bluuebunny/crossref_metadata_2025 huggingface dataset:
Parametrization consequences of constraining soil organic matter models by total carbon and radiocarbon using long-term field data
Authors: Menichetti L. , Kätterer T. , Leifeld J.
Published: January 2016

Abstract. Soil organic carbon (SOC) dynamics result from different interacting processes and controls on spatial scales from sub-aggregate to pedon to the whole ecosystem. These complex dynamics are translated into models as abundant degrees of freedom. This high number of not directly measurable variables and, on the other hand, very limited data at disposal result in equifinality and parameter uncertainty. Carbon radioisotope measurements are a proxy for SOC age both at annual to decadal (bomb peak based) and centennial to millennial time scales (radio decay based), and thus can be used in addition to total organic C for constraining SOC models. By considering this additional information, uncertainties in model structure and parameters may be reduced. To test this hypothesis we studied SOC dynamics and their defining kinetic parameters in the ZOFE experiment, a >60-years old controlled cropland experiment in Switzerland, by utilising SOC and SO14C time-series. To represent different processes we applied five model structures, all stemming from a simple mother model (ICBM): I) two decomposing pools, II) an inert pool added, III) three decomposing pools, IV) two decomposing pools with a substrate control feedback on decomposition, V) as IV but with also an inert pool. These structures were extended to explicitly represent total SOC and 14C pools. The use of different model structures allowed us to explore model structural uncertainty and the impact of 14C on kinet ic parameters. We considered parameter uncertainty by calibrating in a formal Bayesian framework. By varying the relative importance of total SOC and SO14C data in the calibration, we could quantify the effect of the information from these two data streams on estimated model parameters. The weighing of the two data streams was crucial for determining model outcomes, and we suggest including it in future modelling efforts whenever SO14C data are available. The measurements and all model structures indicated a dramatic decline in SOC in the ZOFE experiment after an initial land use change in 1949 from grass- to cropland, followed by a constant but smaller decline. According to all structures, the three treatments (control, mineral fertilizer, farmyard manure) we considered were still far from equilibrium. The estimates of mean residence time (MRT) of the C pools defined by our models were sensitive to the consideration of the SO14C data stream. Model structure had a smaller effect on estimated MRT, which ranged between 5.91 and 4.22 years and 78.93 and 98.85 years for young and old pool, respectively, for structures without substrate interactions. The simplest model structure performed the best according to information criteria, validating the idea that we still lack data for mechanistic SOC models. Although we could not exclude any of the considered processes possibly involved in SOC decomposition, it was not possible to discriminate their relative importance.
Seasonal Variability of the Oxygen Minimum Zone off Peru in a high-resolution regional coupled model
Authors: Vergara O. , Dewitte B. , Montes I. , Garçon V. , Ramos M. , Paulmier A. , Pizarro O.
Published: January 2016

Abstract. In addition to being one of the most productive upwelling systems, the oceanic region off Peru is embedded in one of the most extensive Oxygen Minimum Zones (OMZs) of the world ocean. The dynamics of the OMZ off Peru remain uncertain, partly due to the scarcity of data and to the ubiquitous role of mesoscale activity on the circulation and biogeochemistry. Here we use a high-resolution coupled physical/biogeochemical model simulation to investigate the seasonal variability of the OMZ off Peru. The focus is on characterizing the seasonal cycle in Dissolved O2 (DO) eddy flux at the OMZ boundaries, including the coastal domain, viewed here as the eastern boundary of the OMZ, considering that the mean DO eddy flux in these zones has a significant contribution to the total DO flux. Along the coast, despite the increased seasonal low DO water upwelling, the DO peaks homogeneously over the water column and within the Peru Undercurrent (PUC) in austral winter, which results from mixing associated with the increase in both the intraseasonal wind variability and baroclinic instability of the PUC. The coastal ocean acts therefore as a source of DO in austral winter for the OMZ core through eddy-induced offshore transport that is also shown to peak in Austral winter. In the open ocean, the OMZ can be divided vertically into two zones: an upper zone above 400m where DO eddy flux dominates over the mean seasonal DO flux, and varies seasonally, and a lower part where DO exhibits vertical-zonal propagating features and where the mean seasonal DO flux shares similar characteristics than those of the energy flux associated with the annual extra-tropical Rossby waves. At the OMZ meridional boundaries where the mean eddy flux is large, the DO eddy flux has also a marked seasonal cycle that peaks in austral winter (spring) at the northern (southern) boundary. In the model, the amplitude of the seasonal cycle is 67% larger at the southern boundary than at the northern boundary. Results implications for understanding the OMZ variability at longer timescales are discussed.
Degradation of net primary production in a semi-arid rangeland
Authors: Jackson H. , Prince S. D.
Published: January 2016

