Spring 2021

Tuesdays at 3:30 PM
Natural Science Annex 101

March 30, 2021

Speaker: David McGee, MIT

Title: Permafrost history and carbon cycle conundrums over the last 1.5 Myr inferred from Canadian speleothems

Abstract: Permafrost carbon represents a potentially powerful amplifier of climate change, but little is known about permafrost sensitivity and associated carbon cycling during past intervals of persistent warming. I’ll report our efforts to reconstruct permafrost history in western Canada during Pleistocene interglacials from a large collection of speleothems, cave deposits that only accumulate with deep ground thaw. We infer that permafrost thaw extended to the high Arctic during multiple periods between ~1.5 and 0.5 million years ago, but has been limited to the sub-Arctic since the Marine Isotope Stage 11 interglacial 400,000 years ago. Our Canadian speleothem growth history closely parallels a similar reconstruction from Siberia, suggesting this shift toward more stable permafrost across the Pleistocene may have been Arctic-wide. In contrast, interglacial greenhouse gas concentrations were relatively stable throughout the Pleistocene, suggesting that either permafrost thaw did not trigger substantial carbon release to the atmosphere or it was offset by carbon uptake elsewhere on glacial-interglacial time scales.


April 6, 2021

Speaker: Lillian Ostrach, USGS

Title: Revelations from MESSENGER: New insights and understandings about the planet Mercury

Abstract: From March 2011 through April 2015, the MESSENGER spacecraft orbited Mercury and acquired data from a suite of instruments designed to work in the extreme environment near the Sun. These instruments returned the first data from Mercury orbit and facilitated groundbreaking discoveries that improved, and at times changed, our understanding about the composition and structure of Mercury’s crust and interior, it’s geologic history and impact cratering record, and the nature of its active magnetosphere and tenuous atmosphere. In this talk I will present some of the top science results and discuss in detail my ongoing investigations of the volcanic character and impact cratering history of Mercury, as well as briefly mention some of the outstanding science questions that may be addressed by the BepiColombo mission.


April 13, 2021

Speaker: Kei Shimizu, University of Wisconsin

Title: Water in meteorites: a snapshot of water in the early Solar System

Abstract: Chondritic meteorites are fragments of asteroids that formed in the first few million years of the Solar System history. The similarity between the H isotopic composition of certain chondrites to those of Earth’s water suggests that these chondrites may have been the principal source of Earth’s water. However, the origin and evolution of water in chondrites themselves is a topic of debate, given its potentially significant implications for the dynamical processes in the early Solar System. A particularly less well studied component in chondrites are chondrules, which are small igneous spheres (0.1-1 mm diameter, thought to have formed at high temperatures of ~1700-2100 K and low pressures of 10-6 to 10-3 bars) that comprise between 30 vol.% and 80 vol.% of the chondrites. In this seminar, I will present the results of analyses of water concentration and its isotopic composition (D/H ratio) in chondrules. We found significant variations in water content (8–10,200 ppm) and D/H ratio (δD: 77–15,000‰, ranging from similar to Earth’s water to ~16 times more D-enriched) in the studied chondrules. I will show that the most likely explanation for our observation is the aqueous alteration processes in the meteorite parent body. However, I will also show evidence that a small amount of water in the chondrules are likely to be primary in origin, and discuss its implications for the partial pressure of water during chondrule formation and the origin of the primary water in chondrules.


April 20, 2021

Speaker: Jill Marshall, University of Arkansas

Title: How trees grow their own pot- Quantifying the role of trees as wind-wiggling, tap-dancing and crowbar-wielding Critical Zone architects

Abstract: In thin-soiled settings, we presume that trees play a significant role in creating soil, with models centered on tree throw. However, little is known regarding how - or how often - trees damage rock, create fractures or expand fractures in fresh and weathered bedrock. This question is complicated by a paucity of available data and methods to measure forces at the bedrock-root interface. Combining force sensors at the tree-rock boundary with precipitation, solar radiation, wind, tree sway data, and acoustic emission sensors I have begun to quantify tree-driven soil-production mechanisms at Observatories with diverse forest types and climate conditions. Data suggests that trees damage and detach rock due to daily water uptake, rain, and wind events, while charismatic tree throw may matter less than belowground damage. The frequency, magnitude and style of wind-driven tree forces varies among species. This suggests that changes in water availability and forest structure, driven by variations in lithology and climate, may greatly influence tree-driven physical weathering and the rates at which trees grow their own soil pots.


