UNDERSTANDING INTERRUPTIONS IN HEALTHCARE: DEVELOPING A MODEL

Developing a Model Interruption is a known human factor that contributes to errors and catastrophic events in healthcare as well as other high-risk industries. The landmark Institute of Medicine (IOM) report, To Err is Human, brought attention to the significance of preventable errors in medicine and suggested that interruptions could be a contributing factor. Previous studies of interruptions in healthcare did not offer a conceptual model by which to study interruptions. As a result of the serious consequences of interruptions investigated in other high-risk industries, there is a need to develop a model to describe, understand, explain, and predict interruptions and their consequences in healthcare. Therefore, the purpose of this study was to develop a model grounded in the literature and to use the model to describe and explain interruptions in healthcare. Specifically, this model would be used to describe and explain interruptions occurring in a Level One Trauma Center. A trauma center was chosen because this environment is characterized as intense, unpredictable, and interrupt-driven. The first step in developing the model began with a review of the literature which revealed that the concept interruption did not have a consistent definition in either the healthcare or non-healthcare literature. Walker and Avant’s method of concept analysis was used to clarify and define the concept. The analysis led to the identification of five defining attributes which include (1) a human experience, (2) an intrusion of a secondary, unplanned, and unexpected task, (3) discontinuity, (4) externally or internally initiated, and (5) situated within a context. However, before an interruption could commence, five conditions known as antecedents must occur. For an interruption to take place (1) an intent to interrupt is formed by the initiator, (2) a physical signal must pass a threshold test of detection by the recipient, (3) the sensory system of the recipient is stimulated to respond to the initiator, (4) an interruption task is presented to recipient, and (5) the interruption task is either accepted or rejected by v the recipient. An interruption was determined to be quantifiable by (1) the frequency of occurrence of an interruption, (2) the number of times the primary task has been suspended to perform an interrupting task, (3) the length of time the primary task has been suspended, and (4) the frequency of returning to the primary task or not returning to the primary task. As a result of the concept analysis, a definition of an interruption was derived from the literature. An interruption is defined as a break in the performance of a human activity initiated internal or external to the recipient and occurring within the context of a setting or location. This break results in the suspension of the initial task by initiating the performance of an unplanned task with the assumption that the initial task will be resumed. The definition is inclusive of all the defining attributes of an interruption. This is a standard definition that can be used by the healthcare industry. From the definition, a visual model of an interruption was developed. The model was used to describe and explain the interruptions recorded for an instrumental case study of physicians and registered nurses (RNs) working in a Level One Trauma Center. Five physicians were observed for a total of 29 hours, 31 minutes. Eight registered nurses were observed for a total of 40 hours 9 minutes. Observations were made on either the 0700–1500 or the 1500-2300 shift using the shadowing technique. Observations were recorded in the field note format. The field notes were analyzed by a hybrid method of categorizing activities and interruptions. The method was developed by using both a deductive a priori classification framework and by the inductive process utilizing line-byline coding and constant comparison as stated in Grounded Theory. The following categories were identified as relative to this study: Intended Recipient - the person to be interrupted Unintended Recipient - not the intended recipient of an interruption; i.e., receiving a phone call that was incorrectly dialed Indirect Recipient – the incidental recipient of an interruption; i.e., talking with another, thereby suspending the original activity Recipient Blocked – the intended recipient does not accept the interruption Recipient Delayed – the intended recipient postpones an interruption Self-interruption – a person, independent of another person, suspends one activity to perform another; i.e., while walking, stops abruptly and talks to another person Distraction – briefly disengaging from a task Organizational Design – the physical layout of the workspace that causes a disruption in workflow Artifacts Not Available – supplies and equipment that are not available in the workspace causing a disruption in workflow Initiator – a person who initiates an interruption Interruption by Organizational Design and Artifacts Not Available were identified as two new categories of interruption. These categories had not previously been cited in the literature. Analysis of the observations indicated that physicians were found to perform slightly fewer activities per hour when compared to RNs. This variance may be attributed to differing roles and responsibilities. Physicians were found to have more activities interrupted when compared to RNs. However, RNs experienced more interruptions per hour. Other people were determined to be the most commonly used medium through which to deliver an interruption. Additional mediums used to deliver an interruption vii included the telephone, pager, and one’s self. Both physicians and RNs were observed to resume an original interrupted activity more often than not. In most interruptions, both physicians and RNs performed only one or two interrupting activities before returning to the original interrupted activity. In conclusion the model was found to explain all interruptions observed during the study. However, the model will require an even more comprehensive study in order to establish its predictive value.

