952 resultados para air-sea interaction and Sao Pedro and Sao Paulo Archipelago


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Half-title: Buddhist practices in India.

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Microseisms are continuous vibrations pervasively recorded in the mili Hertz to 1 Hz frequency range. These vibrations are mostly composed of Rayleigh waves and are strongest in the 0.04 to 1 Hz frequency band. Their precise source mechanisms are still a matter of debate but it is agreed that they are related to atmospheric perturbations and ocean gravity waves. The Saint Peter Saint Paul Archipelago (SPSPA) is located in the equatorial region of the Atlantic Ocean about 1,100 km distant from the Brazilian northeastern coast. The SPSPA is composed by a set of several small rocky formations with a total area of approximately 17,000 m². Due to its remote distance from the continent and the lack of cultural noise, this location is a unique location for measuring microseismic noise and to investigate its relation with some climate and oceanographic variables. In the SPSPA we have recorded both primary microseisms (PM) at 0.04 – 0.12 Hz and the secondary microseisms (SM) at 0.12 – 0.4 Hz during 10 months in 2012 and 2013. Our analysis indicates a good correlation between the microseismic noise in the region and a seasonal dependency. In particular, the winter in the northern hemisphere. We have also shown that most of the PM is generated in the SPSPA itself. The SM source location depends with the seasonal climatic and oceanographic variables in the northern hemisphere

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We reviewed the paleoceanographic application of the carbon isotope composition of planktic foraminifera. Major controls on the distribution of d13C of dissolved CO2 (d13CSCO2) in the modern ocean are photosynthesis-respiration cycle, isotopic fractionation during air-sea exchange, and circulation. The carbon isotope composition of surface waters is not recorded without perturbations by planktic foraminifera. Besides d13CSCO2 of the surrounding seawater, the d13C composition of planktic foraminifera is affected by vital effects, the water depth of calcification and postdepositional dissolution. We compared several high-resolution (>10cm/ka) carbon isotope records from the Southern Ocean, the Benguela upwelling system, and the tropical Atlantic. In the Southern Ocean, carbon isotope values are about 1.2 per mil lower during the LGM and up to 1.7 per mil lower during the last deglaciation, when compared to the Holocene. These depletions might be explained with a combination of a subsurface nutrient enrichment and reduced air-sea exchange due to an increased stratification of surface waters. In the Benguela Upwelling system, waters originating in the south are upwelled. While the deglacial minimum is transferred and recorded in its full extent in the d13C record of Globigerina bulloides, glacial values show only little changes. This might suggest, that the lower glacial d13C values of high-latitude surface waters are not upwelled off Namibia, or that G. bulloides records post-upwelling conditions, when increased seasonal production has already increased surface-water d13C. Synchronous to the d13C depletions in high latitudes, low d13C values were recorded in Globigerinoides sacculifer during the LGM and during the last deglaciation in the nutrient-depleted western equatorial Atlantic. Hence, part of the glacial-interglacial variability presumably transferred from high to low latitudes seems to be related to changes in thermodynamic fractionation. The variability in d13C is lowest in the northernmost core M35003-4 from the eastern Caribbean, implying that the Antarctic Intermediate Water might have acted as a conduit to transfer the deglacial minimum to tropical surface waters.