Happening @ Michigan https://events.umich.edu/list/rss RSS Feed for Happening @ Michigan Events at the University of Michigan. Smith Lecture: What Does the Chemistry of Shallow-water Carbonate Sediments Tell Us About the Global Carbon Cycle Over Earth History? (February 23, 2018 3:30pm) https://events.umich.edu/event/46208 46208-10418371@events.umich.edu Event Begins: Friday, February 23, 2018 3:30pm
Location: 1100 North University Building
Organized By: Earth and Environmental Sciences

Shallow-water carbonate sediments are one of the most extensive and well-studied records of the chemistry and temperature of ancient oceans (Kasting et al., 2006; Veizer et al., 1999; Veizer and Hoefs, 1976). One of the major limitations in the utilization of this archive is the potential for changes in the chemical composition of the sediments at any time after they were initially precipitated. Using a large data set of Ca and Mg isotope measurements in Neogene shallow-water carbonate sediments and associated pore-fluids from the platform to the slope in the Bahamas we have shown that stratigraphic variability in these isotopic systems is due to variations in both mineralogy and style of diagenetic alteration (fluid-buffered vs. sediment-buffered). This interpretation is rather counterintuitive given that these elements, and Ca in particular, are major components of the carbonate sediment and should be relatively robust – almost as robust as C – to diagenetic alteration.

The observation that sediment δ44Ca values in Neogene shallow-water carbonate sediments from the platform top, margin, and slope are largely controlled by mineralogy and the extent of fluid-buffered early marine diagenesis and that temporal variations in fluid-buffered diagenesis can generate stratigraphically coherent co-variation between many carbonate-bound geochemical proxies (δ13C, δ18O, Sr/Ca, etc.) has significant implications for the interpretation of both the major and trace element chemistry of shallow-water carbonate sediments in the geologic record. In particular, it suggests that stratigraphic co-variation between carbonate-bound geochemical proxies need not reflect changes in the global geochemical cycles of these elements but rather changes in the composition of bank-top waters and/or the extent of fluid-buffered vs. sediment-buffered early marine diagenesis. Thus, records of secular change and extreme variability in shallow-water carbonate sediments might be better interpreted as records of the effects of global environmental change and evolution on shallow-water carbonate-producing environments and not archives of global geochemical fluxes (e.g. the relative rates of organic carbon and carbonate burial from the δ13C of CaCO3).

]]>
Lecture / Discussion Mon, 12 Feb 2018 11:47:18 -0500 2018-02-23T15:30:00-05:00 2018-02-23T16:30:00-05:00 1100 North University Building Earth and Environmental Sciences Lecture / Discussion 1100 North University Building
Smith Lecture: Chemically-stratified Midwestern Lakes are Relevant to Precambrian AND Modern Global Biogeochemistry (March 9, 2018 3:30pm) https://events.umich.edu/event/46209 46209-10418372@events.umich.edu Event Begins: Friday, March 9, 2018 3:30pm
Location: 1100 North University Building
Organized By: Earth and Environmental Sciences

The physical, chemical, and biological structure of permanently stratified lakes have analogy to the Earth’s Precambrian oceans. Both have deep waters devoid of oxygen, have lower sulfur contents than the modern ocean, and have biogeochemical cycles predominantly driven by microbes. Through two stratified and iron-rich lakes in Minnesota and Michigan, my group is studying the significance of iron-based photosynthesis in primary productivity and its potential biosignatures, methane production, consumption and export in iron-rich (i.e. ferruginous) waters, as well as primary and diagenetic mineral and isotopic signatures of these systems that are recorded in sediments. While our findings are relevant to Precambrian biogeochemistry, I will present evidence that these small, stratified ferruginous lakes might be fairly common in the Midwest, and perhaps are becoming more so. Therefore, our findings from monitoring these two lakes are also relevant to trends in our region’s water quality, and the contribution of similar lakes to global greenhouse gas, nutrient, and metal cycles.

