Browsing by Author "Escobar, Jaime"
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Item Appearance of an enigmatic Pb source in South America around 2000 BP: Anthropogenic vs natural origin(Elsevier, 2020-05) Kamenov, George D.; Escobar, Jaime; Arnold, T. Elliott; Pardo-Trujillo, Andrés; Gangoiti, Gotzon; Hoyos, Natalia; Curtis, Jason H.; Bird, Broxton W.; Velez, Maria Isabel; Vallejo, Felipe; Trejos-Tamayo, Raul; Earth and Environmental Sciences, School of ScienceNeotropical wetlands in the paramo (a unique alpine-tundra ecosystem) region of South America have the potential to be natural archives for metal pollution by modern and past populations. An organic-rich sediment core from the El Triunfo mire, located in the paramo region, provides a record of natural and anthropogenic metal sources in the Northern Andes during the last four millennia. The Triunfo record is complex, as the mire is located in the Northern Volcanic Zone (NVZ) and receives direct input of volcanic material. Regardless of the volcanic input, calculated metal enrichment factors normalized to Sc show metal enrichment in the Northern Andes around 2000 years ago and again in recent industrial times. A number of samples show a shift to lower Pb isotope ratios indicating the appearance of a new, enigmatic Pb source around 2000 years ago. The topmost layer of the core shows the lowest Pb isotope ratios, reflecting input of modern anthropogenic Pb. In contrast to Pb, Nd isotopes do not show significant variations along the entire core, indicating mostly volcanic material input to the mire. The decoupling between Nd and Pb isotopes indicates that the enigmatic Pb source must be anthropogenic in origin. Based on the dominant atmospheric currents in the region, the El Triunfo mire can receive input from long-distance and local sources. Dispersion simulations validate the possibility of pollutant particle transport from Europe to the northern hemisphere Neotropics. As the first metal enrichment coincides with the Roman Empire times, the El Triunfo Pb isotopes are compared to contemporary peat records from Europe. All records show similar decrease in the Pb isotope ratios due to anthropogenic Pb input. Small Pb isotope differences between a record from Spain and El Triunfo indicate that the enigmatic Pb that appeared around 2000 years ago in the mire is unlikely to have originated from long-distance Roman Empire pollution. Instead, a group of deposits, namely San Lucas, San Martin de Loba, and El Bagre, located in north-central Colombia, show low Pb isotope ratios that can potentially explain the observed Pb signal in the El Triunfo sediments. The deposits are located up wind, along the predominant atmospheric currents in the region. Therefore, it is plausible that mining activities in the area of San-Lucas, San-Martin, and/or El Bagre released Pb in the atmosphere that was transported and deposited in the El Triunfo mire. These deposits are not associated with the known regions of influence of any of the early pre-Hispanic cultures in Colombia and there is no evidence for mining in this region around 2000 years ago. However, given that all other possibilities are unlikely, the appearance of lower Pb isotope ratios in the mire suggests the onset of mining in the region at least 400 years earlier than the available archaeological evidence at present. The El Triunfo mire record can be used as indirect evidence for significant metal exploitation by early pre-Hispanic cultures in the northern Andes as early as 2000 years ago.Item Characterizing late Quaternary lake-level variability in Lago de Tota, Colombian Andes, with CHIRP seismic stratigraphy(Springer, 2019) Gibson, Derek K.; Bird, Broxton W.; Wattrus, Nigel J.; Escobar, Jaime; Ahmed, Maliha; Fonseca, Hector; Velasco, Felipe; Fernandez, Alejandro; Polissar, Pratigya J.; Earth Sciences, School of ScienceGeophysical analysis of lacustrine sediment stratigraphy at Lago de Tota (Tota), Boyaca, Colombia provided evidence for significant lake-level fluctuations through the late Quaternary and produced a record that potentially spans the last 60 ka. CHIRP data collected in 2015 from this large, high-elevation lake in the Eastern Cordillera of the northern hemisphere Colombian Andes reveal a series of off-lap and on-lap sequences in the upper ~ 20 m of the lake’s sediment column that indicate large amplitude changes in lake level. Because 14C dated sediment cores are only available for the upper 3 m of the sediment column, known Holocene sedimentation rates were extrapolated in order to assign preliminary ages to the off-lap and on-lap sequence boundaries below 3 m depth. These data suggest that lake levels at Tota were lower than present during marine isotope stage (MIS) 4 between 60 and 57 ka, relatively high during MIS 3 between 57 and 29 ka, fell to their lowest levels during MIS 2 between 29 and 14 ka, and gradually rose to the modern high stand through a series of transgressions during MIS 1 and the