ScholarWorks@UMassAmherst
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Recent Submissions
Publication FEAST: Feedback in Emerging extragAlactic Star ClusTers: JWST Spots Polycyclic Aromatic Hydrocarbon Destruction in NGC 628 during the Emerging Phase of Star Formation(2024)We investigate the emergence phase of young star clusters in the nearby spiral galaxy NGC 628. We use JWST NIRCam and MIRI observations to create spatially resolved maps of the Pa alpha 1.87 mu m and Br alpha 4.05 mu m hydrogen recombination lines, as well as 3.3 and 7.7 mu m emission from polycyclic aromatic hydrocarbons (PAHs). We extract 953 compact H ii regions and analyze the PAH emission and morphology at similar to 10 pc scales in the associated photodissociation regions. While H ii regions remain compact, radial profiles help us to define three PAH morphological classes: compact (similar to 42%), extended (similar to 34%), and open (similar to 24%). The majority of compact and extended PAH morphologies are associated with very young star clusters (<5 Myr), while open PAH morphologies are mainly associated with star clusters older than 3 Myr. We observe a general decrease in the 3.3 and 7.7 mu m PAH band emission as a function of cluster age, while their ratio remains constant with age out to 10 Myr and morphological class. The recovered PAH(3.3 mu m)/PAH(7.7 mu m) ratio is lower than values reported in the literature for reference models that consider neutral and ionized PAH populations and analyses conducted at galactic physical scales. The 3.3 and 7.7 mu m bands are typically associated with neutral and ionized PAHs, respectively. While we expected neutral PAHs to be suppressed in proximity to an ionizing source, the constant PAH(3.3 mu m)/PAH(7.7 mu m) ratio would indicate that both families of molecules disrupt at similar rates in proximity to H ii regions.Publication Retirement Memory Book - Barbara Gravin Wilbur(Center for International Education, UMass Amherst, 2020-11)Honoring Barbara Gravin Wilbur on her retirement CIE would normally have held a large celebration party to honor BGW on her retirement, but due to the COVID pandemic, we decided instead to create a memory book. We invited all who wished to honor her to submit memories, reflections, and stories from their experiences with her over the years. This document is the result. The book starts with a poem from BGW expressing her own feelings about her 35 years at CIE. The rest of the book chronicles her career at CIE through the eyes of more than 85 people ā students, staff, and faculty members ā who sent us their thoughts. Those thoughts are presented in rough chronological order, based on graduation dates for students or periods of specific projects and activities at CIE. Undoubtedly, there are many more CIE folks who intended to send in their thoughts but, in these challenging times, did not get around to it. However, their thoughts are likely mirrored in the comments of those who did respond. The memory book, while focused on BGW, is also a partial history of CIE through the years, with many pictures of events that she helped organize and people who are part of the CIE family. In reading through the comments, BGW says she went through an entire box of Kleenex!Publication Investigating the application of organic geochemical techniques to tropical Anjohibe (Madagascar) stalagmites(2024)Speleothem stable carbon isotopes (delta C-13(carb)) are used to reconstruct past environments, but are a complex signal of karst, soil and plant processes. To help untangle these signals, we used plant waxes, their carbon isotopic values (delta C-13(wax)) and polycyclic aromatic hydrocarbons (PAHs) extracted from stalagmites to evaluate plant photosynthetic pathway (C-3 vs C-4) and biomass burning above a cave. Our test case investigates stalagmites from Anjohibe in Madagascar where at around 1000 CE multiple delta C-13(carb) records increase by similar to 8-10 parts per thousand. This suggests that humans transformed the local landscape from C-3 vegetation to C-4 grasses through agropastoral practices, which rely on burning to promote grass growth. We evaluated different protocols to remove contamination, finding higher biomarker yields after polishing off the surface of the stalagmite versus ultrasonic pre-cleaning in solvent. Anjohibe stalagmites include n-alkanes from trees and grasses; however, bulk organic delta C-13 and delta C-13(wax) from samples dated to after the transition to the modern C-4 landscape yield values suggesting C-3 vegetation. This is likely due to a disproportionally higher contribution of C-3 waxes to the overall n-alkane signal. PAHs are present in the stalagmite but do not match the types found in overlying soils and further testing is required to determine their source. We find that delta C-13 values of bulk organic carbon, or plant waxes extracted from stalagmites, should be interpreted with caution as the proportion of plant matter on the landscape does not necessarily equate to the proportion of organic molecules produced by those plants or preserved in the sedimentary record.Publication Uncertainty in REDD plus carbon accounting: a survey of experts involved in REDD plus reporting(2024)BackgroundReducing Emissions from Deforestation and forest Degradation (REDD+) is a program established under the United Nations Framework Convention on Climate Change (UNFCCC) to reduce carbon emissions from forests in developing countries. REDD+ uses an incentive-based approach whereby participating countries are paid to reduce forest carbon loss and increase carbon storage. Country-level carbon accounting is challenging, and estimates of uncertainty in emission reductions are increasingly required in REDD+ reports. This requirement is hard to meet if countries lack the necessary resources, tools, and capabilities. Some REDD+ programs adjust their payments for the uncertainty reported, which presents a perverse incentive because uncertainties are larger if more sources of uncertainty are reported. We surveyed people involved in REDD+ reporting to assess current capacities and barriers to improving estimates of uncertainty.ResultsRepresentatives from 27 countries (44% of REDD+ countries at the time of survey implementation) responded to the survey. Nearly all respondents thought it important to include uncertainty in REDD+ reports, but most felt that the uncertainty reporting by their countries was inadequate. Our independent assessment of reports by these countries to the UNFCCC supported this opinion: Most countries reported uncertainty in activity data (91%) but not in emission factors (4-14%). Few countries use more advanced approaches to estimate uncertainty, such as Monte Carlo and Bayesian techniques, and many respondents indicated that they lack expertise, knowledge, or technical assistance. Other barriers include lack of financial resources and appropriate data. Despite these limitations, nearly all respondents indicated a strong desire to improve estimates of uncertainty in REDD+ reports.ConclusionsThe survey indicated that people involved in REDD+ reporting think it highly important to improve estimates of uncertainty in forest carbon accounting. To meet this challenge, it is essential to understand the obstacles countries face in quantifying uncertainty so we can identify where best to allocate efforts and funds. Investments in training and resources are clearly needed to better quantify uncertainty and would likely have successful outcomes given the strong desire for improvement. Tracking the efficacy of programs implemented to improve estimates of uncertainty would be useful for making further refinements.Publication Economic shocks and skill acquisition: Evidence from a national online learning platform at the onset of COVID-19(2024)We study how large shocks impact individuals' skilling decisions using data from a large, government- sponsored, online learning platform in Saudi Arabia. The onset of the COVID-19 pandemic brought about a massive increase in online skilling, and demand shifted towards courses that offered skills, such as telework, likely to be immediately valuable during the pandemic. Consistent with a model where individuals trade off reskilling costs with their expectations of future labor market conditions and their duration of work, we find that shifts into telework courses were largest for older workers. In contrast, younger workers increased enrollments in courses related to new skills, such as general, occupation-specific, and computer-related skills. Using national administrative employment data, we provide descriptive evidence that these investments in skills in early 2020 helped users maintain employment over the course of the pandemic.
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