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  • Articles  (922)
  • Wiley  (922)
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  • Articles  (922)
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  • 1
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    Reversal of Increasing Tropical Ocean Hypoxia Trends with Sustained Climate Warming (2018)
    Wiley
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    Publication Date: 2018-03-14
    Description: Dissolved oxygen (O 2 ) is essential for the survival of marine animals. Climate change impacts on future oxygen distributions could modify species biogeography, trophic interactions, biodiversity and biogeochemistry. The Coupled Model Intercomparison Project Phase 5 (CMIP5) models predict a decreasing trend in marine O 2 over the 21 st century. Here we show that this increasing hypoxia trend reverses in the tropics after 2100 in the Community Earth System Model forced by atmospheric CO 2 from the Representative Concentration Pathway (RCP) 8.5 and Extended Concentration Pathway (ECP 8.5). In tropical intermediate waters between 200m and 1000m, the model predicts a steady decline of O 2 and an expansion of oxygen minimum zones (OMZs) during the 21 st century. By 2150, however, the trend reverses with oxygen concentration increasing and OMZ volume shrinking through 2300. A novel, five-box model approach in conjunction with output from the full Earth System Model (ESM) is used to separate the contributions of biological and physical processes to the trends in tropical oxygen. The tropical O 2 recovery is caused mainly by reductions in tropical biological export, coupled with a modest increase in ventilation after 2200. The time-evolving oxygen distribution impacts marine nitrogen cycling, with potentially important climate feedbacks.
    Print ISSN: 0886-6236
    Electronic ISSN: 1944-9224
    Topics: Biology , Chemistry and Pharmacology , Geography , Geosciences , Physics
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  • 2
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    The eMLR(C*) method to determine decadal changes in the global ocean storage of anthropogenic CO2 (2018)
    Wiley
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    Publication Date: 2018-03-14
    Description: The determination of the decadal change in anthropogenic CO 2 in the global ocean from repeat hydrographic surveys represents a formidable challenge, which we address here by introducing a seamless new method. This method builds on the extended multiple linear regression (eMLR) approach [ Friis et al. , 2005] to identify the anthropogenic CO 2 signal, but in order to improve the robustness of this method, we fit C ∗ [ Gruber and Sarmiento , 2002] rather than dissolved inorganic carbon and use a probabilistic method for the selection of the predictors. In order to account for the multi-year nature of the surveys, we adjust all C ∗ observations of a particular observing period to a common reference year by assuming a transient steady-state. We finally use the eMLR models together with global gridded climatological distributions of the predictors to map the estimated change in anthropogenic CO 2 to the global ocean. Testing this method with synthetic data generated from a hindcast simulation with an ocean model reveals that the method is able to reconstruct the change in anthropogenic CO 2 with only a small global bias (〈5%). Within ocean basins, the errors can be larger, mostly driven by changes in ocean circulation. Overall, we conclude from the model that the method has an accuracy of retrieving the column integrated change in anthropogenic CO 2 of about ±10% at the scale of whole ocean basins. We expect that this uncertainty needs to be doubled to about ±20% when the change in anthropogenic CO 2 is reconstructed from observations.
    Print ISSN: 0886-6236
    Electronic ISSN: 1944-9224
    Topics: Biology , Chemistry and Pharmacology , Geography , Geosciences , Physics
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  • 3
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    Issue Information (2018)
    Wiley
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    Publication Date: 2018-03-07
    Description: No abstract is available for this article.
    Print ISSN: 0886-6236
    Electronic ISSN: 1944-9224
    Topics: Biology , Chemistry and Pharmacology , Geography , Geosciences , Physics
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  • 4
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    Limitations on Limitation (2018)
    Wiley
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    Publication Date: 2018-03-06
    Description: Phosphorus is believed to be the globally limiting nutrient in the modern ocean, but a number of nutrients have been invoked as limiting the Proterozoic biosphere. Mass balance calculations suggest that Proterozoic net primary productivity must have been one to two orders of magnitude less than today in order to maintain low oxygen levels despite increased burial efficiency in anoxic environments. The resulting demand for nutrients is so low that nitrogen, molybdenum, and iron could not have limited the rate of primary production following the evolution of extant nitrogenases. Phosphorus demand was approximately equal to the modern riverine flux, making phosphorus the most likely candidate for the limiting nutrient throughout the Proterozoic.
