Display omitted
•New paleogeographical reconstructions of exposed land for the Phanerozoic.•Our new maps show strong fluctuations in exposed land during the early Paleozoic.•New estimates for carbon ...degassing through the Phanerozoic using two proxies.•We ran 12 new models using GEOCARBSULFvolc with changing input parameters.•Elevated degassing estimates leads to higher simulated CO2 levels in the Mesozoic.•Assessing climate gradients produces a better CO2 model-proxy fit over the Mesozoic.
Long-term carbon cycle models are critical for understanding the levels and underlying controls of atmospheric CO2 over geological time-scales. We have refined the implementation of two important boundary conditions in carbon cycle models, namely consumption by silicate weathering and carbon degassing. Through the construction of continental flooding maps for the past 520 million years (Myrs), we have estimated exposed land area relative to the present-day (fA), and the fraction of exposed land area undergoing silicate weathering (fAW-fA). The latter is based on the amount of exposed land within the tropics (±10°) plus the northern/southern wet belts (±40–50°) relative to today, which are the prime regions for silicate weathering. We also evaluated climate gradients and potential weatherability by examining the distribution of climate-sensitive indicators. This is particularly important during and after Pangea formation, when we reduce fAW-fA during times when arid equatorial regions were present. We also estimated carbon degassing for the past 410 Myrs using the subduction flux from full-plate models as a proxy. We further used the subduction flux to scale and normalize the arc-related zircon age distribution (arc-activity), allowing us to estimate carbon degassing in much deeper time. The effect of these refined modelling parameters for weathering and degassing was then tested in the GEOCARBSULFvolc model, and the results are compared to other carbon cycle models and CO2 proxies. The use of arc-activity as a proxy for carbon degassing brings Mesozoic model estimates closer to CO2 proxy values but our models are highly sensitive to the definition of fAW-fA. Considering only variations in the land availability to weathering that occur in tropical latitudes (corrected for arid regions) and the use of our new degassing estimates leads to notably higher CO2 levels in the Mesozoic, and a better fit with the CO2 proxies.
Early flowering plants are thought to have been woody species restricted to warm habitats. This lineage has since radiated into almost every climate, with manifold growth forms. As angiosperms spread ...and climate changed, they evolved mechanisms to cope with episodic freezing. To explore the evolution of traits underpinning the ability to persist in freezing conditions, we assembled a large species-level database of growth habit (woody or herbaceous; 49,064 species), as well as leaf phenology (evergreen or deciduous), diameter of hydraulic conduits (that is, xylem vessels and tracheids) and climate occupancies (exposure to freezing). To model the evolution of species' traits and climate occupancies, we combined these data with an unparalleled dated molecular phylogeny (32,223 species) for land plants. Here we show that woody clades successfully moved into freezing-prone environments by either possessing transport networks of small safe conduits and/or shutting down hydraulic function by dropping leaves during freezing. Herbaceous species largely avoided freezing periods by senescing cheaply constructed aboveground tissue. Growth habit has long been considered labile, but we find that growth habit was less labile than climate occupancy. Additionally, freezing environments were largely filled by lineages that had already become herbs or, when remaining woody, already had small conduits (that is, the trait evolved before the climate occupancy). By contrast, most deciduous woody lineages had an evolutionary shift to seasonally shedding their leaves only after exposure to freezing (that is, the climate occupancy evolved before the trait). For angiosperms to inhabit novel cold environments they had to gain new structural and functional trait solutions; our results suggest that many of these solutions were probably acquired before their foray into the cold.
Celotno besedilo
Dostopno za:
DOBA, IJS, IZUM, KILJ, KISLJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
Teeth are conspicuous features of many leaves. The percentage of species in a flora with toothed leaves varies inversely with temperature, but other ecological controls are less known. This gap is ...critical because leaf teeth may be influenced by water availability and growth potential and because fossil tooth characters are widely used to reconstruct paleoclimate. Here, we test whether ecological attributes related to disturbance, water availability, and growth strategy influence the distribution of toothed species at 227 sites from Australian subtropical rainforest. Both the percentage and abundance of toothed species decline continuously from riparian to ridge-top habitats in our most spatially resolved sample, a result not related to phylogenetic correlation of traits. Riparian lianas are generally untoothed and thus do not contribute to the trend, and there is little association between toothed riparian species and ecological attributes indicating early successional lifestyle and disturbance response. Instead, the pattern is best explained by differences in water availability. Toothed species' proportional richness declines with proximity to the coast, also a likely effect of water availability because salt stress causes physiological drought. Our study highlights water availability as an important factor impacting the distribution of toothed species across landscapes, with significance for paleoclimate reconstructions.
PREMISE
The Eocene–Oligocene transition (EOT; 34–33 Ma) was marked by global cooling and increased seasonality and aridity, leading to a shift in North American floras from subtropical forests to ...deciduous hardwood forests similar to today. This shift is well documented taxonomically and biogeographically, but its ecological nature is less known.
METHODS
Using the relationship between petiole cross‐sectional area and leaf mass, we estimated leaf dry mass per area (LMA), a functional trait tied to plant resource investment and expenditure, at 22 western North American sites spanning the EOT to determine how the broad restructuring of vegetation during this time was reflected in leaf economics.
RESULTS
There was no overall shift in LMA between pre‐EOT and post‐EOT floras; instead, changes in LMA across sites were mostly driven by a negative correlation with dry‐season precipitation and a positive correlation with paleoelevation. These patterns held for both whole sites and subsets of sites containing taxa with similar biogeographical histories (taxa that persisted in the highlands across the EOT or that migrated to the lowlands) and are consistent with most observations in extant floras.