Data Accuracy in Medical Record Abstraction

Clinical Research Data Quality Literature Review and Pooled Analysis We present a literature review and secondary analysis of data accuracy in clinical research and related secondary data uses. A total of 93 papers meeting our inclusion criteria were categorized according to the data processing methods. Quantitative data accuracy information was abstracted from the articles and pooled. Our analysis demonstrates that the accuracy associated with data processing methods varies widely, with error rates ranging from 2 errors per 10,000 files to 5019 errors per 10,000 fields. Medical record abstraction was associated with the highest error rates (70–5019 errors per 10,000 fields). Data entered and processed at healthcare facilities had comparable error rates to data processed at central data processing centers. Error rates for data processed with single entry in the presence of on-screen checks were comparable to double entered data. While data processing and cleaning methods may explain a significant amount of the variability in data accuracy, additional factors not resolvable here likely exist. Defining Data Quality for Clinical Research: A Concept Analysis Despite notable previous attempts by experts to define data quality, the concept remains ambiguous and subject to the vagaries of natural language. This current lack of clarity continues to hamper research related to data quality issues. We present a formal concept analysis of data quality, which builds on and synthesizes previously published work. We further posit that discipline-level specificity may be required to achieve the desired definitional clarity. To this end, we combine work from the clinical research domain with findings from the general data quality literature to produce a discipline-specific definition and operationalization for data quality in clinical research. While the results are helpful to clinical research, the methodology of concept analysis may be useful in other fields to clarify data quality attributes and to achieve operational definitions. Medical Record Abstractor’s Perceptions of Factors Impacting the Accuracy of Abstracted Data Medical record abstraction (MRA) is known to be a significant source of data errors in secondary data uses. Factors impacting the accuracy of abstracted data are not reported consistently in the literature. Two Delphi processes were conducted with experienced medical record abstractors to assess abstractor’s perceptions about the factors. The Delphi process identified 9 factors that were not found in the literature, and differed with the literature by 5 factors in the top 25%. The Delphi results refuted seven factors reported in the literature as impacting the quality of abstracted data. The results provide insight into and indicate content validity of a significant number of the factors reported in the literature. Further, the results indicate general consistency between the perceptions of clinical research medical record abstractors and registry and quality improvement abstractors. Distributed Cognition Artifacts on Clinical Research Data Collection Forms Medical record abstraction, a primary mode of data collection in secondary data use, is associated with high error rates. Distributed cognition in medical record abstraction has not been studied as a possible explanation for abstraction errors. We employed the theory of distributed representation and representational analysis to systematically evaluate cognitive demands in medical record abstraction and the extent of external cognitive support employed in a sample of clinical research data collection forms. We show that the cognitive load required for abstraction in 61% of the sampled data elements was high, exceedingly so in 9%. Further, the data collection forms did not support external cognition for the most complex data elements. High working memory demands are a possible explanation for the association of data errors with data elements requiring abstractor interpretation, comparison, mapping or calculation. The representational analysis used here can be used to identify data elements with high cognitive demands.

INTEGRATIVE BIOMARKER IDENTIFICATION AND CLASSIFICATION USING HIGH THROUGHPUT ASSAYS

It is well accepted that tumorigenesis is a multi-step procedure involving aberrant functioning of genes regulating cell proliferation, differentiation, apoptosis, genome stability, angiogenesis and motility. To obtain a full understanding of tumorigenesis, it is necessary to collect information on all aspects of cell activity. Recent advances in high throughput technologies allow biologists to generate massive amounts of data, more than might have been imagined decades ago. These advances have made it possible to launch comprehensive projects such as (TCGA) and (ICGC) which systematically characterize the molecular fingerprints of cancer cells using gene expression, methylation, copy number, microRNA and SNP microarrays as well as next generation sequencing assays interrogating somatic mutation, insertion, deletion, translocation and structural rearrangements. Given the massive amount of data, a major challenge is to integrate information from multiple sources and formulate testable hypotheses. This thesis focuses on developing methodologies for integrative analyses of genomic assays profiled on the same set of samples. We have developed several novel methods for integrative biomarker identification and cancer classification. We introduce a regression-based approach to identify biomarkers predictive to therapy response or survival by integrating multiple assays including gene expression, methylation and copy number data through penalized regression. To identify key cancer-specific genes accounting for multiple mechanisms of regulation, we have developed the integIRTy software that provides robust and reliable inferences about gene alteration by automatically adjusting for sample heterogeneity as well as technical artifacts using Item Response Theory. To cope with the increasing need for accurate cancer diagnosis and individualized therapy, we have developed a robust and powerful algorithm called SIBER to systematically identify bimodally expressed genes using next generation RNAseq data. We have shown that prediction models built from these bimodal genes have the same accuracy as models built from all genes. Further, prediction models with dichotomized gene expression measurements based on their bimodal shapes still perform well. The effectiveness of outcome prediction using discretized signals paves the road for more accurate and interpretable cancer classification by integrating signals from multiple sources.