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    Electronic ISSN: 1944-9224
    Topics: Biology , Chemistry and Pharmacology , Geography , Geosciences , Physics
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  • 5
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    Sundaland peat carbon dynamics and its contribution to the Holocene atmospheric CO2 concentration (2018)
    Wiley
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    Publication Date: 2018-03-06
    Description: The Sunda Shelf is a large submerged extension of the continental shelf of mainland Asia, joining the islands of Borneo, Java, and Sumatra, and forming the shallow seabed of the South China Sea. Recent studies identified present day peatlands in Southeast Asia as a globally important carbon reservoir. However, little is known about Sundaland paleo-peatlands and their role in the global carbon cycle since the Last Glacial Maximum. Using a topography based, sea level driven model, we estimate the potential spatial extent of peatlands during the late Pleistocene and early Holocene across the low-lying Sundaland plains. We then use the estimated peatland area together with data on carbon accumulation rates to calculate the total peat carbon pool on the Sunda Shelf. Finally, using a global biogeochemical model, we analyze the relative influence of the predicted Sundaland peat dynamics and other carbon change mechanisms, specifically high-latitude forest growth and peat formation, shallow sea carbonate deposition, ocean warming, and combinations of them, on the global carbon cycle of the Holocene. We identify a feedback mechanism between sea level and peatland carbon sequestration in Sundaland that reduced atmospheric CO 2 concentration by about 4–5 ppm and increased δ 13 C by 0.05‰ during the Holocene. We also show that a concurrence of mechanisms that includes Sundaland peat dynamics produces model results that are consistent with proxy records, especially with respect to δ 13 C.
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    Topics: Biology , Chemistry and Pharmacology , Geography , Geosciences , Physics
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  • 6
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    Nitrous oxide emissions estimated with the CarbonTracker-Lagrange North American regional inversion framework (2018)
    Wiley
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    Publication Date: 2018-03-06
    Description: North American nitrous oxide (N 2 O) emissions of 1.6 ± 0.3 Tg N/yr over 2008-2014 are estimated using the CarbonTracker-Lagrange (CT-L) regional inversion framework. The estimated N 2 O emissions are largely consistent with the EDGAR global inventory and with the results of global atmospheric inversions, but offer more spatial and temporal detail over North America. Emissions are strongest from the Midwestern corn/soybean belt, which accounts for nearly one third of the total North American N 2 O source. The emissions are maximum in spring/early summer, consistent with a nitrogen fertilizer-driven source, but also show a late winter spike suggestive of freeze-thaw effects. Interannual variability in emissions across the primary months of fertilizer application is positively correlated to mean precipitation. The estimated N 2 O flux from the Midwestern corn/soybean belt and the more northerly U.S./Canadian wheat belt corresponds to 4.2-4.6% and 2.2-3.0%, respectively, of total synthetic + organic N fertilizer applied to those regions. Consideration of non-agricultural sources and additional N inputs from soybean N 2 fixation could reduce the N 2 O yield from the Midwestern corn/soybean belt to ~2.2-2.4% of total N inputs.
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    Topics: Biology , Chemistry and Pharmacology , Geography , Geosciences , Physics
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  • 7
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    Long-term and seasonal trends in estuarine and coastal carbonate systems (2018)
    Wiley
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    Publication Date: 2018-03-06
    Description: Coastal pH and total alkalinity are regulated by a diverse range of local processes superimposed on global trends of warming and ocean acidification, yet few studies have investigated the relative importance of different processes for coastal acidification. We describe long-term (1972-2016) and seasonal trends in the carbonate system of three Danish coastal systems demonstrating that hydrological modification, changes in nutrient inputs from land, and presence/absence of calcifiers can drastically alter carbonate chemistry. Total alkalinity was mainly governed by conservative mixing of freshwater (0.73-5.17 mmol kg -1 ) with outer boundary concentrations (~2-2.4 mmol kg -1 ), modulated seasonally and spatially (~0.1-0.2 mmol kg -1 ) by calcifiers. Nitrate assimilation by primary production, denitrification, and sulfate reduction increased total alkalinity by almost 0.6 mmol kg -1 in the most eutrophic system during a period without calcifiers. Trends in pH ranged from -0.0088 yr -1 to 0.021 yr -1 , the more extreme of these mainly driven by salinity changes in a sluice-controlled lagoon. Temperature increased 0.05 °C yr -1 across all three systems, which directly accounted for a pH decrease of 0.0008 yr -1 . Accounting for mixing, salinity and temperature effects on dissociation and solubility constants, the resulting pH decline (0.0040 yr -1 ) was about twice the ocean trend, emphasizing the effect of nutrient management on primary production and coastal acidification. Coastal pCO 2 increased ~4 times more rapidly than ocean rates, enhancing CO 2 emissions to the atmosphere. Indeed, coastal systems undergo more drastic changes than the ocean and coastal acidification trends are substantially enhanced from nutrient reductions to address coastal eutrophication.