]]>
Lecture / Discussion Mon, 15 Jan 2018 15:29:44 -0500 2018-03-09T15:30:00-05:00 2018-03-09T16:30:00-05:00 1100 North University Building Earth and Environmental Sciences Lecture / Discussion 1100 North University Building
Smith Lecture: Seismic Investigation of the Magma System beneath Laguna del Maule, Chile (March 16, 2018 3:30pm) https://events.umich.edu/event/46210 46210-10418373@events.umich.edu Event Begins: Friday, March 16, 2018 3:30pm
Location: 1100 North University Building
Organized By: Earth and Environmental Sciences

The Laguna del Maule volcanic field, straddling the Chile-Argentina border at 36° S, is currently the subject of a multi-disciplinary collaborative investigation supported primarily by the U.S. National Science Foundation Integrated Earth Systems program and the Observatorio Volcanológico de Los Andes del Sur (OVDAS) of SERNAGEOMIN. At least 50 post-glacial (younger than 20 ka) eruptions from more than two dozen vents encircling the 25x17 km lake basin have produced rhyodacitic-to-rhyolitic lava flows and ash deposits totaling > 30 km3, suggesting that a large, active, silicic magma reservoir fuels this system. Since 2007, GPS and InSAR geodesy reveal that Laguna del Maule has been experiencing rapid uplift at 20 to 25 cm/year centered within the ring of silicic vents. Moreover, a deformed paleo-shoreline that has been 36Cl-dated implies magma-driven surface uplift of > 60 m and that growth of this large shallow reservoir has occurred over at least the past 9,400 years. UW-Madison, Cornell, and OVDAS have deployed a seismic array covering ~450 km2 that surrounds the lake basin. The array consisted of 18 broadband stations in 2015, and was enlarged to 47 stations in 2016 (37 broadband, 10 short-period). The full array will remain in place until late March 2018. A variety of seismic studies are planned for the seismic array data, including body-wave tomography, surface-wave tomography, attenuation tomography, teleseismic tomography, receiver function analysis, seismic interferometry, and focal mechanism and moment tensor determination. The main goals are to detect the magma chamber underlying Laguna del Maule, characterize its dimensions and properties, and assess the state of stress of the system.

I will report on results from surface-wave tomography, and compare them to the results from other geophysical techniques. Due to the small array aperture (~30 km) and the limited frequency range of usable ambient noise, we combined three types of data for the surface-wave tomography: standard noise correlation analysis using pairs of stations within the array, correlation of earthquake coda at pairs of array stations, and differential dispersion for ambient noise for pairs of array stations correlated with remote stations. Somewhat unexpectedly, the Vs image shows evidence of a strong upper crustal low velocity anomaly along the southwest side of the lake, which does not extend under the entire lake basin. Depending on how the boundaries of the low-Vs anomaly are defined, we obtain estimates of ~25 to ~400 km3, and melt percentages of 5% to 8%. The position of the anomalous body is very close to the estimated source area for the uplift measured by InSAR and GPS. A Bouguer gravity low, interpreted to reflect the magma reservoir, is observed in the same area. In contrast, magnetotelluric results image a large low-resistivity zone near the north side of the lake and much smaller anomalies elsewhere.

Recent fluid dynamic models of bubble migration and accumulation have shown that volatiles can provide a mechanism whereby basaltic magma recharge could catalyze the eruption of rhyolite without imparting a substantial thermal or physical signature on the erupted lavas. This leads to the idea that during the Holocene, rhyolitic magma batches have been repeatedly extracted from a broad spatial footprint beneath the lake basin, but the magma batches that have fed the individual eruptions were likely of relatively modest volume, comparable to the geophysical results.

]]>
Lecture / Discussion Mon, 15 Jan 2018 09:41:43 -0500 2018-03-16T15:30:00-04:00 2018-03-16T16:30:00-04:00 1100 North University Building Earth and Environmental Sciences Lecture / Discussion 1100 North University Building
Smith Lecture: Tidal Tomography: What an Often-neglected Phenomenon Known as Earth Tides Can Tell Us About Buoyancy in the Deepest Part of the Mantle (March 23, 2018 3:30pm) https://events.umich.edu/event/46211 46211-10418374@events.umich.edu Event Begins: Friday, March 23, 2018 3:30pm
Location: 1100 North University Building
Organized By: Earth and Environmental Sciences

