Comprehensive Mass Balance Isotope Schematics for Determining the Provenance of the Moon Forming Impactor.

The goal of this research was to identify areas where deviations from the canonic Moon forming impact scenario (an impactor approximately 12% of the mass of the Earth merging with 100% accretion efficiency with a proto-Earth each of which has a differentiated homologous anatomy of 30% iron and 70% silicates) may greatly reduce the efficacy of the impact mass balance analytics used to determine the provenance of the impactor based on isotope data from terrestrial and lunar samples and physical data from high resolution SPH computer simulations. Modeling the giant Moon forming impact is complicated by a lack of knowledge about the size, composition and origin of the impactor. During the impact the proto-Earth and impactor collide and merge forming the Earth and Moon with each having specific isotope values that are a blend of the stable isotopic signatures of the impacting bodies. This research focused on four particular areas of concern; heterogeneity between the proto-Earth and the Earth, non-homologous impactor iron cores, the addition of an ice layer on the impactor and the importance of inefficient accretion (ejecta losses from the Earth during the collision). This research has shown that simple mass balance equations present an oversimplification of the mass balance relationships used for impact isotope analytics, particularly when the impactor deviates from the canonic scenario. Through careful mathematical modeling of a four body system; two objects colliding (proto-Earth and impactor) forming two different objects (Earth and Moon), a comprehensive isotopic Four Body Mass Balance (4BMB) equation was developed, one which is capable of incorporating impactors which deviate from the canonic model. Based on this research it is readily apparent that for lunar impactor fractions which are in the range indicated by SPH modeling (70% to 90% impactor in the Moon) changing the fraction of impactor’s iron core or accounting for inefficient accretion have a minimal effect on the resulting lunar isotope values and that the incorporation of a layer of ice on the impactor in the cases studied was the dominant factor

Climate control of terrestrial carbon exchange across biomes and continents

Understanding the relationships between climate and carbon exchange by terrestrial ecosystems is critical to predict future levels of atmospheric carbon dioxide because of the potential accelerating effects of positive climate-carbon cycle feedbacks. However, directly observed relationships between climate and terrestrial CO2exchange with the atmosphere across biomes and continents are lacking. Here we present data describing the relationships between net ecosystem exchange of carbon (NEE) and climate factors as measured using the eddy covariance method at 125 unique sites in various ecosystems over six continents with a total of 559 site-years. We find that NEE observed at eddy covariance sites is (1) a strong function of mean annual temperature at mid- and high-latitudes, (2) a strong function of dryness at mid- and low-latitudes, and (3) a function of both temperature and dryness around the mid-latitudinal belt (45°N). The sensitivity of NEE to mean annual temperature breaks down at ∼16 ®C (a threshold value of mean annual temperature), above which no further increase of CO,.2uptake with temperature was observed and dryness influence overrules temperature influence. © 2010 lOP Publishing Ltd

Climate control of terrestrial carbon exchange across biomes and continents

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Climate control of terrestrial carbon exchange across biomes and continents This article has been downloaded from IOPscience. Please scroll down to see the full text article. 2010 Environ. Res. Lett. 5 03400

Climate Control of Terrestrial Carbon Exchange across Biomes and Continents

Understanding the relationships between climate and carbon exchange by terrestrial ecosystems is critical to predicate future levels of atmospheric carbon dioxide because of the potential accelerating effects of positive climate-carbon cycle feedbacks1, 2. However, knowledge of even the broad relationships between climate and terrestrial CO2 exchange with the atmosphere on yearly to decadal scales remains highly uncertain. Here we present data describing net ecosystem exchange of carbon (NEE) and climate factors as measured using the eddy covariance method at 132 unique sites including various ecosystems over 6 continents with a total of 583 site-years. With respect to controlling factors we find two distinct groupings of sites: (1) a temperature-limited group where NEE has an exponential relationship with mean annual temperature; and (2) a dryness-limited group where NEE has an inverse exponential relationship with the dryness index7. A strong latitudinal dependence emerges, with 92% of the temperature-limited sites located above 42oN, and 77% of the dryness-limited sites located below 42oN. The sensitivity of NEE to mean annual temperature breaks down at a threshold value of ~16oC, above which no further increase of CO2 uptake with temperature was observed and dryness influence overrules temperature influence. Our findings suggest that (1) net ecosystem carbon exchange is highly limited by mean annual temperature at mid- and high-latitudes, and (2) net ecosystem carbon exchange is highly limited by dryness at low latitudes.JRC.H.2-Air and Climat