| 541. |
- Ruane, Alex C., et al.
(författare)
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Strong regional influence of climatic forcing datasets on global crop model ensembles
- 2021
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Ingår i: Agricultural and Forest Meteorology. - : Elsevier BV. - 0168-1923. ; 300
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Tidskriftsartikel (refereegranskat)abstract
- We present results from the Agricultural Model Intercomparison and Improvement Project (AgMIP) Global Gridded Crop Model Intercomparison (GGCMI) Phase I, which aligned 14 global gridded crop models (GGCMs) and 11 climatic forcing datasets (CFDs) in order to understand how the selection of climate data affects simulated historical crop productivity of maize, wheat, rice and soybean. Results show that CFDs demonstrate mean biases and differences in the probability of extreme events, with larger uncertainty around extreme precipitation and in regions where observational data for climate and crop systems are scarce. Countries where simulations correlate highly with reported FAO national production anomalies tend to have high correlations across most CFDs, whose influence we isolate using multi-GGCM ensembles for each CFD. Correlations compare favorably with the climate signal detected in other studies, although production in many countries is not primarily climate-limited (particularly for rice). Bias-adjusted CFDs most often were among the highest model-observation correlations, although all CFDs produced the highest correlation in at least one top-producing country. Analysis of larger multi-CFD-multi-GGCM ensembles (up to 91 members) shows benefits over the use of smaller subset of models in some regions and farming systems, although bigger is not always better. Our analysis suggests that global assessments should prioritize ensembles based on multiple crop models over multiple CFDs as long as a top-performing CFD is utilized for the focus region.
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| 542. |
- Salihovic, Samira, Associate Senior Lecturer, 1985-, et al.
(författare)
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Simultaneous determination of perfluoroalkyl substances and bile acids in human serum using ultra-high-performance liquid chromatography-tandem mass spectrometry
- 2020
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Ingår i: Analytical and Bioanalytical Chemistry. - : Springer. - 1618-2642 .- 1618-2650. ; 412:10, s. 2251-2259
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Tidskriftsartikel (refereegranskat)abstract
- There is evidence of a positive association between per- and polyfluoroalkyl substances (PFASs) and cholesterol levels in human plasma, which may be due to common reabsorption of PFASs and bile acids (BAs) in the gut. Here we report development and validation of a method that allows simultaneous, quantitative determination of PFASs and BAs in plasma, using 150 μL or 20 μL of sample. The method involves protein precipitation using 96-well plates. The instrumental analysis was performed with ultra-performance liquid chromatography-tandem mass spectrometry (UHPLC-MS), using reverse-phase chromatography, with the ion source operated in negative electrospray mode. The mass spectrometry analysis was carried out using multiple reaction monitoring mode. The method proved to be sensitive, robust, and with sufficient linear range to allow reliable determination of both PFASs and BAs. The method detection limits were between 0.01 and 0.06 ng mL-1 for PFASs and between 0.002 and 0.152 ng mL-1 for BAs, with the exception of glycochenodeoxycholic acid (0.56 ng mL-1). The PFAS measured showed excellent agreement with certified plasma PFAS concentrations in NIST SRM 1957 reference serum. The method was tested on serum samples from 20 healthy individuals. In this proof-of-concept study, we identified significant associations between plasma PFAS and BA levels, which suggests that PFAS may alter the synthesis and/or uptake of BAs.
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| 543. |
- Sanders, Luciana M., et al.
(författare)
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Historic carbon burial spike in an Amazon floodplain lake linked to riparian deforestation near Santarem, Brazil
- 2018
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Ingår i: Biogeosciences. - : COPERNICUS GESELLSCHAFT MBH. - 1726-4170 .- 1726-4189. ; 15:2, s. 447-455
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Tidskriftsartikel (refereegranskat)abstract
- Forests along the Amazon Basin produce significant quantities of organic material, a portion of which is deposited in floodplain lakes. Deforestation in the watershed may then have potentially important effects on the carbon fluxes. In this study, a sediment core was extracted from an Amazon floodplain lake to examine the relationship between carbon burial and changing land cover and land use. Historical records from the 1930s and satellite data from the 1970s were used to calculate deforestation rates between 1930 to 1970 and 1970 to 2010 in four zones with different distances from the margins of the lake and its tributaries (100, 500, 1000 and 6000m buffers). A sediment accumulation rate of similar to 4 mmyr(-1) for the previous similar to 120 years was determined from the Pu240+239 signatures and the excess Pb-210 method. The carbon burial rates ranged between 85 and 298 gCm(-2) yr(-1), with pulses of high carbon burial in the 1950s, originating from the forest vegetation as indicated by delta C-13 and delta N-15 signatures. Our results revealed a potentially important spatial dependence of the organic carbon (OC) burial in Amazon lacustrine sediments in relation to deforestation rates in the catchment. These deforestation rates were more intense in the riparian vegetation (100m buffer) during the period 1930 to 1970 and the larger open water areas (500, 1000 and 6000m buffer) during 1970 to 2010. The continued removal of vegetation from the interior of the forest was not related to the peak of OC burial in the lake, but only the riparian deforestation which peaked during the 1950s. Therefore, this supports the conservation priority of riparian forests as an important management practice for Amazon flooded areas. Our findings suggest the importance of abrupt and temporary events in which some of the biomass released by deforestation, especially restricted to areas along open water edges, might reach the depositional environments in the floodplain of the Amazon Basin.