Radiolarian biostratigraphy in the central Indian Ocean

Identifiable radiolarians of stratigraphic importance were recovered at eight of the sites drilled on Leg 115. The assemblages range in age from Holocene to middle Eocene (Dictyoprora mongolfieri Zone, about 48 Ma). Faunal preservation is particularly good in two stratigraphic intervals: the Holocene through upper Miocene (0-9 Ma), and the lowermost Oligocene to middle Eocene (35-48 Ma). Fluctuating rates of silica accumulation at these drill sites during the Cenozoic reflect changing tectonic and paleoceanographic conditions. In particular, the gradual closure of the Indonesian and Tethyan seaways and the northward migration of the Indian subcontinent severely restricted zonal circulation and silica accumulation in tropical latitudes during the late Oligocene through middle Miocene. By the late Miocene the Indian subcontinent had moved sufficiently north of the equator to allow trans-Indian zonal circulation patterns to become reestablished, and biosiliceous sedimentation resumed. The composition of the radiolarian assemblages in the tropical Indian Ocean is closely comparable with that of the 'stratotype' sequences in the equatorial Pacific. However, there are some notable exceptions in Indian Ocean assemblages: (1) the scarcity of the genera Pterocanium and Spongaster in the Neogene; (2) the absence of the stratigraphically important Podocyrtis lineage, P. diamesa -> P. phyxis -> P. ampla, in the middle Eocene; and (3) the scarcity of taxa of the genus Dorcadospyris, with the exception of D. ateuchus. The succession of radiolarian events was tabulated for those stratigraphic intervals where the assemblages were well preserved. We identified 55 events in the middle Eocene to earliest Oligocene, and 31 events in the late Miocene to Holocene. The succession of events is closely comparable with that of the tropical Pacific. However, there are exceptions that appear to be real, rather than artifacts of sample preservation, mixing, and core disturbance.

Auxiliary material and basic geochemical and benthic foraminiferal stable isotope data for the interval bracketing Eocene Thermal Maximum 2 (ETM2) at DSDP Sites 401 and 550 in the northeastern Atlantic Ocean

Ever since its discovery, Eocene Thermal Maximum 2 (ETM2; ~53.7 Ma) has been considered as one of the "little brothers" of the Paleocene-Eocene Thermal Maximum (PETM; ~56 Ma) as it displays similar characteristics including abrupt warming, ocean acidification, and biotic shifts. One of the remaining key questions is what effect these lesser climate perturbations had on ocean circulation and ventilation and, ultimately, biotic disruptions. Here we characterize ETM2 sections of the NE Atlantic (Deep Sea Drilling Project Sites 401 and 550) using multispecies benthic foraminiferal stable isotopes, grain size analysis, XRF core scanning, and carbonate content. The magnitude of the carbon isotope excursion (0.85-1.10 per mil) and bottom water warming (2-2.5°C) during ETM2 seems slightly smaller than in South Atlantic records. The comparison of the lateral d13C gradient between the North and South Atlantic reveals that a transient circulation switch took place during ETM2, a similar pattern as observed for the PETM. New grain size and published faunal data support this hypothesis by indicating a reduction in deepwater current velocity. Following ETM2, we record a distinct intensification of bottom water currents influencing Atlantic carbonate accumulation and biotic communities, while a dramatic and persistent clay reduction hints at a weakening of the regional hydrological cycle. Our findings highlight the similarities and differences between the PETM and ETM2. Moreover, the heterogeneity of hyperthermal expression emphasizes the need to specifically characterize each hyperthermal event and its background conditions to minimalize artifacts in global climate and carbonate burial models for the early Paleogene.