Abstract. Anthropogenic land degradation affects many biogeophysical processes including reductions of net primary production (NPP). Degradation occurs at scales from small fields to continental and global. While measurement and monitoring of NPP in small areas is routine in some studies, for scales larger than 1 km2, and certainly global, there is no regular monitoring and certainly no attempt to measure degradation. Quantitative and repeatable techniques to assess the extent of deleterious effects and monitor changes are needed to evaluate its effects on, for example, economic yields of primary products such as crops, lumber and forage, and as a measure of land surface properties which are currently missing from dynamic global vegetation models, assessments of carbon sequestration and land surface models of heat, water, and carbon exchanges. This study employed the Local NPP Scaling (LNS) approach to identify patterns of anthropogenic degradation of NPP in the Burdekin Dry Tropics (BDT) region of Queensland, Australia from 2000 to 2013. The method starts with land classification based on the environmental factors presumed to control (NPP) to group pixels having similar potential NPP. Then, satellite remotely sensing data were used to compare actual NPP with its potential. The difference in units of mass of carbon and percentage loss was the measure of degradation. The method is limited spatially only by the capacity to classify the land. The entire BDT (7.45x106 km2) was investigated at a spatial resolution of 250x250 m. The average annual reduction in NPP due to anthropogenic land degradation in the entire BDT was −2.14 MgC m−2 year−1 or 17 % of the non-degraded potential, and the total reduction was −214 MgC year−1. Extreme average annual losses of 524.8 gC m−2 year−1 were detected. Approximately 20 % of the BDT was classified as ‘degraded’. Varying severities and rates of degradation were found among the river basins, of which the Belyando and Suttor were highest. Inter-annual, negative trends in reductions of NPP, occurred in 7 % of the entire region, indicating on-going degradation. There was evidence of areas that were in a permanently degraded condition. The findings provide strong evidence and quantitative data for reductions in NPP related to anthropogenic land degradation in the BDT.
Cell-free extracellular enzymatic activity is linked to seasonal temperature changes in the Baltic Sea
Authors: Baltar F. , Legrand C. , Pinhassi J.
Published: January 2016

Abstract. Extracellular enzymatic activities (EEA) are a crucial step on the degradation of organic matter. Dissolved (cell-free) extracellular enzymes in seawater can make up a significant contribution of the bulk EEA. However, the factors controlling the proportion of dissolved EEA in the marine environment remain unknown. Here we studied the seasonal changes in the proportion of dissolved relative to total EEA (of alkaline phosphatase [APase], β-glucosidase, [BGase], and leucine aminopeptidase, [LAPase]), in the Baltic Sea for 18 months. The proportio n of dissolved EEA ranged between 37-100%, 0-100%, 34-100% for APase, BGase and LAPase, respectively. A consistent seasonal pattern in the proportion of dissolved EEA was found among all the studied enzymes, with values up to 100% during winter and <40% du ring summer. A significant negative relation was found between the 21proportion of dissolved EEA and temperature, indicating that temperature might be a critical factor controlling the proportion of dissolved relative to total EEA in marine environments. Our results suggest a strong decoupling of hydrolysis rates from mi crobial dynamics in cold waters. This implies that under cold conditions, cell-free enzymes can contribute to substrate availability at large distances from the producing cell, increasing the dissociation between the hydrolysis of organic compounds and the actual microbes producing the enzymes. This also indicates that global warming could come to affect the hydrolysis of organic matter by reducing the hydrolytic activity of cell-free enzymes.
The influence of tillage on N2O fluxes from an intensively managed grazed grassland in Scotland
Authors: Cowan N.J. , Levy P.E. , Famulari D. , Anderson M. , Drewer J. , Carozzi M. , Reay D.S. , Skiba U.M.
Published: January 2016

Abstract. Intensively managed grass production in high rainfall temperate climate zones is a globally important source of N2O. Many of these grasslands are occasionally tilled and can lead to increased N2O emissions. This was investigated by comparing N2O fluxes from two adjacent intensively managed grazed grasslands in Scotland, one of which was tilled. A combination of eddy covariance, high resolution dynamic chamber and static chamber methods greatly improved the temporal and spatial coverage of N2O fluxes before and after the tillage event and is recommended to be followed in future studies. Total cumulative fluxes calculated for the tilled and un-tilled fields over the 175 day measurement period were 2.45 ± 0.27 and 2.08 ± 0.23 kg N2O-N ha−1, respectively. N2O emissions from the tilled field increased significantly for several days immediately after ploughing and remained elevated for approximately two months after the tillage event contributing to an estimated increase in N2O fluxes of 1.08 ± 0.14 kg N2O-N ha−1. Cumulative fluxes calculated over a 28 day period in August after the application of 70 kg-N ha−1 as ammonium nitrate to both fields were estimated at 0.42 ± 0.15 and 0.75 ± 0.14 kg N2O N ha−1 for the tilled and un-tilled fields, respectively. The tillage event appears to have substantially increased N2O fluxes from the tilled grassland field over a two month period; however, this increase may have been fractionally offset by a decrease in emissions after the August fertilisation event.
Response of Export Production and Dissolved Oxygen Concentrations to pCO2 and Temperature Stabilization Scenarios
Authors: Beaty T. , Winguth A. M. E. , Heinze C.
Published: January 2016