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    Topics: Biology , Chemistry and Pharmacology , Geography , Geosciences , Physics
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  • 8
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    Mercury in the Black Sea: new insights from measurements and numerical modeling (2018)
    Wiley
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    Publication Date: 2018-03-06
    Description: Redox conditions and organic matter control marine methylmercury (MeHg) production. The Black Sea is the world's largest and deepest anoxic basin and is thus ideal to study Hg species along the extended redox gradient. Here, we present new dissolved Hg and MeHg data from the 2013 GEOTRACES MEDBlack cruise (GN04_leg2) that we integrated into a numerical 1D model, to track the fate and dynamics of Hg and MeHg. Contrary to a previous study, our new data show highest MeHg concentrations in the permanently anoxic waters. Observed MeHg/Hg percentage (range 9 – 57%) in the anoxic waters is comparable to other subsurface maxima in oxic open-ocean waters. With the modeling we tested for various Hg methylation and demethylation scenarios along the redox gradient. The results show that Hg methylation must occur in the anoxic waters. The model was then used to simulate the time evolution (1850 – 2050) of Hg species in the Black Sea. Our findings quantify: 1) inputs and outputs of Hg T (~31 and ~28 kmol y -1 ) and MeHg T (~5 and ~4 kmol y -1 ) to the basin; 2) the extent of net demethylation occurring in oxic (~1 kmol y -1 ) and suboxic water (~6 kmol y -1 ); 3) and the net Hg methylation in the anoxic waters of the Black Sea (~11 kmol y -1 ). The model was also used to estimate the amount of anthropogenic Hg (85 – 93%) in the Black Sea.
    Print ISSN: 0886-6236
    Electronic ISSN: 1944-9224
    Topics: Biology , Chemistry and Pharmacology , Geography , Geosciences , Physics
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  • 9
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    Present and future mercury concentrations in Chinese rice: Insights from modeling (2018)
    Wiley
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    Publication Date: 2018-02-28
    Description: We construct a rice paddy biogeochemical cycle model to investigate processes governing rice mercury sources, and to understand factors influencing spatiotemporal variability in Chinese rice mercury concentrations. The rice paddy model takes atmospheric mercury deposition, simulated from a global atmospheric-chemistry-transport model (GEOS-Chem), and soil and irrigable surface water mercury concentrations obtained from literature, and calculates rice inorganic (IHg) and methylmercury (MeHg) concentrations. We use ranges of GEOS-Chem simulated future atmospheric mercury deposition-- no-policy and strict-policy to regulate mercury emissions from Chinese coal-fired power plants under the Minamata Convention on Mercury -- to simulate future rice IHg and MeHg concentrations. Sensitivity analyses suggest that rice IHg and MeHg concentrations are more sensitive to the process of soil desorption compared to infiltration of recently introduced mercury (atmospheric and irrigation source). The rate of internal methylation via microbial activity has the largest modeled influence on rice MeHg concentration. We find that soil mercury, rather than atmospheric deposition, explains observed spatial variability in rice IHg and MeHg concentrations and captures locations of rice mercury hotspots (〉 20 ng/g; China National Standard Limit). Under our future scenarios, the Chinese median rice IHg and MeHg concentrations increase by 13% and decrease by 18% under no-policy and strict-policy, respectively. Regions with the largest percentage decline in rice IHg and MeHg concentrations under strict-policy are in central China, which demonstrate high rice mercury concentrations, rice production, and consumption. Our study suggests that addressing Chinese rice mercury contamination requires attention to contaminated soil and regulation of anthropogenic mercury emissions.
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    Topics: Biology , Chemistry and Pharmacology , Geography , Geosciences , Physics
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  • 10
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    Mesoscale effects on carbon export: a global perspective (2018)
    Wiley
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    Publication Date: 2018-02-24
    Description: Carbon export from the surface to the deep ocean is a primary control on global carbon budgets, and is mediated by plankton that are sensitive to physical forcing. Earth system models generally do not resolve ocean mesoscale circulation ( (10–100) km), scales that strongly affect transport of nutrients and plankton. The role of mesoscale circulation in modulating export is evaluated by comparing global ocean simulations conducted at 1°and 0.1°horizontal resolution. Mesoscale resolution produces a small reduction in globally-integrated export production (〈2%); however, the impact on local export production can be large (±50%), with compensating effects in different ocean basins. With mesoscale resolution, improved representation of coastal jets block off-shelf transport, leading to lower export in regions where shelf-derived nutrients fuel production. Export is further reduced in these regions by resolution of mesoscale turbulence, which restricts the spatial area of production. Maximum mixed layer depths are narrower and deeper across the Subantarctic at higher resolution, driving locally stronger nutrient entrainment and enhanced summer export production. In energetic regions with seasonal blooms, such as the Subantarctic and North Pacific, internally-generated mesoscale variability drives substantial interannual variation in local export production. These results suggest that biogeochemical tracer dynamics show different sensitivities to transport biases than temperature and salinity, which should be considered in the formulation and validation of physical parameterizations. Efforts to compare estimates of export production from observations and models should account for large variability in space and time expected for regions strongly affected by mesoscale circulation.
    Print ISSN: 0886-6236
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    Topics: Biology , Chemistry and Pharmacology , Geography , Geosciences , Physics
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