GEOESPELEOLOGIA
URI permanente para esta coleçãohttps://bdc.icmbio.gov.br/handle/cecav/2
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Resultados da Pesquisa
Item Obtaining High‐Resolution Magnetic Records From Speleothems Using Magnetic Microscopy(2024) Borlina, C. S.; Lima, E. A.; Feinberg, J. M; Jaqueto, P.; Lascu, I.; Trindade, R. I. F.; et al.Speleothems are mineral deposits capable of recording detrital and/or chemical remanent magnetization at annual timescales. They can offer high‐resolution paleomagnetic records of short‐term variations in Earth's magnetic field, crucial for understanding the evolution of the dynamo. Owing to limitations on the magnetic moment sensitivity of commercial cryogenic rock magnetometers (∼10− 11 Am2 ), paleomagnetic studies of speleothems have been limited to samples with volumes of several hundreds of mm3 , averaging tens to hundreds of years of magnetic variation. Nonetheless, smaller samples (∼1–10 mm3 ) can be measured using superconducting quantum interference device (SQUID) microscopy, with a sensitivity better than ∼10− 15 Am2 . To determine the application of SQUID microscopy for obtaining robust high‐resolution records from small‐volume speleothem samples, we analyzed three different stalagmites collected from Lapa dos Morcegos Cave (Portugal), Pau d'Alho Cave (Brazil), and Crevice Cave (United States). These stalagmites are representative of a range of magnetic properties and have been previously studied with conventional rock magnetometers. We show that by using SQUID microscopy we can achieve a five‐fold improvement in temporal resolution for samples with higher abundances of magnetic carriers (e.g., Pau d'Alho Cave and Lapa dos Morcegos Cave). In contrast, speleothems with low abundances of magnetic carriers (e.g., Crevice Cave) do not benefit from higher resolution analysis and are best analyzed using conventional rock magnetometers. Overall, by targeting speleothem samples with high concentrations of magnetic carriers we can increase the temporal resolution of magnetic records, setting the stage for resolving geomagnetic variations at short time scales.Item Modern anthropogenic drought in Central Brazil unprecedented during last 700 years(2024-02-26) Stríkis, N.M; Buarque, P.F.S.M; Cruz, F.W; et al.A better understanding of the relative roles of internal climate variability and external contributions, from both natural (solar, volcanic) and anthropogenic greenhouse gas forcing, is important to better project future hydrologic changes. Changes in the evaporative demand play a central role in this context, particularly in tropical areas characterized by high precipitation seasonality, such as the tropical savannah and semi-desertic biomes. Here we present a set of geochemical proxies in speleothems from a well-ventilated cave located in central-eastern Brazil which shows that the evaporative demand is no longer being met by precipitation, leading to a hydrological deficit. A marked change in the hydrologic balance in central-eastern Brazil, caused by a severe warming trend, can be identified, starting in the 1970s. Our findings show that the current aridity has no analog over the last 720 years. A detection and attribution study indicates that this trend is mostly driven by anthropogenic forcing and cannot be explained by natural factors alone. These results reinforce the premise of a severe long-term drought in the subtropics of eastern South America that will likely be further exacerbated in the future given its apparent connection to increased greenhouse gas emissions.