Abstract. Dissolved oxygen (DO) concentration in the ocean is an important component of marine biogeochemical cycles and will be greatly altered as climate change persists. In this study a global oceanic carbon cycle model (HAMOCC 2.0) is used to address how mechanisms of oxygen minimum zones (OMZ) expansion respond to changes in CO2 radiative forcing. Atmospheric pCO2 is increased at a rate of 1% annually and the model is stabilized at 2 X, 4 X, 6 X, and 8 X preindustrial pCO2 levels. With an increase in CO2 radiative forcing, the OMZ in the Pacific Ocean is controlled largely by changes in particulate organic carbon (POC) export, resulting in increased remineralization and thus expanding the oxygen minimum zones within the tropical Pacific Ocean. A potential decline in primary producers in the future as a result of environmental stress due to ocean warming and acidification could lead to a substantial reduction of vertical carbon flux and thus increased DO concentration particularly in the Pacific Ocean at a depth of 600-800 m. In contrast, the vertical expansion of the OMZs within the Atlantic and Indian Oceans are linked to reduced oxygen solubility due to rise in potential temperature and to a lesser extent changes in remineralization rates. Changes in oxygen solubility also lead to the formation of a new OMZ in the western subtrobical Pacific Ocean. The development of the new OMZ results in dissolved oxygen concentration of ≤50 μmols throughout the equatorial Pacific Ocean at 4 times preindustrial pCO2. Total ocean area with dissolved oxygen concentrations of ≤50 μmols increases by 2.5%, 4.5%, and 7.6% for the 2 X, 4X, and 8 X CO2 simulations, respectively.
Variability in 14C contents of soil organic matter at the plot and regional scale across climatic and geologic gradients
Authors: van der Voort T. S. , Hagedorn F. , McIntyre C. , Zell C. , Walthert L. , Schleppi P. , Feng X. , Eglinton T. I.
Published: January 2016

Abstract. Soil organic matter (SOM) forms the largest terrestrial pool of carbon outside of sedimentary rocks. Radiocarbon is a powerful tool for assessing soil organic matter dynamics. However, due to the nature of the measurement, extensive 14C studies of soils systems remain relatively rare. In particular, information on the extent of spatial and temporal variability in 14C contents of soils is limited, yet this information is crucial for establishing the range of baseline properties and for detecting potential modifications to the SOM pool. This study describes a comprehensive approach to explore heterogeneity in bulk SOM 14C in Swiss forest soils that encompass diverse landscapes and climates. We examine spatial variability in soil organic carbon (SOC) 14C, SOC content and C:N ratios over both regional climatic and geologic gradients, on the watershed- and plot-scale and within soil profiles. Results reveal (1) a relatively uniform radiocarbon signal across climatic and geologic gradients in Swiss forest topsoils (0-5 cm, Δ14C=159±36.4, n=12 sites), (2) similar radiocarbon trends with soil depth despite dissimilar environmental conditions, and (3) micro-topography dependent, plot-scale variability that is similar in magnitude to regional-scale variability (e.g., Gleysol, 0-5 cm, Δ14C 126±35.2, n=8 adjacent plots of 10x10m). Statistical analyses have additionally shown that Δ14C signature in the topsoil is not significantly correlated to climatic parameters (precipitation, elevation, primary production) except mean annual temperature at 0-5 cm. These observations have important consequences for SOM carbon stability modelling assumptions, as well as for the understanding of controls on past and current soil carbon dynamics.
Nitrous oxide and methane in two tropical estuaries in a peat-dominated region of North-western Borneo
Authors: Müller D. , Bange H. W. , Warneke T. , Rixen T. , Müller M. , Mujahid A. , Notholt J.
Published: January 2016

Abstract. Estuaries are sources of nitrous oxide (N2O) and methane (CH4) to the atmosphere. However, our present knowledge of N2O and CH4 emissions from estuaries in the tropics is very limited because data is scarce. In this study, we present first measurements of dissolved N2O and CH4 from two estuaries in a peat-dominated region of north-western Borneo. Two campaigns (during the dry seaso n in June 2013 and during the wet season in March 2014) were conducted in the estuaries of the rivers Lupar and Saribas. Median N2O concentrations ranged between 7.2 and 12.3 nmol L-1and were higher in the marine end-member (13.0 ± 7.0 nmol L-1). CH4 concentrations were low in the coastal ocean (3.6 ± 0.2 nmol L-1) and higher in the estuaries (medians between 12.2 and 64.0 nmol L-1). The respiration of abundant organic matter and presumably anthropogenic input caused a slight eutrophication, which did not lead to hypoxia or enhanced N2O concentrations, however. Generally, N2O concentrations were not related to dissolved inorganic nitrogen concentrations. Thus, the use of an emission factor for the calculation of N2O emissions from the inorganic nitrogen load leads to an overestimation of the flux from the Lupar and Saribas estuaries. N2O was negatively correlated with salinity during the dry season, which suggests a riverine source. In contrast, N2O concentrations during the wet season were not correlated with salinity but locally enhanced within the estuaries, implying that there were additional estuarine sources during the wet (i.e. monsoon) season. Estuarine CH4 distributions were not driven by freshwater input but rather by tidal variations. Both N2O and CH4 concentrations were more variable during the wet season. We infer that the wet season dominates the variability of the N2O and CH4 concentrations and subsequent emissions from tropical estuaries. Thus, we speculate that any changes the Southeast Asian monsoon system will lead to changes in the N2O and CH4 emissions from these systems. We also suggest that the ongoing cultivation of peat soil in Borneo is likely to increase N2O emissions from these estuaries, while the effect on CH4 remains uncertain.
Evidence of a prolonged drought ca. 4200 yr BP correlated with prehistoric settlement abandonment from the Gueldaman GLD1 Cave, Northern Algeria
Authors: Ruan J. , Kherbouche F. , Genty D. , Blamart D. , Cheng H. , Dewilde F. , Hachi S. , Edwards R. L. , Régnier E. , Michelot J.-L.
Published: January 2016

