Abstract: Dynamics in the flow rate of sap in trees is a useful metric for those studying transpiration and carbon exchange. For decades, the standard methods for measuring sap flow involve the insertion of arrays of metal probes into the sapwood and observing how heat is advected along the stem. These sensors can work well, but they are prone to misalignment errors and are difficult and expensive to produce in mass quantities. A new design, which relies on the same...
"Tales of magmatic sulfur: origins, redox, degassing, and isotopic fractionation"
Abstract: The behavior of sulfur (S) in magmas has critical effects on a wide array of processes such as volcanic degassing, climatic impacts of volcanic eruptions, or the formation of ore deposits. It also holds clues to the S isotopic signatures associated with different tectonic settings: mid-ocean ridge basalts (MORB), ocean island basalts (OIB), and subduction zone magmas. The speciation of S in magmas has a...
Speaker: Anna Waldeck (on behalf of a cohort including Jack Hensley and Katherine Keller)
"Environmental impacts of food systems"
GSPD comprises scientific talks up to one hour in length by graduate students and post docs, but all are welcome to attend, including faculty and staff. Lunch will be provided. As always, please plan to bring reusable plates and cutlery to reduce waste.
"Big data for small earthquakes: Shaking up seismology with data science"
Speaker: Dr. Karianne Bergen
Abstract: Earthquake detection, the problem of extracting weak earthquake signals from continuous waveform data recorded by sensors in a seismic network, is a critical and challenging task in seismology. New algorithmic advances in “big data” and artificial intelligence have created opportunities to advance the state-of-the-art in...
"Single-thread rivers without land plans: A simple mechanistic model to interpret pre-Silurian and Martian fluvial deposits"
Speaker: Mathieu Lapotre, a John Harvard Distinguished Science Fellow
Abstract: To meander, alluvial rivers need cohesive banks to hold water within a single, relatively narrow and deep channel (low width-to-depth ratio) and thus develop the helical flow that is paramount to sustaining lateral accretion. Although many cohesive agents could in theory...
"Tropical and extratropical general circulation in an high obliquity planet"
Speaker: Wanying Kang, graduate student in the Tziperman group
Abstract: Planets with high obliquity receive more radiation in the polar regions than in low latitudes, and thus, with a relatively high surface capacity, their meridional temperature gradient tends to be reversed for the entire year as shown in previous studies. To reduce the meridional temperature gradient, a...
"Homogeneous early 20th century sea surface warming after correcting for historical artifacts"
Speaker: Duo Chan, graduate student in the Huybers group
Abstract: Existing estimates of early 20th century sea surface temperatures (SSTs) indicate cooling in the Northwestern Pacific and enhanced warming in the North Atlantic. Such a heterogeneous pattern suggests first-order contributions from regional variations in...
"Seismically anisotropic magma reservoirs underlying two western US supervolcanoes"
Speaker: Chengxin Jiang, post-doc in the Denolle group
Abstract: A better understanding of the architecture of existing magmatic reservoirs in the crust is of great value for the evaluation of possible volcanic eruptions in the future. While the location and geometry of magmatic low-velocity bodies are frequently constrained by tomographic inversions, less is known about the configuration of melts within reservoirs or pathways connecting reservoirs. Seismic anisotropy can illuminate structural fabrics or layering with length scales too fine to be resolved as distinct features in most seismic tomography. In this study, seismic anisotropic structures were investigated beneath Yellowstone and Long Valley calderas. Significant positive anisotropy and low isotropic velocities were found beneath both calderas at ~5-18 km depths, which are anomalously strong compared to the surrounding areas. We propose that the anisotropic volumes represent sill complexes of compositionally evolved magma, whose seismic contrast with the crust would largely fade upon crystallization. The similarity of magma reservoir anisotropy in varied tectonic settings suggests that such mid-crustal sill complexes may be ubiquitous features of voluminous silicic magmatic systems, and that anisotropy should be considered to seismically estimate melt content and mobility.
Lunch will be provided. As always, please plan to bring reusable plates and cutlery to reduce waste.
"Aging and preservation of natural organic carbon"
Speaker: Jordon Hemingway
Abstract: Organic carbon (OC) preservation in soils and sediments removes carbon dioxide from the atmosphere and promotes atmospheric oxygen accumulation. This process likely involves both chemical recalcitrance and physical protection, but the relative importance of these mechanisms remains unknown. To directly assess the controls on preservation, we measured radiocarbon age as a function of activation energy (E) using serial oxidation for a...
"The response of the marine nitrogen cycle to past ocean anoxia"
Speaker: Felix Elling
The marine nitrogen cycle has undergone large perturbations throughout Earth history, such as during Mesozoic Oceanic Anoxic Events (OAEs). Reconstructing past environmental changes during these events remains challenging due to the multitude of nitrogen transformation pathways. To better understand the nitrogen cycle during anoxic conditions, we studied Pliocene-Pleistocene sapropels in the Mediterranean Sea, which are organic-rich sediments deposited during multi-millennial anoxic events. By analyzing bulk sedimentary 15N isotopes and the excellently preserved organic biomarkers in these sediments, we were able to reconstruct the occurrence and environmental impact of multiple groups of nitrogen-transforming microorganisms. Our results indicate that the nitrogen cycle during sapropel deposition was drastically different from that of modern oligotrophic conditions in the Mediterranean. The systematic changes in abundances of specific nitrogen-transforming microorganisms over a sapropel cycle suggest the existence of a positive feedback loop controlling both, nitrogen cycling and primary productivity during sapropel events. This feedback loop was likely also present during Mesozoic OAEs and may explain the deposition of enormous amounts of organic matter as black shales (ultimately leading to petroleum source rocks).
Lunch will be provided. As always, please plan to bring reusable plates and cutlery to reduce waste.
