ALBERT

Description: We modeled the regional carbon balance of sub‐Arctic tundra over a decade in a region with lakes, wetlands, and uplands using process‐based biogeochemical models. Interannual variability over the decade was relatively small in comparison with variability among the land cover types. Wetlands were hot spots for C cycling in this sub‐Arctic tundra ecosystem. Capturing the relative fraction of uplands versus wetlands was key to determining the net regional C balance at this and other Arctic tundra sites. Abstract Across the Arctic, the net ecosystem carbon (C) balance of tundra ecosystems is highly uncertain due to substantial temporal variability of C fluxes and to landscape heterogeneity. We modeled both carbon dioxide (CO2) and methane (CH4) fluxes for the dominant land cover types in a ~100‐km2 sub‐Arctic tundra region in northeast European Russia for the period of 2006–2015 using process‐based biogeochemical models. Modeled net annual CO2 fluxes ranged from −300 g C m−2 year−1 [net uptake] in a willow fen to 3 g C m−2 year−1 [net source] in dry lichen tundra. Modeled annual CH4 emissions ranged from −0.2 to 22.3 g C m−2 year−1 at a peat plateau site and a willow fen site, respectively. Interannual variability over the decade was relatively small (20%–25%) in comparison with variability among the land cover types (150%). Using high‐resolution land cover classification, the region was a net sink of atmospheric CO2 across most land cover types but a net source of CH4 to the atmosphere due to high emissions from permafrost‐free fens. Using a lower resolution for land cover classification resulted in a 20%–65% underestimation of regional CH4 flux relative to high‐resolution classification and smaller (10%) overestimation of regional CO2 uptake due to the underestimation of wetland area by 60%. The relative fraction of uplands versus wetlands was key to determining the net regional C balance at this and other Arctic tundra sites because wetlands were hot spots for C cycling in Arctic tundra ecosystems.

Description: Effects of elevated CO2 treatments (ambient: 503 µatm, elevated: 1,179 µatm) and differences in food availability on cod larval growth, skeletogenesis (vertebrate ossification) and gill development were analysed. Larvae fed ad libitum showed little difference in growth and skeletogenesis due to the CO2 treatment, but larvae under energy limitation were significantly larger and had further developed skeletal structures in the elevated CO2 treatment. However, the elevated CO2 group had comparatively smaller functional gills indicating a mismatch between size and function and a trade‐off between growth and organ development, which is critically important to interpret acidification effects on early life stages of fish. Abstract In order to understand the effect of global change on marine fishes, it is imperative to quantify the effects on fundamental parameters such as survival and growth. Larval survival and recruitment of the Atlantic cod (Gadus morhua) were found to be heavily impaired by end‐of‐century levels of ocean acidification. Here, we analysed larval growth among 35–36 days old surviving larvae, along with organ development and ossification of the skeleton. We combined CO2 treatments (ambient: 503 µatm, elevated: 1,179 µatm) with food availability in order to evaluate the effect of energy limitation in addition to the ocean acidification stressor. As expected, larval size (as a proxy for growth) and skeletogenesis were positively affected by high food availability. We found significant interactions between acidification and food availability. Larvae fed ad libitum showed little difference in growth and skeletogenesis due to the CO2 treatment. Larvae under energy limitation were significantly larger and had further developed skeletal structures in the elevated CO2 treatment compared to the ambient CO2 treatment. However, the elevated CO2 group revealed impairments in critically important organs, such as the liver, and had comparatively smaller functional gills indicating a mismatch between size and function. It is therefore likely that individual larvae that had survived acidification treatments will suffer from impairments later during ontogeny. Our study highlights important allocation trade‐off between growth and organ development, which is critically important to interpret acidification effects on early life stages of fish.

