Fall 2017

Tuesday Afternoons at 3:30 PM

Nat Sci Annex 101


October 3, 2017

Speaker: Mark Brandon, Yale

Title: Cenozoic evolution of climate, topography, and tectonics in the Patagonian Andes

Abstract: I will report on work at Yale using precipitation isotopes to study the evolution of topography in the Patagonian Andes. This 1500 km long mountainous range is commonly thought to have formed over the last 15 Ma, due to back-arc thrusting and “collision” of the Chile triple junction and associated Nazca-Pacific spreading center. In contrast, stratigraphic studies indicate that the range may have been established by during the Late Cretaceous.

There are two aspects of our study: 1) Dynamic modeling of orographic precipitation and isotopic fractionation of modern precipitation, which provides a direct estimate of the sensitivity of water isotopes to changes in topography and climate. 2) Measure of deuterium isotopes in hydrated volcanic glass collected from several Cenozoic sections in the lee of the Patagonia Andes.

 Conclusions:

  • Our modeling study demonstrates that the fractionation observed in precipitation isotopes vary linearly with changing topography, but is also significantly influenced by changing surface temperature. For example, a 5°C increase in surface temperature and a 20 percent decrease in topography would produce equivalent shifts in isotopic fractionation associated with orographic precipitation.
  • Our dynamic modeling provides a specific representation of average atmospheric flow during orographic precipitation in the Patagonian Andes. We determine that the relationship of isotopic fractionation to orographic lifting is ~5 ‰/km for 18O and ~38.5 ‰/km for 2H, which is about twice the gradient estimated in empirical studies of global precipitation.
  • Our volcanic ash study indicates that the Patagonian Andes have maintained a steady height for the last 60 Ma. We infer that the topography was formed at ~100 Ma in association with emplacement of the Patagonian batholith, which underlies the core of the range.

Hosts: Jeremy Hourigan


October 10, 2017

Speaker: Adiël Klompmaker, UC Berkeley

Title: Parasitism, Competition, and Predation in the Marine Fossil Record

Hosts: Matthew Clapham


October 17, 2017

Speaker: Rosemary Knight, Director of the Center for Groundwater Evaluation and Management

Title: The Use of Geophysical Methods for Groundwater Evaluation and Management

Abstract: The Sustainable Groundwater Management Act provides a new framework for the evaluation and management of groundwater in California. Unfortunately, the only data typically available for use in the required modeling and monitoring of groundwater systems are limited well data. This has led to a search for new ways to acquire data with the needed levels of spatial and temporal sampling. Over the past ten years, the Center for Groundwater Evaluation and Management at Stanford University has worked in a number of locations in the western U.S., to explore and demonstrate novel ways of acquiring, processing, and analyzing geophysical data to obtain information about subsurface properties and processes. Three examples are the use of electrical resistivity tomography to image saltwater intrusion along the Monterey Coast; the use of a helicopter-deployed electromagnetic method to map out the hydrostratigraphy in an area of the San Joaquin Valley; and the use of satellite (InSAR) data to monitor water levels in a confined aquifer in the San Luis Valley of Colorado. These three examples highlight ways in which geophysical methods can provide the critical information needed to support the sustainable management of groundwater systems.

Hosts: Sarah Beganskas


October 24, 2017

Speaker: Ryan Portner, San Jose State University

Title: What can mid-ocean ridge sediments (MOR-SED) tell us about deep-sea volcanism?

Abstract: A long held debate in the marine geology community has pondered how the extreme environmental conditions of the deep seafloor restrict explosive eruptions and if such explosivity can occur at all. This debate is rooted in the componentry and provenance of deep-sea sedimentary deposits. Recent submersible observation of an explosive eruption at 1200 mbsl has shed light on this topic, yet many uncertainties remain.  The connections between volcaniclastic deposits sampled from the seafloor, and their transport processes, inferred eruption styles and underlying origins remains unclear. How magma composition, volatile contents and conduit processes influence eruption style is particularly important. This study will present results from basaltic and rhyolitic volcaniclastic deposits sampled from the Juan de Fuca Ridge and northern East Pacific Rise, and make the argument that basaltic magmas are better equipped for explosive deep sea eruptions despite higher volatile contents in rhyolite. Our ability to address these and other fundamental questions in marine geology and volcanology is continually expanding with better sampling methods, high resolution seafloor mapping and direct observations of active deep-sea eruptions.

