bluuebunny/crossref_metadata_2025 huggingface dataset:
Imaging the past and present Owen transform fault: preliminary results from the VARUNA seismic cruise
Authors: Janin Alexandre , Rodriguez Mathieu , Chamot-Rooke Nicolas , Rabaute Alain , Delescluse Matthias , Dyment Jérôme , Fournier Marc , Huchon Philippe , Olive Jean-Arthur , Vigny Christophe
Published: March 2020

The Owen transform fault in the northwest Indian Ocean is a >300 km-long active structure that constitutes the active plate boundary between Somalia and India. The first-order fault geometry was reached in the Early Miocene when the Carlsberg Ridge propagated westward into the African plate to open the Gulf of Aden. Presently, it accommodates ~23 mm/yr of left-lateral strike-slip motion between the Sheba and Carlsberg spreading centers.  The fault was recently surveyed in the Spring of 2019 during the VARUNA and CARLMAG cruises on BHO Beautemps-Beaupré, an oceanographic ship operated by the French Navy. Along with geophysical measurements (multibeam bathymetry, gravity and magnetic fields) a set of high-resolution seismic lines (> 5000 km) was acquired across both the active and fossil traces of the fault between 9°N and 15°N. The area is largely buried under the distal Indus turbiditic sediments and therefore offers a fairly unique continuous high-resolution stratigraphic record of past regional tectonic events. Here we present the first multibeam map of the Owen Transform system. A remarkable transpressive ridge borders the active trace of the fault along most of its length. At the intersection with the Carlsberg Ridge, the Owen Transform marks an 11° bend characterized by ~1200 m of seafloor uplift.  Our preliminary interpretation of the seismic lines brings to light the key unconformities related to Global Plate Reorganization Events. Off the main fault, new data reveal the magmatic nature of the Varuna Bank and similar partially buried highs. These have likely grown in the very early stage of formation of the oceanic crust carrying them, although tectonic emplacement cannot be completely ruled out. Some of the highs show internal structure, which can be interpreted either as carbonate caps or layered volcanic formations. This dataset, combined with previous cruises, offers unprecedented coverage of a 1500 km-long transform corridor along the Arabia-India and India-Somalia plate boundaries.
Status of IGS repro3 activities at GFZ
Authors: Männel Benjamin , Brandt Andre , Bradke Markus , Brack Andreas , Sakic Pierre , Nischan Thomas
Published: March 2020

Based on a large network of continuously operated GNSS tracking stations, the International GNSS Service (IGS) has a valuable contribution to the realization of the International Terrestrial Reference System. In order to provide the highest accurate and consistent solution, the IGS refined the strategy and the set of associated models for the ongoing third reprocessing campaign. Beyond updated background models, a major improvement is the combined reprocessing of three GNSS, namely GPS, GLONASS, and Galileo. Furthermore, signal-specific receiving antenna calibrations for Galileo and scale-free transmission phase center positions are applied. These modifications will allow exciting new investigations based on the delivered products. Hosting an IGS Analysis Center and an Analysis Center of the IGS Tide Gauge Benchmark Monitoring Project (TIGA), GFZ will contribute with two solutions to the IGS reprocessing efforts.

In this contribution, we will present the first outcomes of the ongoing preparations and preliminary results of the GFZ reprocessing activities. In the first part, we will present selected results of dedicated tests with a special focus on correction models and parametrization options. Secondly, we will present the initial results of the AC solution as a basis to discuss also further applications of the derived products (e.g., orbits, Earth rotation parameters). Finally, the first results of our TIGA-related reprocessing will be presented which are based on the previously discussed orbits and satellite clocks.
Geographical Evolution of Agricultural Production in China and Its Effects on Water Stress, Economy, and the Environment: The Virtual Water Perspective
Authors: Sun Shikun , Yin Yali , Wu Pute , Wang Yubao
Published: March 2020

Agricultural production is accompanied by a large amount of water consumption, nonpoint source pollution, and greenhouse gas emissions. However, the comprehensive and quantitative analysis of associated impacts on regional water, the environment, and the economy caused by variations in agricultural distribution is insufficient. This paper evaluates the evolution of grain production distribution and its effects on water resources, the economy, and the environment in China by using virtual water theory. The results show that the grain production area located in northern China is characterized by scarce water resources and a less developed economy. Due to the imbalance between grain supply and demand, virtual water embedded in grain will transfer among regions. These flows have formed a pattern where virtual water transfers from the water‐scarce northern region to the water‐rich southern region. Evolution of grain production distribution changes the spatial pattern of grain production and consumption, and it exacerbates water resource pressure, the gray water footprint, and greenhouse gas emissions in the area that exports grain virtual water. The gray water footprint and carbon emissions in the grain export area increased by 10.66% and 31.06% during the study period, respectively. Meanwhile, the distribution of regional grain production influences the allocation of water resources in agriculture and other industries. Due to the difference between the economic benefits created by industry and agriculture, grain virtual water flow will have effects on the regional economic development.
The research of Meinong earthquake induced hydrological anomalies and increased vertical permeability in southwestern Taiwan
Authors: Lin Yan-Yao , Wang Shih-Jung , Lai Wen-Chi
Published: March 2020

Hydrological anomalies induced by the earthquakes are valuable research data to understand the hydrogeology structure. At the same time, a complete hydrogeological data is the key to the study of earthquake hydrology. In this research, we collected the anomalous hydrological data after the Mw 6.4 2016 Meinong Earthquake in Taiwan. The main purpose is to know the mechanism of hydrological changes triggered by earthquake and understand the local hydrogeological characteristics in the southern Taiwan.

