Colloquium Fall 2019-2020



Alison Duvall

University of Washington 

Mountain Building, Strike-Slip Faulting, and Landscape Evolution in New Zealand’s Marlborough Fault System

The ~150 km wide dextral Marlborough Fault System (MFS) and adjacent Kaikōura Mountains accommodate oblique convergence between the Pacific and Australian plates at the southern end of the Hikurangi subduction zone, New Zealand. In this presentation, I will present results from recent investigations of landscape evolution in the MFS. Low-temperature thermochronology data from this region places limits on the timing and style of mountain building and the relationship between the mountains and adjacent faults. We sampled rocks for apatite and zircon (U-Th/He) and apatite fission track dating from a range of elevations spanning ~2 km, including within the Kaikōura Mountains, which stand high above the active Marlborough dextral faults and the Spenser Mountains at a restraining bend in the Alpine fault. The data reveal Miocene cooling localized to hanging wall rocks, first along the Clarence Fault in the Inland Kaikōura Range, then along the Jordan Thrust in the Seaward Kaikōura Range, followed by widespread, rapid cooling reflected in all samples across the study area starting by ~8 Ma. Late Miocene / early Pliocene to present rapid exhumation across the field site, including at low-elevation sample sites, may relate to an increase in relative plate convergence rates and new fault development at this time. Our results suggest that topographic relief in the eastern MFS predate the onset of dextral faulting and that portions of the Marlborough Faults were once thrust faults that coincided with the early development of the transpressive plate boundary. Analysis of river patterns throughout the field area supports our conclusions from thermochronology and indicates a strong structural control to the drainage network and a history of river capture and rearrangement.

Aug. 30

Alison Duvall

University of Washington 

M9 Cascadia Subduction Zone Earthquakes and Landscapes

The last decade has provided unexpected lessons in the enormous risks from great subduction earthquakes: Sumatra 2004, Chile 2010, and Japan 2011 were each devastating, resulting in surprising impacts distinct from shallow seismic events. Similar large-magnitude earthquakes are known to occur on the Cascadia subduction zone (CSZ), with the potential of rupturing the entire 1100 km length of the Pacific Northwest plate boundary. Coseismic landslides represent one of the greatest risks to the millions of people living along the Cascadia Subduction Zone, from northern California to southern British Columbia. Empirically derived relationships between earthquake magnitude and landsliding are well studied, and suggest a magnitude 9 earthquake is likely to trigger widespread landslides. Because a magnitude 9 subduction earthquake is well known to have occurred just over 300 years ago, evidence of coseismic landslides triggered by this event should still be present in the landscapes of the Washington and Oregon Coasts. Here, we use surface roughness dating to estimate the ages of ~10,000 manually mapped deep-seated landslides in the central Oregon Coast Range, where predicted peak ground accelerations are expected to exceed 0.6g during future megathrust earthquakes. We first interrogate the landslide age-frequency data and place estimated bounds on the number of landslides within our study area likely triggered during the 1700 CE earthquake. We then examine spatial patterns in landslides with ages around the time of the 1700 CE earthquake and compare these patterns with predicted susceptibility using traditional Newmark-sliding block analyses. Our results suggest rainfall driven landslides comprise the majority of all recent (<1,000 ybp) deep-seated slope failures, and that spatial patterns in past coseismic landslide occurrence are more complicated than predicted, in places even anticorrelated with predicted landslide susceptibility. These findings suggest that even within the same rock type, variations in strength or structure contribute more towards driving deep seated landslides than peak ground acceleration in the PNW.

Sep. 6

Marine Denolle

Harvard University

The dynamic shallow Earth: monitoring seismic properties and natural resources
Being at the interface between the solid Earth and the fluid Earth, the shallow subsurface is particularly affected by the evolution in atmospheric conditions (temperature, pressure, precipitations) and by the transient effects of seismic activity. The mechanical properties of the subsurface affect the speed and attenuation of seismic waves passing through the medium. We use the ambient seismic field to extract information on the variations in seismic wavespeeds in several examples. One example or application is to monitor groundwater resources by predicting groundwater levels from seismic velocity perturbation in southern California. Another application is to monitor site effects for future predictions of ground motions, which we explore in Jakarta (Indonesia). Finally, another application is to constrain sediments (non)linear rheology as a response to ground shaking, which we perform during the 2011 Tohoku earthquake in Tokyo (Japan). All of these examples highlight how vibrant and dynamic the shallow Earth is at human time scales.
Sep. 11

