Oxygen minimum zones (OMZs) cover extensive areas of eastern boundary ocean regions and play an important role in the cycling of the essential micronutrient iron (Fe). The isotopic composition of ...dissolved Fe (dFe) in shelf and slope waters on the Senegalese margin was determined to investigate the processes leading to enhanced dFe concentrations (up to 2 nM) in this tropical North Atlantic OMZ. On the shelf, the δ56Fe value of dFe (relative to the reference material IRMM-014) was as low as −0.33‰, which can be attributed to input of dFe from both reductive and nonreductive dissolution of sediments. Benthic inputs of dFe are subsequently upwelled to surface waters and recycled in the water column by biological uptake and remineralisation processes. Remineralised dFe is characterised by relatively high δ56Fe values (up to +0.41‰), and the contribution of remineralised Fe to the total dFe pool increases with distance from the shelf. Remineralisation plays an important role in the redistribution of dFe that is mainly supplied by benthic and atmospheric inputs, although dust inputs, estimated from dissolved aluminium concentrations, were low at the time of our study (2–9 nmol dFe m−2 d−1). As OMZs are expected to expand as climate warms, our data provide important insights into Fe sources and Fe cycling in the tropical North Atlantic Ocean.
We present a machine-learning photometric redshift (ML photo- z ) analysis of the Kilo-Degree Survey Data Release 3 (KiDS DR3), using two neural-network based techniques: ANNz2 and MLPQNA. Despite ...limited coverage of spectroscopic training sets, these ML codes provide photo- z s of quality comparable to, if not better than, those from the Bayesian Photometric Redshift (BPZ) code, at least up to z phot ≲ 0.9 and r ≲ 23.5. At the bright end of r ≲ 20, where very complete spectroscopic data overlapping with KiDS are available, the performance of the ML photo- z s clearly surpasses that of BPZ, currently the primary photo- z method for KiDS. Using the Galaxy And Mass Assembly (GAMA) spectroscopic survey as calibration, we furthermore study how photo- z s improve for bright sources when photometric parameters additional to magnitudes are included in the photo- z derivation, as well as when VIKING and WISE infrared (IR) bands are added. While the fiducial four-band ugri setup gives a photo- z bias 〈 δz /(1 + z )〉 = −2 × 10 −4 and scatter σ δz/(1+z) < 0.022 at mean 〈 z 〉 = 0.23, combining magnitudes, colours, and galaxy sizes reduces the scatter by ~7% and the bias by an order of magnitude. Once the ugri and IR magnitudes are joined into 12-band photometry spanning up to 12 μ m, the scatter decreases by more than 10% over the fiducial case. Finally, using the 12 bands together with optical colours and linear sizes gives 〈 δz /(1 + z )〉 < 4 × 10 −5 and σ δz /(1+ z ) < 0.019. This paper also serves as a reference for two public photo- z catalogues accompanying KiDS DR3, both obtained using the ANNz2 code. The first one, of general purpose, includes all the 39 million KiDS sources with four-band ugri measurements in DR3. The second dataset, optimised for low-redshift studies such as galaxy-galaxy lensing, is limited to r ≲ 20, and provides photo- z s of much better quality than in the full-depth case thanks to incorporating optical magnitudes, colours, and sizes in the GAMA-calibrated photo- z derivation.
We present a search for eV-scale sterile neutrino oscillations in the MicroBooNE liquid argon detector, simultaneously considering all possible appearance and disappearance effects within the 3+1 ...active-to-sterile neutrino oscillation framework. We analyze the neutrino candidate events for the recent measurements of charged-current ν_{e} and ν_{μ} interactions in the MicroBooNE detector, using data corresponding to an exposure of 6.37×10^{20} protons on target from the Fermilab booster neutrino beam. We observe no evidence of light sterile neutrino oscillations and derive exclusion contours at the 95% confidence level in the plane of the mass-squared splitting Δm_{41}^{2} and the sterile neutrino mixing angles θ_{μe} and θ_{ee}, excluding part of the parameter space allowed by experimental anomalies. Cancellation of ν_{e} appearance and ν_{e} disappearance effects due to the full 3+1 treatment of the analysis leads to a degeneracy when determining the oscillation parameters, which is discussed in this Letter and will be addressed by future analyses.
This study presents comprehensive strontium stable isotope (88Sr/86Sr) data, measured by multiple-collector inductively-coupled plasma mass spectrometry (MC–ICP-MS), for a suite of carbonaceous ...chondrites, differentiated meteorites, lunar, martian and terrestrial samples.
Carbonaceous chondrites comprise a mixture of refractory inclusions and chondrules that have light δ88Sr values between −0.35 to +0.05‰ and matrix material that possesses a heavy δ88Sr composition of 0.65‰, confirming the results of earlier studies. Consequently, bulk carbonaceous chondrites are relatively heterogeneous in composition ranging from +0.12 to +0.35‰, most likely reflecting clast–matrix variability. The light δ88Sr compositions of the refractory inclusions are consistent with mass dependent fractionation of other refractory elements (Ca and Eu) and are most likely produced by non-equilibrium fractionation (undercooling in the nebula gas) during condensation of hibonite from the solar nebula (Simon and DePaolo, 2010. Stable calcium isotopic composition of meteorites and rocky planets. Earth Planet. Sci. Lett. 289, 457–466).
