Non-destructive evaluation of moisture content in wood using ground-penetrating radar Geoscientific Instrumentation, Methods and Data Systems DOI 10.5194/gi-5-575-2016 16 December 2016 Ground-penetrating radar (GPR) is a powerful tool that uses electromagnetic waves to obtain 3-dimensional images of natural or man-made structures and subsoil. It is employed in a large variety of applications in which non-destructive investigations are required. This paper deals with the use of GPR for the evaluation of moisture content in wood. The results of our work are of great interest for the preservation of timber structures, as moisture content is highly relevant to wood deterioration. Read more
Last Interglacial climate and sea-level evolution from a coupled ice sheet–climate model Climate of the Past DOI 10.5194/cp-12-2195-2016 15 December 2016 We simulate the climate, ice sheet, and sea-level evolution during the Last Interglacial (~ 130 to 115 kyr BP), the most recent warm period in Earth’s history. Our Earth system model includes components representing the atmosphere, the ocean and sea ice, the terrestrial biosphere, and the Greenland and Antarctic ice sheets. Our simulation is in good agreement with available data reconstructions and gives important insights into the dominant mechanisms that caused ice sheet changes in the past. Read more
Graffiti for science – erosion painting reveals spatially variable erosivity of sediment-laden flows Earth Surface Dynamics DOI 10.5194/esurf-4-885-2016 15 December 2016 Spatial bedrock erosion data from stream channels are important for engineering issues and landscape evolution model assessment. However, acquiring such data is challenging and only few data sets exist. Detecting changes in repeated photographs of painted bedrock surfaces easily allows for semi-quantitative conclusions on the spatial distribution of sediment transport and its effects: abrasion on surfaces facing the streamflow and shielding of surfaces by abundant sediment. Read more
North American regional climate reconstruction from ground surface temperature histories Climate of the Past DOI 10.5194/cp-12-2181-2016 14 December 2016 Within the framework of the PAGES NAm2k project, we estimated regional trends in the ground surface temperature change for the past 500 years in North America. The mean North American ground surface temperature history suggests a warming of 1.8 °C between preindustrial times and 2000. A regional analysis of mean temperature changes over the last 5 centuries shows that all regions experienced warming, but this warming displays large spatial variability and is more marked in high-latitude regions. Read more
The acid-catalyzed hydrolysis of an α-pinene-derived organic nitrate: kinetics, products, reaction mechanisms, and atmospheric impact Atmospheric Chemistry and Physics DOI 10.5194/acp-16-15425-2016 13 December 2016 This study provides new insight into the hydrolysis reaction mechanism, which was elucidated for atmospherically relevant organic nitrates using kinetic measurements, product identification, and theoretical calculations. The results help broaden our knowledge of the organic chemistry that impacts the fate of NOx, ozone production, aerosol phase processing, and aerosol composition. Read more
Use of remote-sensing reflectance to constrain a data assimilating marine biogeochemical model of the Great Barrier Reef Biogeosciences DOI 10.5194/bg-13-6441-2016 7 December 2016 Marine biogeochemical models are often used to understand water quality, nutrient and blue-carbon dynamics at scales that range from estuaries and bays, through to the global ocean. We introduce a new methodology allowing for the assimilation of observed remote sensing reflectances, avoiding the need to use empirically derived chlorophyll-a concentrations. This method opens up the possibility to assimilate of reflectances from a variety of missions and potentially non-satellite platforms. Read more
Significant concentrations of nitryl chloride sustained in the morning: investigations of the causes and impacts on ozone production in a polluted region of northern China Atmospheric Chemistry and Physics DOI 10.5194/acp-16-14959-2016 5 December 2016 This work addresses the unclear global significance of chlorine activation processes in the troposphere. The first high-quality measurement data set of ClNO2in northern China revealed strong ClNO2 production in the residual layers, and demonstrated its significant effects on radical budget and ozone production. Our findings imply the widespread effects of ClNO2 over the polluted regions of northern China, which may increase photochemical and haze pollution. Read more
The 1430s: a cold period of extraordinary internal climate variability during the early Spörer Minimum with social and economic impacts in north-western and central Europe Climate of the Past DOI 10.5194/cp-12-2107-2016 1 December 2016 Throughout the last millennium, several cold periods occurred which affected humanity. Here, we investigate an exceptionally cold decade during the 15th century. The cold conditions challenged the food production and led to increasing food prices and a famine in parts of Europe. In contrast to periods such as the “Year Without Summer” after the eruption of Tambora, these extreme climatic conditions seem to have occurred by chance and in relation to the internal variability of the climate system. Read more
Linking hydraulic traits to tropical forest function in a size-structured and trait-driven model (TFS v.1-Hydro) Geoscientific Model Development DOI 10.5194/gmd-9-4227-2016 24 November 2016 We developed a plant hydraulics model for tropical forests based on established plant physiological theory, and parameterized it by conducting a pantropical hydraulic trait survey. We show that a substantial amount of trait diversity can be represented in the model by a reduced set of trait dimensions. The fully parameterized model is able capture tree-level variation in water status and improves simulations of total ecosystem transpiration, showing how to incorporate hydraulic traits in models. Read more
Multi-annual modes in the 20th century temperature variability in reanalyses and CMIP5 models Geoscientific Model Development DOI 10.5194/gmd-9-4097-2016 17 November 2016 This study compares the 20th century multi-annual climate variability modes in reanalysis data sets (ERA-20C and 20CR) and 12 climate model simulations using the randomised multi-channel singular spectrum analysis. The reanalysis data sets are remarkably similar on all timescales, except that the spectral power in ERA-20C is systematically slightly higher than in 20CR. None of the climate models closely reproduce all aspects of the reanalysis spectra, although many aspects are represented well. Read more
