Considering their distribution, thickness, and complexity around the margins of the Quaternary ice-sheets in the Northern Hemisphere, loess sequences can be considered as one of the best records of global environmental changes on the continents. European loess sequences have been intensively studied for many decades, but increasingly higher stratigraphic resolution and the availability of a growing range of climate proxy indicators has resulted in some notable advances in recent years. Climatic variability has been analyzed at high resolution, based on different proxies.
The globally distributed diazotroph Trichodesmium contributes importantly to nitrogen inputs in the oligotrophic oceans. Sites of dissolved organic matter (DOM) accumulation could promote the mixotrophic nutrition of Trichodesmium when inorganic nutrients are scarce. Nano-scale secondary ion mass spectrometry (nanoSIMS) analyses of individual trichomes sampled in the South Pacific Ocean, showed significant 13C-enrichments after incubation with either 13C-labeled carbohydrates or amino acids. These results suggest that DOM could be directly taken up by Trichodesmium or primarily consumed by heterotrophic epibiont bacteria that ultimately transfer reduced DOM compounds to their host trichomes. Although the addition of carbohydrates or amino acids did not significantly affect bulk N2 fixation rates, N2 fixation was enhanced by amino acids in individual colonies of Trichodesmium. We discuss the ecological advantages of DOM use by Trichodesmium as an alternative to autotrophic nutrition in oligotrophic open ocean waters.
The patterns of the large-scale, meso- and submesoscale surface circulation on biogeochemical and biological distributions are examined in the western tropical South Pacific (WTSP) in the context of the OUTPACE cruise (February–April 2015). Multi-disciplinary original in situ observations were achieved along a zonal transect through the WTSP and their analysis was coupled with satellite data. The use of Lagrangian diagnostics allows for the identification of water mass pathways, mesoscale structures, and submesoscale features such as fronts. In particular, we confirmed the existence of a global wind-driven southward circulation of surface waters in the entire WTSP, using a new high-resolution altimetry-derived product, validated by in situ drifters, that includes cyclogeostrophy and Ekman components with geostrophy. The mesoscale activity is shown to be responsible for counter-intuitive water mass trajectories in two subregions: (i) the Coral Sea, with surface exchanges between the North Vanuatu Jet and the North Caledonian Jet, and (ii) around 170° W, with an eastward pathway, whereas a westward general direction dominates. Fronts and small-scale features, detected with finite-size Lyapunov exponents (FSLEs), are correlated with 25 % of surface tracer gradients, which reveals the significance of such structures in the generation of submesoscale surface gradients. Additionally, two high-frequency sampling transects of biogeochemical parameters and microorganism abundances demonstrate the influence of fronts in controlling the spatial distribution of bacteria and phytoplankton, and as a consequence the microbial community structure. All circulation scales play an important role that has to be taken into account not only when analysing the data from OUTPACE but also, more generally, for understanding the global distribution of biogeochemical components.
The western tropical South Pacific (WTSP) Ocean has been recognized as a global hot spot of dinitrogen (N2) fixation. Here, as in other marine environments across the oceans, N2 fixation studies have focused on the sunlit layer. However, studies have confirmed the importance of aphotic N2 fixation activity, although until now only one had been performed in the WTSP. In order to increase our knowledge of aphotic N2 fixation in the WTSP, we measured N2 fixation rates and identified diazotrophic phylotypes in the mesopelagic layer along a transect spanning from New Caledonia to French Polynesia. Because non-cyanobacterial diazotrophs presumably need external dissolved organic matter (DOM) sources for their nutrition, we also identified DOM compounds using Fourier transform ion cyclotron resonance mass spectrometry (FTICRMS) with the aim of searching for relationships between the composition of DOM and non-cyanobacterial N2 fixation in the aphotic ocean. N2 fixation rates were low (average 0.63 ± 0.07 nmol N L−1 d−1) but consistently detected across all depths and stations, representing ∼ 6–88 % of photic N2 fixation. N2 fixation rates were not significantly correlated with DOM compounds. The analysis of nifH gene amplicons revealed a wide diversity of non-cyanobacterial diazotrophs, mostly matching clusters 1 and 3. Interestingly, a distinct phylotype from the major nifH subcluster 1G dominated at 650 dbar, coinciding with the oxygenated Subantarctic Mode Water (SAMW). This consistent pattern suggests that the distribution of aphotic diazotroph communities is to some extent controlled by water mass structure. While the data available are still too scarce to elucidate the distribution and controls of mesopelagic non-cyanobacterial diazotrophs in the WTSP, their prevalence in the mesopelagic layer and the consistent detection of active N2 fixation activity at all depths sampled during our study suggest that aphotic N2 fixation may contribute significantly to fixed nitrogen inputs in this area and/or areas downstream of water mass circulation.
