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The Cryosphere

Modelling the future evolution of glaciers in the European Alps under the EURO-CORDEX RCM ensemble

Glaciers in the European Alps play an important role in the hydrological cycle, act as a source for hydroelectricity and have a large touristic importance. We model the future evolution of all glaciers in the Alps with a novel model that combines both ice flow and melt processes. We find that under a limited warming scenario about one-third of the present-day ice volume will still be present by the end of the century, while under strong warming more than 90 % of the volume will be lost by 2100.

Atmospheric Chemistry and Physics

A new description of probability density distributions of polar mesospheric clouds

In this paper we present a new description of statistical probability density functions (pdfs) of polar mesospheric clouds (PMC). We derive a new class of pdfs that describes successfully the probability statistic of ALOMAR lidar observations of different ice parameters. As a main advantage the new method allows us to connect different observational PMC distributions of lidar and satellite data, and also to compare with distributions from ice model studies.

The Cryosphere

Pathways of ice-wedge degradation in polygonal tundra under different hydrological conditions

We studied the stability of ice wedges (massive bodies of ground ice in permafrost) under recent climatic conditions in the Lena River delta of northern Siberia. For this we used a novel modelling approach that takes into account lateral transport of heat, water, and snow and the subsidence of the ground surface due to melting of ground ice. We found that wetter conditions have a destabilizing effect on the ice wedges and associated our simulation results with observations from the study area.

Geoscientific Model Development

Terrainbento 1.0: a Python package for multi-model analysis in long-term drainage basin evolution

Terrainbento 1.0 is a Python package for modeling the evolution of the surface of the Earth over geologic time (e.g., thousands to millions of years). Despite many decades of effort by the geomorphology community, there is no one established governing equation for the evolution of topography. Terrainbento 1.0 thus provides 28 alternative models that support hypothesis testing and multi-model analysis in landscape evolution.

Atmospheric Chemistry and Physics

Permafrost nitrous oxide emissions observed on a landscape scale using the airborne eddy-covariance method

As frozen soil, called permafrost, increasingly thaws over the years, scientists have put much effort into understanding how this may increase carbon emissions, which would exacerbate climate change. Our work supports the emerging view that these efforts should also include nitrous oxide (N₂O), a more potent greenhouse gas. Using a low-flying aircraft to study thousands of acres of Alaskan permafrost, we observed average N₂O emissions higher than typically assumed for regions such as this.

Geoscientific Model Development

Devito (v3.1.0): an embedded domain-specific language for finite differences and geophysical exploration

This paper presents Devito, a Python-based software. The aim of this software is to provide a high-level simple interface to users for the description and discretization of the mathematical definition of the physics. This research initially started as an attempt to improve research time, portability, and performance in exploration geophysics. We present the latest version of the software that is already making an impact in academics and industry.

Biogeosciences

Carbon cycling in the North American coastal ocean: a synthesis

We review and synthesize available information on coastal ocean carbon fluxes around North America (NA). There is overwhelming evidence, compiled and discussed here, that the NA coastal margins act as a sink. Our synthesis shows the great diversity in processes driving carbon fluxes in different coastal regions, highlights remaining gaps in observations and models, and discusses current and anticipated future trends with respect to carbon fluxes and acidification.

Climate of the Past

The 4.2 ka BP Event in the Mediterranean region: an overview

The Mediterranean region has returned some of the clearest evidence of a climatically dry period occurring approximately 4200 years ago. We reviewed selected proxies to infer regional climate patterns between 4.3 and 3.8 ka. Temperature data suggest a cooling anomaly, even if this is not uniform, whereas winter was drier, along with dry summers. However, some exceptions to this prevail, where wetter condition seems to have persisted, suggesting regional heterogeneity.

Biogeosciences

On the role of soil water retention characteristic on aerobic microbial respiration

Soil water is a medium from which microbes acquire resources and within which they are able to move. Occupancy and availability of water and oxygen gas in soils are mutually exclusive. In addition, as soil dries the remaining water is held with an increasing degree of adhesive energy, which restricts microbes’ ability to extract resources from water. We introduce a mathematical model that describes these interacting effects and organic matter decomposition.

