Fall 2020

Tuesdays at 3:30 PM

Zoom information can be found on the EPS advising Google calendar

October 6, 2020

Speaker: Jane Willenbring, Stanford University

Title: Forged Signatures: Tectonic versus climatic control on Cordilleran mountain heights and Andean topographic asymmetry

Abstract: A long-standing debate in the Earth Sciences bears on the question of whether top-down erosion processes govern mountain building processes, but how do we measure the topographic signature of the climate drivers independent of tectonics? We use two natural experiments to detangle a potential signature of climate and drivers of erosion using the large latitudinal range of Earth’s orogens and their rain shadows in order to vary temperature and precipitation while holding tectonic accretion (relatively) constant. In the past decades, glacial erosion has emerged as a driving surface process controlling the heights of mountains and as the cause of accelerated erosion of mountains in mid-latitudes on Earth. Here, we present topographic and erosion rate data from the Cordilleran-style mountain ranges from South America through Alaska to demonstrate that the distribution of mountain heights and overall mass correlate linearly with the rate of plate convergence. Given the large latitudinal range of our dataset, this should not be expected if climate governed these parameters. Thus, tectonic processes set the limits on mountain heights. In addition, coupled deformation-surface process models predict that orogenic asymmetries may be modified by dominant wind direction and erosion, i.e. the formation of orographic rainfall gradients across strike. We present data comparing the radius of curvature of the subducting Nazca slab with orogenic wedge widths of the Andes and present correlations between slab-dip and arc position to suggest that as the arc position changes with slab dip, the asymmetry of an orogenic wedge may consequently change. Given that erosion rates do not mirror rain shadows, the slab geometry must be accounted for when assessing the climatic influence on orogenic asymmetry. Possibly, climate signals may be imprinted on hillslope processes, but not erosion rate magnitude.


Host: Em Schnorr

October 13, 2020

Speaker: Briony Horgan, Purdue University

Title: The Perseverance rover: NASA's next big step in the search for life beyond Earth


Abstract: The Perseverance rover on the Mars 2020 mission launched on July 30 and is set for a rendezvous with Mars in February 2021. The rover will land in Jezero crater to search for signs of ancient microbial life and select samples for eventual return to Earth. In this talk I'll give an overview of what we know about the geomorphology and mineralogy of Jezero from orbital data, a preview of how we might test current hypotheses for the geological and astrobiological history of the region with the rover, and an example of the sample suite that we might expect to return.

Host: Rachel Maxwell

October 20, 2020

Speaker: Francis Rengers, USGS

Title: The Problem of Wildfire: How Wildfire Leads to Cascading Hydrologic and Geomorphic Hazards

Abstract: Within our solar system, Earth is the only planet that is affected by wildfires, and wildfire has been a constant presence on the planet since at least the Silurian period. However, the effect of wildfire on the earth’s surface remains relatively under-studied. Many studies of earth surface processes focus on how fluids (e.g. wind, water, ice) directly shape the earth through sediment transport. Wildfire does not directly transport sediment. However, wildfire is a remarkable catalyst for earth surface change because it alters two key landscape properties: (1) wildfire greatly increases the susceptibility for overland flow in otherwise well-drained soils, and (2) wildfire increases soil erodibility relative to similar unburned settings. Consequently, order-of-magnitude increases in erosion rates may occur during rainstorms with relatively frequent recurrence intervals. This talk will focus on typical wildfire effects in burned watersheds, with a special focus on the role of wildfire in generating debris flow and landslide hazards.


Host: Noah Finnegan

October 27, 2020

Speaker: Daniel Ibarra, UC Berkeley

Title: Drivers of hot and cold past wet states recorded by lakes in the western United States


Abstract: G.K. Gilbert’s 1890 monograph on Lake Bonneville published by the United States Geological Survey initiated over a century of research on Quaternary lakes in the American west. The continuation of this work is increasingly pertinent today with the need to test climate models used to forecast future water resources in the region as the climate warms. Importantly the presence or absence of lakes in terminal basins provide an unequivocal measure of wetness. In this work I will show that wetter conditions during both colder- and warmer-than-present periods in the past are recorded in shoreline and outcrop data from the latest Pleistocene and the middle-Pliocene. In conjunction with paleotemperature data, derived from pollen, macrofossil assemblages and carbonate clumped isotope measurements, I will show scaling relationships implying that: 1) Pleistocene lakes during glacial maxima in the northern Great Basin do not require substantial precipitation increases to explain lake shoreline extents; and 2) middle-Pliocene lakes would have required up to a doubling of precipitation in the southwest. These inferences provide quantitative targets for assessing the performance of climate model simulations of the terrestrial water cycle. In addition, I will show ongoing work associated with the application of carbonate clumped isotope thermometry and triple oxygen isotope measurement to lacustrine lake sediments in the western United States.