Description: Climate change research has demonstrated that changing temperatures will have an effect on community-level dynamics by altering species’ survival rates, shifting species’ distributions, and ultimately, creating mismatches in community interactions. However, most of this work has focused on increasing temperature, and still little is known about how the variation in temperature extremes will affect community dynamics. We used the model aquatic community held within the leaves of the carnivorous plant, Sarracenia purpurea , to test how food-web dynamics will be affected by high temperature variation. We tested the community response of the first (bacterial density), second (protist diversity and composition), and third trophic level (predator mortality), and measured community respiration. We collected early and late successional stage inquiline communities from S. purpurea from two North American and two European sites with similar average July temperature. We then created a common garden experiment in which replicates of these communities underwent either high or normal daily temperature variation, with the average temperature equal among treatments. We found an impact of temperature variation on the first two, but not on the third trophic level. For bacteria in the high variation treatment, density experienced an initial boost in growth but then decreased quickly through time. For protists in the high variation treatment, alpha-diversity decreased faster than in the normal variation treatment, beta-diversity increased only in the European sites, and protist community composition tended to diverge more in the late successional stage. The mortality of the predatory mosquito larvae was unaffected by temperature variation. Community respiration was lower in the high variation treatment, indicating a lower ecosystem functioning. Our results highlight clear impacts of temperature variation. A more mechanistic understanding of the effects that temperature, and especially temperature variation, will have on community dynamics is still greatly needed. This article is protected by copyright. All rights reserved.

Description: Most chemistry-climate models show an intensification of the Brewer-Dobson circulation (BDC) in the stratosphere associated with increasing greenhouse gas emissions and ozone depletion in the last decades, but this trend remains to be confirmed inobservational data. In this work the evolution of the advective BDC for the period 1979–2012 is evaluated and compared in three modern reanalyses (ERA-Interim, MERRA and JRA-55). Three different estimates of the BDC are computed for each reanalysis, one based on the definition of the residual circulation and two indirect estimates derived from momentum and thermodynamic balances. The comparison among the nine estimates shows substantial uncertainty in the mean magnitude (~40%) but significant common variability. The tropical upwelling series show variability linked to the stratospheric Quasi-Biennial Oscillation (QBO) and to El Nino-Southern Oscillation (ENSO), and also reflect extreme events such as major Sudden Stratospheric Warmings (SSW) and volcanic eruptions. The trend analysis suggests a strengthening of tropical upwelling of around 2-5%/decade throughout the layer 100–10 hPa. The global spatial structure of the BDC trends provides evidence of an overall accelerationof the circulation in both hemispheres, with qualitative agreement among the estimates. The global BDC trends are mainly linked to changes in the boreal winter season and can be tracked to long-term increases in the resolved wave drag in both hemispheres.

Description: Based on multi-annual simulations with the Chemical Lagrangian Model of the Stratosphere (CLaMS), driven by ECMWF ERA-Interim reanalysis, we discuss hemispheric asymmetries and the seasonality of the mean age of air (AoA) in the lower stratosphere. First, the planetary wave forcing of the Brewer-Dobson (BD) circulation is quantified in terms of Eliassen Palm (EP) flux divergence calculated by using the isentropic coordinate θ . While the forcing of the deep branch at θ  = 1000 K (around 10 hPa) has a clear maximum in each hemisphere during the respective winter, the shallow branch of the BD circulation, i.e. between 100 and 70 hPa (380 〈  θ  〈 420 K), shows almost opposite seasonality in both hemispheres with a pronounced minimum between June and September in the SH. Second, we decompose the time-tendency of AoA into the contributions of the residual circulation and of eddy mixing by analyzing the zonally averaged tracer continuity equation. In the tropical lower stratosphere between ± 30 ∘ , the air becomes younger during boreal winter and older during boreal summer. During boreal winter, the decrease of AoA due to tropical upwelling outweighs aging by isentropic mixing. In contrast, weaker isentropic mixing outweighs an even weaker upwelling in boreal summer and fall making the air older during these seasons. Poleward of 60 ∘ , the deep branch locally increases AoA and eddy mixing locally decreases AoA with the strongest net decrease during spring. Eddy mixing in the NH outweighs that in the SH throughout the year.

Description: The Intergovernmental Panel for Climate Change (IPCC) reports that Global Environmental Changes (GEC) are occurring quicker than at any other time over the last 25 million years and impacting upon marine environments (Bellard et al ., 2012). There is overwhelming evidence showing that GEC are affecting both the quality and quantity of the goods and services provided by a wide range of marine ecosystems. In order to discuss regional preparedness for global environmental changes, a workshop was held in Ilhabela, Brazil (22- 26 April 2012) entitled “Evaluating the Sensitivity of Central and South American Benthic Communities to Global Environmental Changes” that drew together scientists from ten Latin American and three European countries. © 2013 Blackwell Publishing Ltd

