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Determining how atmospheric carbon dioxide concentrations have changed during the history of the Earth
The reconstruction of ancient atmospheric carbon dioxide concentrations is essential to understanding the history of the Earth and life. It is also an important guide to identifying the sensitivity of the Earth system to this greenhouse gas and, therefore, constraining its future impact on climate. However, determining the concentration of CO2 in ancient atmospheres is a challenging endeavour requiring the application of state-of-the-art analytical chemistry to geological materials, underpinned by an understanding of photosynthesis and biochemistry. It is truly an interdisciplinary challenge
The International Baccalaureate Learner Profile: A Social Justice Framework in the English Language Arts Classroom
âThe International Baccalaureate Learner Profile: A Social Justice Framework in the English Language Arts Classroom, highlights the story of an expert secondary ELA teacher as she navigates the political climate in the wake of the 2016 presidential election. Through narrative, classroom anecdote, and pedagogical reflection, this story offers readers an authentic portrait of the complex decisions that face teachers as we navigate tenuous political terrain in our classrooms. Central to this story is the International Baccalaureate (IB) Learner Profile (LP), which is the framework from which this teacher operates: the IB LP serves as both the anchor and guide for this teacherâs pedagogical decision-making and a teaching tool in her classroom. In unpacking this teacherâs narrative and practice, this piece offers criteria for establishing a classroom climate of productive political discourse and shares features of a politically engaged classroom, both of which are aimed to inspire readersâ critical inquiry into their own practice as they address politics in their own classrooms
Insensitivity of alkenone carbon isotopes to atmospheric CO<sub>2</sub> at low to moderate CO<sub>2</sub> levels
Atmospheric pCO2 is a critical component of the global carbon system and is considered to be the major control of Earthâs past, present and future climate. Accurate and precise reconstructions of its concentration through geological time are, therefore, crucial to our understanding of the Earth system. Ice core records document pCO2 for the past 800 kyrs, but at no point during this interval were CO2 levels higher than today. Interpretation of older pCO2 has been hampered by discrepancies during some time intervals between two of the main ocean-based proxy methods used to reconstruct pCO2: the carbon isotope fractionation that occurs during photosynthesis as recorded by haptophyte biomarkers (alkenones) and the boron isotope composition (δ11B) of foraminifer shells. Here we present alkenone and δ11B-based pCO2 reconstructions generated from the same samples from the Plio-Pleistocene at ODP Site 999 across a glacial-interglacial cycle. We find a muted response to pCO2 in the alkenone record compared to contemporaneous ice core and δ11B records, suggesting caution in the interpretation of alkenone-based records at low pCO2 levels. This is possibly caused by the physiology of CO2 uptake in the haptophytes. Our new understanding resolves some of the inconsistencies between the proxies and highlights that caution may be required when interpreting alkenone-based reconstructions of pCO2
Three and half million year history of moisture availability of South West Africa: Evidence from ODP site 1085 biomarker records
Ocean Drilling Program Site 1085 provides a continuous marine sediment record off southern South West Africa for at least the last three and half million years. The n-alkane â13 C record from this site records changes in past vegetation and provides an indication of the moisture availability of SW Africa during this time period. Very little variation, and no apparent trend, is observed in the n-alkane δ13C record, suggesting stable long-term conditions despite significant changes in East African tectonics and global climate. Slightly higher n-alkane δ13C values occur between 3.5 and 2.7 Ma suggesting slightly drier conditions than today. Between 2.5 and 2.7 Ma there is a shift to more negative n-alkane δ13C values suggesting slightly wetter conditions during a ~ 0.2 Ma episode that coincides with the intensification of Northern Hemisphere Glaciation (iNHG). From 2.5 to 0.4 Ma the n-alkane δ13C values are very consistent, varying by less than Âą 0.5â° and suggesting little or no long-term change in the moisture availability of South West Africa over the last 2.5 million years. This is in contrast to the long-term drying trend observed further north offshore from the Namib Desert and in East Africa. A comparison of the climate history of these regions suggests that Southern Africa may have been an area of long-term stability over the last 3.5 Myrs
