Surface waters contribute substantially to carbon dioxide (CO₂) emissions to the atmosphere. However, global estimates remain uncertain due to methodological difficulties, such as in precisely ...estimating gas transfer in steep upland streams. Here, we addressed the question of what drives CO₂ evasion from steep mountainous stream network of the European Alps by assessing the spatial and temporal variation of partial pressure of CO₂ (pCO₂) for 148 streams and the gas transfer coefficient for CO₂ (k
CO2) for 88 locations within this 254 km² watershed. Results show that log kCO2 can be predicted reasonably well (r² = 0.71, p<0.001, n = 88) using a statistical model based on slope, average width, flow velocity and stream discharge. Also, most sites were supersaturated in CO₂ with significant variation in pCO₂ due to season (September vs. December) and time of day (day vs. night), but not stream order. Resulting median CO₂ evasion rates were 145, 119, 46, 43, and 50 mg C m−2 h−1 at 1st to 5th order streams, respectively. CO₂ evasion was dependent on season and time of day, with the highest evasion (184.0 kg C h−1) during growing season at nighttime, followed by 124.6 kg C h−1 during daytime. Dormant season nighttime evasion was 30.9 kg C h−1 and daytime evasion only 17.1 kg C h−1. Overall we conclude that CO₂ evasion of steep mountainous streams depends on seasonal and diurnal variation in pCO₂ and reach-specific variability in k
CO2. These controls strongly alter landscape-scale CO₂ evasion estimates, with implications for regional to global carbon budgets.
Intrusions of warm, moist air into the Arctic during winter have emerged as important contributors to Arctic surface warming. Previous studies indicate that temperature, moisture, and hydrometeor ...enhancements during intrusions all make contributions to surface warming via emission of radiation down to the surface. Here, datasets from instrumentation at the Atmospheric Radiation Measurement User Facility in Utqiaġvik (formerly Barrow) for the six months from November through April for the six winter seasons of 2013/14–2018/19 were used to quantify the atmospheric state. These datasets subsequently served as inputs to compute surface downwelling longwave irradiances via radiative transfer computations at 1-min intervals with different combinations of constituents over the six winter seasons. The computed six winter average irradiance with all constituents included was 205.0 W m−2, close to the average measured irradiance of 206.7 W m−2, a difference of −0.8%. During this period, water vapor was the most important contributor to the irradiance. The computed average irradiance with dry gas was 71.9 W m−2. Separately adding water vapor, liquid, or ice to the dry atmosphere led to average increases of 2.4, 1.8, and 1.6 times the dry atmosphere irradiance, respectively. During the analysis period, 15 episodes of warm, moist air intrusions were identified. During the intrusions, individual contributions from elevated temperature, water vapor, liquid water, and ice water were found to be comparable to each other. These findings indicate that all properties of the atmospheric state must be known in order to quantify the radiation coming down to the Arctic surface during winter.
Characterizing variability in the global water cycle is fundamental to predicting impacts of future climate change; understanding the role of the Pacific Walker circulation (PWC) in the regional ...expression of global water cycle changes is critical to understanding this variability. Water isotopes are ideal tracers of the role of the PWC in global water cycling because they retain information about circulation-dependent processes including moisture source, transport, and delivery. We collated publicly available measurements of precipitation 𝛿18O (𝛿18O𝑃) and used novel data processing techniques to synthesize long (34 yr), globally distributed composite records from temporally discontinuous 𝛿18O𝑃 measurements. We investigated relationships between global-scale 𝛿18O𝑃 variability and PWC strength, as well as other possible drivers of global 𝛿18O𝑃 variability—including El Niño–Southern Oscillation (ENSO) and global mean temperature—and used isotope-enabled climate model simulations to assess potential biases arising from uneven geographical distribution of the observations or our data processing methodology. Covariability underlying the 𝛿18O𝑃 composites is more strongly correlated with the PWC (r = 0.74) than any other index of climate variability tested. We propose that the PWC imprint in global 𝛿18O𝑃 arises from multiple complementary processes, including PWC-related changes in moisture source and transport length, and a PWC- or ENSO-driven "amount effect" in tropical regions. The clear PWC imprint in global 𝛿18O𝑃 implies a strong PWC influence on the regional expression of global water cycle variability on interannual to decadal time scales, and hence that uncertainty in the future state of the PWC translates to uncertainties in future changes in the global water cycle.