Holocene from ~ 14 ka to the present. These fluctuations are broadly consistent with trends observed in other lake-level reconstructions from the northern (in phase) and southern (out of phase) hemisphere Andes, possibly supporting the idea that millennial-to-orbital-scale South American hydroclimate variability is linked to shifts in the mean latitude of the intertropical convergence zone due to the influence of insolation- and ocean circulation-driven hemispheric temperature gradients during glacial/stadial and interglacial/interstadial events. Although additional geochronological data will be needed to better resolve the timing of the Tota lake-level changes and their relationships with other records, these preliminary results from Tota, as well as the presence of a thick (> 300 m) sedimentary archive, indicate that this site has significant potential to produce high-resolution, quantitative, paleo-hydroclimate data spanning much of the last 1 million years. Because geophysical surveys and long paleoclimate records from northern hemisphere South America are exceedingly rare, these data provide critical insight into regional hydroclimate trends through the Late Quaternary. Additional work, such as the collection of sediment cores spanning the depth interval represented in the CHIRP data, is required, however, in order to place firmer chronological constraints on the hypothesized timing of lake-level fluctuations at Tota and to investigate their paleo-hydroclimatic implications.Item Late Quaternary hydroclimate variability in the Colombian Andes and the potential for deep sediment core recovery at Lago de Tota revealed through CHIRP and airgun-sourced seismic reflection data(AGU, 2018-12) Gibson, Derek; Bird, Broxton W.; Watruss, Nigel; Escobar, Jaime; Lowell, Thomas V.; Ahmed, Maliha; Fonseca, Hector; Velasco, Felipe; Fernandez, Alejandro; Polissar, Pratigya J.A geophysical investigation of lacustrine stratigraphy at Lago de Tota (Tota), Boyaca, Colombia provides evidence for significant lake level fluctuations during the late Quaternary from ~60 ka to the present. CHIRP data collected in 2015 from this large, high-elevation lake in the Eastern Cordillera of the Northern Hemisphere (NH) Colombian Andes reveal a series of off-lap and on-lap sequences in the upper ~20 m of the lake’s sediment column that indicate large amplitude changes in lake level. These data, temporally constrained by 14C-dated sediment cores and extrapolated Holocene sedimentation rates, suggest that lake levels at Tota were lower than present during Marine Isotope Stage (MIS) 4 between 60 and 57 ka, relatively high during MIS 3 between 57 and 29 ka, fell to their lowest levels during MIS 2 between 29 and 14 ka, and gradually rose to the modern high-stand through a series of transgressions during MIS 1 and the Holocene from ~14 ka to the present. These fluctuations are broadly consistent with trends observed in other lake level reconstructions from the Northern (in phase) and Southern (out of phase) Hemisphere Andes, possibly supporting the idea that millennial-to-orbital-scale South American hydroclimate variability is linked to shifts in the mean latitude of the Intertropical Convergence Zone (ITCZ) due to the influence of insolation- and ocean circulation-driven hemispheric temperature gradients during glacial/stadial and interglacial/interstadial events. These results, as well as the presence of a thick (>300 m) sedimentary archive, indicate that Tota has significant potential to produce high-resolution, quantitative, paleo- hydroclimate data spanning much of the last 1 million years. Because geophysical surveys and long paleoclimate records from NH South America are exceedingly rare, these data provide critical insight into regional hydroclimate trends through the Late Quaternary.Item Paleoclimate support for a persistent dry island effect in the Colombian Andes during the last 4700 years(Sage, 2018-02) Bird, Broxton W.; Rudloff, Owen; Escobar, Jaime; Gilhooly, William P., III; Correa-Metrio, Alex; Vélez, Maria; Polissar, Pratigya J.; Earth Sciences, School of ScienceWe investigated middle- and late-Holocene hydroclimate patterns in the Colombian Andes using indicators of watershed erosion (lithic abundance), precipitation intensity (% silt), lake-level variability (organic carbon and nitrogen, % sand, and diatoms), and fire frequency (fossil charcoal) from a ~4700-year-long sediment archive from Laguna de Ubaque, a small sub-alpine lake on the eastern flank of the eastern Colombian Andes. Our results indicate reduced precipitation, low lake levels, and increased fire occurrence at Ubaque between 4700 and 3500 cal. yr BP (hereafter BP). Precipitation and lake levels increased abruptly while fire occurrence decreased between 3500 and 2100 BP, with the exception of a 300-year dry phase between 2800 and 2500 BP. Although wetter than the 4700–3500 BP interval, precipitation decreased, lake levels fell, and fire occurrence increased after 2100 