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| 544. |
- Sanders, Luciana M., et al.
(författare)
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Pu240+239 DEPOSITIONAL SIGNATURES AS A VIABLE GEOCHRONOLOGICAL TOOL IN THE AMAZON BASIN
- 2017
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Ingår i: Geochronometria. - : DE GRUYTER OPEN LTD. - 1733-8387 .- 1897-1695. ; 44:1, s. 142-149
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Tidskriftsartikel (refereegranskat)abstract
- Anthropogenic radionuclide signatures associated with nuclear testing are increasingly utilized in environmental science to explore recent sedimentation. In this study, we assess the suitability of Pu radioisotope analysis in floodplain lake environments in the Amazon Basin to form geochronologies during the 20th century. The Pu-240 + Pu-239 (Pu240+239) signatures in six sediment cores indicate sediment accumulation rates in the floodplain lakes of the major rivers; Amazon (2.3 mm year(-1)), Tapajos (10.2 and 2.4 mm year(-1)) and Madeira (3.4, 4.2 and 6.2 mm year(-1)). The results from this study show that Pu240+239 fallout activities, and the well documented (Pu-240/Pu-239) atomic ratios of the above ground nuclear tests which began in the 1950s, are sufficient and well preserved in Amazon flood-plain lake sediments to infer chronologies. Lead-210 dating analyses in the same sediment cores produced comparable sediment accumulation rates at three of the six sites. The differences between dating methods may be attributed to the different time scale these dating methods represent and/or in the solubility between Pb and Pu along the sediment column. The geochronologies derived from the Pu240+239 and Pb-210 methods outlined in this work are of interest to identify the effects of changing sediment accumulation rates during the previous century as a result of development, including deforestation, along the Amazon Basin which increased towards the middle of the 20th century. This study shows that Pu dating provides a viable alternative geochronology tool for recent sediment accumulation (previous similar to 60 years) along the Amazon Basin.
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| 545. |
- Sanseverino, Angela M, et al.
(författare)
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Methane Carbon Supports Aquatic Food Webs to the Fish Level
- 2012
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Ingår i: PLOS ONE. - : Public Library of Science. - 1932-6203. ; 7:8
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Tidskriftsartikel (refereegranskat)abstract
- Large amounts of the greenhouse gas methane (CH4) are produced by anaerobic mineralization of organic matter in lakes. In spite of extensive freshwater CH4 emissions, most of the CH4 is typically oxidized by methane oxidizing bacteria (MOB) before it can reach the lake surface and be emitted to the atmosphere. In turn, it has been shown that the CH4-derived biomass of MOB can provide the energy and carbon for zooplankton and macroinvertebrates. In this study, we demonstrate the presence of specific fatty acids synthesized by MOB in fish tissues having low carbon stable isotope ratios. Fish species, zooplankton, macroinvertebrates and the water hyacinth Eichhornia crassipes were collected from a shallow lake in Brazil and analyzed for fatty acids (FA) and carbon stable isotope ratios (delta C-13). The fatty acids 16:1 omega 8c, 16:1 omega 8t, 16:1 omega 6c, 16:1 omega 5t, 18:1 omega 8c and 18:1 omega 8t were used as signature for MOB. The delta C-13 ratios varied from -27.7 parts per thousand to -42.0 parts per thousand and the contribution of MOB FA ranged from 0.05% to 0.84% of total FA. Organisms with higher total content of MOB FAs presented lower delta C-13 values (i.e. they were more depleted in C-13), while organisms with lower content of MOB signature FAs showed higher delta C-13 values. An UPGMA cluster analysis was carried out to distinguish grouping of organisms in relation to their MOB FA contents. This combination of stable isotope and fatty acid tracers provides new evidence that assimilation of methane-derived carbon can be an important carbon source for the whole aquatic food web, up to the fish level.
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| 546. |
- Sathyendranath, Shubha, et al.
