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Browsing by Author "Bird, Broxton W."
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ItemA 2,300-year-long annually resolved record of the South American summer monsoon from the Peruvian Andes(PNAS, 2011-05-24) Bird, Broxton W.; Abbott, Mark B.; Vuille, Mathias; Rodbell, Donald T.; Stansell, Nathan D.; Rosenmeier, Michael F. ItemA 2000 year varve-based climate record from the central Brooks Range, Alaska(Springer, 2009-01-01) Bird, Broxton W.; Abbott, Mark B.; Finney, Bruce P.; Kutchko, BarbaraVarved minerogenic sediments from glacial-fed Blue Lake, northern Alaska, are used to investigate late Holocene climate variability. Varve-thickness measurements track summer temperature recorded at Atigun Pass, located 41 km east at a similar elevation (r2 = 0.31, P = 0.08). Results indicate that climate in the Brooks Range from 10 to 730 AD (varve year) was warm with precipitation inferred to be higher than during the twentieth century. The varve-temperature relationship for this period was likely compromised and not used in our temperature reconstruction because the glacier was greatly reduced, or absent, exposing sub-glacial sediments to erosion from enhanced precipitation. Varve-inferred summer temperatures and precipitation decreased after 730 AD, averaging 0.4°C above the last millennial average (LMA = 4.2°C) from 730 to 850 AD, and 0.1°C above the LMA from 850 to 980 AD. Cooling culminated between 980 and 1030 AD with temperatures 0.7°C below the LMA. Varve-inferred summer temperatures increased between 1030 and 1620 AD to the LMA, though the period between 1260 and 1350 AD was 0.2°C below the LMA. Although there is no equivalent to the European Medieval Warm Period in the Blue Lake record, two warm intervals occurred from 1350 to 1450 AD and 1500 to 1620 AD (0.4 and 0.3°C above the LMA, respectively). During the Little Ice Age (LIA; 1620 to 1880 AD), inferred summer temperature averaged 0.2°C below the LMA. After 1880 AD, inferred summer temperature increased to 0.8°C above the LMA, glaciers retreated, but aridity persisted based on a number of regional paleoclimate records. Despite warming and glacial retreat, varve thicknesses have not achieved pre-730 AD levels. This reflects limited sediment availability and transport due to a less extensive retreat compared to the first millennium, and continued relative aridity. Overall, the Blue Lake record is similar to varve records from the eastern Canadian Arctic that document a cool LIA and twentieth century warming. However, the occurrence and timing of events, such as the LIA and Medieval Warm Period, varies considerably among records, suggesting heterogeneous climatic patterns across the North American Arctic. ItemA 2540-year record of moisture variations derived from lacustrine sediment (Sasikul Lake) on the Pamir Plateau(Sage, 2014-05-06) Lei, Yanbin; Tian, Lide; Bird, Broxton W.; Hou, Juzhi; Ding, Lin; Oimahmadov, Ilhomjon; Gadoev, MustafoAlthough the Pamir Plateau is an ideal place to investigate paleo-environmental changes in the westerlies-dominated high Central Asia, there are only few Holocene records from this region. We present a sub-centennially resolved lacustrine record of moisture variations from Sasikul Lake, central Pamir Plateau, based on geochemical, sedimentological, and mineralogical proxies. Our results show that generally dry conditions at Sasikul Lake during the past 2540 years were interrupted by a pronounced wet period between ad 1550 and 1900, corresponding to the ‘Little Ice Age’ (LIA). More negative values of carbonate δ18O, lower total inorganic carbon (TIC), and sand content during LIA all indicate a relatively wet period with higher lake level. Higher TIC during the ‘Medieval Warm Period’ (MWP; ad 950–1200) reveals a lower lake level relative to the LIA. Low δ18O during this time is probably attributed to changes in the isotopic composition of input water and/or upstream moisture sources. The significant increase in detrital minerals and decrease in carbonate during the LIA provide further evidence for higher allochthonous input during the wet period at Sasikul Lake. The inferred moisture variations are consistent with existing records from regions of the northern Tibetan Plateau and Central Asia that are also influenced by the westerlies, but out-ofphase with those records from the Asian monsoon region, indicating that moisture variations at Sasikul Lake were mainly influenced by the strength and trajectories of the westerlies. The inferred water level at Sasikul Lake decreased significantly during the first half of the 20th century, and then increased in recent decades. This is consistent with the increase in lake area derived from satellite images and the monitoring data of large lake-level changes in Central Asia. ItemA Combined Molecular and Isotopic Study of Sulfur Bacteria in Meromictic Lakes of the Pacific Northwest(2023-12) Harris, James H., IV; Gilhooly, William P., III; Druschel, Gregory K.; Bird, Broxton W.The isotope effects that result from the activity of modern sulfur metabolizing bacteria serve as analogs to interpreting the sulfur isotope values preserved in the geologic record. This biogenic signal is vital to reconstructing the history of Earth’s ancient oceans and