Hydrology and Earth System Sciences

Geostatistical interpolation by quantile kriging

Many variables, e.g., in hydrology, geology, and social sciences, are only observed at a few distinct measurement locations, and their actual distribution in the entire space remains unknown. We introduce the new geostatistical interpolation method ofquantile kriging, providing an improved estimator and associated uncertainty. It can also host variables, which would not fulfill the implicit presumptions of the traditional geostatistical interpolation methods.

Natural Hazards and Earth System Sciences

Exposure-based risk assessment and emergency management associated with the fallout of large clasts at Mount Etna

Natural Hazards and Earth System Sciences
DOI 10.5194/nhess-19-589-2019
20 March 2019

The fallout of large clasts (> 5 cm) from the margins of eruptive plumes can damage local infrastructure and severely injure people close to the volcano. Even though this potential hazard has been observed at many volcanoes, it has often been overlooked. We present the first hazard and risk assessment of large-clast fallout from eruptive plumes and use Mt Etna (Italy) as a case study. The use of dedicated shelters in the case of an explosive event that occurs with no warning is also evaluated.

The Cryosphere

Evaluation of CloudSat snowfall rate profiles by a comparison with in situ micro-rain radar observations in East Antarctica

Evaluation of the vertical precipitation rate profiles of CloudSat radar by comparison with two surface-based micro-rain radars (MRR) located at two antarctic stations gives a near-perfect correlation between both datasets, even though climatic and geographic conditions are different for the stations. A better understanding and reassessment of CloudSat uncertainties ranging from −13 % up to +22 % confirms the robustness of the CloudSat retrievals of snowfall over Antarctica.

Climate of the Past

Pleistocene glacial history of the New Zealand subantarctic islands

The New Zealand subantarctic islands, in the Pacific sector of the Southern Ocean, provide valuable records of past environmental change. We find that the Auckland Islands hosted a small ice cap around 384 000 years ago, but that there was little glaciation during the Last Glacial Maximum, around 21 000 years ago, in contrast to mainland New Zealand. This shows that the climate here is susceptible to changes in regional factors such as sea-ice expanse and the position of ocean fronts.

Atmospheric Chemistry and Physics

Trends in global tropospheric ozone inferred from a composite record of TOMS/OMI/MLS/OMPS satellite measurements and the MERRA-2 GMI simulation

Both a 38-year merged satellite record of tropospheric ozone from TOMS/OMI/MLS/OMPS and a MERRA-2 GMI model simulation show large increases of 6–7 Dobson units from the Near East to India–East Asia and eastward over the Pacific. These increases in tropospheric ozone are attributed to increases in pollution over the region over the last several decades. Secondary 38-year increases of 4–5 Dobson units with both GMI model and satellite measurements occur over central African–tropical Atlantic.

Hydrology and Earth System Sciences

Attributing the 2017 Bangladesh floods from meteorological and hydrological perspectives

In August 2017 Bangladesh faced one of its worst river flooding events in recent history. For the large Brahmaputra basin, using precipitation alone as a proxy for flooding might not be appropriate. In this paper we explicitly test this assumption by performing an attribution of both precipitation and discharge as a flooding-related measure to climate change. We find the change in risk to be of similar order of magnitude (between 1 and 2) for both the meteorological and hydrological approach.

Hydrology and Earth System Sciences

Effects of univariate and multivariate bias correction on hydrological impact projections in alpine catchments

Several multivariate bias correction methods have been developed recently, but only a few studies have tested the effect of multivariate bias correction on hydrological impact projections. This study shows that incorporating or ignoring inter-variable relations between air temperature and precipitation can have a notable effect on the projected snowfall fraction. The effect translated to considerable consequences for the glacio-hydrological responses and streamflow components of the catchments.

Climate of the Past

Late Miocene–Pliocene climate evolution recorded by the red clay cover on the Xiaoshuizi planation surface, NE Tibetan Plateau

Multiple proxies for the XSZ planation surface reveal that the climate was dry and stable during the late Miocene but became intermittently humid with more seasonality at 4.7–3.9 Ma. Regional climatic differences between the central and western CLP reveal that expansion of the paleo-EASM occurred during the early Pliocene. The warming of the high northern latitudes in response to the closure of the Panama Seaway may have been responsible for the thermodynamical enhancement of the paleo–EASM.

