion. As mountain ranges denude, precipitation decreases, but runoff temperature rises, sharply increasing chemical weathering potential and CO2 drawdown. In the final phase, erosion and weathering are throttled by flatter topography. We hypothesise that orogeny acts as a capacitor in the climate system, granting the potential for intense transient CO2 drawdown when mountain ranges are denuded. Intriguingly, depending on the future evolution of the Tibetan Plateau, the mechanism suggests such a scenario potentially happening 10–50 × 106 years in the future.
A Hybrid PCG- Bat Algorithm for 2D Gravity Inversion: Applications for Ore Deposits Exploration and Interpretation of Sedimentary Basins
Authors: Abdrabou Mohamed , Abdelazeem Maha , Gobashy Mohamed
Published: March 2020

Geophysical data such as gravity data can be inverted to get a subsurface image, which depicts the subsurface distribution of physical property. Consequently, inversion of geophysical data has an effective role for interpreting measured geophysical anomalies in hydrocarbons and mineral applications. Interest about ore deposits exploration and sedimentary basins interpretation is associated with their economic importance. The presence of sedimentary basins gives lower amplitude of gravity anomalies with negative signals, due to the negative density contrast as these sedimentary basins have lower density than that of the neighboring basement rocks. In prospecting ore deposits, studying the spatial distributions of densities in the subsurface is essential of significance.Two dimensional forward modelling strategy can be done via locating the rectangular cells with fixed size directly underneath the location of the observed data points using regular grid discretization. Density vector of the subsurface rectangular cells are obtained via solving the 2D gravity inverse problem by optimizing an objective function (i.e., the differences between observed and inverted residual gravity data sets). In this work, a hybrid algorithm merging a bat (BAT) algorithm with the preconditioned conjugate gradient (PCG) method is suggested as a mean for inverting surface gravity anomalies to obtain the density distribution in the subsurface. Like the hybrid, minimization algorithm has the capability to make use of the advantages of both two techniques. In this hybrid algorithm, the BAT algorithm was utilized to construct an initial solution for the PCG technique. The BAT optimizer acts as a rapid build-up of the model, whereas the second modifies the finer model approximated solution. This modern algorithm was firstly applied on a free-noise synthetic data and to a noisy data with three different levels of random noise, and good results obtained through the inversion. The validity and applicability of our algorithm are applied to real residual gravity anomalies across the San Jacinto graben in southern California, USA, and Sierra Mayor - Sierra Pinta graben, USA and prospecting of the Poshi Cu-Ni deposits, Xinjiang, northwest China. The obtained results are in excellent accordance with those produced by researchers in the published literature.

 

Keywords: Gravity data, 2D Inversion, BAT algorithm, Preconditioned Conjugate Gradient, Sedimentary Basins.