Abstract. Middle Holocene cultures have been widely studied around the Eastern-Mediterranean basin in the last 30 years and past cultural activities have been commonly linked with regional climate changes. However, in many cases such linkage is equivocal, in part due to existing climatic evidence that has been derived from areas outside the distribution of ancient settlements, leading to uncertainty from complex spatial heterogeneity in both climate and demography. A few high-resolution well-dated paleoclimate records were recently established using speleothems in the Central and Eastern-Mediterranean basin, however, the scarcity of such records in the western part of the Mediterranean prevents us from correlating past climate evolutions across the basin and deciphering climate–culture relation at fine timescales. Here we report the first decadal-resolved Mid-Holocene climate proxy records from the Western-Mediterranean basin based on the stable carbon and oxygen isotopes analyses of two U/Th dated stalagmites from the Gueldaman GLD1 Cave in Northern Algeria. Comparison of our records with those from Italy and Israel reveals synchronous (multi) centennial dry phases centered at ca. 5600, ca. 5200 and ca. 4200 yr BP across the Mediterranean basin. New calibrated radiocarbon dating constrains reasonably well the age of rich anthropogenic deposits (e.g., faunal remains, pottery, charcoal) excavated inside the cave, which allows the comparison between in situ evidence of human occupation and of climate change. This approach shows that the timing of a prolonged drought at ca. 4400–3800 yr BP blankets the onset of cave abandonment shortly after ca. 4403 cal yr BP, supporting the hypothesis that a climate anomaly may have played a role in this cultural disruption.
Variability of sulfate signal in ice core records based on five replicate cores
Authors: Gautier E. , Savarino J. , Erbland J. , Lanciki A. , Possenti P.
Published: January 2016

Abstract. Current volcanic reconstructions based on ice core analysis have significantly improved over the past few decades by incorporating multiple-core analyses with a high temporal resolution from different parts of the polar regions into a composite common volcanic eruption record. Regional patterns of volcanic deposition are based on composite records, built from cores taken at both poles. However, in many cases only a single record at a given site is used for these reconstructions. This assumes that transport and regional meteorological patterns are the only source of the dispersion of the volcanic products. Here we evaluate the local-scale variability of a sulfate profile in a low-accumulation site (Dome C, Antarctica), in order to assess the representativeness of one core for such a reconstruction. We evaluate the variability with depth, statistical occurrence, and sulfate flux deposition variability of volcanic eruptions detected in five ice cores, drilled 1 m apart from each other. Local-scale variability, essentially attributed to snow drift and surface roughness at Dome C, can lead to a non-exhaustive record of volcanic events when a single core is used as the site reference, with a bulk probability of 30 % of missing volcanic events and close to 65 % uncertainty on one volcanic flux measurement (based on the standard deviation obtained from a five-core comparison). Averaging n records reduces the uncertainty of the deposited flux mean significantly (by a factor 1∕ √ n); in the case of five cores, the uncertainty of the mean flux can therefore be reduced to 29 %.
Holocene climate variability in the North-Western Mediterranean Sea (Gulf of Lions)
Authors: Jalali B. , Sicre M.-A. , Bassetti M.-A. , Kallel N.
Published: January 2016

Abstract. Sea surface temperatures (SSTs) and land-derived input time series were generated from the Gulf of Lions inner-shelf sediments (NW Mediterranean Sea) using alkenones and high-molecular-weight odd-carbon numbered n-alkanes (TERR-alkanes), respectively. The SST record depicts three main phases: a warm Early Holocene ( ∼  18 ± 0.4  °C) followed by a cooling of  ∼  3  °C between 7000 and 1000 BP, and rapid warming from  ∼  1850 AD onwards. Several superimposed multi-decadal to centennial-scale cold events of  ∼  1  °C amplitude were also identified. TERR-alkanes were quantified in the same sedimentary horizons to identify periods of high Rhone River discharge and compare them with regional flood reconstructions. Concentrations show a broad increase from the Early Holocene towards the present with a pronounced minimum around 2500 BP and large fluctuations during the Late Holocene. Comparison with Holocene flood activity reconstructions across the Alps region suggests that sediments of the inner shelf originate mainly from the Upper Rhone River catchment basin and that they are primarily delivered during positive North Atlantic Oscillation (NAO).
Impacts of Tibetan Plateau uplift on atmospheric dynamics and associated precipitation δ18O
Authors: Botsyun S. , Sepulchre P. , Risi C. , Donnadieu Y.
Published: January 2016