atmosphere. However, the isotope compositions imprinted by these bacteria were influenced by multiple factors that must be considered when using these values to make interpretations about environmental change. These factors include: (1) sulfate availability, (2) the rapid and quantitative reoxidation of sulfide (i.e., cryptic sulfur cycling), (3) the initial oxygen isotope compositions of sulfate and water, and (4) the taxonomic structure of sulfur-metabolizing bacterial communities. To address these questions, this project studied four permanently stratified, anoxic and sulfidic (euxinic), lakes in southern British Columbia, Canada, and northern Washington, USA, that have a wide range of sulfate concentrations, from 0.15 – 120 mM. This project resulted in six key findings – (1) the measurement of large Δ34SSO4-H2S values at micromolar sulfate concentrations, (2) the consistent occurrence of δ18OSO4 minima at the chemocline that may be imparted during cryptic sulfur cycling, (3) that subsequent δ18OSO4 enrichments consistently preceded sulfide accumulation and δ34SSO4 enrichment in the suboxic zone of the water column, (4) that initial epilimnion Δ18OSO4-H2O values placed constraints on the maximum extent of δ18OSO4 evolution that occurred beneath the chemocline, (5) that observable changes in the metabolic composition of sulfur bacterial communities accompanied key inflections in the sulfur and oxygen isotope profiles of sulfate and sulfide within the water column, and (6) that, despite large overall differences in community structure, Δ34SSO4-H2S and Δ18OSO4-H2O values ultimately reached similar magnitudes in each lake. ItemAppearance 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 Science, 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. ItemCharacterizing 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. ItemContrasting hydrological and thermal intensities determine seasonal lake-level variations – a case study at Paiku Co on the southern Tibetan Plateau(Copernicus Publications, 2021) Lei, Yanbin; Yao, Tandong; Yang, Kun; Lazhu; Ma, Yaoming; Bird, Broxton W.; Earth Sciences, School of ScienceEvaporation from hydrologically closed lakes is one of the largest components of the lake water budget; however, its effects on seasonal lake-level variations remain unclear on the Tibetan Plateau (TP) due to a lack of comprehensive observations. In this study, weekly lake evaporation and its effects on seasonal lake-level variations are investigated at Paiku Co on the southern TP using in situ observations of thermal structure and hydrometeorology (2015–2018). Lake evaporation from Paiku Co was estimated to be 975±142 mm during the ice-free period (May to December), characterized by low values of 1.7 ± 0.6 mm d−1 during the pre-monsoon season (May to June), high values of 5.5±0.6 mm d−1 during the post-monsoon season (October to December), and intermediate values of 4.0±0.6 mm d−1 during the monsoon season (July to September). There was a ∼ 5-month lag between the maximum net radiation (June) and maximum lake evaporation (November). These results indicate that the seasonal pattern of lake evaporation from Paiku Co was significantly affected by the large lake heat storage. Contrasting hydrological and thermal intensities may play an important role in the large amplitude of seasonal lake-level variations at deep lakes like Paiku Co. High inflow from monsoon precipitation and glacier melting and moderate lake evaporation, for instance, drove rapid lake-level increase during the monsoon season. In contrast, high lake evaporation and reduced inflow caused lake level to decrease significantly during the post-monsoon season. This study implies that lake evaporation may play an important role in the different amplitudes of seasonal lake-level variations on the TP. ItemContrasting sensitivity of lake sediment n-alkanoic acids and n-alkanes to basin-scale vegetation and regional-scale precipitation δ2H in the Adirondack Mountains, NY (USA)(Elsevier, 2020-01) Freimuth, Erika J.; Diefendorf, Aaron F.; Lowell, Thomas V.; Bates, Benjamin R.; Schartman, Anna; Bird, Broxton W.; Landis, Joshua D.; Stewart, Alexander K.; Earth Sciences, School of ScienceThe hydrogen isotope values of plant waxes (δ2Hwax) primarily reflect plant source water. δ2Hwax preserved in lake sediments has therefore been widely used to investigate past hydroclimate. The processes by which plant waxes are integrated at regional and catchment scales are poorly understood and may affect the δ2Hwax values recorded in sediments. Here, we assess the variability of sedimentary δ2Hwax for two plant wax compound classes (n-alkanes and n-alkanoic acids) across 12 lakes in the Adirondack Mountains that receive similar regional precipitation δ2H but vary at the catchment-scale in terms of vegetation structure and basin morphology. Total long-chain (n-C27 to n-C35) alkane concentrations were similar across all sites (191 ± 53 µg/g TOC) while total long-chain (n-C28 and n-C30) alkanoic acid concentrations were more variable (117 ± 116 µg/g TOC) and may reflect shoreline vegetation composition. Lakes with shorelines dominated by evergreen gymnosperm plants had significantly higher concentrations of long-chain n-alkanoic acids relative to n-alkanes, consistent with our