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Online Seminars & Events

Week of March 1, 2021
MONDAY TUESDAY WEDNESDAY THURSDAY FRIDAY
GPS Division Seminar
12:00 pm to 1:00 pm
DIX Planetary Science Seminar
4:00 pm to 5:00 pm
Environmental Science and Engineering Seminar
4:00 pm to 5:00 pm
Geoclub Seminar Series
4:00 pm to 5:00 pm
Seismo Lab Seminar
4:00 pm
Thesis Defense - Usha Lingappa
1:00 pm

Division Seminar

Mondays from 12:00pm to 1:00pm
For more information, please contact: Leticia Calderon

" When climate loads the Earth: rheology from geodesy "

Kristel Chanard , Institut de Physique du Globe de Paris, Université de Paris

Abstract:

At timescales of seconds to minutes, encompassed by global seismological observations, Earth behaves as an almost perfectly elastic body displaying only slight attenuation of seismic waves as they propagate. In contrast, at the timescales of thousands to millions of years associated with major glacial episodes and planetary-scale deep Earth processes, Earth is dominated by the viscous deformation of its mantle which is overlain by a relatively thin lithosphere showing nearly elastic behavior only to depths of the order of several tens of kilometers. Between these end-member timescales, tidal deformation and postseismic relaxation studies have revealed a transient rheological behavior that is neither purely elastic nor purely viscous. Today, emerging geodetic observing technologies and continuous improvements in data accuracy and coverage of measurements provide an unprecedented opportunity to study various transient processes and advance our understanding of Earth's mechanical response across spatial and temporal scales.

In particular, accurate measurements of temporal changes in the Earth's shape and rotation due to shifting hydrological, atmospherical and oceanic mass loads at its surface may bring new information on the Earth's rheology at intermediate timescales. In this talk, I will discuss improvements in geodetic observations arising from innovative data analysis methods, as well as recent advances in probing the Earth's transient rheology using its response to surface mass redistribution over seasonal to decadal time scales. A time-dependent description of Earth's rheology may, in turn, play a central role in better understanding processes deforming the solid Earth, and in monitoring temporal variations in terrestrial water storage.

" Sharpening seasonality and shifting hydrology: Implications for wildfire and flood risk in a warming California "

Daniel Swain, University of California, Los Angeles

Abstract:

California's "Mediterranean" climate, characterized by warm, dry summers and cool, wet winters, predisposes the region to a high intrinsic risk of drought and wildfire. Located near the latitudinal boundary between stable subtropical and more active mid-latitude climate regimes, California also experiences high year-to-year variability in precipitation—leading to sometimes dramatic swings between drought and flood. Recent evidence suggests that the region's already substantial propensity to experience "precipitation whiplash" will increase further in a warming climate, compounding other hydrologic changes arising more directly from the effects of increased evaporation and a declining snowpack. The projected sharpening of California's seasonal cycle of precipitation—with less precipitation falling during the autumn and spring shoulder seasons but more intense precipitation occurring during winter storms—has major implications for both wildfire and (paradoxically) flood severity in the 21st century. In this talk, I will discuss recent work focusing on the complex spatiotemporal expression of climate change in California, with a particular focus on aspects that shed light on the region's simultaneously growing wildfire and flood risk.

" Evolving Conceptual Models of Magmatic Systems from Mantle to Surface "

Christy Till, Arizona State University

Brief bio:

Dr. Christy Till is a geologist, Associate Professor, and the Associate Director for an Inclusive Community in the School of Earth and Space Exploration (SESE) at Arizona State University. She leads a multidisciplinary research program that studies the role of magma in the formation and evolution of planets, known as the EPIC lab, in which example research topics include determining the timescales and triggers for eruptions at active volcanoes in the US, interrogating mantle magma generation in arcs with high pressure and temperature laboratory experiments, and studying the likely compositions of magma and crusts on exoplanets. She received her BS & MS at UC Santa Barbara and PhD at MIT and was employed by the US Geological Survey prior to starting at ASU in 2014.

In this talk, Dr. Till will discuss new petrologic and geochemical data with implications for conceptual models of magmatic systems from mantle to surface, with a focus on the dimensions of time and magmatic flux.

