Browsing by Author "Dee, Sylvia G."
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Item 4500-year paleohurricane record from the Western Gulf of Mexico, Coastal Central TX, USA(Elsevier, 2024) Monica, Sarah B.; Wallace, Davin J.; Wallace, Elizabeth J.; Du, Xiaojing; Dee, Sylvia G.; Anderson, John B.Texas receives the second-highest number of tropical cyclone (TC) landfalls per year in the United States. At present, long-term TC projections from climate models remain uncertain due to the short and biased nature of Atlantic TC observations. Sediment archives of past storms can help extend the observational record of TC strikes over the past few millennia. When a TC makes landfall along the central Texas coast, coastal downwelling channels and storm currents transport and deposit coarse sediment to a zone of rapid accumulation along the shelf, known as the Texas Mud Blanket (TMB). This “backwash” process results in expansive storm deposits along the shelf, making this region ideal for paleotempestological reconstructions. Here, we present two sediment cores, located approximately 6 km southeast of Matagorda Island (TX), that collectively yield a ∼4500-year paleohurricane record. 210Pb and 137Cs are utilized in conjunction with radiocarbon ages to produce high-resolution Bayesian age models. One-centimeter interval grain size analyses are used to identify TC deposits. Two-centimeter interval X-Ray Fluorescence (XRF) is used as an additional measure to verify depositional mechanisms in this shelf environment. We define an intense paleohurricane event threshold through statistical analysis of mean grain size data. The sediment-derived TC record is correlated to Palmer Drought Severity Index (PDSI) data from Paleo Hydrodynamics Data Assimilation (PHYDA) to bolster our interpretation of the TC record, revealing a coupled relationship between PDSI and TCs since ∼300 yr BP. Over the ∼4500-year period, 24 intense TCs were recorded in the sediment record, yielding a long-term annual landfall probability of ∼0.53%. Additionally, comparisons between other TC records within the Atlantic establish a relationship between enhanced TC activity in the Western Gulf of Mexico (GOM) and TCs formed in the Caribbean Sea.Item ENSO's Response to Volcanism in a Data Assimilation-Based Paleoclimate Reconstruction Over the Common Era(Wiley, 2022) Dee, Sylvia G.; Steiger, Nathan J.The tropical response to explosive volcanism remains underconstrained in the paleoclimate record. While the atmosphere cools due to aerosol forcing following volcanic eruptions, modeling evidence suggests that the tropical Pacific responds with compensatory warming. Given the rarity of large volcanic eruptions and the short instrumental record, these modeling results require independent verification. Here, we test for links between volcanism and tropical Pacific dynamics using the newly developed Paleo Hydrodynamics Data Assimilation product (PHYDA), which spans the past 2,000 years. Using Pacific sea surface temperature fields from PHYDA and coincident volcanic eruptions, we test the response of the El Niño–Southern Oscillation (ENSO) to large, tropical volcanic eruptions. We identify a weak El Niño-like response of the tropical Pacific in the year following sufficiently large, tropical volcanic eruptions. While the response is not significant at the 95% confidence level using superposed epoch analysis (SEA) and self-organizing maps, a significant result does emerge when employing probability density functions. Our results indicate that the widely used SEA approach, based on composite averaging, may not be sufficiently sensitive to capture an ENSO response in the presence of large internal variability. We additionally conclude that inconsistencies in both the spatial patterns and magnitudes between climate models and PHYDA results indicate that current models overestimate the regional tropical response to volcanic forcing.Item Increasing Health Risks During Outdoor Sports Due To Climate Change in Texas: Projections Versus Attitudes(Wiley, 2022) Dee, Sylvia G.; Nabizadeh, Ebrahim; Nittrouer, Christine L.; Baldwin, Jane W.; Li, Chelsea; Gaviria, Lizzy; Guo, Selena; Lu, Karen; Saunders-Shultz, Beck Miguel; Gurwitz, Emily; Samarth, Gargi; Weinberger, Kate R.Extreme heat is a recognized threat to human health. This study examines projected future trends of multiple measures of extreme heat across Texas throughout the next century, and evaluates the expected climate changes alongside Texas athletic staff (coach and athletic trainer) attitudes toward heat and climate change. Numerical climate simulations from the recently