observations that deciduous angiosperms produced more long-chain n-alkanes than evergreen gymnosperms (471 and 33 µg/g TOC, respectively). In sediments, the most abundant chain lengths in each compound class were n-C29 alkane and n-C28 alkanoic acid, which had mean δ2H values of −188 ± 6‰ and −164 ± 9‰, respectively. Across sites, the range in sedimentary n-C29 alkane (22‰) and n-C28 alkanoic acid δ2H (35‰) was larger than expected based on the total range in modeled mean annual precipitation δ2H (4‰). We observed larger mean εapp (based on absolute values) for n-alkanes (−123‰) than for n-alkanoic acids (−97‰). Across sites, the δ2H offset between n-C29 alkane and the biosynthetic precursor n-C30 alkanoic acid (εC29-C30) ranged from −8 to −58‰, which was more variable than expected based on observations in temperate trees (−20 to −30‰). Sediments with greater aquatic organic matter contributions (lower C/N ratios) had significantly larger (absolute) εC29-C30 values, which may reflect long-chain n-alkanoic acids from aquatic sources. Concentration and δ2Hwax data in Adirondack lakes suggest that long-chain n-alkanes are more sensitive to regional-scale precipitation signals, while n-alkanoic acids are more sensitive to basin-scale differences in catchment vegetation and wax sourcing. ItemDifferences in forest composition following two periods of settlement by pre-Columbian Native Americans(Springer, 2022-10-01) Commerford, Julie L.; Gittens, Gabrielle; Gainforth, Sydney; Wilson, Jeremy J.; Bird, Broxton W.; Earth Sciences, School of ScienceTemperate broadleaf forests in eastern North America are diverse ecosystems whose vegetation composition has shifted over the last several millennia in response to climatic and human drivers. Yet, detailed records of long-term changes in vegetation composition and diversity in response to known periods of human activity, particularly multiple distinct periods of human activity at the same site, are still relatively sparse. In this study, we examine a sediment record from Avery Lake, Illinois, USA, using multiple metrics derived from pollen data to infer vegetation composition and diversity over the last 3,000 years. This 3,000-year history encompasses the Baumer (300 bce–300 ce) and Mississippian settlements (1150–1450 ce) at Kincaid Mounds (adjacent to Avery Lake), and captures differences in the impact that these groups had on vegetation composition. Both groups actively cleared the local landscape for settlement and horticultural/agricultural purposes. Given the persistence of fire-tolerant Quercus in conjunction with declines in other tree taxa, this clearing likely occurred through the use of fire. We also apply a self-organized mapping technique to the multivariate pollen assemblages to identify similarities and differences in vegetation composition across time. Those results suggest that the vegetation surrounding Avery Lake was compositionally similar before and after the Baumer settlement, but compositionally different after the Mississippian settlement. The end of the Mississippian settlement occurred simultaneously with a regional shift in moisture characterized by drier summers and wetter winters associated with the Little Ice Age (1250–1850 ce), which likely prevented this ecosystem from returning to its pre-Mississippian composition. ItemDisappearance of the last tropical glaciers in the Western Pacific Warm Pool (Papua, Indonesia) appears imminent(National Academy of Sciences, 2019-12-26) Permana, Donaldi S.; Thompson, Lonnie G.; Mosley-Thompson, Ellen; Davis, Mary E.; Lin, Ping-Nan; Nicolas, Julien P.; Bolzan, John F.; Bird, Broxton W.; Mikhalenko, Vladimir N.; Gabrielli, Paolo; Zagorodnov, Victor; Mountain, Keith R.; Schotterer, Ulrich; Hanggoro, Wido; Habibie, Muhammad N.; Kaize, Yohanes; Gunawan, Dodo; Setyadi, Gesang; Susanto, Raden D.; Fernández, Alfonso; Mark, Bryan G.; Earth Sciences, School of ScienceThe glaciers near Puncak Jaya in Papua, Indonesia, the highest peak between the Himalayas and the Andes, are the last remaining tropical glaciers in the West Pacific Warm Pool (WPWP). Here, we report the recent, rapid retreat of the glaciers near Puncak Jaya by quantifying the loss of ice coverage and reduction of ice thickness over the last 8 y. Photographs and measurements of a 30-m accumulation stake anchored to bedrock on the summit of one of these glaciers document a rapid pace in the loss of ice cover and a ∼5.4-fold increase in the thinning rate, which was augmented by the strong 2015–2016 El Niño. At the current rate of ice loss, these glaciers will likely disappear within the next decade. To further understand the mechanisms driving the observed retreat of these glaciers, 2 ∼32-m-long ice cores to bedrock recovered in mid-2010 are used to reconstruct the tropical Pacific climate variability over approximately the past half-century on a quasi-interannual timescale. The ice core oxygen isotopic ratios show a significant positive linear trend since 1964 CE (0.018 ± 0.008‰ per year; P < 0.03) and also suggest that the glaciers’ retreat is augmented by El Niño–Southern Oscillation processes, such as convection and warming of the atmosphere and sea surface. These Papua glaciers provide the only tropical records of ice core-derived climate variability for the WPWP.