Geoscientific Model Development

The Open Global Glacier Model (OGGM) v1.1

Mountain glaciers are one of the few remaining subsystems of the global climate system for which no globally applicable community-driven model exists. Here we present the Open Global Glacier Model (OGGM; www.oggm.org), developed to provide a modular and open-source numerical model framework for simulating past and future change of any glacier in the world.

Hydrology and Earth System Sciences

Conservative finite-volume forms of the Saint-Venant equations for hydrology and urban drainage

A new derivation of the equations for one-dimensional open-channel flow in rivers and storm drainage systems has been developed. The new approach solves some long-standing problems for obtaining well-behaved solutions with conservation forms of the equations. This research was motivated by the need for highly accurate models of large-scale river networks and the storm drainage systems in megacities. Such models are difficult to create with existing equation forms.

Hydrology and Earth System Sciences

Seasonal origins of soil water used by trees

We used stable isotopes of xylem water to study differences in the seasonal origin of water in more than 900 individual trees from three dominant species in 182 Swiss forested sites. We discovered that midsummer transpiration was mostly supplied by winter precipitation across diverse humid climates. Our findings provide new insights into tree vulnerability to droughts, transport of water (and thus solutes) in soils, and the climatic information conveyed by plant-tissue isotopes.

The Cryosphere

The Reference Elevation Model of Antarctica

The Cryosphere
DOI 10.5194/tc-13-665-2019
26 February 2019

The Reference Elevation Model of Antarctica (REMA) is the first continental-scale terrain map at less than 10 m resolution, and the first with a time stamp, enabling measurements of elevation change. REMA is constructed from over 300 000 individual stereoscopic elevation models (DEMs) extracted from submeter-resolution satellite imagery. REMA is vertically registered to satellite altimetry, resulting in errors of less than 1 m over most of its area and relative uncertainties of decimeters.

Atmospheric Measurement Techniques

Revisiting the differential freezing nucleus spectra derived from drop-freezing experiments: methods of calculation, applications, and confidence limits

The abundance of freezing nuclei in water samples is routinely determined by experiments involving the cooling of sample drops and observing the temperatures at which the drops freeze. This is used for characterizing the nucleating abilities of materials in laboratory preparations or to determine the numbers of nucleating particles in rain, snow, river water or other natural waters. The evaluation of drop-freezing experiments in terms of differential nucleus spectra is advocated in the paper.

Earth System Dynamics

The role of moisture transport for precipitation in the inter-annual and inter-daily fluctuations of the Arctic sea ice extension

Ice melting at the scale of inter-annual fluctuations against the trend is favoured by an increase in moisture transport in summer, autumn, and winter and a decrease in spring. On a daily basis extreme humidity transport increases the formation of ice in winter and decreases it in spring, summer, and autumn; in these three seasons it thus contributes to Arctic sea ice melting. These patterns differ sharply from that linked to decline, especially in summer when the opposite trend applies.

Geoscience Communication

Identifying and improving AGU collaborations using network analysis and scientometrics

The American Geophysical Union (AGU) is an Earth and space science professional society. Research conducted by AGU members ranges from the Earth’s deep interior to the outer planets of our solar system. However, little research exists on the AGU meeting itself. We apply network analysis and scientometrics to 17 years of AGU Fall Meetings to examine the network structure of the AGU and explore how data science can facilitate better scientific communication and collaboration.

Climate of the Past

Harmonising plant functional type distributions for evaluating Earth system models

A simple but powerful method for the biomisation of plant functional type distributions is introduced and tested for six different dynamic global vegetation models based on pre-industrial and palaeo-simulations. The method facilitates the direct comparison between vegetation distributions simulated by different Earth system models and between model results and the pollen-based biome reconstructions. It is therefore a powerful tool for the evaluation of Earth system models.

The Cryosphere

Thaw processes in ice-rich permafrost landscapes represented with laterally coupled tiles in a land surface model

The Cryosphere
DOI 10.5194/tc-13-591-2019
18 February 2019

Many permafrost landscapes contain large amounts of excess ground ice, which gives rise to small-scale elevation differences. This results in lateral fluxes of snow, water, and heat, which we investigate and show how it can be accounted for in large-scale models. Using a novel model technique which can account for these differences, we are able to model both the current state of permafrost and how these landscapes change as permafrost thaws, in a way that could not previously be achieved.