Oligotrophic regions play a central role in global biogeochemical cycles, with microbial communities in these areas representing an important term in global carbon budgets. While the general structure of microbial communities has been well documented in the global ocean, some remote regions such as the western tropical South Pacific (WTSP) remain fundamentally unexplored. Moreover, the biotic and abiotic factors constraining microbial abundances and distribution remain not well resolved. In this study, we quantified the spatial (vertical and horizontal) distribution of major microbial plankton groups along a transect through the WTSP during the austral summer of 2015, capturing important autotrophic and heterotrophic assemblages including cytometrically determined abundances of non-pigmented protists (also called flagellates). Using environmental parameters (e.g., nutrients and light availability) as well as statistical analyses, we estimated the role of bottom–up and top–down controls in constraining the structure of the WTSP microbial communities in biogeochemically distinct regions. At the most general level, we found a “typical tropical structure”, characterized by a shallow mixed layer, a clear deep chlorophyll maximum at all sampling sites, and a deep nitracline. Prochlorococcus was especially abundant along the transect, accounting for 68 ± 10.6 % of depth-integrated phytoplankton biomass. Despite their relatively low abundances, picophytoeukaryotes (PPE) accounted for up to 26 ± 11.6 % of depth-integrated phytoplankton biomass, while Synechococcus accounted for only 6 ± 6.9 %. Our results show that the microbial community structure of the WTSP is typical of highly stratified regions, and underline the significant contribution to total biomass by PPE populations. Strong relationships between N2 fixation rates and plankton abundances demonstrate the central role of N2 fixation in regulating ecosystem processes in the WTSP, while comparative analyses of abundance data suggest microbial community structure to be increasingly regulated by bottom–up processes under nutrient limitation, possibly in response to shifts in abundances of high nucleic acid bacteria (HNA).
Cells adapt to familiar changes in their environment by activating predefined regulatory programs that establish adaptive gene expression states. These hard-wired pathways, however, may be inadequate for adaptation to environments never encountered before. Here, we reveal evidence for an alternative mode of gene regulation that enables adaptation to adverse conditions without relying on external sensory information or genetically predetermined cis-regulation. Instead, individual genes achieve optimal expression levels through a stochastic search for improved fitness. By focusing on improving the overall health of the cell, the proposed stochastic tuning mechanism discovers global gene expression states that are fundamentally new and yet optimized for novel environments. We provide experimental evidence for stochastic tuning in the adaptation of Saccharomyces cerevisiae to laboratory-engineered environments that are foreign to its native gene-regulatory network. Stochastic tuning operates locally at individual gene promoters, and its efficacy is modulated by perturbations to chromatin modification machinery.
The current and ongoing expansion of urban areas worldwide represents the largest mass migration in human history. It is well known that the world's coastal zones are associated with large and growing concentrations of population, urban development and economic activity. Among coastal environments, deltas have long been recognized for both benefits and hazards. This is particularly true on the Asian megadeltas, where the majority of the world's deltaic populations reside. Current trends in urban migration, combined with demographic momentum suggest that the already large populations on the Asian megadeltas will continue to grow. In this study, we combine recently released gridded population density (circa 2010) with a newly developed night light change product (1992 to 2012) and a digital elevation model to quantify the spatial distribution of population and development on the nine Asian megadeltas. Bivariate distributions of population as functions of elevation and coastal proximity quantify potential exposure of deltaic populations to flood and coastal hazards. Comparison of these distributions for the Asian megadeltas show very different patterns of habitation with peak population elevations ranging from 2 to 11 m above sea level over a wide range of coastal proximities. Over all nine megadeltas, over 174 million people reside below a peak population elevation of 7 m. Changes in the spatial extent of anthropogenic night light from 1992 to 2012 show widely varying extents and changes of lighted urban development. All of the deltas except the Indus show the greatest increases in night light brightness occurring at elevations < 10 m. At global and continental scales, growth of settlements of all sizes takes the form of evolving spatial networks of development. Spatial networks of lighted urban development in Asia show power law scaling properties consistent with other continents, but much higher rates of growth. The three largest networks of development in China all occur on deltas and adjacent lowlands, and are growing faster than the rest of the urban network in China. Since 2000, the Huanghe Delta + North China Plain urban network has surpassed the Japanese urban network in size and may soon connect with the Changjiang Delta + Yangtze River urban network to form the largest conurbation in Asia.