Arqueologías del ¿Futuro? : Cartografía estética aplicada a territorios específicos

Los Territorios Específicos condicionados socioambiental y/o físicoculturalmente son sistematizados en base a sus cualidades éticas y estéticas en su sentido filosófico y formal respectivamente. Los mismos surgen como entidades orgánicamente integradas a nivel de las prácticas culturales en función de una performatividad autopoiética con gradientes y resonancias ampliamente debatidas académicamente y/o, a través de producciones específicas de las artes visuales contemporáneas. La Cartografía Estética propuesta se conforma de un corpus de obras plásticas y teóricas que, en la trayectoria expositiva abordada para este estudio, conforman una constelación de ejes temáticos y procedimentales en vinculación a los modos de producción en artes visuales. Estos nódulos o modos de hacer en artes visuales, se integran en una fascinante e interesante red epistemológica que, a la luz de las obras de arte seleccionadas son transparentadas no sólo en su complejidad epistémica sino que también son confrontados a interesantes gestos y guiños visuales a modo de cita y figuras conceptuales que en sentido moebiano remisionan formas de inscripción de obra y de la legibilidad de la misma conformando un alfabeto visual contemporáneo indispensable a la hora de pensar y entender la producción artística del último siglo en general y de las artes visuales latinoamericanas y chilenas en particular, todas ellas conforman una panorámica global en lo que hoy se conoce y divulga como arte actual. La unidad espacial abordada como Territorios Específicos se constituyen críticamente por conformar zonas y áreas marginales, espacios residuales y limítrofes, a la vez que contenedores y contenido de resistencia asistémica facilitado por un desinterés administrativo consecuente a su calidad de margen residual naturalizado y sus contenidos subyacentes. Metodológicamente, esta investigación ha sido cuidadosamente sistematizada a partir de herramientas de análisis y medición provenientes de las ciencias sociales y otras más afín a las de la ingeniería como arquitectura y urbanismo y de otras ciencias fronterizas de las biofísicas como la arqueología, etnografía y antropología, adaptadas todas a un interesantísimo protocolo instrumental replicable para las artes visuales. Este compendio procedimental comprende acciones de arte de sitio específico realizadas en una franja costera de 30 kilómetros que abarca desde la ciudad de Valdivia hasta 'La Reserva de Curiñanco' en la recientemente inaugurada XIV Región de Los Ríos en Chile. Estas acciones son confrontadas y tensionadas tanto a nivel de la crítica especializada como de sus afluentes epistemológicos colindantes con las ciencias humanas, donde, este corpus de obra contemporáneas, curatorías, proyectos de sitio y debates especializados, aportan considerablemente a la construcción de futuros posibles no solo de las artes visuales en particular y de las ciencias humanas en general, sino que además conllevan un debate ineludible para el desafío implicado en el debate territorio/globalización

Nuevas armas de una misma guerra : O de cómo las historietas enseñan Historia

En los últimos años, los investigadores dedicados al estudio de la enseñanza de la Historia llamaron la atención sobre la influencia de nuevos "artefactos culturales" en el forjamiento de la cultura histórica de los jóvenes. Videojuegos, series de televisión, documentales, películas y sitios web deben empezar a ser tenidos en cuenta, a la hora de evaluar los principales emisores de contenidos históricos. En este caso, nos dedicamos a estudiar a uno de estos "artefactos": los cómics o historietas históricas. Buscaremos, entonces, conocer su derrotero histórico y, a partir de él, analizar el lugar que actualmente tienen en el currículum, teniendo en cuenta sus límites y posibilidades. A partir de un recorrido por las principales historietas históricas que tuvo la Argentina en el siglo XX y principios del XXI, analizaremos su contenido y la propuesta político-pedagógica que se desprende, tanto de sus autores, como de aquellas organizaciones destinadas a difundirlas en la escuela. La conclusión del trabajo es que, a pesar de la novedad que implica la enseñanza de la Historia por medio de herramientas alternativas a los tradicionales manuales, tanto su contenido como los valores difundidos no difieren de aquellos que difundían los viejos textos escolares. En este sentido, las historietas funcionarían como herramientas al servicio de una enseñanza de la Historia escolar cuya función principal es fomentar una conciencia cívica nacionalista