Biogeosciences

Towards a more complete quantification of the global carbon cycle

Biogeosciences
DOI 10.5194/bg-16-831-2019
14 February 2019

Globally, C is added to the atmosphere from fossil fuels and deforestation, balanced by ocean uptake and atmospheric increase. The difference (residual sink) is equated to plant uptake. But this omits cement carbonation; transport to oceans by dust; riverine organic C and volatile organics; and increased C in plastic, bitumen, wood, landfills, and lakes. Their inclusion reduces the residual sink from 3.6 to 2.1 GtC yr^-1 and thus the inferred ability of the biosphere to alter human C emissions.

Hydrology and Earth System Sciences

A simple topography-driven and calibration-free runoff generation module

Supported by large-sample ecological observations, a novel, simple and topography-driven runoff generation module (HSC-MCT) was created. The HSC-MCT is calibration-free, and therefore it can be used to predict in ungauged basins, and has great potential to be generalized at the global scale. Also, it allows us to reproduce the variation of saturation areas, which has great potential to be used for broader hydrological, ecological, climatological, and biogeochemical studies.

Biogeosciences

Mineral formation induced by cable bacteria performing long-distance electron transport in marine sediments

Biogeosciences
DOI 10.5194/bg-16-811-2019
13 February 2019

Multicellular cable bacteria form long filaments that can reach lengths of several centimeters. They affect the chemistry and mineralogy of their surroundings and vice versa. How the surroundings affect the cable bacteria is investigated. They show three different types of biomineral formation: (1) a polymer containing phosphorus in their cells, (2) a sheath of clay surrounding the surface of the filament and (3) the encrustation of a filament via a solid phase containing iron and phosphorus.

Atmospheric Chemistry and Physics

Evidence for a major missing source in the global chloromethane budget from stable carbon isotopes

Chloromethane is the most important natural carrier of chlorine to the stratosphere. From a newly determined carbon isotope effect of −11.2 ‰ for the tropospheric loss of CH₃Cl we derive a tropical rainforest CH₃Cl source of 670 ± 200 Gg a⁻¹, 60 % smaller than previous estimates. A revision of previous bottom-up estimates using above-ground biomass instead of rainforest area strongly supports this lower estimate. Our results suggest a large unknown tropical value of 1530 ± 200 Gg a⁻¹.

The Cryosphere

Four decades of Antarctic surface elevation changes from multi-mission satellite altimetry

We developed an approach to combine measurements of seven satellite altimetry missions over the Antarctic Ice Sheet. Our resulting monthly grids of elevation changes between 1978 and 2017 provide unprecedented details of the long-term and interannual variation. Derived mass changes agree well with contemporaneous data of surface mass balance and satellite gravimetry and show which regions were responsible for the significant accelerations of mass loss in recent years.

Solid Earth

Power spectra of random heterogeneities in the solid earth

Solid Earth
DOI 10.5194/se-10-275-2019
5 February 2019

Recent seismological observations clarified that the velocity structure of the crust and upper mantle is randomly heterogeneous. I compile reported power spectral density functions of random velocity fluctuations based on various types of measurements. Their spectral envelope is approximated by the third power of wavenumber. It is interesting to study what kinds of geophysical processes created such a power-law spectral envelope at different scales and in different geological environments.

Hydrology and Earth System Sciences

Emergent stationarity in Yellow River sediment transport and the underlying shift of dominance: from streamflow to vegetation

Our study shows that there is declining coupling between sediment concentration and discharge from daily to annual scales for gauges across the Yellow River basin (YRB). Not only the coupling, but also the magnitude of sediment response to discharge variation decreases with long-term mean discharge. This emergent stationarity can be related to sediment retardation by vegetation, suggesting the shift of dominance from water to vegetation as mean annual discharge increases.

Earth Surface Dynamics

Long-term erosion of the Nepal Himalayas by bedrock landsliding: the role of monsoons, earthquakes and giant landslides

We mapped eight monsoon-related (> 100 m²) and large (> 0.1 km²) landslides in the Nepal Himalayas since 1970. Adding inventories of Holocene landslides, giant landslides (> 1 km³), and landslides from the 2015 Gorkha earthquake, we constrain the size–frequency distribution of monsoon- and earthquake-induced landslides. Both contribute ~50 % to a long-term (> 10 kyr) total erosion of ~2 mm yr^-1, matching the long-term exhumation rate. Large landslides rarer than¹⁰Be sampling time drive erosion.