From the distribution of the groundwater level change in the same location but different depths of aquifer, as well as the location of the rupture and liquefaction, it could be found that the co-seismic groundwater level change is large in Chianan Plain in the northwest of the epicenter and accompanied with a lot of ruptures and liquefactions located along the Hsinhua Fault. However, the observations in several wells around the Hsinhua Fault show a different water level change pattern compared with the other wells in Chianan Plain. Actually, these wells show that the co-seismic groundwater level decreases in the deep aquifer and increase in the shallow aquifer. It is shown that the Meinong Earthquake may enhance the connectivity between different aquifers near the fault zone and produce an increased vertical pressure gradient. The anomalous hydrological phenomenon also reflected in the river flow. Based on the river flow data we collected from five stations in the Zengwun River watershed, the river flow at two stations in the upstream dose not change after earthquake. There is a little increase at the midstream station. However, a large river flow increase is observed at the downstream station. After excluding the influence of rainfall, we think that the large amount of anomalous flow is caused by the rise of the co-seismic groundwater level between the middle and downstream sections, and a large amount of liquefaction in this area can prove this hypothesis.

The hypothesis of connectivity changes between different aquifers can be verified by analyzing the tidal response of different aquifers. Many studies have used the tide analysis to obtain the aquifer permeability and compressibility, and compared the changes in the analysis results before and after the earthquake. We think that if different aquifers are vertically connected after earthquake, the tidal analysis results should show a consistent permeability. Tidal analysis is executing now and the results will be provided at conference.
Re-assessing extreme sea level events through interplay of tides and storm surges
Authors: Outten Stephen , Wolf Tobias , Mangini Fabio , Chen Linling , Nilsen Jan Even
Published: March 2020

Flooding events pose an ever increasing threat in a warming world. Safety standards for buildings and infrastructure are often based on past observations of local sea level, as measured by tide gauges and remote sensing systems. However, sea level at a given location is not an isolated property and is determined by a combination of factors. For extreme sea level events, there are two factors that of particular importance: the astronomical tide, and storm surges. In this work, we analysed measurements from 21 stations in the Norwegian tide gauge network, disentangling the factors contributing to the previously observed extreme events.

By separating the observed sea level into a tidal component and a storm surge component, we found that in many cases the observed extreme sea level events were caused by an extreme storm surge coinciding with only a moderate tide, or an extreme tide coinciding with only a moderate storm surge. This raises the possibility of a ‘super-flooding’ event, where an extreme storm surge may occur with an extreme tide. Even in the short records examined in this study (less than 40 years), the combination of the highest observed tide with the highest observed storm surge would greatly exceed in the 1000-year return level event at many locations. This is often used as a national standard for critical infrastructure.  

We further complement the work by analysing the storm tracks close to Norway. By relating the storm surges with the individual storms giving rise to them, we found that many storm surges during extreme sea level events were related to cyclones of only moderate intensity. Combined with the previous findings, this work suggests the need to assess extreme sea level return values for future construction and infrastructure planning as the result of a multi-variable system. This is in contrast to basing such assessments on the single variable of observed sea level as it is done today.
Evaluation of Sentinel-3 SRAL SAR Altimetry over Recently Constructed Global Reservoirs
Authors: Zhang Xingxing , jiang Liguang , Yao Zhijun , Liu Zhaofei , Wang Rui , Liu Jun , Bauer-Gottwein Peter
Published: March 2020

Satellite radar altimetry is increasingly being used for hydrological studies. However, it is still challenging to deliver high quality data over inland water bodies, i.e. lakes, rivers and reservoirs. One of the reasons is that the positioning of the range window is difficult due to highly variable topography and water surface elevation. To address this issue, Sentinel-3, the first SAR altimeter operating at global scale, is configured with a new on-board tracking system, i.e. open-loop mode. An open-loop tracking system can position the range window very efficiently based on a priori surface elevation stored on-board. In this context, a suitable a priori surface elevation of inland water bodies is very important.

Sentinel-3 is operating based on a pseudo-DEM controlled through the Open-Loop Tracking Command (OLTC).  The current OLTC V5 (operated after March 2019) is generated based on an inland water mask and Altimeter corrected Elevations (ACE-2), which is created using multi-mission Satellite Radar Altimetry from 1994-2005 in combination with the Shuttle Radar Topography Mission (SRTM). However, OLTC V5 still misses some inland water bodies and contains some incorrect surface elevations, especially over newly built reservoirs, where the difference between water surface elevation and ACE-2 can exceed 100m.

