Characterizing late Quaternary lake-level variability in Lago de Tota, Colombian Andes, with CHIRP seismic stratigraphy

Geophysical 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

Scientific drilling of Lake Chalco, Basin of Mexico (MexiDrill)

The primary scientific objective of MexiDrill, the Basin of Mexico Drilling Program, is development of a continuous, high-resolution ∼400 kyr lacustrine record of tropical North American environmental change. The field location, in the densely populated, water-stressed Mexico City region gives this record particular societal relevance. A detailed paleoclimate reconstruction from central Mexico will enhance our understanding of long-term natural climate variability in the North American tropics and its relationship with changes at higher latitudes. The site lies at the northern margin of the Intertropical Convergence Zone (ITCZ), where modern precipitation amounts are influenced by sea surface temperatures in the Pacific and Atlantic basins. During the Last Glacial Maximum (LGM), more winter precipitation at the site is hypothesized to have been a consequence of a southward displacement of the mid-latitude westerlies. It thus represents a key spatial node for understanding large-scale hydrological variability of tropical and subtropical North America and is at an altitude (2240 m a.s.l.), typical of much of western North America. In addition, its sediments contain a rich record of pre-Holocene volcanic history; knowledge of the magnitude and frequency relationships of the area's explosive volcanic eruptions will improve capacity for risk assessment of future activity. Explosive eruption deposits will also be used to provide the backbone of a robust chronology necessary for full exploitation of the paleoclimate record. Here we report initial results from, and outreach activities of, the 2016 coring campaign

Southern African HIV Clinicians Society 2022 guideline for the management of sexually transmitted infections : moving towards best practice

Sexually transmitted infections (STIs) are among the most common acute conditions worldwide with sub-Saharan Africa ranking among the regions with the highest burdens globally. Adolescent girls and young women (AGYW), people living with HIV (PLHIV), pregnant women, and key and vulnerable populations are disproportionally affected by STIs. The social determinants of health, gender inequality, and STI-associated stigma and discrimination (at both the community and facility level) are important contributors to the sustained high burden of infection.http://www.sajhivmed.org.za/index.php/hivmeddm2022Medical Microbiolog

Deep drilling at the Chalco lake:A technical report

En este artículo se presenta un resumen de las actividades realizadas para la recuperación de la totalidad de la secuencia lacustre del lago de Chalco. Mediante estudios geofísicos se determinó la distribución y espesor de los sedimentos lacustres con base en lo cual se seleccionó el sitio de perforación. Con datos de los espectros H/V de sísmica pasiva se hizo un mapa de isofrecuencias que definieron una región con sedimentos lacustres y material volcánico granulado de hasta 300 m de espesor. El uso de métodos electromagnéticos mostró cambios en la resistividad eléctrica relacionados con variaciones en la composición de la columna sedimentaria; entre 100 – 120 m de profundidad hay un primer aumento en la resistividad asociado al incremento de materiales volcaniclásticos, y entre 330 – 400 m de profundidad un segundo aumento asociado a la presencia de coladas de basalto. Fueron perforados tres pozos con recuperación continua, llegando a profundidades de 420 m en el pozo A, 310 m en el B y 520 en el C. Durante el trabajo de perforación se tomaron muestras para el análisis geomicrobiológicos y de metagenómica. Durante el proceso de perforación se recuperó un total de 1152 m de sedimentos con una profundidad máxima de 520 m. El porcentaje de recuperación de la columna sedimentaria varió entre 88 a 92 % en los tres sondeos. Los resultados del análisis de susceptibilidad magnética en las tres secuencias indica que los primeros 260 m son sedimentos lacustres, entre 260 y 300 m los sedimentos son más gruesos y debajo de los 300 m son predominantemente volcaniclásticos. El análisis de la secuencia sedimentaria del lago de Chalco de los últimos ~300000 años, permitirá documentar y ampliar el conocimiento acerca de la variabilidad climática de la zona, la historia paleoambiental, la historia del cierre de la cuenca, el desarrollo del sistema lacustre y la recurrencia de la actividad volcánica en la cuenca. Además, el estudio de las propiedades físicas de esta secuencia sedimentaria es importante para la modelación de la propagación de ondas sísmicas y de la estructura de la cuenca, así como para mejorar la capacidad de modelación del proceso de subsidencia del terreno que experimenta esta región. This paper presents a short description of the coring operations undertaken to recover the full lacustrine sedimentary sequence from Chalco. Geophysical techniques were used to determine the distribution and thickness of the sediments in order to select the drilling site. Resonance frequencies determined from H/V spectral ratios were used to determine an area where lake sediments reached 300 m thickness. Electromagnetic survey showed two changes in electric resistivity which were related to changes in sediment composition, the first from 100 to 120 m, related to an increase in volcanoclastic sediments and the second from 330 to 400 m related to the presence of a basaltic flows. Three wells were drilled with continuous recovery, reaching depths of 420 m in well A, 310 in B and 520 in C. Samples for geomicrobiological and metagenomics studies were collected during drilling operations. A total of 1152 m of core sediments were recovered reaching a maximum depth of 520 m. Recovery percentages were between 88 and 92 % in the three wells. Magnetic susceptibility analyses in the three sequences show that the first 260 m are mostly lake sediments, between 260 and 300 m sediments are coarser and below 300 m they are mostly volcaniclastic. Analysis of the sedimentary sequence of Lake Chalco that covers the last ~300000 years will allow documenting and extending the knowledge of climate variability in area, the paleoenvironmental history, basin closure history, lacustrian system development and volcanic activity recurrence. Studies of the physical properties of this sequence will be important for seismic propagation and basin structure modeling, and also will improve modeling of the subsidence process that this region experiences

Results of Deer Creek, Carlton County, Minnesota, Groundwater Seepage Investigation

This document is a Report to Carlton County Planning and Zoning on a groundwater investigation.Deer Creek is a small perennial stream located in Carlton County and is tributary to the Nemadji River. In the early 1990’s beaver constructed a large dam on private property in Sec. 19, T. 47 N., R.16 W. located on the Wrenshall 7.5 minute quadrangle. According to the land owners, groundwater seepage and discharge of sand to the surface began about the time the beaver arrived. The dam was apparently washed out at least twice. On July 4, 1999, the dam was overtopped and washed out during a series of large thunderstorms. The beaver repaired the dam, but apparently during 2001, representatives of the Minnesota Department of Natural Resources removed a beaver dam that impounded a large pond a short distance upstream. This dam was destroyed with dynamite and the rapid drainage of the large pond washed out the dam lower in the drainage. Groundwater discharge is occurring around the perimeter of the former pond. The discharge is focused at discrete points that are easily identified by sand volcanoes. The sand volcanoes are located along fault scarps that are the surface expression of rotational slumps. This report summarizes the results of an investigation of groundwater seepage along a reach of Deer Creek, Carlton County, Minnesota. The groundwater seepage is causing excessive turbidity, which affects all aspects of stream ecology and contributes large amounts of sediment to the Nemadji River