Abstract. Paleoelevation reconstructions of mountain belts have become a focus of modern science since surface elevation provides crucial information for understanding both geodynamic mechanisms of Earth’s interior and influence of mountains growth on climate. Stable oxygen isotopes paleoaltimetry is one of the most popular techniques nowadays, and relies on the difference between δ18O of paleo-precipitation reconstructed using the natural archives, and modern measured values for the point of interest. Our goal is to understand where and how complex climatic changes linked with the growth of mountains affect δ18O in precipitation. For this purpose, we develop a theoretical expression for the precipitation composition and we use the isotope-equipped atmospheric general circulation model LMDZ-iso. Experiments with reduced height over the Tibetan Plateau and the Himalayas have been designed. Our results show that the isotopic composition of precipitation is very sensitive to climate changes related with the growth of the Himalayas and Tibetan Plateau, notably changes in relative humidity and precipitation amount. The relative contribution of controlling factors and their magnitude differ depending on the uplift stage and the region considered. Thus future paleoaltimetry studies should take into account constraints on climatic factors to avoid misestimating ancient altitudes.
An extended history of high-amplitude lake-level changes in tectonically active Lake Issyk-Kul (Kyrgyzstan), as revealed by high-resolution seismic reflection data
Authors: Gebhardt A. C. , Naudts Lieven , De Mol Lies , Klerkx Jan , Abdrakhmatov Kanatbek , Sobel Edward R. , De Batist M.
Published: January 2016

Abstract. A total of 84 seismic profiles mainly from the western and eastern deltas of Lake Issyk-Kul were used to identify lake-level changes. Seven stratigraphic sequences were identified each containing a series of delta lobes that were formed during former lake-level stillstands. Lake-level has experienced at least four cycles of stepwise fall and rise of 400 m or more. These fluctuations were mainly caused by past changes in the atmospheric circulation pattern during the past. During periods of low lake levels, the Siberian High likely was strong, bringing dry air masses from the Mongolian steppe. The strong Siberian High blocked the mid-latitude Westerlies. During periods of high lake levels, the Siberian High must have been weaker or displaced, and the mid-latitude Westerlies could bring moister air masses from the Mediterranean and North Atlantic regions.
Streamflow variability over 1881–2011 period in northern Quebec: comparison of hydrological reconstructions based on tree rings and on geopotential height field reanalysis
Authors: Brigode P. , Brissette F. , Nicault A. , Perreault L. , Kuentz A. , Mathevet T. , Gailhard J.
Published: January 2016

Abstract. Over the last decades, different methods have been used by hydrologists to extend observed hydro-climatic time series, based on other data sources, such as tree rings or sedimentological datasets. For example, tree ring multi-proxies have been studied for the Caniapiscau Reservoir in northern Quebec (Canada), leading to the reconstruction of flow series for the last 150 years. In this paper, we applied a new hydro-climatic reconstruction method on the Caniapiscau Reservoir to compare the obtained streamflow series and study the natural streamflow variability over the 1881–2011 period. This new reconstruction is based, not on natural proxies, but on a historical reanalysis of global geopotential height fields, and aims firstly to produce daily climatic time series, which are then used as inputs to a rainfall-runoff model in order to obtain daily streamflow time series. The performances of the hydro-climatic reconstruction were quantified over the observed period, and showed good performances, both in terms of monthly regimes and interannual variability. The streamflow reconstructions were then compared to two different reconstructions performed on the same catchment by using tree ring data series, one being focused on mean annual flows, and the other one on spring floods. In terms of mean annual flows, the interannual variability of the reconstructed flows were similar (except for the 1930–1940 decade), with significant changes seen in wetter and drier years. For spring floods, the interannual variabilities reconstructed were quite similar for the 1955–2011 period, but significantly different between 1880 and 1940. The results emphasize the need to apply different reconstruction methods on the same catchments. Indeed, comparisons such as those above highlight potential differences between available reconstructions, and finally, allow a retrospective analysis of the proposed reconstructions of past hydro-climatological variabilities.
A conceptual model of oceanic heat transport in the Snowball Earth scenario
Authors: Comeau D. , Kurtze D. A. , Restrepo J. M.
Published: January 2016

Abstract. Geologic evidence suggests that the Earth may have been completely covered in ice in the distant past, a state known as Snowball Earth. This is still the subject of controversy, and has been the focus of modeling work from low dimensional models up to state of the art general circulation models. In our present global climate, the ocean plays a large role in redistributing heat from the equatorial regions to high latitudes, and as an important part of the global heat budget, its role in the initiation a Snowball Earth, and the subsequent climate, is of great interest. To better understand the role of oceanic heat transport in the initiation of Snowball Earth, and the resulting global ice covered climate state, the goal of this inquiry is two-fold: we wish to propose the least complex model that can capture the Snowball scenario as well as the present day climate with partial ice cover, and we want to determine the relative importance of oceanic heat transport. To do this, we develop a simple model, incorporating thermohaline dynamics from traditional box ocean models, a radiative balance from energy balance models, as well as the more contemporary "sea glacier" model to account for viscous flow effects of extremely thick sea ice. The resulting model, consisting of dynamic ocean and ice components, is able to reproduce both Snowball Earth as well as present day conditions through reasonable changes in forcing parameters. We find that including or neglecting oceanic heat transport may lead to vastly different global climate states, and also that the parameterization of under ice heat transfer in the ice/ocean coupling, plays a key role in the resulting global climate state, demonstrating the regulatory effect of dynamic ocean heat transport. Furthermore we find that the ocean circulation direction exhibits bistability in the Snowball Earth regime.
Revolutions in energy input and material cycling in Earth history and human history
Authors: Lenton T. M. , Pichler P. P. , Weisz H.
Published: January 2016