In this study, a comprehensive evaluation of Sentinel-3A (S3A) is conducted at 26 globally-distributed recently constructed large reservoirs. The results show that S3A fails to deliver useful data over most new reservoirs in open loop due to the incorrect a priori elevations stored in OLTC V5. On the contrary, S3A closed-loop (operated before March 2019) can deliver useful data in many cases.

To improve the OLTC table, we propose two approaches. The first one is to use dam height to correct the a priori surface elevation, which is relevant for very recently completed dams or dams under construction. The other is to use water surface elevation from Cryosat-2 to update the OLTC table. The approaches are demonstrated for reservoirs located on the Lancang and Nu rivers in the Southwest of China. The updated OLTC table will help exploit the Sentinel-3 radar altimetry mission to its full potential, enabling it to correctly track water surface elevation in a larger number of water bodies.
Study on multiple rainfall data applied to debris flow warning in Taiwan
Authors: Zeng Yi-Chao , Jan Chyan-Deng , Lin Mu-Jung , Wang Ji-Shang , Yin Hsiao-Yuan , Kuo Li-Hsing
Published: March 2020

Due to climate change, precipitation characteristics have been significantly variation and rainfall patterns are presented more concentrated, high-intensity and long-duration trend in the past two decades. Catastrophic debris-flow disaster threaten lives and property of residents. For mitigation impact of debris-flow, SWCB (Soil and Water Conservation Bureau, Taiwan) has had a leading role in sponsoring debris-flow research and developing a rainfall-based debris-flow warning model. Early warning criteria for debris-flow triggered are also determined depending on the historical rainfall data, and the observational data of rain-gauge are adopted to issue debris-flow warning. However, application of rain-gauge rainfall data has some disadvantages such as low density in mountain area, observation failure to properly represent actual rainfall condition, and data transmission likely interrupted during heavy rainfall or Typhoon. In order to improve the efficiency of debris-flow warning system, two types of gridded precipitation are analyzed and discussed in this study, which are the spatial interpolation rainfall of rain-gauge and the radar-estimated rainfall (QPESUMS). For comparison the differents of multiple rainfall data mentioned above with rain-guage, the third quartile is firstly applied to calculate the regional representative rainfall from grid cells within warning issued area. The results show that the spatial interpolation rainfall underestimates the rainfall intensity and cumulative rainfall owing to the influence of complex topography. By contrast, the radar-estimated rainfall has the advantage in comprehension of the rainfall spatial variability and provide a more complete spatial coverage. Besides, for assessing the appropriate and feasibility of multiple rainfall data applied to debris flow warning, the disaster–capture ratio has been proposed which is defined as the number of debris-flow hazards after issuing warning divided by total number of debris- flow hazards. According to analyis results of historical disaster records from 2012 to 2016, the disaster–capture ratio are 47.6%, 38.1% and 61.9% as warning issued refer to rain gauge, the spatial interpolation rainfall and the radar-estimated rainfall respectively. By the aforementioned process, we realize that the application of radar-estimated rainfall to debris flow warning is obviously increasing efficiency of debris-flow warning ,and gives assistance for reducing uncertainty of rainfall observational data, especially in mountain area.
Comparison of MK-PRISM according to horizontal resolution in South Korea
Authors: Kim Maeng-Ki , Sang Jeong , Yun Ji-hyun , Oh Ji-Seon
Published: March 2020

In this study, we produced grid climate data sets of 1km×1km and 5km×5km horizontal resolutions based on MK (Modified Korean)-PRISM (Parameter-elevation Regressions on Independent Slopes Model), a statistical method that can estimate grid data of horizontal high-resolution using observational station data in Korea. To compare the MK-PRISM performance according to resolution, RMSEs of 1km resolution data and 5km resolution data were calculated and analyzed. The RMSEs of the two data sets were similar, but the results classified according to the elevation were different. The 1km high resolution estimated data was shown to better reflect the impact of the terrain for the daily mean temperature and daily maximum temperature, whereas the difference between the two data sets for daily minimum temperature was not statistically significant at each elevation. Furthermore, we also divided the temperature data into 9-classes based on the observed temperatures, and then compared the estimated performance of the two data sets according to elevation. For the low temperature group, performance of the 1 km resolution data at high elevations outperformed that of the 5 km resolution data, regardless of the season. In addition, we have verified the improved PRIDE (PRism based Dynamic downscaling Error correction) model, which can produce future high-resolution scenarios data using the results of RCM and MK-PRISM.
Legacy effects from historical environmental changes dominate future terrestrial carbon uptake
Authors: Krause Andreas , Arneth Almut , Rammig Anja
Published: March 2020

The carbon balance of terrestrial ecosystems is determined by environmental drivers (chiefly related to climate and land use) which interact with each other and change over time. In particular, ecosystems are presently still affected by past environmental changes because they have not yet reached equilibrium with their environment. However, the magnitude and drivers of this legacy effect for the upcoming decades are still unclear. Here, we use the dynamic global vegetation model LPJ-GUESS to calculate the effects of historical (1850-2015) and future (2015-2099, exemplarily for the high emission/moderate deforestation scenario SSP5-8.5) environmental changes on historical and future terrestrial carbon cycling and to quantify the contributions of the following environmental drivers: climate change, CO2 fertilization, agricultural expansion, shifting cultivation frequency, wood harvest, nitrogen deposition, and nitrogen fertilization.

