Brown SR-EIP — Earth, Environmental and Planetary Sciences
Some of the many possible summer research areas offered by the Department of Earth, Environmental, and Planetary Sciences (DEEPS) are highlighted below.
Climate Science
Mentor: Professor Meredith Hastings
Project title: Investigating spatial and seasonal variability in urban atmospheric chemistry
Science goals: The Hastings research group is focused on using the isotopic composition of reactive nitrogen to investigate variations in its sources, chemistry, atmospheric transport, and deposition. Isotopes represent the same chemical species with slightly different masses (e.g., 14N versus 15N) such that they exhibit different chemical and physical behaviors in the environment that we can quantify. Our aim is to fingerprint different emission sources – such as vehicles, power plants, aircraft, farms, forest fires, and lightning – and track their influence on the environment. Urban areas, in particular, offer a perspective on how humans impact and are impacted by reactive nitrogen. With great variations in space and time for different emissions sources and the implications for human and biosphere health, we are applying new techniques in an array of environments.
Mentor: Professor James Russell
Project title: Climate and environmental change across the Plio-Pleistocene boundary in tropical East Africa
Science goals: About three million years ago, northern hemisphere glaciers expanded dramatically, and began to wax and wane in 41,000-year glacial cycles. Around the same time, parts of Africa became drier, and our human ancestors underwent a set of evolutionary shifts including the appearance of the genus Homo. Many hypotheses have suggested that these changes are linked, wherein global cooling causes drying over Africa, which in turn triggers human evolutionary responses. However, we lack long, highly-resolved records of African environmental change. This project will analyze the hydrogen and carbon isotopic composition of terrestrial leaf wax biomarkers in a well-dated ~750,000-year-long drill core from the Baringo-Tugen-Barsemoi basin, in the Eastern Kenyan Rift, to detect changes in rainfall and vegetation between 3.3 and 2.55 Ma, and use these data to test the relationships between East African climate and vegetation and the onset and intensification of northern hemisphere glaciation.
Mentor: Professor Steve Clemens
Project title: Indian Monsoon Rainfall Reconstruction: Bay of Bengal
Project science goals: Understanding the history of rainfall is key to understanding past climates. Indian summer monsoon rainfall over the past 700,000 years will be reconstructed using a multi-proxy isotopic approach. We will reconstruct Ba surface seawater salinity by removing the temperature and global seawater isotopic signals from the oxygen isotopic composition of planktonic foraminifera, yielding the local seawater oxygen isotopic signal as a residual. This variable changes over time as a function of changes in direct precipitation and outflow from surrounding river basins. We will also measure the hydrogen isotopic composition of terrestrial plant leaf wax, a proxy for the hydrogen isotopic composition of rainfall. In this region, the hydrogen isotopic composition of rainfall varies as a function of local rainfall amount and evaporation/condensation processes that take place along the source to sink transport path of atmospheric moisture. The use of modeling will help to constrain the interpretation of the leaf wax isotopic signal.
Mentor: Professor Timothy Herbert
Project title: Neogene paleoceanography
Science goals: We will investigate the climate system’s trajectory into the Ice Ages, focusing on ocean paleoecology, paleotemperatures, and global sea levels. We will examine sites from across the globe using sediment cores collected from deep-sea drilling. Key questions include: Are temperature changes globally synchronous during warmer geological intervals, or do they show strong regionality? How have phytoplankton productivity patterns changed with the reorganization of ocean fronts as climate evolved? Can we separate ocean temperature and ice volume components from the marine oxygen isotope signal?
Mentor: Professor Baylor Fox-Kemper
Project title: Buoy aren’t you glad you checked the model?
Science goals: The Fox-Kemper group works on ocean processes using models and observations from the global climate change and paleoclimatic scales to small-scale turbulence and the coastal environment (fox-kemper.com). This project emphasizes the smaller-scale end and will involve examining temperature, salinity, and velocity data from buoys, boat profiles, and shuttle data in comparison to the Ocean State Ocean Model (OSOM). The OSOM is a new implementation of an oceanographic fluid dynamics model to examine local environmental issues, such as hypoxia, oyster viruses, and pollution. If the OSOM is successful, future plans include examining how these present environmental concerns will be affected by climate change. We will also go out on the Bay and examine one site in detail, collecting new data! This is an important part of both the modeling and data center aspects of the EPSCoR project (https://web.uri.edu/rinsfepscor). This project involves both field and lab/computer work.
