Browsing by Author "Torres, Mark A."
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Item Arctic Permafrost Thawing Enhances Sulfide Oxidation(Wiley, 2023) Kemeny, Preston Cosslett; Li, Gen K.; Douglas, Madison; Berelson, William; Chadwick, Austin J.; Dalleska, Nathan F.; Lamb, Michael P.; Larsen, William; Magyar, John S.; Rollins, Nick E.; Rowland, Joel; Smith, M. Isabel; Torres, Mark A.; Webb, Samuel M.; Fischer, Woodward W.; West, A. JoshuaPermafrost degradation is altering biogeochemical processes throughout the Arctic. Thaw-induced changes in organic matter transformations and mineral weathering reactions are impacting fluxes of inorganic carbon (IC) and alkalinity (ALK) in Arctic rivers. However, the net impact of these changing fluxes on the concentration of carbon dioxide in the atmosphere (pCO2) is relatively unconstrained. Resolving this uncertainty is important as thaw-driven changes in the fluxes of IC and ALK could produce feedbacks in the global carbon cycle. Enhanced production of sulfuric acid through sulfide oxidation is particularly poorly quantified despite its potential to remove ALK from the ocean-atmosphere system and increase pCO2, producing a positive feedback leading to more warming and permafrost degradation. In this work, we quantified weathering in the Koyukuk River, a major tributary of the Yukon River draining discontinuous permafrost in central Alaska, based on water and sediment samples collected near the village of Huslia in summer 2018. Using measurements of major ion abundances and sulfate (SO42− {\textSO_4^2-\) sulfur (34S/32S) and oxygen (18O/16O) isotope ratios, we employed the MEANDIR inversion model to quantify the relative importance of a suite of weathering processes and their net impact on pCO2. Calculations found that approximately 80% of SO42− {\textSO_4^2-\ in mainstem samples derived from sulfide oxidation with the remainder from evaporite dissolution. Moreover, 34S/32S ratios, 13C/12C ratios of dissolved IC, and sulfur X-ray absorption spectra of mainstem, secondary channel, and floodplain pore fluid and sediment samples revealed modest degrees of microbial sulfate reduction within the floodplain. Weathering fluxes of ALK and IC result in lower values of pCO2 over timescales shorter than carbonate compensation (∼104 yr) and, for mainstem samples, higher values of pCO2 over timescales longer than carbonate compensation but shorter than the residence time of marine SO42− {\textSO_4^2-\ (∼107 yr). Furthermore, the absolute concentrations of SO42− {\textSO_4^2-\ and Mg2+ in the Koyukuk River, as well as the ratios of SO42− {\textSO_4^2-\ and Mg2+ to other dissolved weathering products, have increased over the past 50 years. Through analogy to similar trends in the Yukon River, we interpret these changes as reflecting enhanced sulfide oxidation due to ongoing exposure of previously frozen sediment and changes in the contributions of shallow and deep flow paths to the active channel. Overall, these findings confirm that sulfide oxidation is a substantial outcome of permafrost degradation and that the sulfur cycle responds to permafrost thaw with a timescale-dependent feedback on warming.Item High rates of rock organic carbon oxidation sustained as Andean sediment transits the Amazon foreland-floodplain(National Academy of Sciences, 2023) Dellinger, Mathieu; Hilton, Robert G.; Baronas, J. Jotautas; Torres, Mark A.; Burt, Emily I.; Clark, Kasey E.; Galy, Valier; Ccahuana Quispe, Adan Julian; West, A. JoshuaThe oxidation of organic carbon contained within sedimentary rocks (“petrogenic” carbon, or hereafter OCpetro) emits nearly as much CO2 as is released by volcanism, thereby playing a key role in the long-term global C budget. High erosion rates in mountains have been shown to increase OCpetro oxidation. However, these settings also export unweathered material that may continue to react in downstream floodplains. The relative importance of OCpetro oxidation in mountains versus floodplains remains difficult to assess as disparate methods have been used in the different environments. Here, we investigate the sources and fluxes of rhenium (Re) in the Rio Madre de Dios to quantify OCpetro oxidation from the Andes to the Amazon floodplain using a common approach. Dissolved rhenium concentrations (n = 131) range from 0.01 to 63 pmol L−1 and vary depending on lithology and geomorphic setting. We find that >75% of the dissolved Re derives from OCpetro oxidation and that this proportion increases downstream. We estimate that in the Andes, OCpetro oxidation releases 11.2+4.5/−2.8 tC km−2 y−1 of CO2, which corresponds to ~41% of