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Spring 2023

Tuesdays at 3:30 PM
Earth and Marine Sciences A340

April 4, 2023

Speaker: Alicia Wilson, University of South Carolina

Title: Subseafloor Hydrogeology: Moving beyond watersheds

Abstract: The field of submarine groundwater discharge (SGD) was launched in the 1990s by the remarkable discovery, via naturally-occurring isotopic tracers, that saline groundwater was discharging to the South Atlantic Bight in very large volumes. Subsequent studies confirmed that saline groundwater discharges to the Atlantic Ocean in volumes that rival river discharge. All available evidence indicates that this saline groundwater is highly enriched in nutrients compared to river water, so the nutrient contributions of this submarine discharge exceed that of river discharge. These findings have been slow to find widespread acceptance, however, because it has been exceedingly difficult to confirm this flow by means other than the original isotropic tracers. This discharge does not occur near the shoreline, and no conceptual models for SGD far from shore existed.
This changed recently when new studies using heat as a tracer identified clear pulses of groundwater discharge 10-15 km offshore in the South Atlantic Bight. This talk investigates this 20-year mystery and the recent discoveries that suggest that it may be time to rewrite chemical budgets for the coastal ocean.

Alicia

Host: Andy Fisher

April 11, 2023

Speaker: Benjamin Idini, UCSC

Title: A Tale of Two Planets: Dilute Cores in Jupiter and Saturn from In Situ Spacecraft Observations

Abstract: The interiors of planets contain clues that inform us about the early processes that led to the formation of the solar system. Until lately, gas giant planets were traditionally considered to consist of a compact core of rocky material confined by an envelope of H and He fluid. Recent NASA missions Cassini (Saturn) and Juno (Jupiter) have questioned this traditional picture. Instead of a compact core, the recent missions observe a dilute core defined by a region with a chemical gradient that extends radially over tens of thousands of kilometers. In this talk, I will present evidence favoring dilute over compact cores in gas giant planets and discuss implications for planet formation and evolution. I will put particular emphasis in my own contributions to developing a theory of dynamical tides capable of uncovering the interiors of fluid bodies in the solar system; this includes the gas giant planets and icy satellites with global oceans. I will end this talk discussing potential applications of dynamical tides to the study of icy satellites Europa and Ganymede from future missions Europa Clipper and JUICE, respectively.

Ben

Host: J Fearon

April 13, 2023 - Special WES Seminar at 12:00PM in A340

Speaker: Matt Huber, Purdue

Title: Climate sensitivity to greenhouse gas forcing

Matt

Host: Jim Zachos

April 18, 2023

Speaker: Andrew Dickson, UC San Diego

Title: CO2-in-seawater reference materials: yesterday, today, and tomorrow

Andrew

Host: J Fearon

April 25, 2023

Speaker: Kristin Morell, UC Santa Barbara

Title: Active faults and permanent deformation in subduction zone forearcs: examples from Cascadia and beyond

Kristin

Host: Emily Brodsky

May 2, 2023

Speaker: Patrick Rafter, UCI

Title: Global reorganization of deep-sea circulation and carbon storage after the last ice age

Abstract: Using new and published marine fossil radiocarbon (14C) measurements, a tracer uniquely sensitive to circulation and air-sea gas exchange, we establish several benchmarks for Atlantic, Southern, and Pacific deep-sea circula- tion and ventilation since the last ice age. We find the most 14C-depleted water in glacial Pacific bottom depths, rather than the mid-depths as they are today, which is best explained by a slowdown in glacial deep-sea overturning in addition to a “flipped” glacial Pacific overturning configuration. These observations cannot be produced by changes in air-sea gas exchange alone, and they underscore the major role for changes in the overturning circulation for glacial deep-sea carbon storage in the vast Pacific abyss and the concomitant drawdown of atmospheric CO2.

Patrick

Host: Ryan Green

May 9, 2023

Speaker: Earle Wilson, Stanford

Title: Subpolar gyres and the Southern Ocean overturning circulation

Host: Zach Kaufman

Earle

May 16, 2023

Speaker: Vashan Wright, UC San Diego

Title: A cycle of memory creation, erasure, and phase transitions in granular assemblages sheared by natural faults

Abstract: A hallmark of many natural hazards (i.e., avalanches, landslides, and earthquakes) is the phase transition that frictional granular assemblages undergo, from being structurally arrested to creeping to flowing. Shear jamming, in conjunction with several other granular physics theories, predicts that the phase transitions are governed by the assemblage's temperature, disorder, volume fraction, and the shear rate, and makes several phenomenological predictions that would benefit from being tested in natural granular assemblages and in three dimensions. Here, I use x-ray microtomographic image analyses to assess controls on if and how the shear jamming phenomenologies of memory creation, memory erasure, and phase transitions are recorded in the three-dimensional re-arrangement and fracturing of minimally disturbed fault zone grains that experience slow versus fast tectonic shearing. The samples are from Pallett Creek and Ferrum, within the southern San Andreas fault zone (sSAFZ). The analyses reveal that the fault zone assemblages transition between one or more interrelated but geometrically localized and invisible to the naked eye (mesoscopic) deformation phases that change the stability of the assemblages during the seismic cycle. These phases include (1) bulk grain re-arrangement, (2) localized grain re-arrangements, (3) individual grain breakages, (4) bulk fracturing of the assemblage, and (5) localized zones of grain fracturing. One fault core hosts gas bubbles or nematode burrows that record 300 years of tectonic deformation history after the ~Mw 7 ca. 1726 sSAFZ earthquake. Grain re-arrangement is mostly a global versus local feature. Grain size, which represents one level of disorder, exerts control over the phases of breakage and re-arrangements. Higher shear rates lead to greater numbers of fractured grain, erasure of previous memories of slow shear-rate induced preferred azimuthal grain re-arrangement in the direction of fault slip, and introduce shear-hardened zones with grain preferred inclinations near the slip surface instead. Memory creation and erasure are thus controlled by shear rate and elastoplasticity, and thus vary with the distance from a fault. These findings imply that sheared fault zone grains experience a cycle of memory creation and erasure accompanied by varying deformation phase transitions (creeping, flowing, and structural arrest).

Vashan