Carbonaceous chondrites, angrites and martian meteorites have indistinguishable compositions at the level of analytical uncertainty of this study. However, statistical analysis indicates that melts derived from the Earth's mantle have heavier δ88Sr values than bulk carbonaceous chondrites and martian meteorites, but compositions indistinguishable from eucrites (δ88Sr=+0.26±0.12‰). Moreover, terrestrial basalts and andesites have restricted δ88Sr values (+0.30±0.07‰), suggesting that mantle melting delivers rather homogenous melts to the Earth's surface with respect to δ88Sr.
In contrast, glasses from evolved terrestrial rocks and lunar basalts extend to very light δ88Sr values ~−0.20‰. The Sr stable isotope composition covaries with europium anomaly (Eu/Eu*), as an index of plagioclase fractionation, and δ88Sr can be successfully modelled by the heavy isotopes of Sr being preferentially partitioned into plagioclase with a fractionation factor of ~1.0007 for 88Sr/86Sr. Our results demonstrate that Sr stable isotopes may be significantly fractionated at high temperatures and their measurement can provide insights into planetary evolution and magmatic processes.
► Stable Sr data are reported for meteorites, lunar, martian and terrestrial rocks. ► Carbonaceous chondrites, angrites and martian rocks are statistically identical. ► Melts from the Earth's mantle have significantly heavier stable Sr (δ88Sr) values. ► Some evolved terrestrial rocks and lunar basalts extend to light δ88Sr values. ► δ88Sr variations result from Sr being preferentially partitioned into feldspars.
We present the first search for heavy neutral leptons (HNLs) decaying into νe^{+}e^{-} or νπ^{0} final states in a liquid-argon time projection chamber using data collected with the MicroBooNE ...detector. The data were recorded synchronously with the NuMI neutrino beam from Fermilab's main injector corresponding to a total exposure of 7.01×10^{20} protons on target. We set upper limits at the 90% confidence level on the mixing parameter |U_{μ4}|^{2} in the mass ranges 10≤m_{HNL}≤150 MeV for the νe^{+}e^{-} channel and 150≤m_{HNL}≤245 MeV for the νπ^{0} channel, assuming |U_{e4}|^{2}=|U_{τ4}|^{2}=0. These limits represent the most stringent constraints in the mass range 35<m_{HNL}<175 MeV and the first constraints from a direct search for νπ^{0} decays.
We present the first measurement of the cross section of Cabibbo-suppressed Λ baryon production, using data collected with the MicroBooNE detector when exposed to the neutrinos from the main injector ...beam at the Fermi National Accelerator Laboratory. The data analyzed correspond to 2.2×10^{20} protons on target running in neutrino mode, and 4.9×10^{20} protons on target running in anti-neutrino mode. An automated selection is combined with hand scanning, with the former identifying five candidate Λ production events when the signal was unblinded, consistent with the GENIE prediction of 5.3±1.1 events. Several scanners were employed, selecting between three and five events, compared with a prediction from a blinded Monte Carlo simulation study of 3.7±1.0 events. Restricting the phase space to only include Λ baryons that decay above MicroBooNE's detection thresholds, we obtain a flux averaged cross section of 2.0_{-1.7}^{+2.2}×10^{-40} cm^{2}/Ar, where statistical and systematic uncertainties are combined.
We present a measurement of η production from neutrino interactions on argon with the MicroBooNE detector. The modeling of resonant neutrino interactions on argon is a critical aspect of the neutrino ...oscillation physics program being carried out by the DUNE and Short Baseline Neutrino programs. η production in neutrino interactions provides a powerful new probe of resonant interactions, complementary to pion channels, and is particularly suited to the study of higher-order resonances beyond the Δ(1232). We measure a flux-integrated cross section for neutrino-induced η production on argon of 3.22±0.84(stat)±0.86(syst) 10^{-41} cm^{2}/nucleon. By demonstrating the successful reconstruction of the two photons resulting from η production, this analysis enables a novel calibration technique for electromagnetic showers in GeV accelerator neutrino experiments.
The metals strontium (Sr), lithium (Li), osmium (Os) and calcium (Ca), together with their isotopes, are important tracers of weathering and volcanism – primary processes which shape the long-term ...cycling of carbon and other biogeochemically important elements at the Earth's surface. Traditionally, because of their long residence times in the ocean, isotopic shifts in these four elements observed in the geologic record are almost exclusively interpreted with the aid of isotope-mixing, tracer-specific box models. However, such models may lack a mechanistic description of the links between the cycling of the four metals to other geochemically relevant elements, particularly carbon, or climate. Here we develop and evaluate an implementation of Sr, Li, Os and Ca isotope cycling in the Earth system model cGENIE. The model offers the possibility to study the dynamics of these metal systems alongside other more standard biogeochemical cycles, as well as their relationship with changing climate. We provide examples of how to apply this new model capability to investigate Sr, Li, Os and Ca isotope dynamics and responses to environmental change, for which we take the example of massive carbon release to the atmosphere.
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