Quantifying the loss of processed natural gas within California’s South Coast Air Basin using long-term measurements of ethane and methane Atmospheric Chemistry and Physics DOI 10.5194/acp-16-14091-2016 15 November 2016 This paper investigates the cause of the known underestimate of bottom-up inventories of methane in California’s South Coast Air Basin (SoCAB). We use total column measurements of methane, ethane, carbon monoxide, and other trace gases beginning in the late 1980s to calculate emissions and attribute sources of excess methane to the atmosphere. We conclude that more than half of the excess methane to the SoCAB atmosphere is attributable to processed natural gas. Read more
Refinement of the ice absorption spectrum in the visible using radiance profile measurements in Antarctic snow The Cryosphere DOI 10.5194/tc-10-2655-2016 14 November 2016 The absorption of visible light in ice is very weak but its precise value is unknown. By measuring the profile of light intensity in snow, Warren and Brand (2006) deduced that light is attenuated by a factor 2 per kilometer in pure ice at a wavelength of 400 nm. We replicated their experiment on a large number of samples and found that ice absorption is at least 10 times stronger. The paper explores various potential physical and statistical biases that could impact the experiment. Read more
Accounting for model error in air quality forecasts: an application of 4DEnVar to the assimilation of atmospheric composition using QG-Chem 1.0 Geoscientific Model Development DOI 10.5194/gmd-9-3933-2016 8 November 2016 This paper analyses methods to assimilate chemical measurements in air quality models. We developed a reduced-order atmospheric chemistry model, which was used to compare results from different assimilation algorithms. Using an ensemble variational method (4DEnVar), we exploited the dynamical information provided by hourly measurements of chemical concentrations to diagnose model biases and improve next-day forecasts for several species of interest for air quality. Read more
Brief communication: Impacts of a developing polynya off Commonwealth Bay, East Antarctica, triggered by grounding of iceberg B09B The Cryosphere DOI 10.5194/tc-10-2603-2016 4 November 2016 Here we report new data from in situ oceanographic surveys and high-resolution ocean modelling experiments in the Commonwealth Bay region of East Antarctica, where in 2010 there was a major reconfiguration of the regional icescape due to the collision of the 97 km long iceberg B09B with the Mertz Glacier tongue. Here we compare post-calving observations with high-resolution ocean modelling which suggest that this reconfiguration has led to the development of a new polynya off Commonwealth Bay. Read more
Effects of ocean acidification on pelagic carbon fluxes in a mesocosm experiment Biogeosciences DOI 10.5194/bg-13-6081-2016 4 November 2016 We performed an experiment in the Baltic Sea in order to investigate the consequences of the increasing CO2levels on biological processes in the free water mass. There was more accumulation of organic carbon at high CO2levels. Surprisingly, this was caused by reduced loss processes (respiration and bacterial production) in a high-CO2environment, and not by increased photosynthetic fixation of CO2. Our carbon budget can be used to better disentangle the effects of ocean acidification. Read more
Seasonal evolution of the effective thermal conductivity of the snow and the soil in high Arctic herb tundra at Bylot Island, Canada The Cryosphere DOI 10.5194/tc-10-2573-2016 2 November 2016 The thermal conductivity (TC) of the snow and top soil greatly impacts the permafrost energy budget. We report the first winter-long monitoring of snow and soil TC in the high Arctic. The data and field observations show the formation of a highly insulating basal depth hoar layer overlaid by a more conductive wind slab. Detailed snow physics models developed for alpine snow cannot reproduce observations because they neglect the strong upward vertical water vapor flux prevailing in Arctic snow. Read more
Towards improved and more routine Earth system model evaluation in CMIP Earth System Dynamics DOI 10.5194/esd-7-813-2016 1 November 2016 We argue that the CMIP community has reached a critical juncture at which many baseline aspects of model evaluation need to be performed much more efficiently to enable a systematic and rapid performance assessment of the large number of models participating in CMIP, and we announce our intention to implement such a system for CMIP6. At the same time, continuous scientific research is required to develop innovative metrics and diagnostics that help narrowing the spread in climate projections. Read more
The BErkeley Atmospheric CO2 Observation Network: initial evaluation Atmospheric Chemistry and Physics DOI 10.5194/acp-16-13449-2016 31 October 2016 We describe the design of and first results from the BErkeley Atmospheric CO2 Observation Network, a distributed instrument of 28 CO2 sensors stationed across and around the city of Oakland, California at ~ 2 km intervals. We evaluate the network via 4 performance parameters (cost, reliability, precision, systematic uncertainty) and find this high density technique to be sufficiently cost-effective and rigorous to inform understanding of small-scale urban emissions relevant to climate regulation. Read more
Ice core evidence for a 20th century increase in surface mass balance in coastal Dronning Maud Land, East Antarctica The Cryosphere DOI 10.5194/tc-10-2501-2016 25 October 2016 The reconstruction of past snow accumulation rates is crucial in the context of recent climate change and sea level rise. We measured ~ 250 years of snow accumulation using a 120 m ice core drilled in coastal East Antarctica, where such long records are very scarce. This study is the first to show an increase in snow accumulation, beginning in the 20th and particularly marked in the last 50 years, thereby confirming model predictions of increased snowfall associated with climate change. Read more
Leaf waxes in litter and topsoils along a European transect SOIL DOI 10.5194/soil-2-551-2016 25 October 2016 For this study we systematically investigated the molecular pattern of leaf waxes in litter and topsoils along a European transect to assess their potential for palaeoenvironmental reconstruction. Our results show that leaf wax patterns depend on the type of vegetation. The vegetation signal is not only found in the litter; it can also be preserved to some degree in the topsoil. Read more