Host: Terry Blackburn

November 3, 2020

Speaker: Ying Fan, Rutgers University

Title: Watering the Land from Below: Groundwater Influence on the Terrestrial Environment

Abstract: Much of the water on land is groundwater, which moves through the Earth’s crust at time scales of days near the surface to billions of years kilometers down. I will focus on the shallow and actively circulating groundwater which facilitates many near-surface processes that directly influence water, energy and biogeochemical cycles on Earth. I will examine the modern-day patterns and drivers of continental water storage and drainage, and their influence on land plants such as plant rooting depths and seasonal plant water sources. Then I will pose some hypotheses on how the shallow groundwater may have functioned through the geologic past, with the last deglaciation and land plant evolution as two examples.


Host: Margaret Zimmer

November 10, 2020

Speaker: Matthew Huber, Purdue University

Title: State dependent climate sensitivity and polar amplification

Abstract: Two of the main questions in climate dynamics are: (1) what is the change in global mean surface temperature caused by a doubling of atmospheric carbon dioxide levels, and (2) what is the change equator-to-pole temperature gradient for a given global mean temperature change. One hope is that paleoclimate records can provide key constraints on these two parameters which can constrain predictions of future climate change derived from climate models. In this talks I summarize work on this topic incorporating paleoclimate data and models spanning about 40 millions years from the Eocene, Oligocene, and Miocene. While we find that constraints on the lower bounds on climate sensitivity can be derived from this kind of study, the fact that climate sensitivity can be dependent on climate state and the forcing factors in the past are poorly known may be insurmountable obstacles to further tightening the likely bounds of modern or future climate sensitivity. On the other hand, polar amplification of global warming, and more generally the overall pattern of associated temperature change, appears to be more robust and stationary across a range of climate states and hence a more meaningful target for modeling. The change in temperature gradient for given mean surface temperature change may be a more productive avenue for continued investigation in models and data as it relies less on knowledge of climate change forcing factors and it is of direct relevance for tightening the range of possible future regional climate predictions.


Host: Jim Zachos

November 17, 2020

Speaker: Elizabeth Sibert, Harvard University

Title: A history from the bottom of the sea: fish, microfossils, and 85 million years of global change

Abstract: Fish are the most diverse group of vertebrates on the planet today, and the type and abundance of fish present in the marine ecosystem depends on the environmental conditions and food web processes in that area. Ichthyoliths - isolated microfossil fish teeth and shark scales - preserve a unique history of the abundance, community composition, and evolutionary history of fish. In this talk, I use ichthyoliths preserved in deep-sea sediments to explore how open-ocean fish and sharks respond to Cretaceous and Cenozoic global change, from mass extinctions to global climate events. I will discuss changes in fish production, community structure, and evolutionary processes and their interactions with environmental conditions, as well as share new findings of a major change in marine vertebrate community composition during the Early Miocene. Together these records demonstrate that fish can provide unique insights into the patterns of marine ecosystem evolution and sensitivity to global change.


Host: Matthew Clapham

November 24, 2020

Speaker: Hansi Singh, UVIC

Title: Antarctic Climate and its Climate Change Response: Orography, Moisture Transport, and Natural Variability in the Atmosphere-Ocean-Ice System

Host: Nicole Feldl

December 1, 2020

Speaker: John Gardner, UNC

Title: The persistent sediment delivery problem in rivers

Abstract: Moving sediment from continents to coasts is a fundamental job of rivers. However, humans have dramatically altered how rivers move sediment leading to declining suspended sediment delivery in many rivers around the world. Rarely are we able to look both upstream and downstream of basin outlets to measure where and why sediment delivery is changing. We developed a spatially-explicit suspended sediment database over all large rivers (> 60 m wide) in the continental USA using >234,000 satellite images from 1984-2018. I will present multi-decadal trends in suspended sediment concentrations, river flow, and soil erosion; link basin-scale trends to trends in coastal rivers; and discuss what limits sediment delivery.


Host: Margaret Zimmer

December 8, 2020

Speaker: Aradhna Tripati, UCLA

Title: Carbonate clumped isotope geochemistry as an applied tool in paleoclimate and paleoceanography

Abstract: The carbonate clumped isotope thermometer is a promising proxy for the study of environmental change through time. In principle, this technique can provide a thermodynamically based estimate of carbonate mineral formation temperature and a relatively assumption-free calculation of water 18O/16O ratios. Over the past thirteen years, I have studied the systematics of carbonate clumped isotopes in foraminifera and coccoliths and other geological archives including lacustrine and soil carbonates. In this talk, I will discuss work we have done to improve measurement capabilities, overcome challenges such as sample size requirements and accuracy, and develop its usability for paleoceanographic and paleoclimatic reconstructions. I will highlight applications to reconstruct terrestrial hydroclimates and tropical sea surface temperature in the past, including proxy-model comparisons to understand underlying dynamical mechanisms. My talk will also touch on new developments relating to the physical geochemistry of clumped isotopes in carbonates. We are using both theory and experiments to quantify kinetic isotope effects, and have developed the novel capability to make measurements of multiple clumped isotope species in carbonates. I will also briefly discuss the work we have been doing in my research group and in the Center for Diverse Leadership in Science to support equity, justice and innovation in the geosciences.


Host: Ryan Green