Hosts: Brian Dryer


October 31, 2017

Speaker: Corliss Kin I Sio, Lawrence Livermore National Laboratory

Title: Magmatic thermal histories from diffusive Fe-Mg isotopic fractionation in olivine

Hosts: Myriam Telus


November 7, 2017

Speaker: Jurgen Mienert, UiT The Arctic University of Norway (sabbatical at MBARI)

Title: Integration of Arctic seafloor observatories and 4D seismic: Detecting fluid migration pathways from the deep

Abstract: Vast amounts of the greenhouse gas methane are stored under the ocean floor as ice-like, crystalline compounds called hydrates. These naturally occurring structures form under high pressure and in low temperatures, when water molecules encage and stabilize gases. These hydrocarbon gases originate from thermogenic sources deep below the ocean floor and/or from biogenic shallow sources. The Arctic holds vast undiscovered reserves of hydrates with mixtures of thermogenic and biogenic methane. The last deglaciation some 16,000 years ago and today’s ocean warming cause them to melt and release methane from—for example—craters of the ocean floor (see above illustration).

The most dominant forces to have ever affected the Arctic are the growth and collapse of the ice sheets in the northern hemisphere and the recent climate change. Obviously, we cannot observe firsthand the natural world of the prehistoric past. However, we do have high-resolution seismic, as well as seafloor, observations, and well-constrained numerical modelling. Using this technology, we have been able to see into sub-seabed fluid migration and seabed-fluid expulsion systems. Deep hydrocarbon reservoirs exist today beneath the pressures of the ice sheets in Greenland and Antarctica. Signs of instability and fluid migration may become commonplace under scenarios of fast ice retreat.

Hosts: Nicole Feldl


November 14, 2017

Speaker: Jeffrey Kiehl, UC Santa Cruz

Title: Atmospheric Rivers in Past, Present and Future Climates

Abstract: Atmospheric rivers are major contributors to the poleward transport of moisture from low latitudes to the extra-tropics and polar regions. Although they cover only a small fraction of area at any given latitude they play dominant role in Earth’s atmospheric water cycle. Landfall of atmospheric rivers is often accompanied by extreme rainfall and flooding events. Thus, understanding the physical characteristics of atmospheric rivers is critical to connecting Earth’s water cycle across a wide range of space and time scales. As Earth warms due to increased anthropogenic greenhouse gases one would expect atmospheric rivers to respond to the warming in varied ways, e.g. through additional atmospheric moisture and/or shifts in atmospheric dynamical flow patterns. This presentation reviews the observed characteristics of atmospheric rivers and then explores how well these phenomena can be simulated in a current global climate model, the National Center for Atmospheric Research (NCAR) Community Earth System Model (CESM). High spatial resolution simulations for the present are compared to reanalysis products to evaluate how well the model simulates atmospheric rivers. Connections between landfall of these rivers and simulated extreme precipitation is also described. Finally, simulated atmospheric rivers are shown from a high spatial resolution simulation of the Paleocene-Eocene Thermal Maximum period (55 Mya), which was a time period of elevated greenhouse warming and enhanced atmospheric water cycling.

Hosts: Nicole Feldl


November 21, 2017

Speaker: Isabel Montañez, UC Davis

Title: Reconstructing CO2-climate-vegetation feedbacks during Earth’s penultimate icehouse

Hosts: Sarah White


November 28, 2017

Speaker: Jenna Hill, USGS

Title: Digging into Landscape Evolution: Subtropical Icebergs, Paleodrainage Patterns, Seafloor Seeps, Submarine Slides, and Subduction Zones

Hosts: Noah Finnegan


December 5, 2017

Speaker: Qinghua Ding, UC Santa Barbara

Title: When will we see an ice free summer in the Arctic Ocean?

Abstract: Climate change in the Arctic over the past decades has been attributed widely to anthropogenic factors. Our recent work, however, suggests that a regional atmospheric circulation change over Greenland and the Arctic ocean, which is primarily of natural origin, is an important contributor to the recent warming and sea ice loss in the Arctic. To better understand the relative contributions of anthropogenic and internal variability in the recent sea ice loss, through analyses of observations and community climate models, we quantify how the recent atmospheric circulation variability in the Arctic influences atmospheric thermal states in the Arctic and thereby sea ice changes in summertime. We find that the melting due to the internal variability could contribute about 30 to 40 % of the total sea ice loss in the past three decades. It is thus reasonable to expect to see a slowing down of the recent fast decline of the sea ice in the near future because there is no reason to expect that the internal variability would persist in the same phase in the next decades. However, the next cycle when the internal variability would return to the same phase will be fatal for Arctic sea ice. 

Hosts: Nicole Feldl