A Predictive Algorithm For Wetlands In Deep Time Paleoclimate Models
Methane is a powerful greenhouse gas produced in wetland environments via microbial action in anaerobic conditions. If the location and extent of wetlands are unknown, such as for the Earth many millions of years in the past, a model of wetland fraction is required in order to calculate methane emissions and thus help reduce uncertainty in the understanding of past warm greenhouse climates. Here we present an algorithm for predicting inundated wetland fraction for use in calculating wetland methane emission fluxes in deep time paleoclimate simulations. The algorithm determines, for each grid cell in a given paleoclimate simulation, the wetland fraction predicted by a nearest neighbours search of modern day data in a space described by a set of environmental, climate and vegetation variables. To explore this approach, we first test it for a modern day climate with variables obtained from observations and then for an Eocene climate with variables derived from a fully coupled global climate model (HadCM3BL-M2.2). Two independent dynamic vegetation models were used to provide two sets of equivalent vegetation variables which yielded two different wetland predictions. As a first test the method, using both vegetation models, satisfactorily reproduces modern data wetland fraction at a course grid resolution, similar to those used in paleoclimate simulations. We then applied the method to an early Eocene climate, testing its outputs against the locations of Eocene coal deposits. We predict global mean monthly wetland fraction area for the early Eocene of 8 to 10 Ă 106km2 with corresponding total annual methane flux of 656 to 909 Tg, depending on which of two different dynamic global vegetation models are used to model wetland fraction and methane emission rates. Both values are significantly higher than estimates for the modern-day of 4 Ă 106km2 and around 190Tg (Poulter et. al. 2017, Melton et. al., 2013
Selective chemical degradation of silica sinters of the Taupo Volcanic Zone (New Zealand). Implications for early Earth and Astrobiology
Discours III.
This is the author accepted manuscript. The final version is available from Elsevier via the DOI in this record.Branched glycerol dialkyl glycerol tetraethers (brGDGTs) are increasingly used to
reconstruct past terrestrial temperature and soil pH. Here we compare all available
modern soil brGDGT data (n=350) to a wide range of environmental parameters to
obtain new global temperature calibrations.
We show that soil moisture index (MI), a modeled parameter that also takes
potential evapotranspiration into account, is correlated to the 6-methyl brGDGT
distribution but does not significantly control the distribution of 5-methyl brGDGTs.
Instead, temperature remains the primary control on 5-methyl brGDGTs. We propose the following global calibrations: MAAT soil = 40.01 x MBTâ5me â 15.25 (n=350, R2 22 = 23 0.60, RMSE = 5.3 °C) and growing degree days above freezing (GDD0 soil) = 14344.3 x MBTâ5me - 4997.5 (n=350, R2 24 = 0.63, RMSE = 1779 °C).
Recent studies have suggested that factors other than temperature can impact
arid and/or alkaline soils dominated by 6-methyl brGDGTs. As such, we develop new
global temperature calibrations using samples dominated by 5-methyl brGDGTs only
(IR6me<0.5). These new calibrations have significantly improved correlation
coefficients and lower root mean square errors (RMSE) compared to the global
calibrations: MAATsoilâ = 39.09 x !"#!!"
! â 14.50 (n=177, R2 30 = 0.76, RMSE =
4.1 °C) and GDD0 soilâ = 13498.8 x !"#!!"
! â 4444.5 (n=177, R2 31 = 0.78, RMSE =
1326). We suggest that these new calibrations should be used to reconstruct terrestrial
climate in the geological past; however, care should be taken when employing these
calibrations outside the modern calibration rangThis research was funded through the advanced ERC grant `The greenhouse earth
412 system' (T-GRES, project reference 340923). R.D.P. acknowledges the Royal Society
413 Wolfson Research Merit Award
Evidence of moisture control on the methylation of branched glycerol dialkyl glycerol tetraethers in semi-arid and arid soils
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