" Spectroscopy on Venus: Peeking through Clouds at the Hot Surface "

Darby Dyar

Abstract:

How old is the surface of Venus, and what rock types are present? Answering these fundamental questions presents a formidable challenge due to a lack of data and the thick CO2-rich atmosphere that shrouds The Venus surface. In fact, little is known about its surface geochemistry or mineralogy beyond results from Soviet landers in the 1970's and ‘80's. Spectroscopic characteristics of likely Venus surface rocks at 460°C are poorly constrained, as are the rock types and degree of surface-atmosphere interactions. How is it possible that we know so little about Earth's twin, and the most likely model for exoplanets in our Solar System?

This talk surveys what the outdated spectra and geochemical data from the Soviet landers can tell us about Venus. It reviews modern proof-of-concept data from the VIRTIS instrument on Venus Express, which demonstrated that tiny windows in the CO2 spectra of the Venus clouds do permit orbital observations, albeit of very narrow bands. Machine learning techniques are used to interpret new analog laboratory data acquired at Venus temperatures and apply them to the task of interpreting the rock type and alteration state of the Venus surface. Results place important constraints on the geologic past and likely age of the Venus surface, and highlight the need to return there with modern technology to address the many outstanding questions.

DIX Planetary Science Seminar

Tuesdays at 4:00 pm
For more information, please contact Aida Behmard

"Convective Inhibition in the Solar System and Beyond"

Stephen Markham Graduate Student – Planetary Science, Caltech

Abstract: Sufficiently abundant condensible species in hydrogen atmospheres may inhibit convection by introducing molecular weight gradients near the cloud deck associated with condensation. In this work we place constraints on the effect this can have on the thermal histories of Uranus and Neptune. We demonstrate that convective inhibition should lead to a state of radiative-convective equilibrium with finite activation energy to disrupt. We further constrain possible meteorological consequences on Saturn as well as the ice giants. Finally we extend the argument beyond our solar system and investigate the "infinite reservoir" problem, when a hydrogen envelope overlies an unlimited supply of condensates, for example a super-Earth. We provide some preliminary comments on the implications for the thermal

evolution of such bodies.

"Deep Helium Transits in the V1298 Tau System"

Shreyas Vissapragada, Graduate Student – Planetary Science, Caltech

Abstract: "The early evolution of planetary atmospheres, especially those enduring extreme amounts of ionizing radiation, has profound consequences for the observed distribution of exoplanetary masses and radii. With the recent discovery of metastable helium, a tracer of tenuous gas in escaping atmospheres, both ground- and space-based facilities are sensitive to atmospheric outflows near the wind-launching radius. However, such observations have previously been limited to planets midway through their lives (at a few Gyr of age), after the majority of atmospheric evolution has concluded. Here, we present a search for metastable helium on three of the planets orbiting the young (~23 Myr) solar analogue V1298 Tau. Using a beam-shaping diffuser and a narrowband filter centered on the metastable helium feature, we observed two transits of planet d (P = 12.4 days) and one transit each of planets b (P = 24.1 days) and c (P = 8.2 days) on Palomar/WIRC. We tentatively detect excess absorption for planets b and d in our bandpass. We consider the confounding impacts of stellar activity, and outline the highest-priority measurements needed to confirm these signals. If the observed excesses are due entirely to metastable helium associated with the planets, then the atmospheres of these planets likely overflow their Roche lobes. These may therefore be the first young planets exhibiting long-theorized signs of vigorous atmospheric escape."

"The Root of Anomalously Specular Reflections from Solid Surfaces on Saturn's moon Titan"

Jason Hofgartner, Research Assistant – Planetary Science, Jet Propulsion Laboratory

Abstract: Saturn's moon Titan has a methane cycle with clouds, rain, rivers, lakes, and seas; it is the only world known to presently have a volatile cycle akin to Earth's tropospheric water cycle. Anomalously specular radar reflections (ASRR) from Titan's tropical region were observed with the Arecibo Observatory (AO) and Green Bank Telescope (GBT) and interpreted as evidence for liquid surfaces. The Cassini spacecraft discovered lakes/seas on Titan, however, it did not observe lakes/seas at the AO/GBT anomalously specular locations. A satisfactory explanation for the ASRR has been elusive for more than a decade. Here we show that the ASRR originate from one terrain unit, likely paleolakes/paleoseas. Titan observations provide ground-truth in the search for oceans on exoearths and an important lesson is that identifying liquid surfaces by specular reflections requires a stringent definition of specular; we propose a definition for this purpose.

