Millennial-age glycerol dialkyl glycerol tetraethers (GDGTs) in forested mineral soils: 14C-based evidence for stabilization of microbial necromass Biogeosciences DOI 10.5194/bg-18-189-2021 29 January 2021 Understanding controls on the persistence of soil organic matter (SOM) is essential to constrain its role in the carbon cycle and inform climate–carbon cycle model predictions. Emerging concepts regarding the formation and turnover of SOM imply that it is mainly comprised of mineral-stabilized microbial products and residues; however, direct evidence in support of this concept remains limited. Here, we introduce and test a method for the isolation of isoprenoid and branched glycerol dialkyl glycerol tetraethers (GDGTs) – diagnostic membrane lipids of archaea and bacteria, respectively – for subsequent natural abundance radiocarbon analysis. The method is applied to depth profiles from two Swiss pre-Alpine forested soils. We find that the Δ14C values of these microbial markers markedly decrease with increasing soil depth, indicating turnover times of millennia in mineral subsoils. The contrasting metabolisms of the GDGT-producing microorganisms indicates it is unlikely that the low Δ14C values of these membrane lipids reflect heterotrophic acquisition of 14C-depleted carbon. We therefore attribute the 14C-depleted signatures of GDGTs to their physical protection through association with mineral surfaces. These findings thus provide strong evidence for the presence of stabilized microbial necromass in forested mineral soils. Read more
Increased carbon capture by a silicate-treated forested watershed affected by acid deposition Biogeosciences DOI 10.5194/bg-18-169-2021 28 January 2021 Meeting internationally agreed-upon climate targets requirescarbon dioxide removal (CDR) strategies coupled with an urgent phase-down offossil fuel emissions. However, the efficacy and wider impacts of CDR arepoorly understood. Enhanced rock weathering (ERW) is a land-based CDRstrategy requiring large-scale field trials. Here we show that a low 3.44 t ha-1 wollastonite treatment in an 11.8 ha acid-rain-impacted forested watershed in New Hampshire, USA, led to cumulative carbon capture by carbonic acid weathering of 0.025–0.13 t CO2 ha-1 over 15 years. Despite a 0.8–2.4 t CO2 ha-1 logistical carbon penalty from mining,grinding, transportation, and spreading, by 2015 weathering together withincreased forest productivity led to net CDR of 8.5–11.5 t CO2 ha-1. Our results demonstrate that ERW may be an effective, scalableCDR strategy for acid-impacted forests but at large scales requiressustainable sources of silicate rock dust. Read more
Intercomparison of freshwater fluxes over ocean and investigations into water budget closure Hydrology and Earth System Sciences DOI 10.5194/hess-25-121-2021 27 January 2021 The net exchange of water between the surface and atmosphere is mainly determined by the freshwater flux: the difference between evaporation ( E ) and precipitation ( P ), or E−P . Although there is consensus among modelers that with a warming climate E−P will increase, evidence from satellite data is still not conclusive, mainly due to sensor calibration issues. We here investigate the degree of correspondence among six recent satellite-based climate data records and ERA5 reanalysis E−P data. Read more
Evaluating the dependence structure of compound precipitation and wind speed extremes Earth System Dynamics DOI 10.5194/esd-12-1-2021 26 January 2021 Compound extremes such as heavy precipitation and extreme winds can lead to large damage. To date it is unclear how well climate models represent such compound extremes. Here we present a new measure to assess differences in the dependence structure of bivariate extremes. This measure is applied to assess differences in the dependence of compound precipitation and wind extremes between three model simulations and one reanalysis dataset in a domain in central Europe. Read more
Glider-based observations of CO2 in the Labrador Sea Ocean Science DOI 10.5194/os-17-1-2021 25 January 2021 This paper describes challenges around the direct measurement of CO 2 in the ocean using ocean gliders. We discuss our method of using multiple sensor platforms as test beds to carry out observing experiments and highlight the implications of our study for future glider missions. We also show high-resolution measurements and discuss challenges and lessons learned in the context of future ocean gas measurements. Read more
Southern Ocean Biogeochemical Argo detect under-ice phytoplankton growth before sea ice retreat Biogeosciences DOI 10.5194/bg-18-25-2021 22 January 2021 This paper examines the question of what causes the rapid spring growth of microscopic marine algae (phytoplankton) in the ice-covered ocean surrounding Antarctica. One prominent hypothesis proposes that the melting of sea ice is the primary cause, while our results suggest that this is only part of the explanation. In particular, we show that phytoplankton are able to start growing before the sea ice melts appreciably, much earlier than previously thought. Read more