Biogeosciences

Stable carbon and nitrogen isotopic composition of leaves, litter, and soils of various ecosystems along an elevational and land-use gradient at Mount Kilimanjaro, Tanzania

Mount Kilimanjaro is an iconic environmental asset under serious threat due to increasing human pressures and climate change constraints. We studied variations in the stable isotopic composition of carbon and nitrogen in plant, litter, and soil material sampled along a strong land-use and altitudinal gradient. Our results show that, besides management, increasing temperatures in a changing climate may promote carbon and nitrogen losses, thus altering the stability of Kilimanjaro ecosystems.

Atmospheric Chemistry and Physics

Positive matrix factorization of organic aerosol: insights from a chemical transport model

The ability of positive matrix factorization (PMF) factor analysis to identify and quantify the organic aerosol (OA) sources accurately is tested in this modeling study. The estimated uncertainty of the contribution of fresh biomass burning is less than 30 % and of the other primary sources is less than 40 %, when these sources contribute more than 20 % to the OA. Τhe first oxygenated OA factor includes mainly highly aged OA, while the second oxygenated OA factor contains fresher secondary OA.

Climate of the Past

Heinrich events show two-stage climate response in transient glacial simulations

Heinrich events are among the dominant modes of glacial climate variability. They are caused by massive ice discharges from the Laurentide Ice Sheet into the North Atlantic. In previous studies, the climate changes were either seen as resulting from freshwater released from the melt of the discharged icebergs or by ice sheet elevation changes. With a coupled ice sheet–climate model, we show that both effects are relevant with the freshwater effects preceding the ice sheet elevation effects.

Hydrology and Earth System Sciences

Quantifying new water fractions and transit time distributions using ensemble hydrograph separation: theory and benchmark tests

How long does it take for raindrops to become streamflow? Here I propose a new approach to this old problem. I show how we can use time series of isotope data to measure the average fraction of same-day rainfall appearing in streamflow, even if this fraction varies greatly from rainstorm to rainstorm. I show that we can quantify how this fraction changes from small rainstorms to big ones, and from high flows to low flows, and how it changes with the lag time between rainfall and streamflow.

Biogeosciences

Global atmospheric CO2 inverse models converging on neutral tropical land exchange, but disagreeing on fossil fuel and atmospheric growth rate

We have compared global carbon budgets calculated from numerical inverse models and CO₂ observations, and evaluated how these systems reproduce vertical gradients in atmospheric CO₂ from aircraft measurements. We found that available models have converged on near-neutral tropical total fluxes for several decades, implying consistent sinks in intact tropical forests, and that assumed fossil fuel emissions and predicted atmospheric growth rates are now the dominant axes of disagreement.

Solid Earth

A multi-technology analysis of the 2017 North Korean nuclear test

Solid Earth
DOI 10.5194/se-10-59-2019
15 January 2019

On 3 September 2017 official channels of the Democratic People’s Republic of Korea announced the successful test of a nuclear device. This study provides a multi-technology analysis of the 2017 North Korean event and its aftermath using a wide array of geophysical methods (seismology, infrasound, remote sensing, radionuclide monitoring, and atmospheric transport modeling). Our results clearly indicate that the September 2017 North Korean event was in fact a nuclear test.

Geoscience Communication

Demystifying academics to enhance university–business collaborations in environmental science

Worldwide there is intense interest in converting research excellence in universities into commercial success, but there has been scant attention devoted to exactly how individual scientists’ workload and incentive structures may be a key barrier to this. Our work reveals the real challenge posed by a time-constrained university culture, better describes how work with business might fit into an academic job, and gives tips on working together in anuser guidefor scientists and (re)insurers.

Climate of the Past

Indian winter and summer monsoon strength over the 4.2 ka BP event in foraminifer isotope records from the Indus River delta in the Arabian Sea

A foraminifer oxygen isotope record from the northeastern Arabian Sea was used to reconstruct winter and summer monsoon strength from 5.4 to 3.0 ka. We found a 200-year period of strengthened winter monsoon (4.5–4.3 ka) that coincides with the earliest phase of the Mature Harappan period of the Indus Civilization, followed by weakened winter and summer monsoons by 4.1 ka. Aridity spanning both rainfall seasons at 4.1 ka may help to explain some of the observed archaeological shifts.