Nuevas armas de una misma guerra : O de cómo las historietas enseñan Historia

En los últimos años, los investigadores dedicados al estudio de la enseñanza de la Historia llamaron la atención sobre la influencia de nuevos "artefactos culturales" en el forjamiento de la cultura histórica de los jóvenes. Videojuegos, series de televisión, documentales, películas y sitios web deben empezar a ser tenidos en cuenta, a la hora de evaluar los principales emisores de contenidos históricos. En este caso, nos dedicamos a estudiar a uno de estos "artefactos": los cómics o historietas históricas. Buscaremos, entonces, conocer su derrotero histórico y, a partir de él, analizar el lugar que actualmente tienen en el currículum, teniendo en cuenta sus límites y posibilidades. A partir de un recorrido por las principales historietas históricas que tuvo la Argentina en el siglo XX y principios del XXI, analizaremos su contenido y la propuesta político-pedagógica que se desprende, tanto de sus autores, como de aquellas organizaciones destinadas a difundirlas en la escuela. La conclusión del trabajo es que, a pesar de la novedad que implica la enseñanza de la Historia por medio de herramientas alternativas a los tradicionales manuales, tanto su contenido como los valores difundidos no difieren de aquellos que difundían los viejos textos escolares. En este sentido, las historietas funcionarían como herramientas al servicio de una enseñanza de la Historia escolar cuya función principal es fomentar una conciencia cívica nacionalista

Arqueologías del ¿Futuro? : Cartografía estética aplicada a territorios específicos

Los Territorios Específicos condicionados socioambiental y/o físicoculturalmente son sistematizados en base a sus cualidades éticas y estéticas en su sentido filosófico y formal respectivamente. Los mismos surgen como entidades orgánicamente integradas a nivel de las prácticas culturales en función de una performatividad autopoiética con gradientes y resonancias ampliamente debatidas académicamente y/o, a través de producciones específicas de las artes visuales contemporáneas. La Cartografía Estética propuesta se conforma de un corpus de obras plásticas y teóricas que, en la trayectoria expositiva abordada para este estudio, conforman una constelación de ejes temáticos y procedimentales en vinculación a los modos de producción en artes visuales. Estos nódulos o modos de hacer en artes visuales, se integran en una fascinante e interesante red epistemológica que, a la luz de las obras de arte seleccionadas son transparentadas no sólo en su complejidad epistémica sino que también son confrontados a interesantes gestos y guiños visuales a modo de cita y figuras conceptuales que en sentido moebiano remisionan formas de inscripción de obra y de la legibilidad de la misma conformando un alfabeto visual contemporáneo indispensable a la hora de pensar y entender la producción artística del último siglo en general y de las artes visuales latinoamericanas y chilenas en particular, todas ellas conforman una panorámica global en lo que hoy se conoce y divulga como arte actual. La unidad espacial abordada como Territorios Específicos se constituyen críticamente por conformar zonas y áreas marginales, espacios residuales y limítrofes, a la vez que contenedores y contenido de resistencia asistémica facilitado por un desinterés administrativo consecuente a su calidad de margen residual naturalizado y sus contenidos subyacentes. Metodológicamente, esta investigación ha sido cuidadosamente sistematizada a partir de herramientas de análisis y medición provenientes de las ciencias sociales y otras más afín a las de la ingeniería como arquitectura y urbanismo y de otras ciencias fronterizas de las biofísicas como la arqueología, etnografía y antropología, adaptadas todas a un interesantísimo protocolo instrumental replicable para las artes visuales. Este compendio procedimental comprende acciones de arte de sitio específico realizadas en una franja costera de 30 kilómetros que abarca desde la ciudad de Valdivia hasta 'La Reserva de Curiñanco' en la recientemente inaugurada XIV Región de Los Ríos en Chile. Estas acciones son confrontadas y tensionadas tanto a nivel de la crítica especializada como de sus afluentes epistemológicos colindantes con las ciencias humanas, donde, este corpus de obra contemporáneas, curatorías, proyectos de sitio y debates especializados, aportan considerablemente a la construcción de futuros posibles no solo de las artes visuales en particular y de las ciencias humanas en general, sino que además conllevan un debate ineludible para el desafío implicado en el debate territorio/globalización

Arqueologías del ¿Futuro? : Cartografía estética aplicada a territorios específicos