Earth’s mantle is a key component of the Earth system: its circulation drives plate tectonics, the long-term recycling of Earth’s volatiles, and as such, holds fundamental implications for the Earth’s surface environment. In order to understand this evolution, a key parameter of the mantle must be known, namely its buoyancy. In this talk, I will discuss how Earth’s body tide can provide fresh and independent constraints on deep mantle buoyancy through a newly developed technique called Tidal Tomography. This comes at a time when other interesting and exciting data sets sensitive to deep mantle buoyancy, e.g., Stoneley modes, have been brought to bear, and we will explore our conclusions in the context of other recent finds.

In particular, we will focus on two regions of the deep mantle known as the Large Low Shear Velocity Provinces (LLSVPs), the buoyancy of which has attracted much debate over the past few decades. Using a global GPS data set of high precision measurements of the Earth’s body tide, we perform a tomographic inversion to constrain the integrated buoyancy of these LLSVPs at the base of the mantle. As a consequence of the long-wavelength and low frequency nature of the Earth’s body tide, these observations are particularly sensitivity to LLSVP buoyancy. Using a probabilistic approach we find that the data are best fit when the bottom two thirds (~700 km) of the LLSVPs have an integrated excess density of ~0.60%.
The detailed distribution of this buoyancy, for example whether it primarily resides in a thin layer at the base of the mantle, will require further testing and the augmentation of the inversions to include independent data sets (e.g., seismic observations). Nevertheless, our inference of excess density requires the preservation of chemical heterogeneity associated with the enrichment of high-density chemical components, possibly linked to subducted oceanic plates and/or primordial material, in the deep mantle. This conclusion has important implications for the stability of these structures and, in turn, the history and ongoing evolution of the Earth system.

]]>
Lecture / Discussion Thu, 18 Jan 2018 11:18:39 -0500 2018-03-23T15:30:00-04:00 2018-03-23T16:30:00-04:00 1100 North University Building Earth and Environmental Sciences Lecture / Discussion 1100 North University Building
Smith Lecture: Surprises in Iron Cycling at the Peru Margin (March 30, 2018 3:30pm) https://events.umich.edu/event/46213 46213-10418375@events.umich.edu Event Begins: Friday, March 30, 2018 3:30pm
Location: 1100 North University Building
Organized By: Earth and Environmental Sciences

Iron is the most important micronutrient in the ocean, yet its sources and sinks to and from the ocean are poorly constrained. The GP16 Eastern Pacific Zonal Transect cruise from Peru to Tahiti in 2013 along 12-15°S crossed the large eastern tropical South Pacific oxygen deficient zone (ODZ) in the eastern half of the transect and the East Pacific Rise (EPR) hydrothermal plume in the western half. Both features were expected to be important sources of dissolved iron into the ocean interior. The EPR hydrothermal iron plume was found to extend for several thousands of kilometers around 2500 m, greatly exceeding prior expectations. In contrast, there was no significant iron plume in the heart of the ODZ around 300 m that extended beyond the coastal margin, despite the ODZ penetrating several thousand of kilometers into the interior. Surprisingly, a deep coastal iron plume in oxygenated waters centered around 2000 m was observed to penetrate >1000 km into the interior. In this talk, I’ll examine the reasons behind the unexpected high Fe from the oxygenated deep slope relative to the more reducing ODZ above.

]]>
Lecture / Discussion Thu, 18 Jan 2018 11:17:51 -0500 2018-03-30T15:30:00-04:00 2018-03-30T16:30:00-04:00 1100 North University Building Earth and Environmental Sciences Lecture / Discussion 1100 North University Building
Smith Lecture: Chemical Insights into Earth’s Microbiomes (April 6, 2018 3:30pm) https://events.umich.edu/event/46214 46214-10418376@events.umich.edu Event Begins: Friday, April 6, 2018 3:30pm
Location: 1100 North University Building
Organized By: Earth and Environmental Sciences