The Victoria mode (VM) is the second dominant sea surface temperature mode in the North Pacific, forced by North Pacific Oscillation–like extratropical atmospheric variability. Observational studies ...have shown that the boreal spring VM is closely connected to the following winter El Niño, with the VM efficiently acting as a precursor signal to El Niño events. This study evaluates the relationship of the spring VM with subsequent winter El Niño in the preindustrial simulations of phases 5 and 6 of the Coupled Model Intercomparison Project (CMIP5 and CMIP6).We found that most CMIP5 and CMIP6 models can simulate the basic characteristics of the VM reasonably well. The current CMIP6 models simulate the VM–El Niño connections more realistically as compared to the earlier CMIP5 models. The analysis further suggests that the improved capability of the CMIP6 models to simulate the VM–El Niño relationship is because the CMIP6 models are better able to capture the VM-related surface air–sea thermodynamic coupling process over the subtropical/tropical Pacific and the seasonal evolution of VM-related anomalous subsurface ocean temperature in the equatorial Pacific.
As with many social trans fer schemes, pension systems around the world are often progressive: individuals with lower incomes receive a higher percent age of their income as a subsequent pension. On ...the other hand, those with lower earn ings have higher mortality and thus accumulate fewer years of pension income. Both of these opposing factors influence the progressiveness of pension systems. Empirical efforts to disentangle the effects of mortality inequality on life time pension inequality have been scarce. Using Swedish taxation data linked with death registers for 1970–2018, we study how education and preretirement earnings relate to lifetime pensions from age 60 onward and how mortalityi nequalities contribute to overall inequalities in life time pensions. The results show that a progressive replacement structure and mortality differences contribute to the over all distribution of pension payments over the life course. Up to one quarter of life time pension inequality is attributable to the greater longevity of socially advan taged groups—particularly among men. Hence, mortality inequalities are an important determinant of the over all degree of between-group income trans fers in a pension system, but they are not as important as inequalities in prior earnings.
Accurate estimates of subnational populations are important for policy formulation and monitoring population health indicators. For example, estimates of the number of women of reproductive age are ...important to understand the population at risk of maternal mortality and unmet need for contraception. However, in many low-income countries, data on population counts and components of population change are limited, and so subnational levels and trends are unclear. We present a Bayesian constrained cohort component model for the estimation and projection of subnational populations. The model builds on a cohort component projection framework, incorporates census data and estimates from the United Nation’s World Population Prospects, and uses characteristic mortality schedules to obtain estimates of population counts and the compo nents of population change, including internal migration. The data required as inputs to the model are minimal and available across a wide range of countries, including most low-income countries. The model is applied to estimate and project populations by county in Kenya for 1979–2019 and is validated against the 2019 Kenyan census.
The tropical seagrass Halophila stipulacea exhibits a limited capacity to use nitrate, but has a high uptake capacity and efficiency for ammonium. Consequently, N₂ fixation by associated diazotrophic ...epiphytes may be important in providing ammonium needed for seagrass photosynthesis and growth. When exposed to seasonality, this association could provide a competitive advantage for H. stipulacea in relation to other seagrass species, but related knowledge is scarce. Here, we thus report measurements of net photosynthesis (O₂ fluxes) and N₂ fixation (acetylene reduction) associated with H. stipulacea from the Northern Red Sea over all four seasons of 2013. In parallel, we characterized the seagrass meadow areal extent, shoot and leaves density, and the leaf area index. Using this data, we quantified meadow net primary production and N₂ fixation and estimated the photo-metabolic N demand met by N₂ fixation at the community level. Results revealed a marked seasonality of meadow N₂ fixation, with rates ranging from 0.06 in winter to 4.60 mmol N m−2 d−1 in summer, i.e., an increase by two orders of magnitude. In summer, when nutrient concentrations in the water column were lowest and light intensity and temperature highest, there was a significant positive linear relationship between meadow net primary production and N₂ fixation, with the latter accounting for ca. 20% of the photo-metabolic N demand. These findings suggest that N₂ fixation by associated diazotrophic epiphytes can mitigate N limitation of H. stipulacea meadows under N scarcity. This trait may also favor the ongoing geographical expansion of H. stipulacea.