BP, but with high-frequency variability. Comparison of the Ubaque results with other Colombian paleoclimate records (e.g. Lakes Fúquene and La Cocha) supports an antiphase pattern of precipitation between the high/interior Andes and frontal slope sites. This spatial pattern of variability is consistent with modern responses to the changes in terrestrial atmospheric convection associated with the so-called ‘dry island’ effect. Further comparison with paleoclimate records from Venezuela suggests that the millennial trend toward increasing frontal slope precipitation is consistent with orbitally induced increases in Andean atmospheric convection. Sub-orbital dry island–like hydroclimate variability suggests that other mechanisms that affect Northern Hemisphere convection may act to enhance or diminish this effect on centennial and shorter timescales.Item Pre-Columbian lead pollution from Native American galena processing and land use in the midcontinental United States(GSA, 2019-10) Bird, Broxton W.; Wilson, Jeremy J.; Escobar, Jaime; Kamenov, George D.; Pollard, Harvie J.; Monaghn, G. William; Earth Sciences, School of ScienceThe presence and sources of pre-Columbian (before 1492 CE) lead (Pb) pollution in the midcontinental United States were investigated using geochemical and Pb isotope analyses on sediment cores recovered from Avery Lake, a floodplain lake located directly adjacent to the Kincaid Mounds archaeological site on the lower Ohio River, Illinois. Geochemical results indicate the presence of Pb pollution during the Baumer (300 BCE to 300 CE) and Mississippian (1150–1450 CE) occupations, and since the 1800s. Pb isotope results link Mississippian Pb pollution to the processing and use of galena primarily from southeastern and/or central Missouri, and to a lesser extent the upper Mississippi River valley, with ∼1.5 t (metric tons) of galena-derived Pb deposited in Avery Lake during this time. Pb pollution during the Baumer phase, equating to ∼0.4 t of Pb, was not accompanied by a Pb isotope excursion and most likely originated from local biomass burning. These results provide new information about the environmental impacts associated with pre-Columbian Native Americans’ interaction with and utilization of their landscape and its resources.Item Using sediment accumulation rates in floodplain paleochannel lakes to reconstruct climate-flood relationships on the lower Ohio River(Elsevier, 2022-12-15) Gibson , Derek K.; Bird, Broxton W.; Pollard, Harvie J.; Nealy, Cameron A.; Barr, Robert C.; Escobar, Jaime; Earth and Environmental Sciences, School of ScienceLate Holocene flood frequencies on the lower Ohio River were investigated using 14C-based sedimentation rates from three floodplain lakes located in Illinois (Avery Lake), Kentucky (Grassy Pond), and Indiana (Goose Pond). Changes in sediment accumulation rates were attributed to variability in the delivery of overbank sediment to each site as controlled by the frequency of Ohio River flooding. Sedimentation rates reached their lowest values in all three lakes between 400 and 1230 CE, indicating a regional reduction in flood frequencies on the lower Ohio River during a period that included the Medieval Climate Anomaly (MCA; ca. 950–1250 CE). Sedimentation rates increased after ca. 1230 CE and remained moderately high through the Little Ice Age (LIA; 1350–1820 CE) until the onset of extensive land clearance during the early 1800s CE. After 1820 CE, sedimentation rates increased further and were higher than any other time during the late Holocene. A comparison of regional paleoclimatic proxies with the above floodplain sedimentation records shows that Ohio River flooding during the late Holocene was responsive to mean-state changes in atmospheric circulation. During the MCA, when clockwise mean-state atmospheric circulation advected southerly moisture from the Gulf of Mexico into the Ohio River Valley primarily in the form of convective rainstorms, flooding on the Ohio River was least frequent. During the LIA, meridional mean-state atmospheric circulation increased the proportion of midcontinental moisture that was sourced from the northern Pacific and Arctic and delivered as snowfall, hence increasing flooding on the Ohio River. We attribute the increase in Ohio River flooding during the LIA to an increase in snowpack volume across the Ohio River Valley and the watershed-scale integration of runoff during spring snowmelt. Following Euro-American land clearance in the early 1800s, flood frequencies decoupled from this relationship and the lower Ohio River became susceptible to frequent flooding, despite a return to southerly and clockwise synoptic atmospheric conditions. These modern climate-flood dynamics are fundamentally different than those of the paleo-record and suggest that land-use changes – such as deforestation, tile draining, and landscape conversion to intensive row crop agriculture – have fundamentally altered the modern Midwestern hydrologic cycle.