According to our simulations, the land represented a cumulative net carbon source (-154 GtC) over the historical period mainly due to deforestation, wood harvest, and negative climate change impacts partly offset by carbon uptake via increased CO2 levels and nitrogen input. In contrast, the land is simulated to act as a net carbon sink (+118 GtC) over the 21st century. This is mostly a result of historical environmental changes as ecosystems still adapt to present-day CO2 and nitrogen availability as well as long-term vegetation regrowth following agricultural abandonment and wood harvest. The net impact of future environmental changes on future carbon cycling is much smaller because effects from individual environmental drivers largely compensate. Historical environmental changes dominate future terrestrial carbon cycling at least until mid-century when legacy effects gradually diminish and future environmental changes start to trigger carbon accumulation. Our results suggest that legacy effects persist even many decades after environmental changes occurred and need to be considered when interpreting alterations of the terrestrial carbon cycle.
A spatial covariance model for GRACE and GRACE-FO terrestrial water storage data
Authors: Thomas Maik , Boergens Eva , Dobslaw Henryk , Dill Robert , Dahle Christoph , Flechtner Frank
Published: March 2020

Gridded terrestrial water storage (TWS) observed by GRACE or GRACE-FO typically show a spatial error structure that is anisotropic (direction depending), non-homogeneous (latitude depending), and non-stationary (time depending).

We will introduce a new covariance model characterizing this error behavior analytically with a direction depending Bessel function of the first kind. The anisotropy of this function is governed by a shape parameter allowing for longer correlation lengths in longitudinal than in latitudinal direction. The wave-effect of the Bessel function allows us to account for the residuals of the GRACE striping errors. Both size as well as shape parameters of the Bessel function vary smoothly with latitude. These variations are implemented via even Legendre polynomials. The non-stationarity of the covariance is modeled with time-varying point variances. The validity of this covariance model on the sphere was thoroughly tested with a Monte-Carlo approach.

First, we apply this covariance model to 5 years of simulated GRACE data (Flechtner et al., 2016) where true errors are readily available from the differences of the synthetic input and the finally recovered gravity fields. For the 50 largest discharge basins, we obtain more realistic time series uncertainties than from propagating the formal errors associated with the Stokes coefficients. For smaller basins, however, the covariance model tends to provide overly pessimistic uncertainty estimates.

Second, the model is adapted to real GRACE and GRACE-FO data to obtain realistic error covariance information for arbitrarily shaped basins from globally gridded error information. We will show the current plans to update GFZ’s GravIS portal (http://gravis.gfz-potsdam.de/home) so that area- and time-dependent error information which is critically important for the assimilation of GRACE-based TWS data into numerical models will become readily available to the user community.
The effect of insect disturbance on forest carbon flux: a multisite analysis
Authors: Chen Lingle
Published: March 2020

Insect outbreaks have a substantial effect on forest carbon cycle, including turning forests from carbon sink to carbon source. However, there is still lack of evaluation of the impact of insect disturbance on forests carbon cycle across different forest types at the global scale. Hence, we conducted a multi-site analysis to compare ecosystem CO2 fluxes’ change after an insect outbreak by compiling flux data from the literature or flux database. The final database consists of 21 site-years of eddy covariance data from 17 forest sites among diversity of forest types, namely temperate forest, mangrove, larch forest, etc. Our research showed that insect outbreak had significant negative effects on GEP that GEP reduces -186 gCm-2y-1 on average, as well as NEP reducing -146 gCm-2y-1 while had no significant positive effect on Re. Additionally, similar conclusion was gained when analyzing the recovery procedure that GEP increases with time at the slope of 67.6 gCm-2y-2 and NEP increases at slightly lower rate of 49.2 gCm-2y-2. But there is no evidence that Re will increase. As insects cause more severe damage to forests, all three carbon variables share negative correlation that GEP drops at the slope of -6.7 gCm-2y-1 and NEP also decreases in relatively similar rate at 66.3 gCm-2y-1 with Re decreasing by -3.4 gCm-2y-1. Also, it was found that girdling experiments has different impact on carbon budget from normal insect outbreaks while drought could dampen the damage to GEP followed with a greater recovery rate.
GIS-based Landslide Susceptibility Mapping Using Logistic Regression Analysis: A Case study in the Kadernath valley, Central Himalaya.
Authors: Das Suman
Published: March 2020

