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New research in Bolivia suggests that sedimentation on the Amazon flood plain is closely associated with the El Niño/Southern Oscillation (ENSO) cycle — the main source of variability in weather and climate around the world from one year to the next. The research, published in this week's Nature, also provides new insights into interpreting the Earth's history according to the sediments left behind by floodwater.

Rolf Aalto of the University of Washington, Seattle, United States, and colleagues analysed sediment from the banks of two tributaries of the Amazon — the rivers Beni and Mamore. The researchers show that this sedimentation occurs in fits and starts. The thickest layers are formed during the cold phases of the ENSO cycle when high rainfall flushes large volumes of sediment, along with associated nutrients and carbon, from the Andes.

In an accompanying article in Nature, Chris Paola of the University of Minnesota, United States, says that the results highlight the dangers of using sediment cores as a continuous record of geological time. "Imagine what it would be like if you remembered only one year of each decade, and of that year, only one of every ten days, and so on," he says.

Link to News and Views article in Nature by Chris Paola

Link to research paper in Nature by Rolf Aalto et al

References: Nature 425, 459 (2003)/Nature 425, 493 (2003)

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