The Planet Earth is a microbial world, and the health of its inhabitants rests on the proverbial backs of microscopic organisms within oceans, rivers, soils and air. The oceans, in particular, are fundamental to the life-sustaining capabilities of Planet Earth, enabling all organisms from microbes to humans to persist and thrive. Within the oceans, microbes have an essential role, making the oxygen we breathe, removing greenhouse gas carbon dioxide from the atmosphere, anchoring the marine food web, fueling life within coral reefs, and promoting the health of fisheries and marine mammals. Detailed studies of microbial metabolism, therefore, provide fundamental knowledge about the life-sustaining processes on Earth. Recent work in this field has focused on the first order question of “who is there?” but second-order questions such as “what are they doing” and “how” are equally critical to assessing the role of microbial reactions in the global carbon cycle. Metabolomics, or the study of biochemical molecules, is one lens through which the chemical capacity of microbes can be viewed. In this presentation, I offer two case studies in which we use metabolomics to understand the chemical interplay of microbes. First, I will present work showing the role of microbes in particle remineralization in the open ocean, with implications for global carbon cycling. Second, I will present work showing the role of human and earth microbiomes in the chemistry of human sewage. These case studies are linked by the over-arching theme of microbial metabolism and its sentinel roles in understanding critical processes on our planet and will highlight the continuing role of analytical chemistry in elucidating fundamental earth system functions.

]]>
Lecture / Discussion Mon, 26 Mar 2018 09:32:03 -0400 2018-04-06T15:30:00-04:00 2018-04-06T16:30:00-04:00 1100 North University Building Earth and Environmental Sciences Lecture / Discussion 1100 North University Building
Smith Lecture: Fluids of the Lower Crust and Upper Mantle: Deep is Different (April 13, 2018 3:30pm) https://events.umich.edu/event/46215 46215-10418378@events.umich.edu Event Begins: Friday, April 13, 2018 3:30pm
Location: 1100 North University Building
Organized By: Earth and Environmental Sciences

Deep fluids are important for the evolution and properties of the lower crust and upper mantle in tectonically active settings. Uncertainty about their chemistry has led past workers to use upper crustal fluids as analogues. However, recent results show that fluids at >15 km differ fundamentally from shallow fluids and help explain high-pressure metasomatism and resistivity patterns. Deep fluids are comprised of four components: H2O, non-polar gases (chiefly CO2), salts (mostly alkali chlorides), and rock-derived solutes (dominated by aluminosilicates and related components). The first three generally define the solvent properties of the fluid, and models must account for observations that H2O activity may be quite low. The contrasting behavior of H2O-gas and H2O-salt mixtures yields immiscibility in the ternary system, which can lead to separation of two phases with fundamentally different chemical and transport properties. Thermodynamic modeling of equilibrium between rocks and H2O using simple ionic species known from shallow-crustal systems yields solutions possessing total dissolved solids and ionic strength that are too low to be consistent with experiments and resistivity surveys. Addition of CO2 further lowers bulk solubility and conductivity. Therefore, additional species must be present in H2O, and H2O-salt solutions likely explain much of the evidence for fluid action in high-P settings. At low salinity, H2O-rich fluids are powerful solvents for aluminosilicate rock components that are dissolved as previously unrecognized polymerized clusters. Experiments show that, near H2O-saturated melting, Al-Si polymers comprise >80% of solutes. The stability of these species facilitates critical critical mixing in rock-H2O systems. Addition of salt (e.g., NaCl) changes solubility patterns, but aluminosilicate contents remain high. Thermodynamic models indicate that the ionic strength of fluids with Xsalt = 0.05 to 0.4 and equilibrated with model crustal rocks have predicted bulk conductivities of 10-1.5 to 100 S/m at porosity of 0.001. Such fluids are thus consistent with conductivity anomalies commonly observed in the lower crust (e.g., the “G” anomaly), and are capable of the mass transfer commonly seen in metamorphic rocks exhumed from the lower crust and subduction zones.

]]>
Lecture / Discussion Fri, 19 Jan 2018 08:20:48 -0500 2018-04-13T15:30:00-04:00 2018-04-13T16:30:00-04:00 1100 North University Building Earth and Environmental Sciences Lecture / Discussion 1100 North University Building