Los Territorios Específicos condicionados socioambiental y/o físicoculturalmente son sistematizados en base a sus cualidades éticas y estéticas en su sentido filosófico y formal respectivamente. Los mismos surgen como entidades orgánicamente integradas a nivel de las prácticas culturales en función de una performatividad autopoiética con gradientes y resonancias ampliamente debatidas académicamente y/o, a través de producciones específicas de las artes visuales contemporáneas. La Cartografía Estética propuesta se conforma de un corpus de obras plásticas y teóricas que, en la trayectoria expositiva abordada para este estudio, conforman una constelación de ejes temáticos y procedimentales en vinculación a los modos de producción en artes visuales. Estos nódulos o modos de hacer en artes visuales, se integran en una fascinante e interesante red epistemológica que, a la luz de las obras de arte seleccionadas son transparentadas no sólo en su complejidad epistémica sino que también son confrontados a interesantes gestos y guiños visuales a modo de cita y figuras conceptuales que en sentido moebiano remisionan formas de inscripción de obra y de la legibilidad de la misma conformando un alfabeto visual contemporáneo indispensable a la hora de pensar y entender la producción artística del último siglo en general y de las artes visuales latinoamericanas y chilenas en particular, todas ellas conforman una panorámica global en lo que hoy se conoce y divulga como arte actual. La unidad espacial abordada como Territorios Específicos se constituyen críticamente por conformar zonas y áreas marginales, espacios residuales y limítrofes, a la vez que contenedores y contenido de resistencia asistémica facilitado por un desinterés administrativo consecuente a su calidad de margen residual naturalizado y sus contenidos subyacentes. Metodológicamente, esta investigación ha sido cuidadosamente sistematizada a partir de herramientas de análisis y medición provenientes de las ciencias sociales y otras más afín a las de la ingeniería como arquitectura y urbanismo y de otras ciencias fronterizas de las biofísicas como la arqueología, etnografía y antropología, adaptadas todas a un interesantísimo protocolo instrumental replicable para las artes visuales. Este compendio procedimental comprende acciones de arte de sitio específico realizadas en una franja costera de 30 kilómetros que abarca desde la ciudad de Valdivia hasta 'La Reserva de Curiñanco' en la recientemente inaugurada XIV Región de Los Ríos en Chile. Estas acciones son confrontadas y tensionadas tanto a nivel de la crítica especializada como de sus afluentes epistemológicos colindantes con las ciencias humanas, donde, este corpus de obra contemporáneas, curatorías, proyectos de sitio y debates especializados, aportan considerablemente a la construcción de futuros posibles no solo de las artes visuales en particular y de las ciencias humanas en general, sino que además conllevan un debate ineludible para el desafío implicado en el debate territorio/globalización

Nuevas armas de una misma guerra : O de cómo las historietas enseñan Historia

En los últimos años, los investigadores dedicados al estudio de la enseñanza de la Historia llamaron la atención sobre la influencia de nuevos "artefactos culturales" en el forjamiento de la cultura histórica de los jóvenes. Videojuegos, series de televisión, documentales, películas y sitios web deben empezar a ser tenidos en cuenta, a la hora de evaluar los principales emisores de contenidos históricos. En este caso, nos dedicamos a estudiar a uno de estos "artefactos": los cómics o historietas históricas. Buscaremos, entonces, conocer su derrotero histórico y, a partir de él, analizar el lugar que actualmente tienen en el currículum, teniendo en cuenta sus límites y posibilidades. A partir de un recorrido por las principales historietas históricas que tuvo la Argentina en el siglo XX y principios del XXI, analizaremos su contenido y la propuesta político-pedagógica que se desprende, tanto de sus autores, como de aquellas organizaciones destinadas a difundirlas en la escuela. La conclusión del trabajo es que, a pesar de la novedad que implica la enseñanza de la Historia por medio de herramientas alternativas a los tradicionales manuales, tanto su contenido como los valores difundidos no difieren de aquellos que difundían los viejos textos escolares. En este sentido, las historietas funcionarían como herramientas al servicio de una enseñanza de la Historia escolar cuya función principal es fomentar una conciencia cívica nacionalista