Description: [1]  Through an analysis of multiple global fossil fuel CO 2 emission data sets, Vulcan emission data for the United States, Canada's National Inventory Report, and NO 2 variability based on satellite observations, we derive scale factors that can be applied to global emission data sets to represent weekly and diurnal CO 2 emission variability. This is important for inverse modeling and data assimilation of CO 2 , which use in situ or satellite measurements subject to variability on these time scales. Model simulations applying the weekly and diurnal scaling show that, although the impacts are minor far away from sources, surface atmospheric CO 2 is perturbed by up to 1.5−8 ppm and column-averaged CO 2 is perturbed by 0.1−0.5 ppm over some major cities, suggesting the magnitude of model biases for urban areas when these modes of temporal variability are not represented. In addition, we also derive scale factors to account for the large per capita differences in CO 2 emissions between Canadian provinces that arise from differences in per capita energy use and the proportion of energy generated by methods that do not emit CO 2 , which are not accounted for in population-based global emission data sets. The resulting products of these analyses are global 0.25° × 0.25° gridded scale factor maps that can be applied to global fossil fuel CO 2 emission data sets to represent weekly and diurnal variability and 1° × 1° scale factor maps to redistribute spatially emissions from two common global data sets to account for differences in per capita emissions within Canada.

Description: Cats are generalist predators that have been widely introduced to the world's ~179,000 islands. Once introduced to islands, cats prey on a variety of native species many of which lack evolved defenses against mammalian predators and can suffer severe population declines and even extinction. Because islands house a disproportionate share of terrestrial biodiversity, the impacts of invasive cats on islands may have significant biodiversity impacts. Much of this threatened biodiversity can be protected by eradicating cats from islands. Information on the relative impacts of cats on different native species in different types of island ecosystems can increase the efficiency of this conservation tool. We reviewed feral cat impacts on native island vertebrates. Impacts of feral cats on vertebrates have been reported from at least in 120 different islands on at least 175 vertebrates (25 reptiles, 123 birds and 27 mammals), many of which are listed by the International Union for the Conservation of Nature. A meta-analysis suggests that cat impacts were greatest on endemic species, particularly mammals and greater when non-native prey species were also introduced. Feral cats on islands are responsible for at least 14% global bird, mammal and reptile extinctions and are the principal threat to almost 8% of Critically Endangered birds, mammals and reptiles.

Description: The uncertainty of broadband shortwave radiation monitoring is determined for direct, diffuse and global irradiance for measurements obtained at the Payerne (Switzerland) station of the Baseline Surface Radiation Network (BSRN). The uncertainty estimates include sources that reflect realistic long-term operation conditions. The uncertainties are derived using the methodology specified by the “Guide to the expression of uncertainty in measurement”. The differences between redundant determinations of direct, diffuse and global irradiance are analyzed and are shown to be compatible with the uncertainties. In addition, the signatures of some uncertainty sources are sought within the error statistics, to find out if corrections can be applied and what their magnitude is. The global and diffuse irradiance uncertainties range from 1.8% to 2.4% without correction, and are less than 1.8% with corrections. These uncertainties are close to or satisfy the BSRN targets for large signals (global: 1000 Wm -2 , diffuse: 500 Wm -2 ). For small signals (50 Wm -2 ), the targets are not achieved, mainly as a result of uncertainties associated with the data acquisition electronics (DAQ). The direct irradiance uncertainty is ~1.5%, 3 times larger than the BSRN uncertainty target. An accuracy gain can also be achieved at the DAQ level, but even without considering the DAQ uncertainty, the target is exceeded by a factor of about two. The direct irradiance uncertainty remains ~1% even using an absolute cavity radiometer as transfer standard for correcting the pyrheliometer sensitivity. Thus, the direct irradiance accuracy target of 0.5% is probably not achievable with the best commercially available technology.

Description: Abstract It has recently been recognized that, in addition to greenhouse gases, anthropogenic emissions of ozone depleting substances (ODS) can induce long‐term trends in the Brewer‐Dobson circulation (BDC). Several studies have shown that a substantial fraction of the residual circulation acceleration over the last decades of the 20th century can be attributed to increasing ODS. Here, the mechanisms of this influence are examined, comparing model runs to reanalysis data and evaluating separately the residual circulation and mixing contributions to the mean age of air (AoA) trends. The effects of ozone depletion in the Antarctic lower stratosphere are found to dominate the ODS impact on the BDC, while the direct radiative impact of these substances is negligible over the period of study. We find qualitative agreement in austral summer BDC trends between model and reanalysis data, and show that ODS are the main driver of both residual circulation and isentropic mixing trends over the last decades of the 20th century. Moreover, isentropic mixing is shown to play a key role on ODS‐driven AoA trends.