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陕西快乐十分最新开奖:Ecological and hydroclimate responses to strengthening of the Hadley circulation in South America during the Late Miocene cooling
广东快乐十分投注下载 www.hmclip.net Edited by Gilles Ramstein, Commissariat à l'énergie Atomique et aux énergies Alternatives - CNRS - Universite de Versailles Saint-Quentin, Gif-Sur-Yvette, France, and accepted by Editorial Board Member Jean Jouzel March 27, 2019 (received for review June 22, 2018)
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This paper analyzes the Late Miocene continental record of hydroclimate from the central Andes and subsequent ecological response to climatic change during this interval. The Late Miocene cooling (LMC) is characterized by a sharp decrease (up to 6 °C) of sea-surface temperatures and has been shown to have driven ecosystem reorganization, leading to conditions similar to Quaternary. We use the stable isotopic record preserved in pedogenic carbonate nodules as a proxy for hydroclimate changes during the LMC. This, combined with general circulation simulations, shows that strengthening of the Hadley circulation in South America during the LMC enhanced subtropical aridification and in turn promoted expansion of C4 grasses and evolution of high-crowned teeth in mammals.
Near-modern ecosystems were established as a result of rapid ecological adaptation and climate change in the Late Miocene. On land, Late Miocene aridification spread in tandem with expansion of open habitats including C4 grassland ecosystems. Proxy records for the central Andes spanning the Late Miocene cooling (LMC) show the reorganization of subtropical ecosystems and hydroclimate in South America between 15 and 35°S. Continental pedogenic carbonates preserved in Neogene basins record a general increase of δ18O and δ13C values from pre-LMC to post-LMC, most robustly occurring in the subtropics (25 to 30°S), suggesting aridification and a shift toward a more C4-plant-dominated ecosystem. These changes are closely tied to the enhancement of the Hadley circulation and moisture divergence away from the subtropics toward the Intertropical Convergence Zone as revealed by climate model simulations with prescribed sea-surface temperatures (SSTs) reflecting different magnitudes of LMC steepening of equator-to-pole temperature gradient and CO2 decline.
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Author contributions: B.C. designed research; B.C., M.C., and R.F. performed research; B.C., M.C., and R.F. analyzed data; and B.C., M.C., and R.F. wrote the paper.
The authors declare no conflict of interest.
This article is a PNAS Direct Submission. G.R. is a guest editor invited by the Editorial Board.
This article contains supporting information online at www.pnas.org/lookup/suppl/doi:10.1073/pnas.1810721116/-/DCSupplemental.
Published under the PNAS license.