Abstract. Major revolutions in energy capture have occurred in both Earth and human history, with each transition resulting in higher energy input, altered material cycles and major consequences for the internal organization of the respective systems. In Earth history, we identify the origin of anoxygenic photosynthesis, the origin of oxygenic photosynthesis, and land colonization by eukaryotic photosynthesisers as step changes in free energy input to the biosphere. In human history we focus on the Paleolithic use of fire, the Neolithic revolution to farming, and the Industrial revolution as step changes in free energy input to human societies. In each case we try to quantify the resulting increase in energy input, and discuss the consequences for material cycling and for biological and social organization. For most of human history, energy use by humans was but a tiny fraction of the overall energy input to the biosphere, as would be expected for any heterotrophic species. However, the industrial revolution gave humans the capacity to push energy inputs towards planetary scales and by the end of the 20th century human energy use had reached a magnitude comparable to the biosphere. By distinguishing world regions and income brackets we show the unequal distribution in energy and material use among contemporary humans. Looking ahead, a prospective sustainability revolution will require scaling up new solar energy technologies and the development of much more efficient material recycling systems – thus creating a more autotrophic social metabolism. Such a transition must also anticipate a level of social organization that can implement the changes in energy input and material cycling without losing the large achievements in standard of living and individual liberation associated with industrial societies.
Coherence among the Northern Hemisphere land, cryosphere, and ocean responses to natural variability and anthropogenic forcing during the satellite era
Authors: Gonsamo A. , Chen J. M. , Shindell D. T. , Asner G. P.
Published: January 2016

Abstract. A lack of long-term measurements across Earth's biological and physical systems has made observation-based detection and attribution of climate change impacts to anthropogenic forcing and natural variability difficult. Here we explore coherence among land, cryosphere and ocean responses to recent climate change using three decades (1980−2012) of observational satellite and field data throughout the Northern Hemisphere. Our results show coherent interannual variability among snow cover, spring phenology and thaw, solar radiation, Scandinavian Pattern, and North Atlantic Oscillation. The interannual variability of the atmospheric peak-to-trough CO2 amplitude is mostly impacted by temperature-mediated effects of ENSO, North American Pattern and East Atlantic Pattern, whereas CO2 concentration is affected by Polar Pattern control on sea ice extent dynamics. This is assuming the trend in anthropogenic CO2 emission remains constant, or the interannual changes in the trends are negligible. Our analysis suggests that sea ice decline-related CO2 release may outweigh increased CO2 uptake through longer growing seasons and higher temperatures. The direct effects of variation in solar radiation and leading teleconnections, at least in part via their impacts on temperature, dominate the interannual variability of land, cryosphere and ocean indicators. Our results reveal a coherent long-term changes in multiple physical and biological systems that are consistent with anthropogenic forcing of Earth's climate and inconsistent with natural drivers.
Hazard Interactions and Interaction Networks (Cascades) within Multi-Hazard Methodologies
Authors: Gill J. C. , Malamud B. D.
Published: January 2016

Abstract. This paper combines research and commentary to reinforce the importance of integrating hazard interactions and interaction networks (cascades) into multi-hazard methodologies. We present a synthesis of the differences between ‘multilayer single hazard’ approaches and ‘multi-hazard’ approaches that integrate such interactions. This synthesis suggests that ignoring interactions between important environmental and anthropogenic processes could distort management priorities, increase vulnerability to other spatially relevant hazards or underestimate disaster risk. In this paper we proceed to present an enhanced multi-hazard framework, through the following steps: (i) describe and define three groups (natural hazards, anthropogenic processes and technological hazards/disasters) as relevant components of a multi-hazard environment; (ii) outline three types of interaction relationship (triggering, increased probability, and catalysis/impedance); and (iii) assess the importance of networks of interactions (cascades) through case-study examples (based on literature, field observations and semi-structured interviews). We further propose visualisation frameworks to represent these networks of interactions. Our approach reinforces the importance of integrating interactions between different aspects of the Earth system, together with human activity, into enhanced multi-hazard methodologies. Multi-hazard approaches support the holistic assessment of hazard potential, and consequently disaster risk. We conclude by describing three ways by which understanding networks of interactions contributes to the theoretical and practical understanding of hazards, disaster risk reduction and Earth system management. Understanding interactions and interaction networks helps us to better (i) model the observed reality of disaster events, (ii) constrain potential changes in physical and social vulnerability between successive hazards, and (iii) prioritise resource allocation for mitigation and disaster risk reduction.
A Lagrangian analysis of the present-day sources of moisture for major ice-core sites
Authors: Drumond A. , Taboada E. , Nieto R. , Gimeno L. , Vicente-Serrano S. M. , Lopez-Moreno J. I.
Published: January 2016