Himalayan Terrain is highly susceptible to landslide events triggered by frequent earthquakes and heavy rainfall. In the recent past, cloud burst events are on rising, causing massive loss of life and property, mainly attributed to climate change and extensive anthropogenic activities in the mountain region as experienced in case of 2013 Kedarnath Tragedy. The study aimed to identify the potential landslide hazard zone in Mandakini valley by utilizing different types of data including Survey of India toposheet, geological (lithological and structural) maps, IRS-1D, LISS IV multispectral and PAN satellite sensor data and field observations. Relevant 18 thematic layers pertaining to the causative factors for landslide occurrences, such as slope, aspect, relative relief, lithology, tectonic structures, lineaments, LULC, NDVI, distance to drainage, drainage density and anthropogenic factors like distance to road, have been generated using remote sensing images, field survey, ancillary data and GIS techniques.  A detailed landslide susceptibility map was produced using a logistic regression method with datasets developed in GIS. which has further been categorized into four landslide susceptibility zones from high to very low. Finally, the receiver operating characteristic (ROC) curve was used to evaluate the accuracy of the logistic regression analysis model. ROC curve analysis showing an accuracy of 87.3 % for an independent set of test samples. The result also showed a strong agreement between the distribution of existing landslides and predicted landslide susceptibility zones. Consequently, this study could serve as an effective guide for further land-use planning and for the implementation of development.
The weather diary of Felipe de Zúñiga (1775-1786): A key documentary source to understand the hunger year in Mexico
Authors: Domínguez-Castro Fernando , Gallego María Cruz , Vaquero José M. , García Herrera Ricardo , Vicente-Serrano Sergio M.
Published: March 2020

The weather diary of Felipe de Zúñiga y Ontiveros (FZO) (Oaxtepec, 1717–Mexico City, 1793) provides daily meteorological information for rain frequency, temperature, frost, hail, thunderstorms, and windy days, from January 1775 to December 1786. It is the earliest obser­vational data collection with daily resolution retrieved in the region so far and it has higher time resolution than any other climate proxy available for this period. Some of the meteorological information provided by FZO could be compared with current meteorological records i.e. frequency of rain, hail, and thunderstorm. The seasonal distribution of these variables corresponds well during the FZO period and the present climate. 1781 was the warmest year in the FZO record while 1785 and 1778 were the coldest. FZO also identified a wet period (1782/1783) and two dry periods (1780/1781 and 1785/1786). The later coincides with the hunger year. It is considered the worst famine in Mexico during the colonial period (1521–1821).  A combination of adverse climate, lack of food, and an outbreak of typhus epidemic killed around 300,000 people. During these years a drought event extended over almost all the Mexican territory and was particularly severe over the central and northeastern regions. During the period 1785/86 FZO only recorded 188 rainy days. A similar record of low rainy days only occurred two times in the instrumental period: i) 1909/10 (188 days) and ii) 2010/11 (189 days). Both episodes with harmful consequences to the country e.g. water shortages, important loses in agriculture, farming, and forest fires. However, the climate during the hunger year was worse than during the instrumental droughts due to the high frequency of early killing frost. During 1785, frost events happened on April, August and September. FZO describes the impact of the frost and the attempt of the government to alleviate the famine “the frosts since August 28th have been so general that the fruits have been lost throughout the Kingdom, with the excep­tion of the warm lands; the government has asked them to sow corn, beans and other seeds in the irri­gated lands immediately so that they can be harvested by March 1786 and partially remedy the hunger that threatens”. Nevertheless, this decision was no useful because 1786 was driest than the 1785 impeding the growing of any crop. The annual summary of FZO for 1786 was, “It has been an unfortunate year due to scarcity of rain, supplies and everything needed for life, also in misfortune and public diseases”. The FZO´s diary is a good example of a documentary source that allows understanding the climate situation and the socio-economic response in detail during an extreme event.
Livestock carrying capacity: assessment of world`s grasslands based on MODIS data products.
Authors: Piipponen Johannes , Rizayeva Afag , de Leeuw Jan , Jalava Mika , Kummu Matti
Published: March 2020

Despite the consensus among researchers that future diets should include more plant-based proteins, animal-based foodstuffs are unlikely to disappear completely from our diet. Natural grasslands yield a notable part of the world`s animal protein production, but little is known about the sustainable potential of different areas, and thus the level of meat production that could be achieved globally by grazing. Whilst heavy stocking densities and overgrazing occurs in many regions, there still remain areas that have the potential to increase grazing from a carrying capacity perspective. This study aims to estimate the aboveground biomass that is sustainably available for grazers on the grasslands and savannas based on the MODIS Net Primary Production (NPP) approach at the global scale. We then use this information to calculate reasonable livestock-carrying capacities, using slopes, forest cover densities, proper use factors, and animal forage requirements as restrictions. The use of remote sensing to assess carrying capacities is still in its infancy, and this study represents the first global application of this novel approach. In addition, this study provides a methodology for examining the spatial and temporal variability of carrying capacities between seasons and years. Here we define the regional upper limits for pasture-based animal production, identify where future production could sustainably concentrate, and quantify the amount of protein intake that can be fulfilled by grazing animals.
Earth's core magnetic field model Mag.num and the IGRF 13 candidate
Authors: Rother Martin , Korte Monika , Matzka Jürgen , Morschhauser Achim , Stolle Claudia , Vervelidou Foteini
Published: March 2020