Mg/Ca ratios in planktonic foraminifera

The primary Mg/Ca ratio of foraminiferal shells is a potentially valuable paleoproxy for sea surface temperature (SST) reconstructions. However, the reliable extraction of this ratio from sedimentary calcite assumes that we can overcome artifacts related to foraminiferal ecology and partial dissolution, as well as contamination by secondary calcite and clay. The standard batch method for Mg/Ca analysis involves cracking, sonicating, and rinsing the tests to remove clay, followed by chemical cleaning, and finally acid-digestion and single-point measurement. This laborious procedure often results in substantial loss of sample (typically 30-60%). We find that even the earliest steps of this procedure can fractionate Mg from Ca, thus biasing the result toward a more variable and often anomalously low Mg/Ca ratio. Moreover, the more rigorous the cleaning, the more calcite is lost, and the more likely it becomes that any residual clay that has not been removed by physical cleaning will increase the ratio. These potentially significant sources of error can be overcome with a flow-through (FT) sequential leaching method that makes time- and labor-intensive pretreatments unnecessary. When combined with time-resolved analysis (FT-TRA) flow-through, performed with a gradually increasing and highly regulated acid strength, produces continuous records of Mg, Sr, Al, and Ca concentrations in the leachate sorted by dissolution susceptibility of the reacting material. Flow-through separates secondary calcite from less susceptible biogenic calcite and clay, and further resolves the biogenic component into primary and more resistant fractions. FT-TRA reliably separates secondary calcite (which is not representative of original life habitats) from the more resistant biogenic calcite (the desired signal) and clay (a contaminant of high Mg/Ca, which also contains Al), and further resolves the biogenic component into primary and more resistant fractions that may reflect habitat or other changes during ontogeny. We find that the most susceptible fraction of biogenic calcite in surface dwelling foraminifera gives the most accurate value for SST and therefore best represents primary calcite. Sequential dissolution curves can be used to correct the primary Mg/Ca ratio for clay, if necessary. However, the temporal separation of calcite from clay in FT-TRA is so complete that this correction is typically <=2%, even in clay-rich sediments. Unlike hands-on batch methods, that are difficult to reproduce exactly, flow-through lends itself to automation, providing precise replication of treatment for every sample. Our automated flow-through system can process 22 samples, two system blanks, and 48 mixed standards in <12 hours of unattended operation. FT-TRA thus represents a faster, cheaper, and better way to determine Mg/Ca ratios in foraminiferal calcite.

Stable carbon and oxygen isotope ratios of benthic foraminifera from Paleocene to Oligocene sediments

Benthic oxygen and carbon isotopic results from a depth transect on Maud Rise, Antarctica, provide the first evidence for Warm Saline Deep Water (WSDW) in the Paleogene oceans. Distinct reversals occur in the oxygen isotopic gradient between the shallower Hole 689B (Eocene depth ~1400 m; present-day depth 2080 m) and the deeper Hole 690B (Eocene depth ~2250 m; present-day depth 2914 m). The isotopic reversals, well developed by at least 46 Ma (middle middle Eocene), existed for much of the remaining Paleogene. We do not consider these reversals to be artifacts of differential diagenesis between the two sites or to have resulted from other potentially complicating factors. This being so, the results show that deep waters at Hole 690B were significantly warmer than deep waters at the shallower Hole 689B. A progressive decrease and eventual reversal in benthic to planktonic delta18O gradients in Hole 690B, demonstrate that the deeper waters became warmer relative to Antarctic surface waters during the Eocene. The warmer deep waters of the Paleogene are inferred to have been produced at middle to low latitudes, probably in the Tethyan region which contained extensive shallow-water platforms, ideal sites for the formation of high salinity water through evaporative processes. The ocean during the Eocene, and perhaps the Paleocene, is inferred to have been two-layered, consisting of warm, saline deep waters formed at low latitudes and overlain by cooler waters formed at high latitudes. This thermospheric ocean, dominated by halothermal circulation we name Proteus. The Neogene and modern psychrospheric ocean Oceanus is dominated by thermohaline circulation of deep waters largely formed at high latitudes. An intermediate condition existed during the Oligocene, with a three-layered ocean that consisted of cold, dense deep waters formed in the Antarctic (Proto-AABW), overlain by warm, saline deep waters from low latitudes, and in turn overlain by cool waters formed in the polar regions. This we name Proto-oceanus which combined both halothermal and thermohaline processes. The sequence of high latitude, major, climatic change inferred from the oxygen isotopic records is as follows: generally cooler earlier Paleocene; warming during the late Paleocene; climax of Cenozoic warmth during the early Eocene and continuing into the early middle Eocene; cooling mainly in a series of steps during the remainder of the Paleogene. Superimposed upon this Paleogene pattern, the Paleocene/Eocene boundary is marked by a brief but distinct warming that involved deep to surface waters and a reduction in surface to deep carbon and oxygen isotopic gradients. This event coincided with major extinctions among the deep-sea benthic foraminifers as shown by Thomas (1990 doi:10.2973/odp.proc.sr.113.123.1990). Salinity has played a major role in deep ocean circulation, and thus paleotemperatures cannot be inferred directly from the oxygen isotopic composition of Paleogene benthic foraminifers without first accounting for the salinity effect.

