Ben Bond-Lamberty, Pacific Northwest National Laboratory
A 1014 scaling problem: what can soil respiration observations tell us about the global land carbon sink?
February 7, 2025 at 11:00 am (ESJ 0215)
The soil-to-atmosphere flow of CO2 generated by microbes and plant roots is intrinsically linked with the vulnerability of global soils to climate change. Despite this importance, "soil respiration" is one of the least well constrained components of the global carbon cycle, and most of our understanding of it comes from ~1 m2 chamber measurements. How consistent are upscaled estimates with satellite-driven projections of a robust land carbon sink? Why our global soil respiration flux estimates diverging, not converging? This talk will explore the role of open-source data and science in tackling one of the most uncertain parts of the global carbon cycle.
Daniel Segessenman, George Mason University
North America’s Ediacaran Story: A Tale of Global Environmental Change as told by Carbonate Quantity and Carbon Isotope Values
February 14, 2025 at 11:00 am (ESJ 0215)
Strata of the Ediacaran Period record many Earth-life features that distinguish the Neoproterozoic-Phanerozoic transition, including a snowball Earth deglaciation, the oldest known complex macroscopic fossil assemblages, the greatest magnitude negative carbon isotope excursion in the rock record, the last stages of Rodinia’s rifting, and the assembly of Gondwana. However, it is difficult to determine cause and effect relationships between these Ediacaran events, due in part to a relative rarity of sampling locations. Here we focus on quantitative properties of carbonate rock area, volume, geochemistry, and depositional environments from the Ediacaran System of North America. Patterns of carbonate sedimentation and geochemistry are broadly coincident with proposed transgressive/regressive cycles which have been linked to glacioeustacy and global tectonics. Highly negative carbonate carbon isotope values distinguishing the Shuram-Wonoka carbon isotope excursion (SW-CIE) occur against the backdrop of the largest increase in carbonate rock quantity observed in the Ediacaran, which spans nearshore, outer shelf, and slope/basin depositional environments. An increase in the extent of carbonate sedimentation, when combined with existing indications of global marine transgression, increased continental weathering, and evidence of glacially influenced sediments before and after, but not during, the SW-CIE, may indicate that the excursion occurred during an interglacial warm period. A subsequent increase in carbonate rock quantity in the latest Ediacaran, particularly among nearshore environments, coincides with an expansion of biocalcifying taxa, potentially indicating common cause drivers for both the extent of carbonate sedimentation on the continents and macroevolution. Although this analysis does not solve current limitations of Ediacaran geochronology, it does provide new evidence of environmental correlates for several key Ediacaran features and provides a foundation for future hypothesis testing of Earth systems evolution during the dawn of animal life.
Erica Jawin, National Air and Space Museum, Smithsonian Institute
Shattered Fragments: Origins and evolution of asteroid (101955) Bennu and the OSIRIS-REx mission
February 21, 2025 at 11:00 am (ESJ 0215)
NASA's OSIRIS-REx asteroid sample return mission investigated near-Earth asteroid (101955) Bennu and collected over 100 g of rocky material from its surface, after several years spent orbiting the asteroid. In September 2023, the spacecraft safely delivered its sample to Earth. Bennu proved to be a surprising object from the very first images showing an unexpectedly rugged surface, documented active particle ejections, and an extremely weak surface probed during sample collection. This lecture will discuss Bennu’s diverse surface geology and its rubble pile structure, as well as initial perspectives from analysis of the returned sample. The OSIRIS-REx spacecraft is now on its way to a new target, the asteroid (99942) Apophis, following its close approach with Earth in 2029.
Alexander Halliday, Columbia University
Isotopes and the Origin of the Earth
March 7, 2025 at 11:00 am (ESJ 0215)
Earth formed from bodies colliding in a protoplanetary disk, although exactly how, and how fast, are still debated. There exists a range of Giant Impact models for the Moon’s exact origin, all focused on explaining its isotopic similarity to the silicate Earth. Regardless of its origin, the isotopic age of the Moon constrains terrestrial accretionary processes and timescales, providing evidence that the final ~10% of Earth accretion took place between 50 and 120 million years after the start of the Solar System. Within this range, earlier estimates are perhaps more readily reconciled with the remarkable 129Xe and 182W anomalies in the Earth’s mantle. However, fluxes from, or equilibration with, core material has also been advocated as a contributor to some of the W anomalies. There also is considerable uncertainty still about the origins of Earth’s building blocks. While, there is strong isotopic evidence for a dominance of inner solar system feeding zones, the volatile components, such as carbon, nitrogen, water, are more complex. They were not delivered principally in a late veneer as often argued, but rather in many complex stages, that included solar, chondritic and cometary components. A major challenge is to understand how this earliest history segued into an Earth with crustal growth, but isotope geochemistry is also providing new constraints on this.
The coordinator for the Colloquium Series is Dr. Mengqiang "Mike" Zhu. You can contact him at mqzhu [at] umd [dot] edu.
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