Environmental Science and Engineering Seminar

Wednesdays from 4:00pm to 5:00pm
For more information, please contact: Bronagh Glaser

" Molecules, Microbes, and the Ocean Carbon Cycle "

Mary Ann Moran, University of Georgia in Athens

Abstract: Microbially-derived metabolites dissolved in seawater are rapidly cycled through the sunlit ocean. This process involves almost half of the ocean's annual net primary production, and therefore even minor changes in its functioning are quantitatively significant on a global scale. Low standing stocks and residence times of a just few hours make these molecules difficult to study. This talk focuses on the ecological and biogeochemical implications of microbial-metabolite linkages in surface seawater.

Geoclub Seminar Series

Thursdays from 4:00pm to 5:00pm
For more information, please contact: Sarah Zeichner

"Groundwater noble gas tracers of past temperature, hydrology, and hydrogeology"

Alan Seltzer, WHOI scientist

Abstract: The Last Glacial Maximum (LGM, ~25-17 ka) is a relatively recent period of stable climate that was substantially different than present and thus serves as a useful test case for climate models and for evaluating estimates of Earth's climate sensitivity. However, substantial disagreement exists over the magnitude of cooling during the LGM, especially at low latitudes and on land at low elevation. One promising proxy to fill the need for robust terrestrial paleotemperature reconstruction is the dissolved noble gas composition of ancient groundwater, which is linked through robust physical principles to the mean annual surface temperature at the time and place of groundwater recharge. A handful of prominent low-latitude groundwater noble gas studies have suggested 5-6 ⁰C of LGM cooling, but slight differences in their statistical treatment and modeling of bubble entrainment and dissolution have limited the widespread adoption of this quantitative tracer. In this talk, I will discuss recent efforts to synthesize several dozen groundwater noble gas records of LGM temperature, systematically evaluate different model parameterizations, conduct sensitivity tests of potential mechanisms by which temperature and noble gases are decoupled, and finally produce a quantitative constraint of low-latitude cooling on land during the LGM. I will also share recent analytical advances that have enabled high-precision noble gas isotope measurements in groundwater and opened the door to a new proxy for paleohydrology and a hydrogeological tool for understanding groundwater flow pathways.

"Exploring relationships among major element cations and organic preservation in silica"

Kelsey Moore, JPL

Seismo Lab Seminar

Fridays from 4:00 pm to 5:00 pm
For more information, please contact Seismo Seminar Committee.

"The origin of seismic heterogeneities beneath subduction regions of Earth's lowermost mantle"

Mingming Li, ASU

ABSTRACT:

Understanding the lowermost mantle structure and dynamics remains one of the most important challenges in deep solid Earth sciences. The Earth's lowermost mantle is characterized by two large low shear velocity provinces (LLSVPs). The regions outside the LLSVPs have been suggested to be strongly influenced by subducted slabs and, therefore, much colder than the LLSVPs. However, localized low‐velocity seismic anomalies have been detected in the subduction – influenced regions, whose origin remains unclear. Here, through three-dimensional geodynamic modeling experiments, we explore the origin of thermal and compositional heterogeneities in the subduction-influenced regions of Earth's lowermost mantle. We find that the morphology of subducted slabs in the lowermost mantle greatly controls the origin and structure of thermal and chemical heterogeneities in the lowermost mantle, and thus the nature of seismic heterogeneities in these regions.

"TBD"

Jay Fineberg, The Hebrew University of Jerusalem

Thesis Defense Seminars

For more information, please contact Julie Lee; julielee@caltech.edu

Usha Lingappa - March 3, 2021, 1:00 pm

"Manganese through time and other stories concerning Cyanobacteria and the world around them"

Members of the Ph.D. examining committee are: Victoria Orphan (chair), Woody Fischer (thesis advisor), John Grotzinger, Dianne Newman

Hao Xie - Wednesday, March 10, 2021, 1:00 PM

"Road to Equilibrium: Stable Isotope Distribution in Gaseous Alkanes and Thermal History of Geological Hydrocarbons"

Members of the Ph.D. examining committee are: Ken Farley (chair), John Eiler (thesis advisor), Thomas Miller (CCE), Alex Sessions