Chemical and Sr isotopic compositions of pore fluids and marine carbonates from ODP Hole 130-807A

The 87Sr/86Sr ratios and Sr concentrations in sediment and pore fluids are used to evaluate the rates of calcite recrystallization at ODP Site 807A on the Ontong Java Plateau, an 800-meter thick section of carbonate ooze and chalk. A numerical model is used to evaluate the pore fluid chemistry and Sr isotopes in an accumulating section. The deduced calcite recrystallization rate is 2% per million years (%/Myr) near the top of the section and decreases systematically in older parts of the section such that the rate is close to 0.1/age (in years). The deduced recrystallization rates have important implications for the interpretation of Ca and Mg concentration profiles in the pore fluids. The effect of calcite recrystallization on pore fluid chemistry is described by the reaction length, L, which varies by element, and depends on the concentration in pore fluid and solid. When L is small compared to the thickness of the sedimentary section, the pore fluid concentration is controlled by equilibrium or steady-state exchange with the solid phase, except within a distance L of the sediment-water interface. When L is large relative to the thickness of sediment, the pore fluid concentration is mostly controlled by the boundary conditions and diffusion. The values of L for Ca, Sr, and Mg are of order 15, 150, and 1500 meters, respectively. L_Sr is derived from isotopic data and modeling, and allows us to infer the values of L_Ca and L_Mg. The small value for L_Ca indicates that pore fluid Ca concentrations, which gradually increase down section, must be equilibrium values that are maintained by solution-precipitation exchange with calcite and do not reflect Ca sources within or below the sediment column. The pore fluid Ca measurements and measured alkalinity allow us to calculate the in situ pH in the pore fluids, which decreases from 7.6 near the sediment-water interface to 7.1+/-0.1 at 400-800 mbsf. While the calculated pH values are in agreement with some of the values measured during ODP Leg 130, most of the measurements are artifacts. The large value for L_Mg indicates that the pore fluid Mg concentrations at 807A are not controlled by calcite-fluid equilibrium but instead are determined by the changing Mg concentration of seawater during deposition, modified by aqueous diffusion in the pore fluids. We use the pore fluid Mg concentration profile at Site 807A to retrieve a global record for seawater Mg over the past 35 Myr, which shows that seawater Mg has increased rapidly over the past 10 Myr, rather than gradually over the past 60 Myr. This observation suggests that the Cenozoic rise in seawater Mg is controlled by continental weathering inputs rather than by exchange with oceanic crust. The relationship determined between reaction rate and age in silicates and carbonates is strikingly similar, which suggests that reaction affinity is not the primary determinant of silicate dissolution rates in nature.

Chemistry of gabbroic rocks from ODP Hole 118-735B

Gabbroic rocks and their late differentiates recovered at Site 735 represent 500 m of oceanic layer 3. The original cooling of a mid-ocean ridge magma chamber, its penetration by ductile shear zones and late intrusives, and the subsequent penetration of seawater through a network of cracks and into highly permeable magmatic hydrofracture horizons are recorded in the metamorphic stratigraphy of the core. Ductile shear zones are characterized by extensive dynamic recrystallization of primary phases, beginning in the granulite facies and continuing into the lower amphibolite facies. Increasing availability of seawater during dynamic recrystallization is reflected in depletions in 18O, increasing abundance of amphibole of variable composition and metamorphic plagioclase of intermediate composition, and more complete coronitic or pseudomorphous static replacement of magmatic minerals. Downcore correlation of synkinematic assemblages, bulk-rock oxygen isotopic compositions, and vein abundance suggest that seawater is introduced into the crust by way of small cracks and veins that mark the end of the ductile phase of deformation. This "deformation-enhanced" metamorphism dominates the upper 180 and the lower 100 m of the core. In the lower 300 m of the core, mineral assemblages of greenschist and zeolite facies are abundant within or adjacent to brecciated zones. Leucocratic veins found in these zones and adjacent host rock contain diopside, sodic plagioclase, epidote, chlorite, analcime, thomsonite, natrolite, albite, quartz, actinolite, sphene, brookite, and sulfides. The presence of zircon, Cl-apatite, sodic plagioclase, sulfides, and diopside in leucocratic veins having local magmatic textures suggests that some of the veins originated from late magmas or from hydrothermal fluids exsolved from such magmas that were subsequently replaced by (seawater-derived) hydrothermal assemblages. The frequent association of these late magmatic intrusive rocks within the brecciated zones suggests that they are both artifacts of magmatic hydrofracture. Such catastrophic fracture and hydrothermal circulation could produce episodic venting of hydrothermal fluids as well as the incorporation of a magmatically derived hydrothermal component. The enhanced permeability of the brecciated zones produced lower temperature assemblages because of larger volumes of seawater that penetrated the crust. The last fractures were sealed either by these hydrothermal minerals or by late carbonate-smectite veins, resulting in the observed low permeability of the core.