Plateaus and jumps in the atmospheric radiocarbon record – potential origin and value as global age markers for glacial-to-deglacial paleoceanography, a synthesis Climate of the Past DOI 10.5194/cp-16-2547-2020 21 January 2021 The dating technique of 14 C plateau tuning uses U/Th-based model ages, refinements of the Lake Suigetsu age scale, and the link of surface ocean carbon to the globally mixed atmosphere as basis of age correlation. Our synthesis employs data of 20 sediment cores from the global ocean and offers a coherent picture of global ocean circulation evolving over glacial-to-deglacial times on semi-millennial scales to be compared with climate records stored in marine sediments, ice cores, and speleothems. Read more
Long-term deposition and condensation ice-nucleatingparticle measurements from four stations across the globe Atmospheric Chemistry and Physics DOI 10.5194/acp-20-15983-2020 20 January 2021 Long-term ice-nucleating particle (INP) data are presented from four semi-pristine sites located in the Amazon, the Caribbean, Germany and the Arctic. Average INP concentrations did not differ by orders of magnitude between the sites. For all sites short-term variability dominated the time series, which lacked clear trends and seasonalities. Common drivers to explain the INP levels and their variations could not be identified, illustrating the complex nature of heterogeneous ice nucleation. Read more
Emergent constraints on equilibrium climate sensitivity in CMIP5: do they hold for CMIP6? Earth System Dynamics DOI 10.5194/esd-11-1233-2020 19 January 2021 As an important measure of climate change, the Equilibrium Climate Sensitivity (ECS) describes the change in surface temperature after a doubling of the atmospheric CO 2 concentration. Climate models from the Coupled Model Intercomparison Project (CMIP) show a wide range in ECS. Emergent constraints are a technique to reduce uncertainties in ECS with observational data. Emergent constraints developed with data from CMIP phase 5 show reduced skill and higher ECS ranges when applied to CMIP6 data. Read more
Brief communication: Heterogenous thinning and subglacial lake activity on Thwaites Glacier, West Antarctica The Cryosphere DOI 10.5194/tc-14-4603-2020 18 January 2021 The West Antarctic Ice Sheet has long been considered geometrically prone to collapse, and Thwaites Glacier, the largest glacier in the Amundsen Sea, is likely in the early stages of disintegration. Using observations of Thwaites Glacier velocity and elevation change, we show that the transport of ~2 km 3 of water beneath Thwaites Glacier has only a small and transient effect on glacier speed relative to ongoing thinning driven by ocean melt. Read more
Downsizing parameter ensembles for simulations of rare floods Natural Hazards and Earth System Sciences DOI 10.5194/nhess-20-3521-2020 15 January 2021 This work proposes methods for reducing the computational requirements of hydrological simulations for the estimation of very rare floods that occur on average less than once in 1000 years. These methods enable the analysis of long streamflow time series (here for example 10 000 years) at low computational costs and with modelling uncertainty. They are to be used within continuous simulation frameworks with long input time series and are readily transferable to similar simulation tasks. Read more
Biases in the albedo sensitivity to deforestation in CMIP5 models and their impacts on the associated historical radiative forcing Earth System Dynamics DOI 10.5194/esd-11-1209-2020 14 January 2021 Trees are darker than crops or grasses; hence, they absorb more solar radiation. Therefore, land cover changes modify the fraction of solar radiation reflected by the land surface (its albedo), with consequences for the climate. We apply a new statistical method to simulations conducted with 15 recent climate models and find that albedo variations due to land cover changes since 1860 have led to a decrease in the net amount of energy entering the atmosphere by −0.09 W m 2 on average. Read more
Quantifying CO2 emissions of a city with the Copernicus Anthropogenic CO2 Monitoring satellite mission Atmospheric Measurement Techniques DOI 10.5194/amt-13-6733-2020 13 January 2021 The European CO2M mission is a proposed constellation of CO 2 imaging satellites expected to monitor CO 2 emissions of large cities. Using synthetic observations, we show that a constellation of two or more satellites should be able to quantify Berlin’s annual emissions with 10–20 % accuracy, even when considering atmospheric transport model errors. We therefore expect that CO2M will make an important contribution to the monitoring and verification of CO 2 emissions from cities worldwide. Read more
