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

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

A qualitative and quantitative model for climate-driven lake formation on carbonate platforms based on examples from the Bahamian archipelago

Lakes on carbonate platform islands such as the Bahamas display wide variability in morphometry, chemistry, and fauna. These parameters are ultimately driven by climate, sea level, and carbonate accumulation and dissolution. The authors propose a model that integrates climatological, geomorphological, and stratigraphic frameworks to understand processes of carbonate-hosted lake formation and limnological characteristics in modern day environments, with applications to carbonate lake sedimentary records. Fifty-two lakes from San Salvador Island and Eleuthera, Bahamas, were examined for water chemistry, basin morphology, conduit development, conductivity, and major ions. Using non-metric, multi-dimensional scaling ordination methods, the authors derived a model dividing lakes into either constructional or destructional formational modes. Constructional lakes were further divided into pre-highstand and highstand types based on whether their formation occurred during a marine regressive or transgressive phase. Destructional lakes are created continually by dissolution of bedrock at fresh/saline water interfaces and their formation is therefore related to changing climate and sea level. This model shows that lake formation is influenced by the hydrologic balance associated with climatic conditions that drives karst dissolution as well as the deposition of aeolian dune ridges that isolate basins due to sea-level fluctuations. It allows for testing and examining the climatic and hydrologic regime as related to carbonate accumulation and dissolution through time, and for an improved understanding of lake sensitivity and response to climate as preserved in the lacustrine sedimentary record

Radiocarbon Dating Suitability of Aquatic Plant Macrofossils

Paleolimnological and plant physiological literature were reviewed to determine which types of aquatic plant macrofossils are suitable for radiocarbon dating, with a particular focus on the uptake of reservoir-aged dissolved inorganic carbon (DIC) by emergent plants. Submerged aquatic plants utilize large amounts of DIC and are clearly not suitable for radiocarbon dating. Under certain environmental conditions, some emergent aquatic plants can metabolize DIC in quantities large enough to introduce old-carbon error to radiocarbon dates acquired from their remains (plant macrofossils). Over 300 plant macrofossil images are included in the online resource Tool for Microscopic Identification; http://tmi.laccore.umn.edu) along with guidance on identification and suitability for radiocarbon dating

Transformative Earth Sciences through Data:Neotoma, EarthCube & Flyover Country

Presentation for the Mozilla Science UBC Data Science Day - 04/04/2016

A Qualitative and Quantitative Model for Climate-Driven Lake Formation on Carbonate Platforms Based on Examples from the Bahamian Archipelago

Lakes on carbonate platform islands such as the Bahamas display wide variability in morphometry, chemistry, and fauna. These parameters are ultimately driven by climate, sea level, and carbonate accumulation and dissolution. The authors propose a model that integrates climatological, geomorphological, and stratigraphic frameworks to understand processes of carbonate-hosted lake formation and limnological characteristics in modern day environments, with applications to carbonate lake sedimentary records. Fifty-two lakes from San Salvador Island and Eleuthera, Bahamas, were examined for water chemistry, basin morphology, conduit development, conductivity, and major ions. Using non-metric, multi-dimensional scaling ordination methods, the authors derived a model dividing lakes into either constructional or destructional formational modes. Constructional lakes were further divided into pre-highstand and highstand types based on whether their formation occurred during a marine regressive or transgressive phase. Destructional lakes are created continually by dissolution of bedrock at fresh/saline water interfaces and their formation is therefore related to changing climate and sea level. This model shows that lake formation is influenced by the hydrologic balance associated with climatic conditions that drives karst dissolution as well as the deposition of aeolian dune ridges that isolate basins due to sea-level fluctuations. It allows for testing and examining the climatic and hydrologic regime as related to carbonate accumulation and dissolution through time, and for an improved understanding of lake sensitivity and response to climate as preserved in the lacustrine sedimentary record

The Chungará lake basin: a record of environmental change in the tropical Andes

1 Poster with Figs. and Tabl.Lago Chungará (18° 15' S, 69° 10' W, 4520 m a.s.l.) is located at the northeastern edge of the Lauca Basin. It lies in a tectonic-volcanic basin, with a maximum water depth of 40 m, a surface area of 21.5 km2, and a volume of about 385 million m3. The main inflows are the Chungará River (300 to 500 ls-1) and several springs on the western margin. There is no surface outlet. Hydrological balance suggested a large groundwater outflow to the Cotacotani lakes to the north. However, a chemical and isotopic survey of the Chungará and Cotacotani lakes shows a more complex picture, and a more independent hydrological evolution of each lake. The Chungará lake is polymictic, oligotrophic, contains 1.2 g l-1 TDS, and the water chemistry is alkaline (pH ranges between 7 and 10) and of (Na+)-(Mg 2+)- (HCO3-) – (SO4 2-) type. Lake water temperatures in spring (early November) range between 12 ºC (surface) and 6 ºC (bottom); electric conductivity showed no changes with depth (1450 mS). Oxic conditions at the bottom of the lake allow development of invertebrate benthic communities. The origin of the lake is related to the emplacement of the Parinacota volcano debris avalanche that blocked the Chungará River. The age of this episode is controversial, ranging from late Pleistocene (ca. 18 ka) to early Holocene (8 Ka). A seismic survey in the lake revealed two seismic units overlying the massive volcanic bedrock in the smaller, shallower eastern subbasin and also in the main, deeper, NW-SE trending basin. An older seismic unit, with less well-defined reflections, is found in the northwestern basin. Detailed sedimentological studies of short cores in the western bay (20 m water depth) and Livingstone cores in the eastern shelf (5 m water depth) have shown large depositional, paleohydrological and limnological changes in the lake during the late Holocene (ca. 4ka - modern). Sedimentary sequences identified in a 3.6 m long core from the eastern subbasin show alternation of lake sub environments (lacustrine shelf, macrophyte-dominated littoral, and peat bog) that reflect century- to millennial-scale limnological and hydrological changes in the lake during the last 4000 years. Diatom assemblages show fluctuations in the percentages of the dominant freshwater planktonic species in the lower units, and a sharp decrease in the upper unit (55 cm) where meso- to polisaline benthic diatom percentages slightly increase. Modern sediments in the deeper areas are composed of black, organic-rich, massive to faintly laminated mud. The sedimentological, chemical and stable isotope composition of a 210Pb-dated short core indicated large changes in the water balance of the lake, during the last 500 years. The results obtained from the short cores studies and the seismic survey showed the potential of Chungará Lake sedimentary sequence as a high-resolution archive of environmental and climate change in the tropical Andes during the Holocene. In November 2002 an international expedition, including Spanish, Chilean and US- institutions, retrieved fifteen Kullenberg cores along several transects in the lake. The longest ones (up to 8 meters) reached the basal seismic unit and recovered the whole post-Parinacota volcano collapse sequence. Basal sediments are coarse and contain gravels and sands. Preliminary core catcher studies showed a variety of sedimentary facies. Magnetic susceptibility analyses also show several sequences reflecting changes in the depositional sub environments in the lake. The on-going multidisciplinary study of the cores will help to solve some of the regional controversies related to Holocene climate change and the relationships between human communities and environmental changes in the past and it will provide useful data for the preservation and management of this Reserve of the Biosphere.Peer reviewe