Events

UTIG Seminar Series: Kristine DeLong, Louisiana State

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Speaker: Kristine DeLong, Associate Professor of Geography, Louisiana State University

Host: Jud Partin

Title: The Alabama Underwater Forest: A Time Capsule from the Last Ice Age

Abstract: In 2004, energetic waves from Hurricane Ivan exposed the stumps of bald cypress trees (Taxodium distichum) preserved in their growth position below the seafloor on the northern Gulf of Mexico continental shelf. These in situ stumps located ~13 km offshore Gulf Shores, Alabama in ~18 m of water represents the only identified submerged Pleistocene forest assemblage found thus far. We dated the site using optically stimulated luminescence and radiocarbon dating yielding ages between 74–42 ka suggesting this wood was preserved for ~50 ka during falling sea levels of the last ice age and eventual transition to the Holocene marine environment. Phase 1 of the project mapped the site area with bathymetric and sub-bottom surveys, characterize the sediment and depositional environment using vibracores, and developed tree-ring, pollen, seed, and foraminifera chronologies to better understand the environment the trees lived in. Foraminiferal assemblage analysis reveals that the transitional layer of interbedded sand and mud above the Pleistocene floodplain facies is late Holocene in origin and is part of a lower shoreface or marine-dominated estuarine environment. Seeds recovered from the Pleistocene floodplain sediments, which also contains woody remnants, generally agrees with pollen results. Stratigraphy within the study area suggests paleo-topographic relief was established prior to 56 ka and persisted until Holocene transgression. This site is likely a bald cypress backwater swamp with little water mixing promoting anoxic conditions in sediments that lead to the preservation of organic materials for more than ~50 ka. We suggest that paleo-topographic relief created enough accommodation space for sediment infill to bury and preserve this forest during the late Pleistocene lowstand. We hypothesized that rapid increases in global sea level occurring ~60 ka and ~40 ka provided opportunities for local floodplain aggradation to bury the swamp thus preserving the tree stumps. We are developing a geophysical methodology to identify and map buried tree remains and a model to predict other forest sites on the continental shelf in Phase 2 that will start this year.

UTIG Seminar Series: Charles Jackson, UTIG

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Speaker: Charles Jackson, Research Scientist, UTIG

Host: Yuko Okumura

Title: Non-Convective Precipitation and the Law of Unintended Consequences

Abstract: I will present a set of recent findings concerning a structural error in the organization of tropical precipitation, or the lack thereof, that has large consequences for how rainfall is affected by greenhouse gas forcing (Stephens et al., JCLI, 2019). These connections were elicited within ensembles of alternate configurations of the Community Atmosphere Model versions CAM3.1 and CAM5.3, which represent some of the parametric uncertainties that exist in the representation of deep convection and cloud microphysics. The range of outcomes from these ensembles mimic many of the outcomes seen within the Climate Model Intercomparison Project (CMIP5) ensemble but with more clarity. This is due to the more focused and thorough nature of the exploration of cloud and convective processes using Bayesian calibration of a single model as compared to the CMIP5 “ensemble of opportunity.” The structure of the errors revealed in the CAM ensembles suggests a distinctive role in climate of the mesoscale organization of tropical convection. I will emphasize some of the ways that scientific considerations have shaped the statistical and computational approaches used to generate the CAM ensembles. I will also share my vision for how these tools and considerations fit into data-driven model development and predictability of the Earth System.

Stephens, B.A., C.S. Jackson, and B.M Wagman, 2019. Effect of Tropical Nonconvective Condensation on Uncertainty in Modeled Projections of Rainfall. Journal of Climate, 32(19), 6571–6588, doi:10.1175/JCLI-D-18-0833.1

UTIG Brown Bag: James Biemiller (PhD talk)

Informal weekly presentations by UTIG students and researchers. Bring your lunch!

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Speaker: James Biemiller, Graduate Research Assistant, UTIG

Title: Mixed-Mode Seismic and Aseismic Slip of an Active Low-Angle Normal Fault in Papua New Guinea

UTIG Brown Bag: Kelly Olsen

Informal weekly presentations by UTIG students and researchers. Bring your lunch!

Speaker: Kelly Olsen, Graduate Research Assistant, UTIG

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UTIG Seminar Series: Manasij Santra, UTIG

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Speaker: Manasij Santra, Postdoctoral Fellow, UTIG

Host: Steve Phillips

Title: Insight on Major Components and Behavior of Marine Gas Hydrate Systems from Seismic-Scale Observations in Abyssal Gulf of Mexico

Abstract: Marine gas hydrates are naturally occurring ice-like solid made of water and gas (predominantly methane) that occur in deep marine sediments. They are stable at low temperature and high pressure, which limits their occurrence to a certain depth below the sea floor: the hydrate stability zone. Marine gas hydrates may represent as much as 15% of Earth’s mobile carbon. However, gas hydrate in marine sediment is usually highly disseminated. Concentrated gas hydrates are relatively rare and the processes that concentrate hydrate in marine sediments are not well understood. We studied a concentrated (~90% saturation) hydrate accumulation that we recently drilled and sampled in the deepwater Gulf of Mexico. Seismic analysis in this area shows that gas hydrate occurs in a submarine channel-levee system within a faulted anticlinal structure. The faults act as a conduit for gas migration both below and above the hydrate-bearing reservoir. We interpret that the high hydrate concentration was the result of sustained long-distance free gas transport into a reservoir that was partly within the hydrate stability zone. I discuss this mechanism and explore some highly debated topics in the study of marine methane hydrate systems:- i) apparent non-equilibrium behavior of natural methane-water-hydrate systems, ii) the role of a seal in hydrate accumulation, and iii) maximum depth of significant microbial methanogenesis.

DeFord Lecture: Peng Ni

UTIG Brown Bag: Natalie Wolfenbarger

Informal weekly presentations by UTIG students and researchers. Bring your lunch!

Speaker: Natalie Wolfenbarger, Graduate Research Assistant, UTIG

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DeFord Lecture: Peng Ni

DeFord Lecture: Shuo Ding