Studies of the Earth’s Interior
Mentor: Professor Christian Huber
Project title: Experiments to study repacking in multiphase magmas
Science goals: As magma reservoirs evolve, competing mechanical processes cause different phases (melt-crystal-gas) to segregate. Phase separation is an important driving force for chemical differentiation and the build-up to volcanic eruptions. Interestingly, little is known about the rate and processes that dominate phase separation as they vary with the respective volume fraction of the phases considered. We propose a set of analog experiments, using 3D printed “crystals” of various size and shape distributions, immersed in lighter fluid. The mixture will be placed in a coffee press-type apparatus that allows us to compress (filter press) and extract the interstitial liquid as the granular media changes its packing. The efficiency of that process (repacking) is critical to melt extraction and eruption in magma reservoirs at relatively high (> 0.2-0.3) melt volume fractions, but has not received much attention.
Mentor: Professor Colleen Dalton
Project title: Seismic imaging of the Earth’s interior beneath Greenland
Science goals: Ice loss from the Greenland ice sheet contributes significantly to global sea-level rise. The Earth’s mantle plays an important role in ice sheet stability through its viscosity and the rate of heat flowing to the surface. The goal of this project is to image the speeds of seismic waves as they propagate in the crust and upper mantle beneath Greenland. The seismic velocity of a rock is a proxy for its temperature and volatile content, and thus it can be used to estimate viscosity and heat flux. The student will measure the arrival times of Rayleigh seismic waves from distant earthquakes to the 35 stations of the GLISN seismic network in Greenland. These travel times will in turn be used to image high-resolution variations in seismic velocity by tracking the evolution of the wavefront’s shape as it propagates across Greenland.
Mentor: Professor Karen Fischer
Project title: Measuring the properties of the lithosphere-asthenosphere transition beneath Alaska
Science goals: The concept of a strong, cold lithospheric plate underlain by a weaker, warmer asthenosphere is fundamental to plate tectonics, yet the relative roles of temperature, chemical composition, and partial melt in creating the lithosphere-asthenosphere transition are still vigorously debated. Sp phases (seismic shear waves from distant earthquakes that convert to P waves when they hit rapid gradients in wave velocity) are a powerful tool for measuring the thickness of the lithosphere and the shear wave velocity gradient that occurs across its base. Application of this approach to data recorded by the seismic stations of the NSF EarthScope Transportable Array in Alaska will reveal how lithospheric thickness changes across tectonic terranes, and will help to determine where the lithosphere-asthenosphere velocity gradient is so strong and sharp that it indicates the presence of small amounts of partial melt pooled below the base of the plate. These findings will help us understand where the lithosphere is particularly strong or weak, shedding light on the dramatic variations in present-day surface deformation that exist in Alaska.
Mentor: Professor Donald Forsyth
Project title: Seismic tomography of lithosphere and asthenosphere structure in the South Pacific
Science goals: Using surface-wave imaging from an ocean-bottom seismometer array deployed on South Pacific seafloor approximately 30 Ma in age, we will answer several critical questions regarding the state of the oceanic asthenosphere, the character of small-scale convection, and the role convective processes play in off-axis volcanism (Harmon et al., 2011) and the apparent shallowing of the seafloor. Specifically: 1) Are seismic velocity and attenuation in the asthenosphere (Ruan et al., 2018) consistent with recently proposed (grain-boundary sliding) models of mantle viscosity weakening? 2) Do seismic velocity variations in the asthenosphere correlate with gravity lineations and are they consistent with thermal predictions of small-scale convection? 3) Is the pattern of seismic velocity anisotropy in the asthenosphere indicative of small-scale convection? 4) Can small-scale convection explain the flattening of the seafloor age-depth curve with time? Addressing these questions will substantially improve our understanding of convection in the oceanic asthenosphere and its control of the evolution of Earth’s surface.
Mentor: Professor Yan Liang
Project title: Thermal history of mafic and ultramafic rocks as derived from rare earth element and major element based thermobarometers
Science goals: Major rock-forming minerals in the Earth’s upper mantle include olivine, pyroxene, garnet, and plagioclase. The distribution of rare earth elements (REE) between mantle minerals and basaltic melt is important to the interpretation of igneous rock thermal histories and their tectonic implications. The partitioning of REE between two minerals depends on temperature, pressure, and mineral composition and can be used as a thermometer or barometer. We have recently developed a suite of REE-in-two-mineral thermobarometers. The science goal of this project is to use these new thermobarometers to study the thermal histories of mafic and ultramafic rocks. Since diffusion rates of REE are considerably lower than diffusion rates of Ca, Mg, and Fe in the mantle minerals, REE-based two-mineral thermometers may have very different closure temperatures than major element-based thermometers, which may shed new light on igneous rock thermal histories.