August 2008 Geology and GSA Today media ...(late Pleistocene (50000-12000 cal yr B.P...)

Date:7/23/2008

late Pleistocene (50,000-12,000 cal yr B.P.), relative to present. Their data show the occurrence of a distinct transition from cooler temperatures and variable precipitation prior to the Last Glacial Maximum (LGM, ~21,000 cal yr B.P.) to a period of warmer temperatures and relative dryness that extends to the mid-Holocene (5000-3000 cal yr B.P.). This prolonged reduction in precipitation occurs against the backdrop of increasing atmospheric CO₂ concentrations, suggesting that the mixed savanna and dry forest communities in northeastern Bolivia during the LGM were not just the result of low CO₂ levels, as suggested previously, but also of lower precipitation. The results of Punyasena et al.'s analysis demonstrate the potential for using the distribution and abundance structure of modern Neotropical plant families to infer paleoclimate from the fossil pollen record.

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GSA Today Science Article

Is there enough sand? Evaluating the fate of Grand Canyon sandbars

Scott A. Wright et al., U.S. Geological Survey, California Water Science Center, 6000 J Street, Sacramento, California 95819, USA. Pages 4-10.

Large dams are spectacular feats of engineering, and few are as impressive as the 216-m-high Glen Canyon Dam that sits astride Colorado River and supplies electricity to more than 650,000 households. By trapping the entire incoming sediment load in Lake Powell and eliminating spring snowmelt floods, the dam has, however, significantly impacted the Colorado River and the ecosystems that depend upon the river. It was the recognition of the imperilled state of the river that prompted this past spring's 60 hour "high-flow experiment" during which 41,000 cubic feet of water were released per second into the river. The question posed by Scott Wright of the U.S. Geological Survey and colleagues is whether the dam can be operated such that sandbars, which are crucial to the riparian ecosystem, be rebuilt
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Contact: Christa Stratton cstratton@geosociety.org 303-357-1093 Geological Society of America Source:Eurekalert

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