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
Iron and aluminum association with microbially processed organic matter viameso-density aggregate formation across soils: organo-metallic gluehypothesis SOIL DOI 10.5194/soil-6-597-2020 1 January 2021 Global significance of metals (extractable Fe and Al phases) to control organic matter (OM) in recognized. Next key questions include the identification of their localization and mechanism behind OM–metal relationships. Across 23 soils of contrasting mineralogy, Fe and Al phases were mainly associated with microbially processed OM as meso-density microaggregates. OM- and metal-rich nanocomposites with a narrow OM : metal ratio likely acted as binding agents. A new conceptual model was proposed. Read more
The Antarctic sea ice cover from ICESat-2 and CryoSat-2: freeboard, snow depth, and ice thickness The Cryosphere DOI 10.5194/tc-14-4453-2020 31 December 2020 Our current understanding of Antarctic ice cover is largely informed by ice extent measurements from passive microwave sensors. These records, while useful, provide a limited picture of how the ice is responding to climate change. In this paper, we combine measurements from ICESat-2 and CryoSat-2 missions to assess snow depth and ice thickness of the Antarctic ice cover over an 8-month period (April through November 2019). The potential impact of salinity in the snow layer is discussed. Read more
The catastrophic thermokarst lake drainage events of 2018 in northwesternAlaska: fast-forward into the future The Cryosphere DOI 10.5194/tc-14-4279-2020 30 December 2020 In summer 2018, northwestern Alaska was affected by widespread lake drainage which strongly exceeded previous observations. We analyzed the spatial and temporal patterns with remote sensing observations, weather data and lake-ice simulations. The preceding fall and winter season was the second warmest and wettest on record, causing the destabilization of permafrost and elevated water levels which likely led to widespread and rapid lake drainage during or right after ice breaku Read more
Focus on glaciers: a geo-photo exposition of vanishing beauty Geoscience Communication DOI 10.5194/gc-3-381-2020 29 December 2020 We organized an exhibition on the climate crisis using high-quality images shot by scientists, who are amateur photographers, during their campaigns in glacier regions. Working-age people, attracted by the gorgeous images, received the message that such beauty is in danger of vanishing. Twice, the visitors could talk directly with the experts to discuss geoscience, photography, and aesthetic choices and, of course, climate change, a problem that each of us has to play a part in to solve. Read more
Investigating the sensitivity of soil heterotrophic respiration to recent snow cover changes in Alaska using a satellite-based permafrost carbon model Biogeosciences DOI 10.5194/bg-17-5861-2020 28 December 2020 We developed a 1 km satellite-data-driven permafrost carbon model to evaluate soil respiration sensitivity to recent snow cover changes in Alaska. Results show earlier snowmelt enhances growing-season soil respiration and reduces annual carbon uptake, while early cold-season soil respiration is linked to the number of snow-free days after the land surface freezes. Our results also show nonnegligible influences of subgrid variability in surface conditions on model-simulated CO 2 seasonal cycles. Read more