Atmospheric Chemistry and Physics

Volatile organic compounds and ozone in Rocky Mountain National Park during FRAPPÉ

Rocky Mountain National Park experiences high ozone concentrations that can exceed the National Ambient Air Quality Standard. As part of the FRAPPÉ field campaign, a suite of volatile organic compounds were measured to characterize the sources of ozone precursors that contribute to high ozone in the park. These measurements indicate emissions from the Front Range in Colorado tied to oil and gas operations, urban areas, and the stratosphere contribute to episodes of elevated ozone.

Ocean Science

Atmospheric histories, growth rates and solubilities in seawater and other natural waters of the potential transient tracers HCFC-22, HCFC-141b, HCFC-142b, HFC-134a, HFC-125, HFC-23, PFC-14 and PFC-116

Ocean Science
DOI 10.5194/os-15-33-2019
11 January 2019

Use of CFCs as oceanic transient tracers is difficult for recently ventilated water masses as their atmospheric mole fractions have been decreasing. To explore novel tracers, we synthesized consistent annual mean atmospheric histories of HCFC-22, HCFC-141b, HCFC-142b, HFC-134a, HFC-125, HFC-23, PFC-14 (CF4) and PFC-116 in both hemispheres and reconstructed their solubility functions in water and seawater. This work is also potentially useful for tracer studies in a range of natural waters.

Atmospheric Chemistry and Physics

Structural changes in the shallow and transition branch of the Brewer–Dobson circulation induced by El Niño

This paper assesses the structural changes in the shallow and transition branches of the BDC induced by El Nino using the Lagrangian model simulations driven by ERAi and JRA-55 combined with MLS observations. We found a clear evidence of a weakening of the transition branch due to an upward shift in the dissipation height of the planetary and gravity waves and a strengthening of the shallow branch due to enhanced GW breaking in the tropics–subtropics and PW breaking at high latitudes.

SOIL

Refining physical aspects of soil quality and soil health when exploring the effects of soil degradation and climate change on biomass production: an Italian case study

SOIL
DOI 10.5194/soil-5-1-2019
10 January 2019

This study is restricted to soil physical aspects of soil quality and health with the objective to define procedures with worldwide rather than only regional applicability, reflecting modern developments in soil physical research and focusing on important questions regarding possible effects of soil degradation and climate change.

Hydrology and Earth System Sciences

Exploring the use of underground gravity monitoring to evaluate radar estimates of heavy rainfall

In this study, we explore the use of an underground superconducting gravimeter as a new source of in situ observations for the evaluation of radar-based precipitation estimates. The comparison of radar and gravity time series over 15 years shows that short-duration intense rainfall events cause a rapid decrease in the measured gravity. Rainfall amounts can be derived from this decrease. The gravimeter allows capture of rainfall at a much larger spatial scale than a traditional rain gauge.

Climate of the Past

The onset of neoglaciation in Iceland and the 4.2 ka event

Compositing climate proxies in sediment from seven Iceland lakes documents abrupt summer cooling between 4.5 and 4.0 ka, statistically indistinguishable from 4.2 ka. Although the decline in summer insolation was an important factor, a combination of superposed changes in ocean circulation and explosive Icelandic volcanism were likely responsible for the abrupt perturbation recorded by our proxies. Lake and catchment proxies recovered to a colder equilibrium state following the perturbation.

Atmospheric Measurement Techniques

A shape model of internally mixed soot particles derived from artificial surface tension

We developed a shape model of coated soot particles and created a dataset of their optical properties. To simulate the detailed shape properties of mixtures of soot aggregates and adhered water-soluble substances, we propose a simple model of surface tension derived from the artificial surface potential. The results of some single-scattering properties including lidar backscattering were discussed.

Earth System Dynamics

ESD Ideas: Photoelectrochemical carbon removal as negative emission technology

Current CO₂ emission rates are incompatible with the 2 °C target for global warming. Negative emission technologies are therefore an important basis for climate policy scenarios. We show that photoelectrochemical CO₂ reduction might be a viable, high-efficiency alternative to biomass-based approaches, which reduce competition for arable land. To develop them, chemical reactions have to be optimized for CO₂ removal, which deviates from energetic efficiency optimization in solar fuel applications.