How does rising atmospheric CO2 affect marine organisms?

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Pampa del Tamarugal Basin, Atacama Desert, Chile
Nester, P.L., Gayo, E., Latorre, C., Jordan, T.E. and Blanco, N. 2007. Perennial stream discharge in the hyper-arid Atacama Desert of northern Chile during the latest Pleistocene. Proceedings of the National Academy of Sciences, USA 104: 19,724-19,729.

The authors studied fluvial terraces in the Pampa del Tamarugal (PdT) basin (~21°S, 69°W) of the Atacama Desert of northern Chile, which contains widespread fossil wood, in situ roots, and well preserved leaf litter deposits indicative of perennial surface flow in now-dry channels, where streams once cut canyons in the desert's currently hyper-arid core. This work revealed that the period from AD 900 to 1300 was the wettest interval of the past 11,000-plus years, which "is of opposite hydrological impact (wet) to that of coastal Peru (dry), where lithic concentrations in a marine core document diminished strength of El Niņo events during the Medieval Climatic Anomaly." This unique set of regional circumstances is thus a strong indication of the dramatic but varied hydrological effects of the global Medieval Warm Period in this particular part of the world.