U.S. background ozone (O3) includes O3 produced from anthropogenic O3 precursors emitted outside of the U.S.A., from global methane, and from any natural sources. Using a suite of sensitivity simulations in the GEOS-Chem global chemistry-transport model, we estimate the influence from individual background versus U.S. anthropogenic sources on total surface O3 over ten continental U.S. regions from 2004–2012. Evaluation with observations reveals model biases of +0–19ppb in seasonal mean maximum daily 8-hour average (MDA8) O3, highest in summer over the eastern U.S.A. Simulated high-O3 events cluster too late in the season. We link these model biases to regional O3 production (e.g., U.S. anthropogenic, biogenic volatile organic compounds (BVOC), and soil NOx, emissions), or coincident missing sinks. On the ten highest observed O3 days during summer (O3_top10obs_JJA), U.S. anthropogenic emissions enhance O3 by 5–11ppb and by less than 2ppb in the eastern versus western U.S.A. The O3 enhancement from BVOC emissions during summer is 1–7ppb higher on O3_top10obs_JJA days than on average days, while intercontinental pollution is up to 2ppb higher on average vs. on O3_top10obs_JJA days. In the model, regional sources of O3 precursor emissions drive interannual variability in the highest observed O3 levels. During the summers of 2004–2012, monthly regional mean U.S. background O3 MDA8 levels vary by 10–20ppb. Simulated summertime total surface O3 levels on O3_top10obs_JJA days decline by 3ppb (averaged over all regions) from 2004–2006 to 2010–2012 in both the observations and the model, reflecting rising U.S. background (+2ppb) and declining U.S. anthropogenic O3 emissions (−6ppb). The model attributes interannual variability in U.S. background O3 on O3_top10obs days to natural sources, not international pollution transport. We find that a three-year averaging period is not long enough to eliminate interannual variability in background O3.
The political differences we see on climate issues globally reflect different cultures and distinct stages of economic development. Just as global treaty negotiations work to bridge the divide between nations, Americans need to renew our search for common ground. For most of the 21st century, our national politics has been about how we differ. With the phrase “climate change” disappearing from U.S. federal government websites and increased talk of regulatory overreach, it is obvious that protecting the environment will continue to be a fault line in American political ideology. While there are plenty of examples of environmental regulations being administered with rigidity and inflexibility, there are far more examples of accommodation and a process that provides plenty of time for businesses and localities to comply with environmental standards.
The humanitarian system is struggling to adapt to changes in the global political environment, trends in armed conflict and displacement, and advances in science and technology. In recent years, the international community has undertaken a number of efforts to overcome these challenges, such as the Agenda for Humanity, a plan that outlines the changes needed to alleviate suffering, reduce risk, and lessen vulnerability on a global scale. This article reviews recent evidence from a range of disciplines to inform these efforts, especially as they relate to the protection of children. Early childhood and adolescence constitute two critical periods of child development that lay the foundations for future health and wellbeing. Exposure to adversity in crisis contexts can compromise this development, with potentially life-long consequences. Evidence suggests that relationships with caregivers and peers play a central role in mediating childhood experiences of adversity. Unfortunately, interventions for children affected by crises are usually too fragmented to maximize the protective effects of healthy relationships. This article stresses the importance of developing multisectoral and relational interventions capable of promoting healthy development across the life course. Given the central role of caregivers, the household is an especially powerful level of intervention for combining approaches from different sectors. More concerted efforts are needed to develop household interventions that combine traditional sectoral approaches with innovative, cross-cutting measures, such as cash transfers and parental support. Household interventions should also be an integral part of broader community and society level actions, which together form more comprehensive systems of care.