Jennifer Taylor

Scripps Institution of Oceanography

The crustacean exoskeleton: an example of extreme versatility

An iconic aspect of crustaceans (crabs, shrimp, and lobsters) is the calcified exoskeleton, which is a remarkable structure built upon a standard template. Yet, the exoskeleton can vary in construction and material properties to yield tremendous versatility. Within a single animal it may be used for an assortment of critical functions, such as locomotion, support, communication, protection, sensing, feeding, and mating. Thus, this structure plays a crucial role in nearly every aspect of the animal’s biology and ecology. Moreover, the exoskeleton is responsive to the physical and chemical environment, both over evolutionary (adaptation to new habitats) and physiological (molting under changing ocean conditions) time scales. I will discuss the functional morphology of the crustacean exoskeleton and how its versatility enables crustaceans to function in new and changing environments. The goal is to highlight the unique properties of the crustacean exoskeleton along with its ecological significance.

Sep. 19

Sarah Penniston-Dorland

University of Maryland

Sep. 27

Andreas Kappler

University of Tübingen

Geomicrobiological processes in Banded Iron Formation deposition, banding and mineral diagenesis

Banded Iron Formations (BIFs) are marine sediments with alternating Fe- and Si-rich layers which were mainly deposited between 3.8-1.85 Ga. Their deposition spans a time of major transition in the oxidation state of Earth’s atmosphere and oceans, the so-called Great Oxidation Event. However, their interpretation can be hindered by diagenetic and metamorphic over-printing thought to be present in even the most well-preserved BIFs found today. In this talk I will present how microorganisms could have been responsible for the characteristic banding of Banded Iron Formations, even in the presence of
harmful UV radiation, how such microorganisms could have been preserved in the fossil record and how diagenetic and metamorphic processes transformed primary biogenic minerals leading to those found in the rock record today.
Oct. 4

Johannes Müller

Museum für Naturkunde 

Bones, limbs, and lizards: tracking convergent and environmental adaptations in squamate reptiles

Squamate reptiles, i.e. lizards and snakes, are one of the most diverse clades of modern tetrapods, and are known to have evolved similar phenotypes multiple times independently. Whereas progress in our understanding of squamate relationships allowed us to better identify the number of such independent events, the extrinsic and intrinsic circumstances under which similar phenotypes evolve remain largely unknown. In our lab, we investigate these issues using a variety of model systems, such as the fossorial, limbless worm lizards (Amphisbaenia) and the closely related but terrestrial Lacertidae, which all show high amounts of convergent and parallel evolution at different taxonomic scales. Using X-ray computed tomography of both hard and soft tissues, geometric morphometrics, as well as data from ecology and the fossil record we try to answer questions such as how often limblessness evolved independently in worm lizards, which role heterochrony plays in the convergent skeletal evolution of environmental specialists, and why some clades are more homoplastic than others. Apart from that, we also combine our data with information from community ecology and physiology to examine how these lizards evolutionarily adapted to modern environments, and in which way current climate change might affect them in the future.

Oct. 11


Oct. 25

Allison Wing

Florida State University

The role of radiative-convective feedbacks in tropical cyclone formation in numerical simulations

Interactions between convection, moisture, clouds, and radiation can cause tropical convection to “self-aggregate” in idealized numerical simulations. Here, we explore the role of these processes in tropical cyclone formation. First, we perform idealized numerical simulations of rotating radiative-convective equilibrium with a cloud-resolving model, in which, rather than using a weak vortex or moist bubble to initialize the circulation, we allow a circulation to form spontaneously in a homogeneous environment. We compare the resulting tropical cyclogenesis to non-rotating self-aggregation. We find that in the initial development of a broad circulation, the feedback processes leading to cyclogenesis are similar to the initial phase of non-rotating aggregation. Sensitivity tests in which the degree of interactive radiation is modified are also performed to determine the extent to which the radiative feedbacks that are essential to non-rotating self-aggregation are important for tropical cyclogenesis. Radiative feedbacks are found to significantly accelerate cyclogenesis but are not strictly necessary for it to occur.
We then explore the tropical cyclogenesis and intensification processes in realistic historical simulations of tropical cyclones with five high-resolution global climate models. We track the formation and evolution of tropical cyclones in the climate model simulations and apply a moist static energy budget analysis both along the individual tracks and composited over many tropical cyclones. We find that the genesis processes, in terms of the contributions to the moist static energy variance budget, are qualitatively similar across all models and to the cloud-resolving model simulations. Radiative feedbacks contribute to TC development in all models, especially in storms of weaker intensity or earlier stages of development, while the surface flux feedback is stronger in models that simulate more intense TCs. These results imply that the representation of the interaction between spatially varying surface fluxes and the developing TC is responsible for at least part of the intermodal spread in TC simulation by climate models.
Nov. 1