The Earth's core magnetic field model Mag.num was the parent model for the GFZ IGRF 13 candidate submission. The model is based on geomagnetic ground observatory and Swarm satellite observations. Epochs 2020.0 and beyond were not covered by the data available at the time of submission and our results were based on predictions. In this study, we investigate the effect of the more recent available data on our results of the 2020.0 epoch and the predicted secular variation by generating an updated Mag.num version. We especially focus on the spatial and temporal patterns of the local geomagnetic field minimum of the South Atlantic Anomaly (SAA). Recently, global geomagnetic field models have shown that an additional, although shallow, secondary minimum at Earth's surface has developed since around 2005. The location and significance of the secondary minimum and of the saddle point between the two minima are assessed also in view of the respective differences among the candidate models.
Studying soil erosion rates through landscape fragmentation. A case study in Crete, Greece.
Authors: Alexakis Dimitrios D. , Polykretis Christos , Grillakis Manolis G.
Published: March 2020

The regular patterns of soil erosion tend to change at different scales of observation, affecting the mechanism of soil erosion and its evolution characteristics. Fragmentation and land loss are two critical, interrelated processes that influence the entire landscape. In this study, we examine how the relationship between landscape fragmentation and soil loss is diversified in different scales and contexts. Thus, different Earth Observation (EO) products, in terms of spatial analysis, such as Landsat 8, Sentinel 2 and Planetscope imageries are utilized to search the influence of scale effect in fragmentation rate. Land use / Land Cover (LULC) maps were developed in different scales through the use of sophisticated classification algorithms. Following, FRAGSTATS software was employed to calculate spatial metrics in order to capture important aspects of landscape patterns such as edge density, largest patch index, number of patches, contagion etc. In this context we calculated fractal dimensions and Moran’s I spatial autocorellation statistics and used them to represent the degree of landscape fragmentation. Soil loss data, estimated in different scales were incorporated in the overall study as derived from RUSLE (Revised Universal Soil Loss Estimation) soil loss estimation model. Ordinary least square (OLS) and Geographical Weighted Regression (GWR) methodologies were applied in order to correlate both spatially and quantitavely soil loss rates with landscape fragmentation The results denoted the fact that areas of larger patches with least fragmentation suffer less from soil loss phenomena. The overall approach can be used as a road map in order to extract crucial conclusions about landscape’s diachronic evolution and how this is affected both from natural and anthropogenic interventions.
Disentangling the effects of particles and circulation on 231Pa/230Th during Heinrich Stadials
Authors: Lippold Jörg , Süfke Finn , Grützner Jens , Pöppelmeier Frerk
Published: March 2020

It has been shown that during Heinrich stadials northern deep water production ceased leading to an enhanced inflow of southern sourced water. Although Heinrich events are not considered to represent the primary trigger of Heinrich stadials the reorganisation of Atlantic ocean dynamics during their occurrences is an active field of research. In particular, Heinrich stadial 2 (HS2) is of high interest, based on the observation that the interplay with the climate system was very different during HS2 compared to HS1, although the magnitude of iceberg and freshwater discharge was similar (Hemming, 2004). During HS2 sea-level was still decreasing while the atmospheric CO­2 content was relatively stable unlike the climatic evolution during Heinrich HS1.

The notion of a reduced Atlantic Meridional Overturning Circulation (AMOC) during Heinrich Stadials is mainly strengthened by the 231Pa/230Th records from the Bermuda Rise. However, other influencing factors, capable of increasing the sedimentary 231Pa/230Th without according decreases in AMOC strength, need to be considered as well. Besides biogenic opal, high dust fluxes may also result in enhanced scavenging rate of both radionuclides and consequently higher sedimentary 231Pa/230Th signals, since another distinct feature that accompanies Heinrich Stadials is the high atmospheric concentration of dust in the northern hemisphere. Furthermore, high dust concentrations might be an indicator of a vigorous wind system and therefore strong ocean mixing, which can lead to the enhanced formation of nepheloid layers These layers are suspected to cause strong bottom scavenging and consequently high sedimentary 231Pa/230Th. Very high dust fluxes were observed e.g. during HS2 and MIS4. Here, we compare 231Pa/230Th with dust records in order to disentangle the effects of scavenging and circulation on the recorded sedimentary 231Pa/230Th from the northwestern Atlantic.
GPS measurements during two major calving events at Bowdoin Glacier, Greenland
Authors: van Dongen Eef , Jouvet Guillaume , Lindner Fabian , Bauder Andreas , Walter Fabian , Sugiyama Shin
Published: March 2020

Future mass loss predictions, and thereby sea level rise predictions, are strongly affected by the representation of iceberg calving in numerical ice sheet models. Despite recent advances, gaps in our understanding of calving mechanisms remain and there exists a lack of data to constrain mechanical properties related to ice fracturing. For instance, observed critical strain rates for crevasse initiation span two orders of magnitude.

