A Diatom Phosphorus Inference Model for 30 Freshwater Lakes in NE Ohio and NW Pennsylvania

Nutrient enrichment in the form of anthropogenic phosphorous and nitrogen inputs has occurred in lakes worldwide. In the absence of historical water chemistry data, the extent to which this disturbance has impacted lakes in the Erie/Ontario drift and lake plain and Western Allegheny Plateau ecoregions remains to be determined. The objective of this study was to develop a diatom calibration set through analysis of surface sediments and water chemistry from 30 lakes spanning a phosphorous and nitrogen gradient in the glaciated regions of northeast Ohio and northwest Pennsylvania with an additional lake in New York. No current training set exists for this unique geographic region. The relationship between diatom species and environmental variables was established using ordination techniques involving multiple regression and weighted-averaging methods. Canonical correspondence analysis (CCA) was used to determine environmental variables that have a strong influence on diatoms from the ecoregions studied. Total phosphorus, ammonia, and magnesium were the three most statistically significant variables determined through multivariate analyses, although maximum depth and nickel concentrations were also found to be important. At a total phosphorus inference model was developed from recent diatom fossil remains and contemporary water chemistry measurements. The ecological indicator values (optima and tolerances) of 40 abundant diatom species were defined using C2 computer software. The root mean squared error associated with prediction of the TP inference model was 17 ug/L, and the R2 linear coefficient of correlation between observed and diatom-inferred TP values was 0.77. The optima developed in this research match closely those constructed from calibration studies covering similar or longer TP gradients (12 ug/L-153 ug/L TP). A comparison with optima developed from other studies yields values much lower than those in this project and illustrates the need for regional calibration studies. This calibration set will be u

A Diatom Phosphorus Inference Model for 30 Freshwater Lakes in NE Ohio and NW Pennsylvania

Nutrient enrichment in the form of anthropogenic phosphorous and nitrogen inputs has occurred in lakes worldwide. In the absence of historical water chemistry data, the extent to which this disturbance has impacted lakes in the Erie/Ontario drift and lake plain and Western Allegheny Plateau ecoregions remains to be determined. The objective of this study was to develop a diatom calibration set through analysis of surface sediments and water chemistry from 30 lakes spanning a phosphorous and nitrogen gradient in the glaciated regions of northeast Ohio and northwest Pennsylvania with an additional lake in New York. No current training set exists for this unique geographic region. The relationship between diatom species and environmental variables was established using ordination techniques involving multiple regression and weighted-averaging methods. Canonical correspondence analysis (CCA) was used to determine environmental variables that have a strong influence on diatoms from the ecoregions studied. Total phosphorus, ammonia, and magnesium were the three most statistically significant variables determined through multivariate analyses, although maximum depth and nickel concentrations were also found to be important. At a total phosphorus inference model was developed from recent diatom fossil remains and contemporary water chemistry measurements. The ecological indicator values (optima and tolerances) of 40 abundant diatom species were defined using C2 computer software. The root mean squared error associated with prediction of the TP inference model was 17 ug/L, and the R2 linear coefficient of correlation between observed and diatom-inferred TP values was 0.77. The optima developed in this research match closely those constructed from calibration studies covering similar or longer TP gradients (12 ug/L-153 ug/L TP). A comparison with optima developed from other studies yields values much lower than those in this project and illustrates the need for regional calibration studies. This calibration set will be u

On the Sensitivity of the Devonian Climate to Continental Configuration, Vegetation Cover, Orbital Configuration, CO 2 Concentration, and Insolation

During the Devonian (419 to 359 million years ago), life on Earth witnessed decisive evolutionary breakthroughs, most prominently the colonization of land by vascular plants and vertebrates. However, it was also a period of major marine extinctions coinciding with marked changes in climate. The cause of these changes remains unknown, and it is therefore instructive to explore systematically how the Devonian climate responds to changes in boundary conditions. Here we use coupled climate model simulations to investigate separately the influence of changes in continental configuration, vegetation cover, carbon dioxide (CO2) concentrations, the solar constant, and orbital parameters on the Devonian climate. The biogeophysical effect of changes in vegetation cover is small, and the cooling due to continental drift is offset by the increasing solar constant. Variations of orbital parameters affect the Devonian climate, with the warmest climate states at high obliquity and high eccentricity. The prevailing mode of decadal to centennial climate variability relates to temperature fluctuations in high northern latitudes which are mediated by coupled oscillations involving sea ice cover, ocean convection, and a regional overturning circulation. The temperature evolution during the Devonian is dominated by the strong decrease in atmospheric CO2. Albedo changes due to increasing vegetation cover cannot explain the temperature rise found in Late Devonian proxy data. Finally, simulated temperatures are significantly lower than estimates based on oxygen isotope ratios, suggesting a lower d18O ratio of Devonian seawater. ©2019. The Authors

Environmentally driven extinction and opportunistic origination explain fern diversification patterns.