Abstract. A Lagrangian approach was used to identify the moisture sources for fourteen ice-core sites located worldwide for the period 1980–2012. The sites were classified into three domains: Arctic, Central (Andes, Alps and Kilimanjaro), and Antarctic. The approach was used to compute budgets of evaporation minus precipitation by calculating changes in the specific humidity along 10-day backward trajectories. The results indicate that the oceanic regions around the subtropical high-pressure centers provide most of moisture, and their contribution varies throughout the year following the annual cycles of the centers. For the Arctic domain, the sources lie in the subtropical North Atlantic and Pacific. The subtropical south Atlantic, Indian and Pacific provide moisture for the Antarctic domain. The sources for South America are the Atlantic and southern Pacific, for Europe the sources are in the Mediterranean and the north Atlantic, and for Asia the sources are the Indian Ocean and the Arabian Sea.
Headwater sediment dynamics in debris flow catchment: implication of debris supply using high resolution topographic surveys
Authors: Loye A. , Jaboyedoff M. , Theule J. I. , Liébault F.
Published: January 2016

Abstract. Debris flows have been recognized to be linked to amounts of material temporary stored in torrent channels. Consequently, sediment production, debris supply and storage changes from low-order channels of the Manival catchment (French Alps) were surveyed periodically during 16 months using terrestrial laser scanning (TLS) to study the coupling between sediment dynamics and torrent responses in terms of debris flow events, which happened twice during the monitoring period. Sediment transfer in the main torrent was monitored with cross-section surveys. Sediment budgets were generated seasonally using sequential TLS data differencing and morphological extrapolations. Debris production depends strongly on rockfall occurring during winter–early spring season, following power law distribution for volumes of rockfall events above 0.1 m3, while hillslope sediment reworking dominates debris recharge from spring to autumn. Both debris flows originate in channels exclusively, but their occurrence is linked to recharge from previous debris pulses coming from the hillside and from bedload transport. Headwater debris sources display an equivocal behaviour in sediment transfer: despite of rainstorms inducing debris flows in torrent, low geomorphic activity occurred in production zone. Still, a general reactivation of sediment transport in headwater channels was observed in autumn without new debris supply, suggesting no exhaustion of debris storages. The seasonal cycle of sediment yield seems therefore to depend not only on debris supply and runoff (flow capacity), but also on geomorphic conditions that destabilize remnant debris stocks. This study shows that a monitoring of torrent in-channel storage changes coupled to debris supply can readily improve knowledge on recharge threshold leading to debris flow, so their prediction.
Gravel threshold of motion: A state function of sediment transport disequilibrium?
Authors: Johnson Joel P. L.
Published: January 2016

Abstract. In most sediment transport models, a threshold variable dictates the shear stress at which non-negligible bedload transport begins. Previous work has demonstrated that nondimensional transport thresholds (τ*c) vary with many factors related not only to grain size and shape, but also with characteristics of the flow and surrounding grains. Both a conceptual model and flume experiments suggest that τ*c should evolve as a function of local entrainment and deposition. Net entrainment preferentially removes more mobile particles while leaving behind more stable grains, gradually increasing τ*c and reducing transport rates. Net deposition tends to fill in topographic lows, progressively leading to less stable distributions of surface grains, decreasing τ*c and increasing transport rates. A new model is proposed for the temporal evolution of τ*c as a power-law function of net erosion or deposition, which shares some similarities with the Exner equation. Model parameters are calibrated based on flume experiments that explore transport disequilibrium. The τ*c-evolution equation is then incorporated into a simple morphodynamic model. The evolution of τ*c acts as negative feedbacks on morphologic change, while also allowing reaches to equilibrate to sediment supply at different slopes. Finally, τ*c is interpreted to be an important but nonunique state variable for channel morphology, in a manner consistent with the role that state variables such as temperature play in describing the evolution of thermodynamic systems.
Bedrock incision by bedload: insights from direct numerical simulations
Authors: Aubert Guilhem , Langlois Vincent J. , Allemand Pascal
Published: January 2016

Abstract. Bedload sediment transport is one of the main processes that contribute to bedrock incision in a river and is therefore one of the key control parameters in the evolution of mountainous lanscapes. In recent years, many studies have addressed this issue through experimental setups, direct measurements in the ﬁeld or various analytical models. In this article, we present a new direct numerical approach: using the classical methods of discrete element simulations applied to granular materials, we compute explicitely the trajectories of a number of pebbles entrained by a turbulent water stream over a rough solid surface. This method allows us to extract quantitatively the amount of energy that successive impacts of pebbles deliver to the bedrock, as a function of both the amount of sediment available and the Shields number. We show that we reproduce qualitatively the behaviour observed experimentally by Sklar and Dietrich (2001) and observe both a "tool-effect" and a "cover- effect". Converting the energy delivered to the bedrock into an average long-term incision rate of the river leads to predictions consistent with observations in the ﬁeld. Finally, we reformulate the dependency of this incision rate with Shields number and sediment ﬂux, and predict that the cover term should decay linearly at low sediment supply and exponentially at high sediment supply.
Modelling long-term, large-scale sediment storage using a simple sediment budget approach
Authors: Naipal V. , Reick C. , Van Oost K. , Hoffmann T. , Pongratz J.
Published: January 2016