CONCLUSIONS
Our data provide a geological context for understanding environmentally paced changes in leaf‐economic strategies, particularly linking leaf economic strategies to dry‐season precipitation and paleoelevation.
In 1966, David Baker, a Black man and esteemed jazz musician and composer, created and developed the Jazz Studies program at Indiana University (IU). The purpose of this study was to investigate how ...David Baker came to join the faculty and created the Jazz Studies program at IU through an examination of the school’s course offerings and historical context between the years 1949–1969. This time period captures when jazz was evolving from its roots as an informally learned art form into one that was taught in academic settings, as well as important evolutionary moments in jazz, specifically the transition from bebop and cool jazz through the development of hard bop, modal jazz, and Third Stream. Finally, it captures the tumultuous Civil Rights Movement of the 1950s and 1960s which coincided with IU’s hiring of David Baker and the school’s decision to begin to include jazz courses in its curricular offerings. This examination concludes with a discussion of relevant implications for jazz and music education.
Earth's atmospheric CO2 concentration (ca) for the Phanerozoic Eon is estimated from proxies and geochemical carbon cycle models. Most estimates come with large, sometimes unbounded uncertainty. ...Here, we calculate tightly constrained estimates of ca using a universal equation for leaf gas exchange, with key variables obtained directly from the carbon isotope composition and stomatal anatomy of fossil leaves. Our new estimates, validated against ice cores and direct measurements of ca, are less than 1000 ppm for most of the Phanerozoic, from the Devonian to the present, coincident with the appearance and global proliferation of forests. Uncertainties, obtained from Monte Carlo simulations, are typically less than for ca estimates from other approaches. These results provide critical new empirical support for the emerging view that large (~2000–3000 ppm), long‐term swings in ca do not characterize the post‐Devonian and that Earth's long‐term climate sensitivity to ca is greater than originally thought.
Key Points
A novel CO2 proxy calculates past atmospheric CO2 with improved certainty
CO2 is unlikely to have exceeded ~1000 ppm for extended periods post Devonian
Earth's long‐term climate sensitivity to CO2 is greater than originally thought
The living species Ginkgo biloba is phylogenetically isolated, has a relictual distribution, and is morphologically very similar to Mesozoic and Cenozoic congenerics. To investigate what adaptations ...may have allowed this lineage to persist with little or no morphological change for over 100 Myr, we analyzed both sedimentological and floral data from 51 latest Cretaceous to middle Miocene Ginkgo-bearing fossil plant sites in North America and northern Europe. The resulting data indicate that throughout the late Cretaceous and Cenozoic Ginkgo was largely confined to disturbed streamside and levee environments, where it occurred with a consistent set of other plants. These inferred habitats are surprising because the life-history traits of Ginkgo (e.g., slow growth rate, late reproductive maturity, extended reproductive cycle, large and complex seeds, large and slowly developing embryos) are counter to those considered advantageous in modern disturbed habitats. Many flowering plant lineages first appeared or became common in disturbed riparian habitats, and are inferred to have had reproductive and growth traits (e.g., rapid reproduction, small easily dispersed seeds, rapid growth) suited to such habitats. Paleoecological inferences based on both morphology and sedimentary environments thus support the idea that Ginkgo was displaced in riparian habitats by angiosperms with better adaptations to frequent disturbance.
The end-Cretaceous mass extinctions, 65 million years ago, profoundly influenced the course of biotic evolution. These extinctions coincided with a major extraterrestrial impact event and massive ...volcanism in India. Determining the relative importance of each event as a driver of environmental and biotic change across the Cretaceous-Tertiary boundary (KTB) crucially depends on constraining the mass of CO 2 injected into the atmospheric carbon reservoir. Using the inverse relationship between atmospheric CO 2 and the stomatal index of land plant leaves, we reconstruct Late Cretaceous-Early Tertiary atmospheric CO 2 concentration ( p CO 2 ) levels with special emphasis on providing a p CO 2 estimate directly above the KTB. Our record shows stable Late Cretaceous/Early Tertiary background p CO 2 levels of 350–500 ppm by volume, but with a marked increase to at least 2,300 ppm by volume within 10,000 years of the KTB. Numerical simulations with a global biogeochemical carbon cycle model indicate that CO 2 outgassing during the eruption of the Deccan Trap basalts fails to fully account for the inferred p CO 2 increase. Instead, we calculate that the postboundary p CO 2 rise is most consistent with the instantaneous transfer of ≈4,600 Gt C from the lithic to the atmospheric reservoir by a large extraterrestrial bolide impact. A resultant climatic forcing of +12 W⋅m −2 would have been sufficient to warm the Earth's surface by ≈7.5°C, in the absence of counter forcing by sulfate aerosols. This finding reinforces previous evidence for major climatic warming after the KTB impact and implies that severe and abrupt global warming during the earliest Paleocene was an important factor in biotic extinction at the KTB.
Understanding the link between the greenhouse gas carbon dioxide (CO(2)) and Earth's temperature underpins much of paleoclimatology and our predictions of future global warming. Here, we use the ...inverse relationship between leaf stomatal indices and the partial pressure of CO(2) in modern Ginkgo biloba and Metasequoia glyptostroboides to develop a CO(2) reconstruction based on fossil Ginkgo and Metasequoia cuticles for the middle Paleocene to early Eocene and middle Miocene. Our reconstruction indicates that CO(2) remained between 300 and 450 parts per million by volume for these intervals with the exception of a single high estimate near the Paleocene/Eocene boundary. These results suggest that factors in addition to CO(2) are required to explain these past intervals of global warmth.
PDF
