Nitrification controls the oxidation state of bioavailable nitrogen. Distinct clades of chemoautotrophic microorganisms - predominantly ammonia-oxidizing archaea (AOA) and nitrite-oxidizing bacteria (NOB) - regulate the two steps of nitrification in the ocean, but explanations for their observed relative abundances and nitrification rates remain incomplete and their contributions to the global marine carbon cycle via carbon fixation remain unresolved. Using a mechanistic microbial ecosystem model with nitrifying functional types, we derive simple expressions for the controls on AOA and NOB in the deep, oxygenated open ocean. The relative biomass yields, loss rates, and cell quotas of AOA and NOB control their relative abundances, though we do not need to invoke a difference in loss rates to explain the observed relative abundances. The supply of ammonium, not the traits of AOA or NOB, controls the relatively equal ammonia and nitrite oxidation rates at steady state. The relative yields of AOA and NOB alone set their relative bulk carbon fixation rates in the water column. The quantitative relationships are consistent with multiple in situ datasets. In a complex global ecosystem model, nitrification emerges dynamically across diverse ocean environments, and ammonia and nitrite oxidation and their associated carbon fixation rates are decoupled due to physical transport and complex ecological interactions in some environments. Nevertheless, the simple expressions capture global patterns to first order. The model provides a mechanistic upper estimate on global chemoautotrophic carbon fixation of 0.2-0.5 Pg C yr(-1), which is on the low end of the wide range of previous estimates. Modeled carbon fixation by AOA (0.2-0.3 Pg C yr(-1)) exceeds that of NOB (about 0.1 Pg C yr(-1)) because of the higher biomass yield of AOA. The simple expressions derived here can be used to quantify the biogeochemical impacts of additional metabolic pathways (i.e., mixotrophy) of nitrifying clades and to identify alternative metabolisms fueling carbon fixation in the deep ocean.

Synchrotron X-ray powder diffraction and infrared (IR) spectroscopy studies on natural brucite were conducted up to 31 GPa using diamond-anvil cell (DAC) techniques at beamlines X17C and U2A of National Synchrotron Light Source (NSLS). The lattice parameters and unit-cell volumes were refined in P (3) over bar m1 space group throughout the experimental pressure range. The anisotropy of lattice compression decreases with pressure due to a more compressible c axis and the compression becomes nearly isotropic in the pressure range of 10-25 GPa. The unit-cell volumes are fitted to the third-order Birch-Mumaghan equation of state, yielding K-0 = 39.4(1.3) GPa, K-0' = 8.4(0.4) for the bulk modulus and its pressure-derivative, respectively. No phase transition or amorphization was resolved from the X-ray diffraction data up to 29 GPa, however, starting from 4 GPa, a new infrared vibration band (similar to 3638 cm(-1)) 60 cm(-1) below the OH stretching A(2u) band of brucite was found to coexist with the A(2u) band and its intensity continuously increases with pressure. The new OH stretching band has a more pronounced redshift as a function of pressure (-4.7 cm(-1)/GPa) than the A(2u) band (-0.7 cm(-1)/GPa). Comparison with first-principles calculations suggests that a structural change involving the disordered H sublattice is capable of reconciling the observations from X-ray diffraction and infrared spectroscopy studies.

Zebrafish are a valuable model for mammalian lipid metabolism; larvae process lipids similarly through the intestine and hepatobiliary system and respond to drugs that block cholesterol synthesis in humans. After ingestion of fluorescently quenched phospholipids, endogenous lipase activity and rapid transport of cleavage products results in intense gall bladder fluorescence. Genetic screening identifies zebrafish mutants, such as fat free, that show normal digestive organ morphology but severely reduced phospholipid and cholesterol processing. Thus, fluorescent lipids provide a sensitive readout of lipid metabolism and are a powerful tool for identifying genes that mediate vertebrate digestive physiology.

We consider the effects of non-constant star formation histories (SFHs) on H alpha and GALEX far-ultraviolet (FUV) star formation rate (SFR) indicators. Under the assumption of a fully populated Chabrier initial mass function (IMF), we compare the distribution of H alpha-to-FUV flux ratios from similar to 1500 simple, periodic model SFHs with observations of 185 galaxies from the Spitzer Local Volume Legacy survey. We find a set of SFH models that are well matched to the data, such that more massive galaxies are best characterized by nearly constant SFHs, while low-mass systems experience burst amplitudes of similar to 30 (i.e., an increase in the SFR by a factor of 30 over the SFR during the inter-burst period), burst durations of tens of Myr, and periods of similar to 250 Myr; these SFHs are broadly consistent with the increased stochastic star formation expected in systems with lower SFRs. We analyze the predicted temporal evolution of galaxy stellar mass, R-band surface brightness, H alpha-derived SFR, and blue luminosity, and find that they provide a reasonable match to observed flux distributions. We find that our model SFHs are generally able to reproduce both the observed systematic decline and increased scatter in H alpha-to-FUV ratios toward low-mass systems, without invoking other physical mechanisms. We also compare our predictions with those from the Integrated Galactic IMF theory with a constant SFR. We find that while both predict a systematic decline in the observed ratios, only the time variable SFH models are capable of producing the observed population of low-mass galaxies (M-* less than or similar to 10(7) M-circle dot) with normal H alpha-to-FUV ratios. These results demonstrate that a variable IMF alone has difficulty explaining the observed scatter in the H alpha-to-FUV ratios. We conclude by considering the limitations of the model SFHs and discuss the use of additional empirical constraints to improve future SFH modeling efforts.