Abstract. Currently, the anthropogenic disturbances to the biogeochemical cycles remain unquantiﬁed due to the poor representation of lateral ﬂuxes of carbon and nutrients in Earth System Models (ESMs) that couple the terrestrial and ocean systems. Soil redistribution plays an important role in the transport of carbon and nutrients between terrestrial ecosystems, however, quantiﬁcation of soil redistribution and its effects on the global biogeochemical cycles is missing. This study aims at developing new tools and methods to represent soil redistribution on a global scale, and contribute to the quantiﬁcation of anthropogenic disturbances to the biogeochemical cycles. We present a new large-scale coarse resolution sediment budget model that is compatible with ESMs. This model can simulate spatial patterns and long-term trends in soil redistribution in ﬂoodplains and on hillslope, resulting from external forces such as climate and land use change. We applied this model on the Rhine catchment using climate and land cover data from the Max Planck Institute Earth System Model (MPI-ESM) for the last millennium (850-2005 AD). Validation is done using observed Holocene sediment storage data and observed scaling relations between sediment storage and catchment area from the Rhine catchment. We found that the model reproduces the spatial distribution of ﬂoodplain sediment storage and the scaling relationships for ﬂoodplains and hillslopes as found in observations. The exponents of the scaling relationships can be modiﬁed by changing the spatial distribution of erosion or by changing the residence time for ﬂoodplains. However, the main feature of the scaling behavior, which is that sediment storage in ﬂoodplains increases stronger with catchment area than sediment stored on hillslopes, is not changed. Based on this we argue that the scaling behavior is an emergent feature of the model and mainly dependent on the underlying topography. Additionally, we identiﬁed that land use change explains most of the temporal variability in sediment storage for the last millennium in the Rhine catchment.
Tectonic geomorphology at small catchment sizes – extensions of the stream-power approach and the χ method
Authors: Hergarten S. , Robl J. , Stüwe K.
Published: January 2016

Abstract. Quantitative tectonic geomorphology hinges on the analysis of longitudinal river profiles. The model behind almost all approaches in this field originates from an empirical relationship between channel slope and catchment size, often substantiated in the form of the stream-power model for fluvial incision. Significant methodological progress was recently achieved by introducing the χ transform. It defines a nonlinear length coordinate in such a way that the inherent curvature of river profiles due to the increase of catchment sizes in the downstream direction is removed from the analysis. However, the limitation to large catchment sizes inherited from the stream-power approach for fluvial incision persists. As a consequence, only a small fraction of all nodes of a digital elevation model (DEM) can be used for the analysis. In this study we present and discuss some empirically derived extensions of the stream power law towards small catchment sizes in order to overcome this limitation. Beyond this, we introduce a simple method for estimating the adjustable parameters in the original χ method as well as in our extended approaches. As a main result, an approach originally suggested for debris flow channels seems to be the best approximation if both large and small catchment sizes are included in the same analysis.
Short-term velocity variations at three rock glaciers and their relationship with meteorological conditions
Authors: Wirz V. , Gruber S. , Purves R. S. , Beutel J. , Gärtner-Roer I. , Gubler S. , Vieli A.
Published: January 2016

Abstract. In recent years, strong variations in the speed of rock glaciers have been detected, raising questions about their stability under changing climatic conditions. In this study, we present continuous time series of surface velocities over 3 years of six GPS stations located on three rock glaciers in Switzerland. Intra-annual velocity variations are analysed in relation to local meteorological factors, such as precipitation, snow(melt), and air and ground surface temperatures. The main focus of this study lies on the abrupt velocity peaks, which have been detected at two steep and fast-moving rock glacier tongues ( ≥  5 m a−1), and relationships to external meteorological forcing are statistically tested.The continuous measurements with high temporal resolution allowed us to detect short-term velocity peaks, which occur outside cold winter conditions, at these two rock glacier tongues. Our measurements further revealed that all rock glaciers experience clear intra-annual variations in movement in which the timing and the amplitude is reasonably similar in individual years. The seasonal decrease in velocity was typically smooth, starting 1–3 months after the seasonal decrease in temperatures, and was stronger in years with colder temperatures in mid winter. Seasonal acceleration was mostly abrupt and rapid compared to the winter deceleration, always starting during the zero curtain period. We found a statistically significant relationship between the occurrence of short-term velocity peaks and water input from heavy precipitation or snowmelt, while no velocity peak could be attributed solely to high temperatures. The findings of this study further suggest that, in addition to the short-term velocity peaks, the seasonal acceleration is also influenced by water infiltration, causing thermal advection and an increase in pore water pressure. In contrast, the amount of deceleration in winter seems to be mainly controlled by winter temperatures.