Browsing by Subject "South America"

Now showing 1 - 4 of 4
  • Thumbnail Image
    Item
    A 4600-year record of lake level and hydroclimate variability from an eastern Andean lake in Colombia
    (2016-05) Rudloff, Owen M.; Bird, Broxton Williams; Gilhooly, William, III; Filippelli, Gabriel M.
    Hydroclimatic variability in the eastern Colombian Andes is examined using a decadally-resolved, multiproxy lake sediment record from Laguna de Ubaque, Colombia. Hydroclimate trends are examined and compared to existing local, regional, and trans-Andean records to enhance existing knowledge of Late Holocene Colombian precipitation and assess potential hydroclimatic forcing mechanisms in tropical South America. Sedimentological analyses, including percent lithics, grain size, C:N and magnetic susceptibility are sensitive to hydroclimate and lake level while charcoal size and concentrations reflect fire variability. Results show that deep lacustrine conditions characterized by laminated deposits were not established until approximately 3500 cal yr B.P., prior to which, terrestrial C:N values and unstructured sediments indicate that drier, marsh-like conditions prevailed. Between 3500 and 2000 cal yr B.P., interrupted only by a 300-year arid interval from 2800 to 2500 cal yr B.P., greatly increased overall clastic deposition indicates a broad precipitation maximum while decreased sand deposition and the preservation of finely laminated sediment indicate deep lake conditions. After 2000 cal yr B.P., decreased clastic deposition suggests reduced precipitation, but the continued accumulation of laminated sediments indicates that conditions were wet enough to fill the basin continuously until the present day. These observations address two of the driving questions of Andean paleoclimate: were the northern and southern Andes in vi phase during the Holocene, or out of phase, and what are the main drivers of Holocene Andean climate? We find that the early part of Ubaque’s record more closely resembles southern Andean precipitation records until 2000 cal yr B.P., at which point it abruptly switches to resemble northern precipitation records. We attribute this to a combination of the southward migration of the intertropical convergence zone (ITCZ), and an increase in eastern Pacific sea surface temperatures (SST). In addition, we find that Colombian hydroclimate records exhibit a bimodal precipitation pattern, which we attribute to their location either on the Andean slopes or in the high interior Andes.
  • Thumbnail Image
    Item
    Detecting Counterfeit Pharmaceuticals through UV Spectrophotometry
    (Office of the Vice Chancellor for Research, 2015-04-17) Figueroa, Gabriela; Palacio, Luis A.; Ray, Bruce D.; Petrache, Horia I.; Lopez-Yunez, Alfredo
    According to the World Health Organization between 10%-30% of medicines, in Africa, Asia and South America, are counterfeit or sub-standard, affecting the health of millions of people. Currently, there is no effective way to check the quality of a medicine at the point of care, leaving many with treatable diseases at risk. The goal of this study is to identify UV-Vis (240nm - 500nm) absorbance patterns that would indicate if a drug is sub-standard or counterfeit. UV-Vis spectroscopy was selected as the method for testing due to the maturity and availability of the technology. Pure Acetaminophen and Tylenol were used as controls for proof of concept. Samples were prepared by dissolving different combinations of the pure active ingredient and adulterants such as cement, rice flour, vitamin C and lactose in three different types of solvents (H2O, 0.1 M HCl, 0.1 NaOH). Various concentrations (ranging from 0.01mg/ml to 0.04mg/ml) and mixing ratios were analyzed using a UV-Vis Spectrophotometer. It was found that adulterants significantly decrease the absorption of acetaminophen at 245nm by interacting with its benzene ring, while showing a slight increase in other parts of the spectrum. UV-Vis scans show that the amount of change in absorbance at specific wavelengths, coupled with characteristic wavelength shifts produced by different solvents, can be used for detection of counterfeit drugs. The methods presented here could be used for quality control of medicines at or near the point of care in parts of the world at higher risk of encountering defective pharmaceuticals.
  • Thumbnail Image
    Item
    Pictured Politics: Visualizing Colonial History in South American Civic Portrait Collections
    (Office of the Vice Chancellor for Research, 2013-04-05) Engel, Emily A.
    This presentation addresses the history of institutional art collecting in Spanish colonial South America. In viceregal South America, political changes inspired adjustments to pictorial convention in portraits, imbuing portraiture with a previously unutilized social relevance in the negotiation of history, authority, and political relationships. My study of the material remains of colonial history suggests that collected artworks contributed to the maintenance of repressive social hierarchies which remain politically influential into the present. Because individuals and institutions were consistently grappling for effective power and local authority, painted portraits participated in the visualization of the history of the viceroyalties from an internal perspective. Through the lens of official portrait collections in three prominent South American capitals, Lima, Buenos Aires, and Bogotá, this presentation considers how works of art were active components in the construction of American colonial histories and political relationships. Official portraits in particular were introduced into civic politics early in the sixteenth century when local and international bureaucrats used the images to establish or create the illusion of political alliances. Viceregal portraits were later recontextualized in civic spaces where they were exhibited for their historic value, documenting the socio-political past of South American regions.
  • Thumbnail Image
    Item
    A review of the South American monsoon history as recorded in stable isotopic proxies over the past two millennia
    (European Geosciences Union, 2012-08-23) Vuille, M.; Burns, S. J.; Taylor, B. L.; Cruz, F. W.; Bird, Broxton W.; Abbott, M. B.; Kanner, L. C.; Cheng, H.; Novello, V. F.
    We review the history of the South American summer monsoon (SASM) over the past ~2000 yr based on high-resolution stable isotope proxies from speleothems, ice cores and lake sediments. Our review is complemented by an analysis of an isotope-enabled atmospheric general circulation model (GCM) for the past 130 yr. Proxy records from the monsoon belt in the tropical Andes and SE Brazil show a very coherent behavior over the past 2 millennia with significant decadal to multidecadal variability superimposed on large excursions during three key periods: the Medieval Climate Anomaly (MCA), the Little Ice Age (LIA) and the current warm period (CWP). We interpret these three periods as times when the SASM's mean state was significantly weakened (MCA and CWP) and strengthened (LIA), respectively. During the LIA each of the proxy archives considered contains the most negative δ18O values recorded during the entire record length. On the other hand, the monsoon strength is currently rather weak in a 2000-yr historical perspective, rivaled only by the low intensity during the MCA. Our climatic interpretation of these archives is consistent with our isotope-based GCM analysis, which suggests that these sites are sensitive recorders of large-scale monsoon variations. We hypothesize that these centennial-scale climate anomalies were at least partially driven by temperature changes in the Northern Hemisphere and in particular over the North Atlantic, leading to a latitudinal displacement of the ITCZ and a change in monsoon intensity (amount of rainfall upstream over the Amazon Basin). This interpretation is supported by several independent records from different proxy archives and modeling studies. Although ENSO is the main forcing for δ18O variability over tropical South America on interannual time scales, our results suggest that its influence may be significantly modulated by North Atlantic climate variability on longer time scales. Finally, our analyses indicate that isotopic proxies, because of their ability to integrate climatic information on large spatial scales, could complement more traditional proxies such as tree rings or documentary evidence. Future climate reconstruction efforts could potentially benefit from including isotopic proxies as large-scale predictors in order to better constrain past changes in the atmospheric circulation.