New global characterisation of landslide exposure Natural Hazards and Earth System Sciences DOI 10.5194/nhess-20-3413-2020 12 January 2021 Landslides cause thousands of fatalities and cost billions of dollars of damage worldwide every year, but different inventories of landslide events can have widely diverging completeness. This can lead to spatial biases in our understanding of the impacts. Here we use a globally homogeneous model of landslide hazard and exposure to provide consistent estimates of where landslides are most likely to cause damage to people, roads and other critical infrastructure at 1 km resolution. Read more
Tropical Pacific climate variability under solar geoengineering: impacts onENSO extremes Atmospheric Chemistry and Physics DOI 10.5194/acp-20-15461-2020 11 January 2021 Solar geoengineering has been introduced to mitigate human-caused global warming by reflecting sunlight back into space. This research investigates the impact of solar geoengineering on the tropical Pacific climate. We find that solar geoengineering can compensate some of the greenhouse-induced changes in the tropical Pacific but not all. In particular, solar geoengineering will result in significant changes in rainfall, sea surface temperatures, and increased frequency of extreme ENSO events. Read more
Sea ice dynamics in the Bransfield Strait, Antarctic Peninsula, during the past 240 years: a multi-proxy intercomparison study Climate of the Past DOI 10.5194/cp-16-2459-2020 8 January 2021 We tested the applicability of the organic biomarker IPSO 25 for sea ice reconstructions in the industrial era at the western Antarctic Peninsula. We successfully evaluated our data with satellite sea ice observations. The comparison with marine and ice core records revealed that sea ice interpretations must consider climatic and sea ice dynamics. Sea ice biomarker production is mainly influenced by the Southern Annular Mode, while the El Niño–Southern Oscillation seems to have a minor impact. Read more
Optical characterization of pure pollen types using a multi-wavelength Raman polarization lidar Atmospheric Chemistry and Physics DOI 10.5194/acp-20-15323-2020 7 January 2021 Measurements of the multi-wavelength Raman polarization lidar Polly XT have been combined with measurements of pollen type and concentration using a traditional pollen sampler at a rural forest site in Kuopio, Finland. The depolarization ratio was enhanced when there were pollen grains in the atmosphere, illustrating the potential of lidar to track pollen grains in the atmosphere. The depolarization ratio of pure pollen particles was assessed for birch and pine pollen using a novel algorithm. Read more
Combined use of Mie–Raman and fluorescence lidar observations for improving aerosol characterization: feasibility experiment Atmospheric Measurement Techniques DOI 10.5194/amt-13-6691-2020 6 January 2021 To study the feasibility of a fluorescence lidar for aerosol characterization, the fluorescence channel is added to the multiwavelength Mie-Raman lidar of Lille University. A part of the fluorescence spectrum is selected by the interference filter of 44 nm bandwidth centered at 466 nm. Such an approach has demonstrated high sensitivity, allowing fluorescence signals from weak aerosol layers to be detected. The technique can also be used for monitoring the aerosol inside the cloud layers. Read more
The dual-field-of-view polarization lidar technique: a new concept in monitoring aerosol effects in liquid-water clouds – theoretical framework Atmospheric Chemistry and Physics DOI 10.5194/acp-20-15247-2020 5 January 2021 A novel lidar method to study cloud microphysical properties (of liquid water clouds) and to study aerosol–cloud interaction (ACI) is developed and presented in this paper. In Part 1, the theoretical framework including an error analysis is given together with an overview of the aerosol information that the same lidar system can obtain. The ACI concept based on aerosol and cloud information is also explained. Applications of the proposed approach to lidar measurements are presented in Part 2. Read more
Evolution of events before and after the 17 June 2017 rock avalanche at Karrat Fjord, West Greenland – a multidisciplinary approach to detecting andlocating unstable rock slopes in a remote Arctic area Earth Surface Dynamics DOI 10.5194/esurf-8-1021-2020 4 January 2021 The 17 June 2017 Karrat landslide in Greenland caused a tsunami that killed four people. We apply a multidisciplinary workflow to reconstruct a timeline of events and find that three historic landslides occurred in 2009, 2016, and 2017. We also find evidence of much older periods of landslide activity. Three newly discovered active slopes might pose a future hazard. We speculate that the trigger for the recent events is melting permafrost due to a warming climate. Read more