Christy Rowe 

McGill University

Nov. 8

Sarah Stewart

University of California, Davis 

Earth after a giant impact: Synestias and surprises
The power deposited during a giant impact is comparable to the power from the Sun. Most giant impacts that form an Earth-mass body create a synestia, a new type of planetary object. The physical properties of synestias are very different from traditional ideas about magma oceans. As a result, the standard interpretations of geochemical processes at the end of Earth’s formation must be re-examined. 
Nov. 15

Jacky Austermann

Columbia University 

Reconstructing last interglacial sea level on a deforming Earth
The last interglacial (MIS 5e, 125 ka) marks a time during which global mean temperatures were 1-2º warmer than pre-industrial values. This time period has therefore been used as a natural laboratory for studying ice sheet stability and sea level rise in a warmer world and insights gained from this period can be used to improve predictions of future sea level change. Local sea level during the last interglacial can be reconstructed using sea level indicators such as fossil corals. In order to infer global mean sea level, or equivalent ice volume, one needs to correct local sea level estimates for post-depositional deformation. In this talk I will discuss two geodynamic processes that cause post-depositional deformation, namely glacial isostatic adjustment and dynamic topography. I will show that dynamic topography contributes to sea level change over this time period and that model predictions are significantly correlated with observed sea level highstands. I will further discuss how glacial isostatic adjustment affects last interglacial sea level and that this signal is very sensitive to the penultimate deglaciation (MIS 6). I will combine these insights with field data from the Bahamas to put first order constraints on MIS 6 ice sheets and derive a new estimate of global mean sea level during the last interglacial. I will present this estimate, put it in context of earlier work, and provide an outlook of how these findings can affect predictions of future sea level change. 
Nov. 22

Andy Thompson

California Institute of Technology

Closing the loop: Re-configuring the ocean’s global overturning circulation in a changing climate

The ocean’s overturning circulation is the primary mechanism for storing heat and carbon in the climate system from centennial to millennial time scales.  Traditionally, deep water formation in polar regions have been assumed to set the strength and structure of the overturning.  However, this neglects the role of surface processes, such as heating of the tropical Indo-Pacific and sea ice melt in the Southern Ocean, that create lighter waters and close the ocean’s heat, freshwater and buoyancy budgets.

In this talk, I will use a hierarchy of numerical models to tell two stories about changes to the ocean’s overturning structure; both are based on a water mass transformation framework that emphasizes how the overturning circulation arises from the need to transport water between regions of surface buoyancy gain and loss.  Considering steady-state climates, we show that global overturning strengthens monotonically in response to increased heat uptake in the low-latitude Indo-Pacific as the climate warms.  However, upper and lower overturning cells show a more complex evolution with climate state, which can be explained through mechanistic differences between North Atlantic (advective) and Southern Ocean (eddy diffusive) heat transport.  Considering transient climate responses, I will show that the seasonal cycle of sea ice formation and melt in the Southern Ocean modulates the global ocean’s response to perturbations in North Atlantic deep water formation.  These dynamics are consistent with both an observed inter-hemispheric asymmetry and a 200-year phase lag between Greenland and Antarctic warming/cooling during the last glacial period:  the so-called bipolar seesaw.  

Dec. 6

Tina van de Flierdt 

Imperial College London

Drilling back to the future: History of the East Antarctic Ice Sheet

Polar ice is an important component of the modern climate system, affecting – among others - global sea level, ocean circulation and heat transport. Today most of the Antarctic continent is covered by up to four kilometres of ice. Drilling marine sediment sequences in proximity to this vast ice sheet can provide unique insights into ice extent under different (and warmer) climatic conditions in the past. I will introduce how we can use the geochemical fingerprint of detrital marine sediment to determine its provenance and learn about past ice margins. I will subsequently apply the approach to Pliocene and Pleistocene drill cores from IODP Expedition 318, which are well positioned to monitor ice dynamics in the Wilkes Subglacial Basin, one of the major marine-based areas of the East Antarctic ice sheet. Our results suggest a dynamic East Antarctic ice sheet in the early, warm Pliocene, and timescales of 1000s of years for large scale glacial retreat and re-advance. Late Pleistocene provenance variations are similar in magnitude to the ones observed during the warm Pliocene. In detail, regional warming above 2°C for more than a few thousand years was probably enough to cause significant ice retreat in the Wilkes Subglacial Basin during the Last Interglacial. But what are the implications for the future?