Carbon loss by deciduous trees in a CO2-rich ancient polar environment

Fossils demonstrate that deciduous forests covered the polar regions for much of the past 250 million years 1 when the climate was warm and atmospheric CO2 high 2. But the evolutionary significance of their deciduous character has remained a matter of conjecture for almost a century 3. The leading hypothesis 1,4-7 argues that it was an adaptation to photoperiod, allowing the avoidance of carbon losses by respiration from a canopy of leaves unable to photosynthesize in the darkness of warm polar winters 8-11. Here we test this proposal with experiments using 'living fossil' tree species grown in a simulated polar climate with and without CO2 enrichment. We show that the quantity of carbon lost annually by shedding a deciduous canopy is significantly greater than that lost by evergreen trees through wintertime respiration and leaf litter production, irrespective of growth CO2 concentration. Scaling up our experimental observations indicates that the greater expense of being deciduous persists in mature forests, even up to latitudes of 83 [degrees]N, where the duration of the polar winter exceeds five months. We therefore reject the carbon-loss hypothesis as an explanation for the deciduous nature of polar forests

The Geological Record of Ocean Acidification

Ocean acidification may have severe consequences for marine ecosystems; however, assessing its future impact is difficult because laboratory experiments and field observations are limited by their reduced ecologic complexity and sample period, respectively. In contrast, the geological record contains long-term evidence for a variety of global environmental perturbations, including ocean acidification plus their associated biotic responses. We review events exhibiting evidence for elevated atmospheric CO2, global warming, and ocean acidification over the past ~300 million years of Earth's history, some with contemporaneous extinction or evolutionary turnover among marine calcifiers. Although similarities exist, no past event perfectly parallels future projections in terms of disrupting the balance of ocean carbonate chemistry—a consequence of the unprecedented rapidity of CO2 release currently taking place

The nuclear energy density functional formalism

The present document focuses on the theoretical foundations of the nuclear energy density functional (EDF) method. As such, it does not aim at reviewing the status of the field, at covering all possible ramifications of the approach or at presenting recent achievements and applications. The objective is to provide a modern account of the nuclear EDF formalism that is at variance with traditional presentations that rely, at one point or another, on a {\it Hamiltonian-based} picture. The latter is not general enough to encompass what the nuclear EDF method represents as of today. Specifically, the traditional Hamiltonian-based picture does not allow one to grasp the difficulties associated with the fact that currently available parametrizations of the energy kernel $E[g',g]$ at play in the method do not derive from a genuine Hamilton operator, would the latter be effective. The method is formulated from the outset through the most general multi-reference, i.e. beyond mean-field, implementation such that the single-reference, i.e. "mean-field", derives as a particular case. As such, a key point of the presentation provided here is to demonstrate that the multi-reference EDF method can indeed be formulated in a {\it mathematically} meaningful fashion even if $E[g',g]$ does {\it not} derive from a genuine Hamilton operator. In particular, the restoration of symmetries can be entirely formulated without making {\it any} reference to a projected state, i.e. within a genuine EDF framework. However, and as is illustrated in the present document, a mathematically meaningful formulation does not guarantee that the formalism is sound from a {\it physical} standpoint. The price at which the latter can be enforced as well in the future is eventually alluded to.Comment: 64 pages, 8 figures, submitted to Euroschool Lecture Notes in Physics Vol.IV, Christoph Scheidenberger and Marek Pfutzner editor

Gaia Early Data Release 3: The celestial reference frame (Gaia-CRF3)