Because continuous meteorological observations across Antarctica did not start until the middle of the twentieth century, little is known about the full spatial pattern of pressure variability across ...the extratropical Southern Hemisphere (SH) in the early twentieth century, defined here as the period from 1905 to 1956. To fill this gap, this study analyzes pressure observations across the SH in conjunction with seasonal pressure reconstructions across Antarctica, which are based on observed station-to-station statistical relationships between pressure over Antarctica and the southern midlatitudes. Using this newly generated dataset, it is found that the early twentieth century is characterized by synchronous but opposite-signed pressure relationships between Antarctica and the SH midlatitudes, especially in austral summer and autumn. The synchronous pressure relationships are consistent with the southern annular mode, extending its well-known influence on SH extratropical pressure since 1957 into the early twentieth century. Apart from connections with the southern annular mode, regional and shorter-duration pressure trends are found to be associated with influences from tropical variability and potentially the zonal wavenumber 3 pattern. Although the reduced network of SH observations and Antarctic reconstruction captures the southern annular mode in the early twentieth century, reanalysis products show varying skill in reproducing trends and variability, especially over the oceans and high southern latitudes prior to 1957, which stresses the importance of continual efforts of historical data rescue in data-sparse regions to improve their quality.
Transcranial direct current stimulation (tDCS) may be a viable tool to improve motor and cognitive function in advanced age. However, although a number of studies have demonstrated improved cognitive ...performance in older adults, other studies have failed to show restorative effects. The neural effects of beneficial stimulation response in both age groups is lacking. In the current study, tDCS was administered during simultaneous fMRI in 42 healthy young and older participants. Semantic word generation and motor speech baseline tasks were used to investigate behavioral and neural effects of uni- and bihemispheric motor cortex tDCS in a three-way, crossover, sham tDCS controlled design. Independent components analysis assessed differences in task-related activity between the two age groups and tDCS effects at the network level. We also explored whether laterality of language network organization was effected by tDCS. Behaviorally, both active tDCS conditions significantly improved semantic word retrieval performance in young and older adults and were comparable between groups and stimulation conditions. Network-level tDCS effects were identified in the ventral and dorsal anterior cingulate networks in the combined sample during semantic fluency and motor speech tasks. In addition, a shift toward enhanced left laterality was identified in the older adults for both active stimulation conditions. Thus, tDCS results in common network-level modulations and behavioral improvements for both age groups, with an additional effect of increasing left laterality in older adults.
Energetics of the major atmospheric teleconnection patterns of the Northern Hemisphere winter are examined to investigate the role of baroclinic and barotropic energy conversions in their growth. ...Based on characteristics of the energetics and the horizontal structures, the patterns are classified into three general types: meridional dipole (D-type), wave (W-type), and hybrid (H-type). The primary energy conversion term that differentiates these patterns is the baroclinic energy conversion of the available potential energy from the climatology to the eddy field associated with the teleconnections. For this conversion term, D-type patterns exhibit the comparable conversion of potential energy via the eddy heat flux across the climatological thermal gradient in both the zonal and meridional directions. In contrast, baroclinic conversion for W-type patterns occurs primarily in the meridional direction, while H-type patterns exhibit a structure that combines the characteristics of the other two pattern types.An important secondary factor is barotropic conversion from the climatology to the eddy field, which takes place mainly in the regions where the climatological shear is strong. For the D-type patterns, conversion occurs on the flank of the climatological jet exit, while it occurs at the center of the jet exit for the W-type patterns. Last, for all the patterns, synoptic-time-scale eddies make a negative contribution via the baroclinic process, but a positive contribution via the barotropic process. Damping by diabatic heating weakens the temperature anomalies associated with the patterns.
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