(författare)
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An Ocean-Colour Time Series for Use in Climate Studies : The Experience of the Ocean-Colour Climate Change Initiative (OC-CCI)
- 2019
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Ingår i: Sensors. - : MDPI AG. - 1424-8220. ; 19:19
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Tidskriftsartikel (refereegranskat)abstract
- Ocean colour is recognised as an Essential Climate Variable (ECV) by the Global Climate Observing System (GCOS); and spectrally-resolved water-leaving radiances (or remote-sensing reflectances) in the visible domain, and chlorophyll-a concentration are identified as required ECV products. Time series of the products at the global scale and at high spatial resolution, derived from ocean-colour data, are key to studying the dynamics of phytoplankton at seasonal and inter-annual scales; their role in marine biogeochemistry; the global carbon cycle; the modulation of how phytoplankton distribute solar-induced heat in the upper layers of the ocean; and the response of the marine ecosystem to climate variability and change. However, generating a long time series of these products from ocean-colour data is not a trivial task: algorithms that are best suited for climate studies have to be selected from a number that are available for atmospheric correction of the satellite signal and for retrieval of chlorophyll-a concentration; since satellites have a finite life span, data from multiple sensors have to be merged to create a single time series, and any uncorrected inter-sensor biases could introduce artefacts in the series, e.g., different sensors monitor radiances at different wavebands such that producing a consistent time series of reflectances is not straightforward. Another requirement is that the products have to be validated against in situ observations. Furthermore, the uncertainties in the products have to be quantified, ideally on a pixel-by-pixel basis, to facilitate applications and interpretations that are consistent with the quality of the data. This paper outlines an approach that was adopted for generating an ocean-colour time series for climate studies, using data from the MERIS (MEdium spectral Resolution Imaging Spectrometer) sensor of the European Space Agency; the SeaWiFS (Sea-viewing Wide-Field-of-view Sensor) and MODIS-Aqua (Moderate-resolution Imaging Spectroradiometer-Aqua) sensors from the National Aeronautics and Space Administration (USA); and VIIRS (Visible and Infrared Imaging Radiometer Suite) from the National Oceanic and Atmospheric Administration (USA). The time series now covers the period from late 1997 to end of 2018. To ensure that the products meet, as well as possible, the requirements of the user community, marine-ecosystem modellers, and remote-sensing scientists were consulted at the outset on their immediate and longer-term requirements as well as on their expectations of ocean-colour data for use in climate research. Taking the user requirements into account, a series of objective criteria were established, against which available algorithms for processing ocean-colour data were evaluated and ranked. The algorithms that performed best with respect to the climate user requirements were selected to process data from the satellite sensors. Remote-sensing reflectance data from MODIS-Aqua, MERIS, and VIIRS were band-shifted to match the wavebands of SeaWiFS. Overlapping data were used to correct for mean biases between sensors at every pixel. The remote-sensing reflectance data derived from the sensors were merged, and the selected in-water algorithm was applied to the merged data to generate maps of chlorophyll concentration, inherent optical properties at SeaWiFS wavelengths, and the diffuse attenuation coefficient at 490 nm. The merged products were validated against in situ observations. The uncertainties established on the basis of comparisons with in situ data were combined with an optical classification of the remote-sensing reflectance data using a fuzzy-logic approach, and were used to generate uncertainties (root mean square difference and bias) for each product at each pixel.
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| 547. |
- Sawakuchi, Henrique O., et al.
(författare)
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Oxidative mitigation of aquatic methane emissions in large Amazonian rivers
- 2016
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Ingår i: Global Change Biology. - : WILEY-BLACKWELL. - 1354-1013 .- 1365-2486. ; 22:3, s. 1075-1085
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Tidskriftsartikel (refereegranskat)abstract
- The flux of methane (CH4) from inland waters to the atmosphere has a profound impact on global atmospheric greenhouse gas (GHG) levels, and yet, strikingly little is known about the dynamics controlling sources and sinks of CH4 in the aquatic setting. Here, we examine the cycling and flux of CH4 in six large rivers in the Amazon basin, including the Amazon River. Based on stable isotopic mass balances of CH4, inputs and outputs to the water column were estimated. We determined that ecosystem methane oxidation (MOX) reduced the diffusive flux of CH4 by approximately 28-96% and varied depending on hydrologic regime and general geochemical characteristics of tributaries of the Amazon River. For example, the relative amount of MOX was maximal during high water in black and white water rivers and minimal in clear water rivers during low water. The abundance of genetic markers for methane-oxidizing bacteria (pmoA) was positively correlated with enhanced signals of oxidation, providing independent support for the detected MOX patterns. The results indicate that MOX in large Amazonian rivers can consume from 0.45 to 2.07 Tg CH4 yr(-1), representing up to 7% of the estimated global soil sink. Nevertheless, climate change and changes in hydrology, for example, due to construction of dams, can alter this balance, influencing CH4 emissions to atmosphere.
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| 548. |
- Schreck, Simon, et al.