Context. Gaia-CRF3 is the celestial reference frame for positions and proper motions in the third release of data from the Gaia mission, Gaia DR3 (and for the early third release, Gaia EDR3, which contains identical astrometric results). The reference frame is defined by the positions and proper motions at epoch 2016.0 for a specific set of extragalactic sources in the (E)DR3 catalogue. Aims. We describe the construction of Gaia-CRF3 and its properties in terms of the distributions in magnitude, colour, and astrometric quality. Methods. Compact extragalactic sources in Gaia DR3 were identified by positional cross-matching with 17 external catalogues of quasi-stellar objects (QSO) and active galactic nuclei (AGN), followed by astrometric filtering designed to remove stellar contaminants. Selecting a clean sample was favoured over including a higher number of extragalactic sources. For the final sample, the random and systematic errors in the proper motions are analysed, as well as the radio-optical offsets in position for sources in the third realisation of the International Celestial Reference Frame (ICRF3). Results. Gaia-CRF3 comprises about 1.6 million QSO-like sources, of which 1.2 million have five-parameter astrometric solutions in Gaia DR3 and 0.4 million have six-parameter solutions. The sources span the magnitude range G = 13-21 with a peak density at 20.6 mag, at which the typical positional uncertainty is about 1 mas. The proper motions show systematic errors on the level of 12 μas yr-1 on angular scales greater than 15 deg. For the 3142 optical counterparts of ICRF3 sources in the S/X frequency bands, the median offset from the radio positions is about 0.5 mas, but it exceeds 4 mas in either coordinate for 127 sources. We outline the future of Gaia-CRF in the next Gaia data releases. Appendices give further details on the external catalogues used, how to extract information about the Gaia-CRF3 sources, potential (Galactic) confusion sources, and the estimation of the spin and orientation of an astrometric solution

Ozonolyses of 3-benzoyloxy- and 3-trimethylsiloxy-substituted 2- phenylindenes in methanol:Substituent-dependent modes of capture of the carbonyl oxide intermediates by the solvent

Segmenting an image into multiple components is a central task in computer vision. In many practical scenarios, prior knowledge about plausible components is available. Incorporating such prior knowledge into models and algorithms for image segmentation is highly desirable, yet can be non-trivial. In this work, we introduce a new approach that allows, for the first time, to constrain some or all components of a segmentation to have convex shapes. Specifically, we extend the Minimum Cost Multicut Problem by a class of constraints that enforce convexity. To solve instances of this NP-hard integer linear program to optimality, we separate the proposed constraints in the branch-and-cut loop of a state-of-the-art ILP solver. Results on photographs and micrographs demonstrate the effectiveness of the approach as well as its advantages over the state-of-the-art heuristic

Phanerozoic atmospheric CO2 reconstructed with proxies and models: Current understanding and future directions

Knowledge of paleo-atmospheric CO2 is critical to understanding how Earth System processes respond to a full range of CO2 concentrations, both past and future. This review addresses the terrestrial and marine proxies used to estimate paleo-CO2 concentrations and how the biological and/or geochemical properties of each proxy encodes the ambient CO2 signal, as well as the associated assumptions and uncertainties of the CO2 estimates. The Phanerozoic history of atmospheric CO2 is discussed, highlighting a new high-fidelity Cenozoic CO2 curve and its implications. Subsequently, pre-Cenozoic CO2 as is currently understood is outlined, in the context of its temporal relationship to climate and evolutionary changes. An overview of carbon cycle modeling for estimating paleo-CO2 is presented, including the key principles, models, and updates in the field, as well as the key emerging patterns and planned next steps. The review concludes by addressing next steps in advancing the science of CO2 reconstruction and for improving our understanding of the evolution of atmospheric CO2 over the past half-billion years

Early Miocene CO2 estimates from a Neotropical fossil leaf assemblage exceed 400 ppm

Premise of the Study: The global climate during the early Miocene was warmer than the present and preceded the even warmer middle Miocene climatic optimum. The paleo-CO2 records for this interval suggest paradoxically low concentrations (<450 ppm) that are difficult to reconcile with a warmer-than-present global climate. Methods: In this study, we use a leaf gas-exchange model to estimate CO2 concentrations using stomatal characteristics of fossil leaves from a late early Miocene Neotropical assemblage from Panama that we date to 18.01 ± 0.17 Ma via 238U/206Pb zircon geochronology. We first validated the model for Neotropical environments by estimating CO2 from canopy leaves of 21 extant species in a natural Panamanian forest and from leaves of seven Neotropical species in greenhouse experiments at 400 and 700 ppm. Key Results: The results showed that the most probable combined CO2 estimate from the natural forests and 400 ppm experiments is 475 ppm, and for the 700 ppm experiments is 665 ppm. CO2 estimates from the five fossil species exhibit bimodality, with two species most consistent with a low mode (528 ppm) and three with a high mode (912 ppm). Conclusions: Despite uncertainties, it is very likely (at >95% confidence) that CO2 during the late early Miocene exceeded 400 ppm. These results revise upwards the likely CO2 concentration at this time, more in keeping with a CO2-forced greenhouse climate. © 2018 Botanical Society of Americ