published Community Earth System Model version 2 and the Climate Model Intercomparison Project were used to predict changes in summer temperatures, heat indices, and wet bulb temperatures across Texas and also within specific metropolitan areas. A survey examining attitudes toward the effects of climate change on athletic programs and student athlete health was also distributed to high-school and university athletic staff. Heat indices are projected to increase beyond what is considered healthy/safe limits for outdoor sports activity by the mid-to-late 21st century. Survey results reveal a general understanding and acceptance of climate change and a need for adjustments in accordance with more dangerous heat-related events. However, a portion of athletic staff still do not acknowledge the changing climate and its implications for student athlete health and their athletic programs. Enhancing climate change and health communication across the state may initiate important changes to athletic programs (e.g., timing, duration, intensity, and location of practices), which should be made in accordance with increasingly dangerous temperatures and weather conditions. This work employs a novel interdisciplinary approach to evaluate future heat projections alongside attitudes from athletic communities toward climate change.Item Lipid Biomarker Record Documents Hydroclimatic Variability of the Mississippi River Basin During the Common Era(Wiley, 2020) Muñoz, Samuel E.; Porter, Trevor J.; Bakkelund, Aleesha; Nusbaumer, Jesse; Dee, Sylvia G.; Hamilton, Brynnydd; Giosan, Liviu; Tierney, Jessica E.Floods and droughts in the Mississippi River basin are perennial hazards that cause severe economic disruption. Here we develop and analyze a new lipid biomarker record from Horseshoe Lake (Illinois, USA) to evaluate the climatic conditions associated with hydroclimatic extremes that occurred in this region over the last 1,800 years. We present geochemical proxy evidence of temperature and moisture variability using branched glycerol dialkyl glycerol tetraethers (brGDGTs) and plant leaf wax hydrogen isotopic composition (δ2Hwax) and use isotope‐enabled coupled model simulations to diagnose the controls on these proxies. Our data show pronounced warming during the Medieval era (CE 1000–1,600) that corresponds to midcontinental megadroughts. Severe floods on the upper Mississippi River basin also occurred during the Medieval era and correspond to periods of enhanced warm‐season moisture. Our findings imply that projected increases in temperature and warm‐season precipitation could enhance both drought and flood hazards in this economically vital region.Item PRYSM v2.0: A Proxy System Model for Lacustrine Archives(Wiley, 2018) Dee, Sylvia G.; Russell, James M.; Morrill, Carrie; Chen, Zihan; Neary, AshlingReconstructions of temperature and hydrology from lake sedimentary archives have made fundamental contributions to our understanding of past, present, and future climate and help evaluate general circulation models (GCMs). However, because paleoclimate observations are an indirect (proxy) constraint on climatic variables, confounding effects of proxy processes complicate interpretations of these archives. To circumvent these uncertainties inherent to paleoclimate data‐model comparison, proxy system models (PSMs) provide transfer functions between climate variables and the proxy. We here present a new PSM for lacustrine sedimentary archives. The model simulates lake energy and water balance, sensors including leaf wax δD and carbonate δ18O, bioturbation, and compaction of sediment to lend insight toward how these processes affect and potentially obfuscate the original climate signal. The final product integrates existing and new models to yield a comprehensive, modular, adaptable, and publicly available PSM for lake systems. Highlighting applications of the PSM, we forward model lake variables with GCM simulations of the last glacial maximum and the modern. The simulations are evaluated with a focus on sensitivity of lake surface temperature and mixing to climate forcing, using Lakes Tanganyika and Malawi as case studies. The PSM highlights the importance of mixing on interpretations of air temperature reconstructions from lake archives and demonstrates how changes in mixing depth alone may induce nonstationarity between in situ lake and air temperatures. By placing GCM output in the same reference frame as lake paleoclimate archives, we aim to improve interpretations of past changes in terrestrial temperatures and water cycling.Item Race and ethnic minority, local pollution, and COVID-19 deaths in