During November-December 2009 community rates of gross photosynthesis (P-g), respiration (R) and net calcification (G(net)) were estimated from low-tide slack water measurements of dissolved oxygen, dissolved inorganic carbon and total alkalinity at the historical station DK13 One Tree Island reef, Great Barrier Reef, Australia. Compared to measurements made during the 1960s-1970s at DK13 in the same season, P-g increased from 833 to 914 mmol O-2 center dot m(-2).d(-1) and P-g:R increased from 1.14 to 1.30, indicating that the reef has become more autotrophic. In contrast, G(net) decreased from 133 mmol C.m(-2).d(-1) to 74 +/- 24 mmol C.m(-2).d(-1). This decrease stems primarily from the threefold increase in nighttime CaCO3 dissolution from -2.5 mmol.m(-2).h(-1) to -7.5 mmol.m(-2).h(-1). Comparison of the benthic community survey results from DK13 and its vicinity conducted during this study and in studies from the 1970s, 1980s and 1990s suggest that there have been no significant changes in the live coral coverage during the past 40 years. The reduced G(net) most likely reflects the almost threefold increase in dissolution rates, possibly resulting from increased bioerosion due to changes in the biota (e.g., sea cucumbers, boring organisms) and/or from greater chemical dissolution produced by changing abiotic conditions over the past 40 years associated with climate change, such as increased temperatures and ocean acidification. However, at this stage of research on One Tree Island the effects of these changes are not entirely understood.

The optimisation of synthetic and natural microbial communities has vast potential for emerging applications in medicine, agriculture and industry. Realising this goal is contingent on a close correlation between theory, experiments, and the real world. Although the temporal pattern of resource supply can play a major role in microbial community assembly, resource dynamics are commonly treated inconsistently in theoretical and experimental research. Here we explore how the composition of communities varies under continuous resource supply, typical of theoretical approaches, versus pulsed resource supply, typical of experiments. Using simulations of classical resource competition models, we show that community composition diverges rapidly between the two regimes, with almost zero overlap in composition once the pulsing interval stretches beyond just four hours. The implication for the rapidly growing field of microbial community optimisation is that the resource supply regime must be tailored to the community being optimised. As such, we argue that resource supply dynamics should be considered both a constraint in the design of novel microbial communities and as a tuning mechanism for the optimisation of pre-existing communities like those found in the human gut.

The extraterrestrial materials returned from asteroid (162173) Ryugu consist predominantly of low-temperature aqueously formed secondary minerals and are chemically and mineralogically similar to CI (Ivuna-type) carbonaceous chondrites. Here, we show that high-temperature anhydrous primary minerals in Ryugu and CI chondrites exhibit a bimodal distribution of oxygen isotopic compositions: 16O-rich (associated with refractory inclusions) and 16O-poor (associated with chondrules). Both the 16O-rich and 16O-poor minerals probably formed in the inner solar protoplanetary disk and were subsequently transported outward. The abundance ratios of the 16O-rich to 16O-poor minerals in Ryugu and CI chondrites are higher than in other carbonaceous chondrite groups but are similar to that of comet 81P/Wild2, suggesting that Ryugu and CI chondrites accreted in the outer Solar System closer to the accretion region of comets.

Initial analyses showed that asteroid Ryugu's composition is close to CI (Ivuna-like) carbonaceous chondrites (CCs) - the chemically most primitive meteorites, characterized by near-solar abundances for most elements. However, some isotopic signatures (for example, Ti, Cr) overlap with other CC groups, so the details of the link between Ryugu and the CI chondrites are not yet fully clear. Here we show that Ryugu and CI chondrites have the same zinc and copper isotopic composition. As the various chondrite groups have very distinct Zn and Cu isotopic signatures, our results point at a common genetic heritage between Ryugu and CI chondrites, ruling out any affinity with other CC groups. Since Ryugu's pristine samples match the solar elemental composition for many elements, their Zn and Cu isotopic compositions likely represent the best estimates of the solar composition. Earth's mass-independent Zn isotopic composition is intermediate between Ryugu/CC and non-carbonaceous chondrites (NCs), suggesting a contribution of Ryugu-like material to Earth's budgets of Zn and other moderately volatile elements.

Meteorites record processes that occurred before and during the formation of the Solar System in the form of nucleosynthetic anomalies: isotopic compositions that differ from the Solar System patterns. Nucleosynthetic anomalies are rarely seen in volatile elements such as potassium at bulk meteorite scale. We measured potassium isotope ratios in 32 meteorites and identified nucleosynthetic anomalies in the isotope potassium-40. The anomalies are larger and more variable in carbonaceous chondrite (CC) meteorites than in noncarbonaceous (NC) meteorites, indicating that CCs inherited more material produced in supernova nucleosynthesis. The potassium-40 anomaly of Earth is close to that of the NCs, implying that Earth's potassium was mostly delivered by NCs.

We present a spectroscopic survey of 248 white dwarf candidates within 40 pc of the Sun; of these 244 are in the Southern hemisphere. Observations were performed mostly with the Very Large Telescope (X-Shooter) and Southern Astrophysical Research Telescope. Almost all candidates were selected from Gaia Data Release 3 (DR3). We find a total of 246 confirmed white dwarfs, 209 of which had no previously published spectra, and two main-sequence star contaminants. Of these, 100 white dwarfs display hydrogen Balmer lines, 69 have featureless spectra, and two show only neutral helium lines. Additionally, 14 white dwarfs display traces of carbon, while 37 have traces of other elements that arc heavier than helium. We observe 35 magnetic white dwarfs through the detection of Zeeman splitting of their hydrogen Balmer or metal spectral lines. High spectroscopic completeness (> 97 percent) has now been reached, such that we have 1058 confirmed Gala DR3 white dwarfs out of 1083 candidates within 40 pc of the Sun at all declinations.