We report the discovery in Lake Cuitzeo in central Mexico of a black, carbon-rich, lacustrine layer, containing nanodiamonds, microspherules, and other unusual materials that date to the early Younger Dryas and are interpreted to result from an extraterrestrial impact. These proxies were found in a 27-m-long core as part of an interdisciplinary effort to extract a paleoclimate record back through the previous interglacial. Our attention focused early on an anomalous, 10-cm-thick, carbon-rich layer at a depth of 2.8 m that dates to 12.9 ka and coincides with a suite of anomalous coeval environmental and biotic changes independently recognized in other regional lake sequences. Collectively, these changes have produced the most distinctive boundary layer in the late Quaternary record. This layer contains a diverse, abundant assemblage of impact-related markers, including nanodiamonds, carbon spherules, and magnetic spherules with rapid melting/quenching textures, all reaching synchronous peaks immediately beneath a layer containing the largest peak of charcoal in the core. Analyses by multiple methods demonstrate the presence of three allotropes of nanodiamond: n-diamond, i-carbon, and hexagonal nanodiamond (lonsdaleite), in order of estimated relative abundance. This nanodiamond-rich layer is consistent with the Younger Dryas boundary layer found at numerous sites across North America, Greenland, and Western Europe. We have examined multiple hypotheses to account for these observations and find the evidence cannot be explained by any known terrestrial mechanism. It is, however, consistent with the Younger Dryas boundary impact hypothesis postulating a major extraterrestrial impact involving multiple airburst(s) and and/or ground impact(s) at 12.9 ka.black mat | cosmic impact

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A B S T R A C TPart 1 of this study investigated evidence of biomass burning in global ice records, and here we continue to test the hypothesis that an impact event at the Younger Dryas boundary (YDB) caused an anomalously intense episode of biomass burning at ∼12.8 ka on a multicontinental scale (North and South America, Europe, and Asia). Quantitative analyses of charcoal and soot records from 152 lakes, marine cores, and terrestrial sequences reveal a major peak in biomass burning at the Younger Dryas (YD) onset that appears to be the highest during the latest Quaternary. For the Cretaceous-Tertiary boundary (K-Pg) impact event, concentrations of soot were previously utilized to estimate the global amount of biomass burned, and similar measurements suggest that wildfires at the YD onset rapidly consumed ∼10 million km 2 of Earth's surface, or ∼9% of Earth's biomass, considerably more than for the K-Pg impact. Bayesian analyses and age regressions demonstrate that ages for YDB peaks in charcoal and soot across four continents are synchronous with the ages of an abundance peak in platinum in the Greenland Ice Sheet Project 2 (GISP2) ice core and of the YDB impact event (12,835-12,735 cal BP). Thus, existing evidence indicates that the YDB impact event caused an anomalously large episode of biomass burning, resulting in extensive atmospheric soot/dust loading that triggered an "impact winter." This, in turn, triggered abrupt YD cooling and other climate changes, reinforced by climatic feedback mechanisms, including Arctic sea ice expansion, rerouting of North American continental runoff, and subsequent ocean circulation changes.

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La familia Lamiaceae es una de las más diversas en México; sin embargo, para Michoacán no se contaba con datos actualizados sobre la riqueza y distribución de sus integrantes. Con base en la revisión bibliográfica y de ejemplares depositados en los herbarios CIMI, EBUM, ENCB, IEB y MEXU se registraron 14 géneros y 105 especies nativas o naturalizadas, siendo Salvia el género mejor representado, seguido de Stachys, Hyptis y Scutellaria. Se encontraron cinco especies endémicas de Salvia y una de Stachys, además de dos nuevos registros para Scutellaria. La mayoría de las especies se encuentran en la provincia del Sistema Neovolcánico Transversal en la que prevalecen ambientes templados con vegetación de bosques de coníferas, encinos y mesófilo de montaña. La provincia de la Sierra Madre del Sur tiene menor representación para la mayoría de los géneros, excepto Vitex que se encuentra principalmente en las Depresiones de los ríos Balsas y Tepalcatepec. Aquellos géneros con afinidad Laurásica Norteamericana se encuentran dentro del Sistema Neovolcánico Transversal y la Sierra Madre del Sur principalmente en bosques de coníferas, mientras que Hyptis y Vitex de afinidad Gondwánica Sudamericana son más frecuentes en bosques tropicales secos de la Sierra Madre del Sur. Michoacán se ubica entre los estados más diversos en Lamiaceae para la República Mexicana; sin embargo, las cifras proporcionadas podrían aumentar cuando se subsane la escasez de ejemplares procedentes principalmente de la Sierra Madre del Sur, región que ha sido poco colectada.

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Here, we use 30 long-term, high-resolution palaeoecological records from Mexico, Central and South America to address two hypotheses regarding possible drivers of resilience in tropical forests as measured in terms of recovery rates from previous disturbances. First, we hypothesize that faster recovery rates are associated with regions of higher biodiversity, as suggested by the insurance hypothesis. And second, that resilience is due to intrinsic abiotic factors that are location specific, thus regions presently displaying resilience in terms of persistence to current climatic disturbances should also show higher recovery rates in the past. To test these hypotheses, we applied a threshold approach to identify past disturbances to forests within each sequence. We then compared the recovery rates to these events with pollen richness before the event. We also compared recovery rates of each site with a measure of present resilience in the region as demonstrated by measuring global vegetation persistence to climatic perturbations using satellite imagery. Preliminary results indeed show a positive relationship between pre-disturbance taxonomic richness and faster recovery rates. However, there is less evidence to support the concept that resilience is intrinsic to a region; patterns of resilience apparent in ecosystems presently are not necessarily conservative through time.

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