Bowdoin Glacier in Northwest Greenland provides a unique opportunity to conduct in-situ measurements near the calving front due to its accessibility via a crevasse-free walkable moraine. In July 2019, two major calving events were surveyed by 10 GPS stations installed along the front in close vicinity to the calving events. Measurements show glacier uplift prior to the first calving event and horizontal compression prior to the second major calving event.

In contrast to previously observed major events, no precursor such as a large surface crack was visible on the field. Our data suggest a change in calving behaviour from surface crevasses due to hydro-fracturing to basal crevasse formation due to buoyancy, which may be favoured by observed thinning (~4 m yr-1 since 2013).
Controls on microplastic flux mechanisms in a large river
Authors: Mendrik Freija , Parsons Daniel , Hackney Christopher , Waller Cath , Cumming Vivien , Dorrell Robert , Vasilopoulos Grigorios
Published: March 2020

The majority of marine plastic pollution originates from land-based sources with the dominant transport agent being riverine. Despite many of the potential ecotoxicological consequences of plastics being well known, research has only just recently begun to explore the source to sink dynamics of plastics in the environment. Despite the widespread recognition that rivers dominate the global flux of plastics to the ocean, there is a key knowledge gap regarding the nature of the flux, the behaviour of microplastics (<5mm) in transport and its pathways from rivers into the ocean. Additionally, little is presently known about the role of biota in the transport of microplastics through processes such as biofilm formation and how this influences microplastic fate. This prevents progress in understanding microplastic fate and hotspot formation, as well as curtailing the evolution of effective mitigation and policy measures.

 

As part of the National Geographic Rivers of Plastic project, a combined-laboratory and field investigation was conducted. Fieldwork was undertaken in the Mekong River, one of the top global contributors to marine plastic pollution with an estimated 37,000 tonnes of plastic being discharged from the Mekong Delta each year. This flux is set to grow significantly in accordance with the projected population increase in the basin. The results presented herein outline a suite of laboratory experiments that explore the role of biofilms on the generation of microplastic flocs and the impact on buoyancy and settling velocities. Aligned fieldwork details the particulate flux and transport of microplastic, throughout the vertical velocity profile, across the river-delta-coast system, including the Tonle Sap Lake. The results also highlight potential areas of highest ecological risk related to the dispersal and distribution of microplastics. Finally, pilot data on the levels of microplastics within fish from the Mekong system are also quantified to explore the potential impact of biological uptake on the fate and sinks of plastics within the system.
Late Cretaceous to Paleogene sand provenance, deposition and tectonomagmatic development in the southern Møre Basin, Norway
Authors: Kjøll Hans Jørgen , Midtkandal Ivar , Planke Sverre
Published: March 2020

Upper Cretaceous and Paleocene sandstone strata represent promising reservoirs along the NE Atlantic margins, including new discoveries in recent years that has spurred increased activity in the area. Exploration and seismic imaging is complicated by massive Paleocene magmatism related to late rifting and early breakup, forming voluminous sill and dyke complexes hosted in the sedimentary succession and extrusive complexes, such as volcanic edifices and lava flows along the margin. Such igneous activity may have played an important role in the thermal and chemical history of reservoir zones. Their diagenetic properties as well as their physical appearance is expected to have been altered by the intrusions, breaking predictive trends otherwise common for deep-marine sedimentary strata. A new understanding of the nature and implication of igneous processes and deposition of sediments, combined with new understanding of sand source-to-sink systems in the region, is thus important to better evaluate the prospectivity of the southern Møre Basin. The focus of this project will therefore be to asses sand provenance and depositional systems in basins in this area by incorporating on shore field work with integrated borehole and seismic studies. The main goal is to develop a new understanding of deposition of sand fairways during the Late Cretaceous and Paleogene to better understand this part of the break-up history of the NE Atlantic.
Moisture sources of summer precipitation over eastern China during 1979–2009: A Lagrangian transient simulation
Authors: Hu Qin
Published: March 2020