the total OCpetro denudation (sum of oxidized and solid OCpetro). A Re mass balance across the Rio Madre de Dios shows that 46% of OCpetro oxidation takes place in the Andes, 14% in the foreland-lowlands, and 40% in the Andean-fed floodplains. This doubling of OCpetro oxidation flux downstream of the Andes demonstrates that, when present, floodplains can greatly increase OCpetro oxidation and CO2 release.Item Land Use and Land Cover Shape River Water Quality at a Continental Caribbean Land-Ocean Interface(Frontiers Media S.A., 2022) Clark, Kasey E.; Bravo, Viviana D.; Giddings, Sarah N.; Davis, Kristen A.; Pawlak, Geno; Torres, Mark A.; Adelson, Anne E.; César-Ávila, Carolina I.; Boza, Ximena; Collin, RachelLand use and land cover (LULC) can significantly alter river water, which can in turn have important impacts on downstream coastal ecosystems by delivering nutrients that promote marine eutrophication and hypoxia. Well-documented in temperate systems, less is known about the way land cover relates to water quality in low-lying coastal zones in the tropics. Here we evaluate the catchment LULC and the physical and chemical characteristics of six rivers that contribute flow into a seasonally hypoxic tropical bay in Bocas del Toro, Panama. From July 2019 to March 2020, we routinely surveyed eight physical and chemical characteristics (temperature, specific conductivity, salinity, pH, dissolved oxygen (DO), nitrate and nitrite, ammonium, and phosphate). Our goals were to determine how these physical and chemical characteristics of the rivers reflect the LULC, to compare the water quality of the focal rivers to rivers across Panama, and to discuss the potential impacts of river discharge in the Bay. Overall, we found that the six focal rivers have significantly different river water characteristics that can be linked to catchment LULC and that water quality of rivers 10 s of kilometers apart could differ drastically. Two focal catchments dominated by pristine peat swamp vegetation in San San Pond Sak, showed characteristics typical of blackwater rivers, with low pH, dissolved oxygen, and nutrients. The remaining four catchments were largely mountainous with >50% forest cover. In these rivers, variation in nutrient concentrations were associated with percent urbanization. Comparisons across Panamanian rivers covered in a national survey to our focal rivers shows that saltwater intrusions and low DO of coastal swamp rivers may result in their classification by a standardized water quality index as having slightly contaminated water quality, despite this being their natural state. Examination of deforestation over the last 20 years, show that changes were <10% in the focal catchments, were larger in the small mountainous catchments and suggest that in the past 20 years the physical and chemical characteristics of river water that contributes to Almirante Bay may have shifted slightly in response to these moderate land use changes. (See supplementary information for Spanish-language abstract).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 Riverine evidence for isotopic mass balance in the Earth’s early sulfur cycle(Springer Nature, 2018) Torres, Mark A.; Paris, Guillaume; Adkins, Jess F.; Fischer, Woodward W.During a time of negligible atmospheric pO2, Earth’s early sulfur cycle generated a spectacular geological signal seen as the anomalous fractionation of multiple sulfur isotopic ratios. The disappearance of this signal from the geologic record has been hypothesized to constrain the timing of atmospheric oxygenation, although interpretive challenges exist. Asymmetry in existing S isotopic data, for example, suggests that the Archaean crust was not mass balanced, with the implication that the loss of S isotope anomalies from the geologic record might lag the rise of atmospheric O2. Here, we present new S isotopic analyses of modern surface and groundwaters that drain Archaean terrains in order to independently evaluate Archaean S cycle mass balance. Natural waters contain sulfur derived from the underlying bedrock and thus can be used to ascertain its S isotopic composition at scales larger than typical geological samples allow. Analyses of 52 water samples from Canada and South Africa suggest that the Archaean crust was mass balanced with an average multiple S isotopic composition equivalent to the bulk Earth. Overall, our work supports the hypothesis that the disappearance of multiple S isotope anomalies from the sedimentary record provides a robust proxy for the timing of the first rise in atmospheric O2.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.