Combining palaeontological and neontological data offers a unique opportunity to investigate the relative roles of biotic and abiotic controls of species diversification, and the importance of origination versus extinction in driving evolutionary dynamics. Ferns comprise a major terrestrial plant radiation with an extensive evolutionary history providing a wealth of modern and fossil data for modelling environmental drivers of diversification. Here we develop a novel Bayesian model to simultaneously estimate correlations between diversification dynamics and multiple environmental trajectories. We estimate the impact of different factors on fern diversification over the past 400 million years by analysing a comprehensive dataset of fossil occurrences and complement these findings by analysing a large molecular phylogeny. We show that origination and extinction rates are governed by fundamentally different processes: originations depend on within-group diversity but are largely unaffected by environmental changes, whereas extinctions are strongly affected by external factors such as climate and geology. Our results indicate that the prime driver of fern diversity dynamics is environmentally driven extinction, with origination being an opportunistic response to diminishing ecospace occupancy

Climate model boundary conditions for four Cretaceous time slices

International audienceGeneral circulation models (GCMs) are useful tools for investigating the characteristics and dynamics of past climates. Understanding of past climates contributes significantly to our overall understanding of Earth's climate system. One of the most time consuming, and often daunting, tasks facing the paleoclimate modeler, particularly those without a geological background, is the production of surface boundary conditions for past time periods. These boundary conditions consist of, at a minimum, continental configurations derived from plate tectonic modeling, topography, bathymetry, and a vegetation distribution. Typically, each researcher develops a unique set of boundary conditions for use in their simulations. Thus, unlike simulations of modern climate, basic assumptions in paleo surface boundary conditions can vary from researcher to researcher. This makes comparisons between results from multiple researchers difficult and, thus, hinders the integration of studies across the broader community. Unless special changes to surface conditions are warranted, researcher dependent boundary conditions are not the most efficient way to proceed in paleoclimate investigations. Here we present surface boundary conditions (land-sea distribution, paleotopography, paleobathymetry, and paleovegetation distribution) for four Cretaceous time slices (120 Ma, 110 Ma, 90 Ma, and 70 Ma). These boundary conditions are modified from base datasets to be appropriate for incorporation into numerical studies of Earth's climate and are available in NetCDF format upon request from the lead author. The land-sea distribution, bathymetry, and topography are based on the 1°×1° (latitude × longitude) paleo Digital Elevation Models (paleoDEMs) of Christopher Scotese. Those paleoDEMs were adjusted using the paleogeographical reconstructions of Ronald Blakey (Northern Arizona University) and published literature and were then modified for use in GCMs. The paleovegetation distribution is based on published data and reconstructions and consultation with members of the paleobotanical community and is represented as generalized biomes that should be easily translatable to many vegetation-modeling schemes

Elevated CO2 degassing rates prevented the return of Snowball Earth during the Phanerozoic

The Cryogenian period (~720–635 Ma) is marked by extensive Snowball Earth glaciations. These have previously been linked to CO₂ draw-down, but the severe cold climates of the Cryogenian have never been replicated during the Phanerozoic despite similar, and sometimes more dramatic changes to carbon sinks. Here we quantify the total CO₂ input rate, both by measuring the global length of subduction zones in plate tectonic reconstructions, and by sea-level inversion. Our results indicate that degassing rates were anomalously low during the Late Neoproterozoic, roughly doubled by the Early Phanerozoic, and remained comparatively high until the Cenozoic. Our carbon cycle modelling identifies the Cryogenian as a unique period during which low surface temperature was more easily achieved, and shows that the shift towards greater CO₂ input rates after the Cryogenian helped prevent severe glaciation during the Phanerozoic. Such a shift appears essential for the development of complex animal life

A horseshoe crab (Arthropoda: Chelicerata: Xiphosura) from the Lower Devonian (Lochkovian) of Yunnan, China

This is the publisher's version, also available electronically from http://journals.cambridge.org/action/displayAbstract?fromPage=online&aid=8826898&fileId=S0016756812000891A single specimen of a new species of the synziphosurine Kasibelinurus Pickett, 1993 is described from the Lower Devonian (Lochkovian) Xiaxishancun Formation of Yunnan Province, China. The new species, K. yueya sp. nov., extends the geographic extent of the family Kasibelinuridae from the Australian palaeocontinent to the South China palaeocontinent, and the stratigraphic range back some 50 Ma from Late to Early Devonian

Environmentally driven extinction and opportunistic origination explain fern diversification patterns

Combining palaeontological and neontological data offers a unique opportunity to investigate the relative roles of biotic and abiotic controls of species diversification, and the importance of origination versus extinction in driving evolutionary dynamics. Ferns comprise a major terrestrial plant radiation with an extensive evolutionary history providing a wealth of modern and fossil data for modelling environmental drivers of diversification. Here we develop a novel Bayesian model to simultaneously estimate correlations between diversification dynamics and multiple environmental trajectories. We estimate the impact of different factors on fern diversification over the past 400 million years by analysing a comprehensive dataset of fossil occurrences and complement these findings by analysing a large molecular phylogeny. We show that origination and extinction rates are governed by fundamentally different processes: originations depend on within-group diversity but are largely unaffected by environmental changes, whereas extinctions are strongly affected by external factors such as climate and geology. Our results indicate that the prime driver of fern diversity dynamics is environmentally driven extinction, with origination being an opportunistic response to diminishing ecospace occupancy