Presentations

Lauren McLeod

Crustal Thickness Behind the Tonga Arc Measured by Stacking of pP Precursors

Contact: lcm99@cornell.edu

Advisor: Larry Brown

Abstract

Underside reflections from internal discontinuities within the lithosphere, particularly the Moho, can sometimes be observed as precursors to the depth phase pP. If these precursors are recorded by dense arrays of seismometers, the signal processing techniques developed for reflection surveys using controlled sources at the surface can be applied to create an “upside-down” seismic reflection profile. Previous studies with this technique have largely been used to measure the depth of upper-mantle discontinuities or the thickness of continental crust. Here we use recordings from Japan’s Hi-net array of intermediate- and deep-focus earthquakes in the Tonga-Kermadec subduction zone to measure crustal thickness within the Lau Basin and along the Lau Ridge. Our measurements sample areas that have been inaccessible to traditional surface seismic measurements. We have found the crust to vary in thickness from about 7 km to 20 km. Our measurements agree with existing measurements of crustal thickness from surface seismic refraction surveys where they overlap and demonstrate the feasibility of using this technique to measure crustal thickness in oceanic regions.

Matthew Pruden

Using Molluscs to Assess Ecological Quality Status of Coastal and Estuarine Soft-bottom Habitats

Contact: mjp368@cornell.edu

Advisor: Gregory Dietl

Abstract

AMBI and M-AMBI are widely used biotic indices for assessing the ecological quality status of benthic macroinvertebrate communities in estuarine and coastal soft-bottom habitats. Identifying the species needed for estimating these indices, however, is both expensive and time-consuming, and requires a high degree of taxonomic expertise. The use of proxy taxa as a means of subsampling the target community may save time, resources, and the breadth of taxonomic expertise needed. Our study used macroinvertebrate benthic survey data from the Atlantic Coast of the United States to test the fidelity of molluscs as proxies of the whole community. We calculated the AMBI and M-AMBI scores for both the molluscan and whole communities and then adjusted the molluscan-only index scores to that of the whole community using the linear relationship between the two communities within a Bayesian framework. We found that the mollusc-only AMBI approach underperformed at classifying the ecological quality of the whole community, particularly regarding sample sites classified as needing remediation. The low performance of the mollusc-only AMBI approach is likely due to the dearth of molluscs with high environmental stress tolerances. In contrast, the mollusc-only M-AMBI outperformed AMBI at classifying ecological quality. The M-AMBI linear model correctly classified nearly all of the adjusted mollusc-only sample sites needing remediation. The increased efficacy of the mollusc-only M-AMBI may be due to the incorporation of species richness and diversity into the index, as both metrics were highly correlated between the molluscan and whole communities. Mollusc-only M-AMBI did have some drawbacks, however, with fidelity decreasing as ecological quality decreased. Overall, our study highlights the potential utility of a mollusc-only approach for assessing the ecological quality of estuarine and coastal soft-bottom habitats.

Nicholas Sitaras

Diffusivity of Water through Embayments from Pico Do Fogo 1951 Eruption

Contact: nps48@cornell.edu

Advisor: Esteban Gazel

Abstract

This project aims to measure the diffusivity of water through two embayments from the 1951 eruption of Pico Do Fogo in Cape Verde in order to ascertain information from before the eruption.

Preston Ancello

Stratospheric Atlantic Anticyclones and their Relationship to Tropospheric Cold Air Outbreaks

Contact: pna9@cornell.edu

Advisor: Stephen Colucci

Abstract

Stratospheric anticyclones over the Atlantic Ocean can have a profound effect on weather patterns at the mid-latitudes such as cold air outbreaks over the Eastern US. To allow for a better understanding of such events, a catalog of all 114 Atlantic High Events, defined as regions with a geopotential height >30.8 km and area >1.84 million km^2, was analyzed using MERRA2 datasets to understand the thermodynamic evolution of these events and correlations with cold air outbreaks (CAOs).

Noah Fuller

Defining the Coiled Oyster Morphospace and its Consequence for their Generic Diversity and Proposed Causes of Coiled Oyster Extinction

Contact: ncf25@cornell.edu

Advisor: Warren Allmon

Abstract

“Coiled oysters” are characterized by extremely inequivalent spiral coiling and are a dominating presence in Mesozoic marine life.  Yet what actually constitutes a coiled oyster has never been defined. A proper definition is important since coiled oysters are not a monophyletic group. Defining their shape using some standard measure of morphospace, such as Raup parameters, permits  comparison to other bivalve morphologies. Using Raup parameters enables classification of taxa that appear to be coiled while also revealing that many taxa not usually thought of as coiled, such as  certain ostreids and the cardiid genus Chama, also inhabit this morphospace. Additionally, this information allows the diversity of coiled genera to be tracked through time, revealing the existence of three different coiled oyster faunas for the Jurassic, Cretaceous, and Cenozoic. The resulting diversity challenges the hypothesis that the rise of durophagous predators and increased sediment reworking of the Marine Mesozoic Revolution (MMR) by themselves caused the extinction of gryphaeid and exogyrid recliners. That hypothesis is not sufficient to explain the overall disappearance of their morphologies, since many morphologically similar genera persisted and even independently evolved in the Cenozoic, and more importantly, two genera that were found to possess this kind of morphology, Neopycnodonte and Chama, are still extant today.

Leena Sen

Assessing the Collapse of Basin BC of the Academy of Sciences Ice Cap Using Remote Sensing

Contact: lps57@cornell.edu

Advisor: Matthew Pritchard

Abstract

Many glaciers are located in the Russian High Arctic (RHA), but the response of these glaciers to recent warming has been less intensively investigated that the Antarctic and Greenlandic glaciers. Yet, there is evidence that the glaciers of RHA contribute a significant percentage of melt water to sea level rise despite their small size. Basin BC of the Academy of Sciences Ice Cap on the Severnaya Zemlya (SZ) archipelago in the RHA is a marine-terminating glacier that has shown considerable change in elevation and velocity since the early 2000s. Previous work in this region has indicated that the glacier accelerated between 2002 and 2016. In this study, I examine elevation and velocity data and make observations based on optical images that were collected during this timeframe (2002-2016) to better determine the temporal evolution of changes to glacier BC. Based on satellite Synthetic Aperture Radar observations, I find evidence that glacier BC started showing initial signs of destabilization between November 2005 and January/February 2006. Observations from the ICESat-1 satellite laser altimeter also reveal a slight thickening signal between 2003 and 2009 based on comparisons of yearly profiles from Track 154, one of the more complete ICESat tracks that crosses basin BC. These observations, combined with comparison to weather data from the nearest weather station (Golomyanny Island, SZ), confirm the anomalous behavior of the glacier during these years and further clarify the beginning dates of BC’s destabilizing behavior. Further analysis in this region can use this newfound time range of 2005-2007 or 2005-2006 to search for the novel or standard environmental, mechanical or geological causes for the glacier collapse, possibly contributing to our understanding of what might trigger destabilization in Arctic ice caps.

Nidhi Desai

Modeling Future Ammonia Emissions from Manure Production

Advisor: Peter Hess & Natalie Mahowald