April 27, 2021

Speaker: Jon Hawkings, Florida State University/GFZ-Potsdam

Title: The role of glaciers in global biogeochemical cycles

Abstract: Glaciers have covered ~10-30 % of land surface over the past 100,000 years and are sensitive barometers of climatic change, yet are rarely considering in conceptual models of global biogeochemical cycles. For example, textbooks illustrating river catchment fluxes of solute and sediment to the ocean regularly display ice sheets (continental glaciers) as blank spots. Research over the past two decades now indicates that far from being sterile, adynamic blocks of ice, glaciers are biomes harbouring truncated ecosystems on their surfaces (a “living skin”) and at their beds (the subglacial environment). Glaciers can also maintain very high physical denudation rates and chemical weathering rates at or above most global riverine catchments, with consequences for cycling of rock-derived nutrients and the carbon cycle. During this seminar I will present research linking subglacial weathering, elemental mobilization and export of bioessential elements to downstream systems. The focus of my talk will be on the sources, concentrations, speciation and transport of the essential micronutrient iron from glaciers into fjord and near-coastal ecosystems, using examples from the Greenland Ice Sheet, an Antarctic subglacial lake and the rivers and fjords of Chilean Patagonia. I will argue that glaciers are far from the frozen wastelands they are often portrayed and should be considered as dynamic components of global biogeochemical cycles both now and in the past.


May 4, 2021

Speaker: Cecilia Bitz, University of Washington


May 11, 2021

Speaker: Daniella Rempe, University of Texas at Austin


May 18, 2021

Speaker: Corinne Myers, University of New Mexico

Title: Do “pre-existing conditions” prime the Earth for mass extinction?

Research/Abstract: My general research focuses on macroevolution and macroecology of Late Cretaceous marine invertebrates, including K/Pg boundary biogeography, mostly in the US Western Interior Seaway and Gulf Coastal Plains. I use quantitative ecological modeling techniques designed for modern ecologists in combination with geochemical/sedimentological/GCM climate proxies to better understand how species respond to environmental change over their lifetimes (e.g., in response to warming and sea level rise, anoxia, asteroid impacts). I also use multivariate statistical methods to look at how fossil species’ abiotic niches change (or not) over evolutionary timescales. A second arm of my research program investigates biomineral and organic compound preservation in bivalve fossils from the present back to the Jurassic. The current talk describes a study led by my masters student, Dustin Perriguey, looking at how abiotic environmental conditions preceding periods of elevated extinction may contribute to enhanced extinction rates; we then apply this model to comparative predictions of future extinction potential given Earth system conditions in our immediate past.


May 25, 2021

Speaker: Jasper Oshun, Humboldt State University

Title: Bonanza en los Andes - Investigations of Water Resources in the puna

Abstract: Zurite, Perú (3400 m.a.s.l.) derives irrigation water from the 2.12 square kilometer Upper Ramuschaka Watershed (URW) ~ 1000 m above. The URW is part of the puna biome - a seasonally dry grass and shrub ecosystem existing at the altitudinal limits of vegetation and from which non-glacially fed streams originate. Faculty, 29 students from the U.S. and from Perú, and local community members completed a two year investigation of water resources in the URW and collaborated with the community to build 1.3 km of irrigation canals to serve over 100 families. We have quantified seasonal dynamics in water resources and identified hydrologically important low gradient peat forming wetlands, known locally as bofedales. Dry season release of large quantities of stored water from bofedales appears to sustain baseflow, suggesting bofedales are key features in achieving regional water security.


June 1, 2021

Speaker: Oscar Branson, University of Cambridge


Special Seminar - June 8, 2021

Speaker: Jun Yang, Peking University

Title: Climate and Habitability of Tidally Locked Planets


Host: Xi Zhang