In this study, moisture sources for summer (June–July–August) precipitation over eastern China are investigated by performing a transient simulation for the period 1979–2009 using the Lagrangian particle dispersion model FLEXPART. The results show that the Indochinese Peninsula plus southern China, the South China Sea, the northwestern Pacific Ocean, the Asian continent, and the Bay of Bengal are major moisture source regions for summer precipitation over eastern China and that the moisture originated from eastern China, the Arabian Sea, and the Indian subcontinent has minor contributions. The contribution of the oceanic sources significantly surpasses that of the continental sources. The contributions of the various moisture source regions exhibited significant interannual variations during 1979–2009, especially the Indochinese Peninsula plus southern China, the South China Sea, the northwestern Pacific Ocean, the Asian continent, and the Bay of Bengal. Moreover, moisture sources have obvious monthly variations and seasonal cycle features, which are responsible for providing moisture for precipitation in the different stages of the monsoon over eastern China. In addition, it is revealed that a great amount of moisture for the slight precipitation over eastern China originates from the local and northwestern continental regions and eastern oceanic regions adjacent to eastern China, while more moisture comes from southwestern oceanic source regions and their adjacent continental regions for heavy precipitation.
Global wave resource classification and application to marine energy deployments
Authors: Fairley Iain , Lewis Matthew , Robertson Bryson , Hemer Mark , Masters Ian , Horrillo-Caraballo Jose , Karunarathna Harshinie , Reeve Dominic
Published: March 2020

Understanding and classification of the global wave energy resource is vital to facilitate wave energy converter technology development and global roll-out of this promising renewable energy technology. To date, many wave energy converters have been developed based on Northern European wave climates; these are not representative of wave climates worldwide and may not be the best for large scale energy extraction. Classification of resources will highlight alternative wave resource types that may prove fruitful for deployment of future technologies; equally it will enable existing technology to define regions worthy of site exploration. Therefore k-means clustering is used here to classify the global resource from a data-driven, device agnostic perspective.

Parameters relevant to energy extraction (significant wave height, peak wave period, extreme wave height, spectral and directional properties) were extracted from the ECMWF ERA5 reanalysis dataset and used to split the global resource into 6 classes. Only areas within 3 degrees of land (feasible energy transport to user) were considered. The 6 classes returned by the analysis consisted of: 1) low energy high variability areas in enclosed seas; 2) low energy moderate variability areas in semi-enclosed seas and sheltered ocean coasts; 3) moderate energy areas, largely on eastern oceanic coastlines and influenced by local storm activity; 4) moderate energy areas primarily influenced by long period swell and largely on western oceanic coastlines; 5) higher energy areas, with variable conditions, primarily in the northern hemisphere; 6) highest energy areas, primarily on the tips of continents in the southern hemisphere. Consideration of device power matrices show that existing devices only perform well in classes 5 and 6, despite these areas having limited global coverage, which suggests devices should be developed for lower energy classes.

To refine global roll-out planning for existing devices, based on a request from a wave energy converter developer, a second classification is currently being developed with two additional constraints on the areas tested. These constraints are excluding any areas with a mean wave power of less than 15 kW/m (an often-used value for the lower power limit for commercial viability) and a maintenance constraint whereby wave heights must drop below 3m for a minimum of 48hrs per month. These newer results will be presented at the annual assembly and contrasted with our more device agnostic classification.
Contemporary challenges for Shoreline Change Analysis
Authors: Brooks Sue , Pollard Jamie , Spencer Tom
Published: March 2020

Shoreline change analysis has been deployed across a range of spatio-temporal scales. Accordingly, shoreline change studies have sought to capture shoreline dynamics at a variety of scales, ranging from the local impacts of individual storms to global trends measured over multiple decades. The scale at which we can approach the issue of shoreline change is, to a large extent, determined by the availability of data over time and space. With existing threats from the interactions between accelerated sea level rise, changing storminess and human intervention, shoreline change analysis has never been more relevant or challenging. Historic, centennial-scale shoreline change analysis relies on historic maps where there is normally just a single proxy indicator for consistent shoreline position; the mean water level of ordinary tides on UK Ordnance Survey maps, for example. Occasionally where there are specific coastal landforms that can be mapped, there might be a second proxy such as cliff top position. Shoreline change rates can be determined by extracting these proxies from sequential map surveys, provided the survey dates (ie: not the map publication date) are known.

 

Shoreline change quantification for more recent decadal-scale periods has been greatly enhanced by increased data availability. This is exemplified by analyses that use widespread coverage available from aerial photographs (past 3 decades). Even more recently on near-annual scales Light Detection and Ranging (LiDAR) data are becoming the norm for capturing storm impacts and shoreline change, enabling volumetric assessments of change in addition to the more traditional linear approaches. LiDAR is enhanced by ground survey Real Time Kinematic (RTK) Instrumentation that can be timed to coincide with storms. As the frequency of dataset capture has increased so has the spatial scale of coverage. Hence the latest shoreline change assessments are global in scale and use Landsat images to focus on hotspots of shoreline change (advance as well as retreat) over the past 30 years. Considering all scales together raises three central questions for shoreline change analysis and these are addressed in this paper.

 

Firstly, what methodological approach is most suitable for delimiting shorelines and generating the underpinning digitised shorelines for shoreline change assessment?

Secondly, what lessons can be learnt from using an approach that combines both proxy-based (visually discernible signatures) and datum-based (related to a particular water level) shorelines that change differentially with respect to different process-drivers?

Thirdly, given the current state-of-the-art around data availability, what is the most appropriate scale to approach shoreline change assessments?