ALBERT

Description: Climate variability can induce rapid changes in peatland ecosystems, affecting both carbon cycling and vegetation succession. Diatoms are an important group of ubiquitous and diverse algae in peatlands. Until now, the responses of diatom communities to climate variability have rarely been explored in peatlands, especially in subtropical regions. In this study, monitoring and paleolimnological datasets were combined to decipher environmental changes of a subtropical montane peatland (central China) over the last two centuries. Seasonal monitoring data revealed that diatom communities were closely correlated with precipitation, depth to the water table, conductivity, nitrate and temperature. Sedimentary records revealed that temporal changes in diatom assemblages and geochemical elements displayed similar trends in two peat cores after the 1950s. The first gradient in diatom composition represented a shift from Pinnularia species to taxa preferring less-acidic habitats, which was closely linked to climate warming and the enrichment of inorganic elements (e.g. sodium and calcium) since the early 20th century. Meanwhile, changes in diatom communities were further related to precipitation variability, atmospheric deposition and local hydrogeomophic setting. Taken together, the succession of diatom communities was closely linked to climate-regulated availability of nutrients and moisture in this subtropical peatland over the last two centuries. In order to achieve sustainable management of these scarce peatlands, further biological monitoring and paleoecological studies are needed to improve our knowledge of peatland ecosystem evolution in response to future climate change.

Description: In situ measurements of aerosol microphysical, chemical, and optical properties were made during global-scale flights from 2016–2018 as part of the Atmospheric Tomography Mission (ATom). The NASA DC-8 aircraft flew from ∼ 84∘ N to ∼ 86∘ S latitude over the Pacific, Atlantic, Arctic, and Southern oceans while profiling nearly continuously between altitudes of ∼ 160 m and ∼ 12 km. These global circuits were made once each season. Particle size distributions measured in the aircraft cabin at dry conditions and with an underwing probe at ambient conditions were combined with bulk and single-particle composition observations and measurements of water vapor, pressure, and temperature to estimate aerosol hygroscopicity and hygroscopic growth factors and calculate size distributions at ambient relative humidity. These reconstructed, composition-resolved ambient size distributions were used to estimate intensive and extensive aerosol properties, including single-scatter albedo, the asymmetry parameter, extinction, absorption, Ångström exponents, and aerosol optical depth (AOD) at several wavelengths, as well as cloud condensation nuclei (CCN) concentrations at fixed supersaturations and lognormal fits to four modes. Dry extinction and absorption were compared with direct in situ measurements, and AOD derived from the extinction profiles was compared with remotely sensed AOD measurements from the ground-based Aerosol Robotic Network (AERONET); this comparison showed no substantial bias. The purpose of this work is to describe the methodology by which ambient aerosol properties are estimated from the in situ measurements, provide statistical descriptions of the aerosol characteristics of different remote air mass types, examine the contributions to AOD from different aerosol types in different air masses, and provide an entry point to the ATom aerosol database. The contributions of different aerosol types (dust, sea salt, biomass burning, etc.) to AOD generally align with expectations based on location of the profiles relative to continental sources of aerosols, with sea salt and aerosol water dominating the column extinction in most remote environments and dust and biomass burning (BB) particles contributing substantially to AOD, especially downwind of the African continent. Contributions of dust and BB aerosols to AOD were also significant in the free troposphere over the North Pacific. Comparisons of lognormally fitted size distribution parameters to values in the Optical Properties of Aerosols and Clouds (OPAC) database commonly used in global models show significant differences in the mean diameters and standard deviations for accumulation-mode particles and coarse-mode dust. In contrast, comparisons of lognormal parameters derived from the ATom data with previously published shipborne measurements in the remote marine boundary layer show general agreement. The dataset resulting from this work can be used to improve global-scale representation of climate-relevant aerosol properties in remote air masses through comparison with output from global models and assumptions used in retrievals of aerosol properties from both ground-based and satellite remote sensing.