Earth and Environmental Sciences - Student Publications

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    Gregarious suspension feeding in a modular Ediacaran organism
    (SCIENCE ADVANCES, 2019-06) Gibson, Brandt M.; Rahman, Imran A.; Maloney, Katie M.; Racicot, Rachel A.; Mocke, Helke; Laflamme, Marc; Darroch, Simon A. F.
    Reconstructing Precambrian eukaryotic paleoecology is pivotal to understanding the origins of the modern, animal-dominated biosphere. Here, we combine new fossil data from southern Namibia with computational fluid dynamics (CFD) to test between competing feeding models for the Ediacaran taxon Ernietta. In addition, we perform simulations for multiple individuals, allowing us to analyze hydrodynamics of living communities. We show that Ernietta lived gregariously, forming shallow marine aggregations in the latest Ediacaran, 548 to 541 million years (Ma) ago. We demonstrate enhanced vertical mixing of the water column above aggregations and preferential redirection of current into body cavities of downstream individuals. These results support the reconstruction of Ernietta as a macroscopic suspension feeder and also provide a convincing paleoecological advantage to feeding in aggregations analogous to those recognized in many extant marine metazoans. These results provide some of the oldest evidence of commensal facilitation by macroscopic eukaryotes yet recognized in the fossil record.
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    Compression and Decay of Hillslope Topographic Variance in Fourier Wavenumber Domain - Data and Python Scripts
    (2018) Doane, Tyler H.; Roth, D. L.; Roering, Joshua J.; Furbish, David Jon
    These files consist of topographic profile data, images from an acoustic hillslope experiment, and python codes to read the data and analyze the Fourier transforms of the profiles. There are four folders containing different datasets and codes: 1. Moraine: -BXZ.txt: X and Z coordinates of elevation from Bloody Canyon Moraine, CA. -Collected Summer 2015 using a self-leveling transit. -Collected at spatial intervals of 1-3 meters. -ProfileFourier.txt: python script that reads XZ data, interpolates to regularly spaced intervals, and calculates the Fourier transform. 2. Terrace: -FishermansRoadT2_2.txt. and FishermansRoadT3_2.txt: X and Z coordinates of elevation from a buttressed lateral moraine near Twin Lakes, CA. -Collected 2015 using a laser range-finder. -Collected at spatial intervals of 1-3 meters. -optimization.py: a script containing functions that estimate the initial condition of terraces -XZread2.py: python script that uses optimization to read X-Z data, interpolate to regularly spaced intervals, and calculate the Fourier transform. 3. Incised Moraine -TwinLakesXZ1.txt and TwinLakesXZ2.txt: X and Z coordinates of elevation from a flight of fluvial terraces near Jackson, WY. -Collected summer 2017 using a laser range-finder. -Collected at spatial intervals of 1-3 meters. -TwinLakes.py: python script that reads, interpolates, and returns the profile and Fourier transform. 4. Acoustic Hillslope -AcousticFileRead.py: python script that filters and returns a profile and Fourier transform of the profile from each image. -AcousticProfileFuncs.py: a script containing several functions used by AcousticFileRead.py -Images of an acoustic experiment that is lit by a blacklight to highlight the profile of the surface. -Collected at temporal intervals of 5 seconds.
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    Nonlocal Sediment Transport on Steep Lateral Moraines, Eastern Sierra Nevada, California, USA
    (Journal of Geophysical Research, 2017) Doane, Tyler H.; Furbish, David Jon; Roering, Joshua J.; Schumer, Rina; Morgan, Daniel J.
    Recent work has highlighted the significance of long-distance particle motions in hillslope sediment transport. Such motions imply that the flux at a given hillslope position is appropriately described as a weighted function of surrounding conditions that influence motions reaching the given position. Although the idea of nonlocal sediment transport is well grounded in theory, limited field evidence has been provided. We test local and nonlocal formulations of the flux and compare their ability to reproduce land-surface profiles of steep moraines in California. We show that nonlocal and nonlinear models better reproduce evolved landsurface profiles, notably the amount of lowering and concavity near the moraine crest and the lengthening and straightening of the depositional apron. The analysis provides the first estimates of key parameters that set sediment entrainment rates and travel distances in nonlocal formulations, and highlights the importance of correctly specifying the entrainment rate when modeling land-surface evolution. Moraine evolution associated with nonlocal and nonlinear transport formulations, when described in terms of the evolution of the Fourier transform of the moraine surface, displays a distinct behavior involving growth of certain wavenumbers, in contrast to the decay of all wavenumbers associated with linear transport. Nonlinear and nonlocal formulations share key mathematical elements yielding a nonlinear relation between the flux and the land-surface slope.