Texas(Springer Nature, 2022) Xu, Annie; Loch-Temzelides, Ted; Adiole, Chima; Botton, Nathan; Dee, Sylvia G.; Masiello, Caroline A.; Osborn, Mitchell; Torres, Mark A.; Cohan, Daniel S.The costs of COVID-19 are extensive, and, like the fallout of most health and environmental crises in the US, there is growing evidence that these costs weigh disproportionately on communities of color. We investigated whether county-level racial composition and fine particulate pollution (PM2.5) are indicators for COVID-19 incidence and death rates in the state of Texas. Using county-level data, we ran linear regressions of percent minority as well as historic 2000–2016 PM2.5 levels against COVID-19 cases and deaths per capita. We found that a county's percent minority racial composition, defined as the percentage of population that identifies as Black or Hispanic, highly correlates with COVID-19 case and death rates. Using Value-of-Statistical-Life calculations, we found that economic costs from COVID-19 deaths fall more heavily on Black and Hispanic residents in Harris County, the most populous county in Texas. We found no consistent evidence or significant correlations between historic county-average PM2.5 concentration and COVID-19 incidence or death. Our findings suggest that public health and economic aid policy should consider the racially-segregated burden of disease to better mitigate costs and support equity for the duration and aftermath of health crises.Item Reduced Lower Mississippi River Discharge During the Medieval Era(Wiley, 2021) Wiman, Charlotte; Hamilton, Brynnydd; Dee, Sylvia G.; Muñoz, Samuel E.Changes in climate are expected to influence discharge of the lower Mississippi River, but projections disagree on whether discharge will increase or decrease over the coming century. Using a reconstructed median peak annual flow for the past 1,500 years based on geomorphic scaling laws, we show that discharge on the lower Mississippi River decreased during the Medieval era (c. 1000–1200 CE)—a period of regionally warm and dry conditions that serves as a partial analog for projected warming. These changes in discharge inferred from channel morphology track discharge simulated in the Community Earth System Model Last Millennium Ensemble. Simulations show that decreased Medieval era discharge is driven primarily by regionally enhanced evapotranspiration. Our findings are consistent with 21st century projections of decreased discharge on the lower Mississippi River under moderate greenhouse forcing scenarios, and demonstrate consistency between reconstructed and simulated discharge over the last millennium.Item The Future of Reef Ecosystems in the Gulf of Mexico: Insights From Coupled Climate Model Simulations and Ancient Hot-House Reefs(Frontiers, 2019) Dee, Sylvia G.; Torres, Mark A.; Martindale, Rowan C.; Weiss, Anna; DeLong, Kristine L.Shallow water coral reefs and deep sea coral communities are sensitive to current and future environmental stresses, such as changes in sea surface temperatures (SST), salinity, carbonate chemistry, and acidity. Over the last half-century, some reef communities have been disappearing at an alarming pace. This study focuses on the Gulf of Mexico, where the majority of shallow coral reefs are reported to be in poor or fair condition. We analyze the RCP8.5 ensemble of the Community Earth System Model v1.2 to identify monthly-to-decadal trends in Gulf of Mexico SST. Secondly, we examine projected changes in ocean pH, carbonate saturation state, and salinity in the same coupled model simulations. We find that the joint impacts of predicted higher temperatures and changes in ocean acidification will severely degrade Gulf of Mexico reef systems by the end of the twenty-first century. SSTs are likely to warm by 2.5–3°C; while corals do show signs of an ability to adapt toward higher temperatures, current coral species and reef systems are likely to suffer major bleaching events in coming years. We contextualize future changes with ancient reefs from paleoclimate analogs, periods of Earth's past that were also exceptionally warm, specifically rapid “hyperthermal” events. Ancient analog events are often associated with extinctions, reef collapse, and significant ecological changes, yet reef communities managed to survive these events on evolutionary timescales. Finally, we review research which discusses the adaptive potential of the Gulf of Mexico's coral reefs, meccas of biodiversity and oceanic health. We assert that the only guaranteed solution for long-term conservation and recovery is substantial, rapid reduction of anthropogenic greenhouse gas emissions.