(författare)
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Atom-specific activation in CO oxidation
- 2018
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Ingår i: Journal of Chemical Physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 149:23
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Tidskriftsartikel (refereegranskat)abstract
- We report on atom-specific activation of CO oxidation on Ru(0001) via resonant X-ray excitation. We show that resonant 1s core-level excitation of atomically adsorbed oxygen in the co-adsorbed phase of CO and oxygen directly drives CO oxidation. We separate this direct resonant channel from indirectly driven oxidation via X-ray induced substrate heating. Based on density functional theory calculations, we identify the valence-excited state created by the Auger decay as the driving electronic state for direct CO oxidation. We utilized the fresh-slice multi-pulse mode at the Linac Coherent Light Source that provided time-overlapped and 30 fs delayed pairs of soft X-ray pulses and discuss the prospects of femtosecond X-ray pump X-ray spectroscopy probe, as well as X-ray two-pulse correlation measurements for fundamental investigations of chemical reactions via selective X-ray excitation.
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| 549. |
- Schrijver, Lieske H, et al.
(författare)
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Oral contraceptive use and ovarian cancer risk for BRCA1/2 mutation carriers : an international cohort study
- 2021
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Ingår i: American Journal of Obstetrics and Gynecology. - : Elsevier BV. - 1097-6868 .- 0002-9378. ; 225:1, s. 1-51
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Tidskriftsartikel (refereegranskat)abstract
- BACKGROUND: Ovarian cancer risk in BRCA1 and BRCA2 mutation carriers has been shown to decrease with longer duration of oral contraceptive preparations (OCPs) use. While the effects of OCPs in the general population are well established (∼50% reduction), the estimated risk reduction in mutation carriers is much less precise due to potential bias and small sample sizes. In addition, only a few studies have examined the associations between duration of use, time since last use, starting age, and calendar year of start with risk of ovarian cancer.OBJECTIVE(S): To investigate in more detail the associations between various characteristics of OCP use and risk of ovarian cancer, to provide health care providers and carriers with better risk estimates.STUDY DESIGN: In this international retrospective study, ovarian cancer risk associations were assessed using OCP data on 3,989 BRCA1 and 2,445 BRCA2 mutation carriers. Age-dependent weighted Cox regression analyses were stratified by study and birth cohort and included breast cancer diagnosis as covariate. To minimize survival bias, analyses were left-truncated at 5 years before baseline questionnaire. Separate analysis were conducted for each of the aspects of OCP use and in a multivariate analysis including all these aspects. In addition, the analysis of duration of OCP use was stratified by recency of use.RESULTS: OCPs were less often used by mutation carriers who were diagnosed with ovarian cancer (Ever use: BRCA1 58.6%, BRCA2 53.5%) than by unaffected carriers (Ever use: BRCA1 88.9%, BRCA2 80.7%. The median duration of use was 7 years for both BRCA1 and BRCA2 carriers who developed ovarian cancer, and 9 and 8 years for ovarian cancer unaffected BRCA1 and BRCA2 carriers, respectively. For BRCA1 mutation carriers univariate analyses showed that both a longer duration of OCP use and more recent use of OCPs were inversely associated with risk of ovarian cancer. However, in multivariate analyses including duration of use, age at first use and time since last use, duration of use proved to be the prominent protective factor (compared with <5 years, 5-9 years HR=0.67;95%CI 0.40-1.12, 10+ years HR=0.37;95%CI 0.19-0.73; ptrend=0.008). The inverse association between duration of use and ovarian cancer risk persisted for more than 15 years (Duration of ≥10 years; BRCA1: <15 years since last use: HR=0.24 95%CI 0.14-0.43, 15+ years since last use: HR 0.56 95%CI 0.18-0.59). Univariate results for BRCA2 mutation carriers were similar, but due to limit sample size inconclusive.CONCLUSION: For BRCA1 mutation carriers, a longer duration of OCP use is associated with a greater reduction of ovarian cancer risk and the protection is long term.
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| 550. |
- Schrodi, Fabian, et al.
(författare)
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Cascade of replica bands in flat-band systems : Predictions for twisted bilayer graphene
- 2021
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Ingår i: Physical Review B. - : American Physical Society. - 2469-9950 .- 2469-9969. ; 103:14
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Tidskriftsartikel (refereegranskat)abstract
- We investigate the effect of electron-phonon interactions (EPI) in systems exhibiting one or more flat electron bands close to the Fermi level and a comparatively large phonon energy scale. After solving the self-consistent full-bandwidth Eliashberg equations, we compute angular resolved photoemission spectroscopy (ARPES) and scanning tunneling spectroscopy/microscopy (STS/STM) spectra. We obtain a sequence of quasiparticle replica bands in both the normal and superconducting states that originate from frequency-dependent features of the electron mass renormalization function. We show that these replica bands can be used to extract the relevant phonon energy scale from experiments. Focusing in particular on twisted bilayer graphene, we predict replicaband formation, which, when observed, will shed light on the role of EPI in this archetypal flat-band system.
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