Date:6/29/2012

cycling of material from Earth's interior to exterior and back again forms one of the planet's primary geochemical cycles. Oceanic crust reacts chemically with the ocean, and this process changes the composition of that crust. Thus, when oceanic crust is recycled back into the interior of the Earth, it adds components that were not present when it was first formed. One of the most interesting and least well known changes in the composition of ocean crust is its oxidation by the ocean. It has been proposed that subduction of this oxidized ocean crust, and release of the oxidized components within the Earth, cause portions of Earth's mantle to oxidize, and that this oxidation is a necessary prerequisite to the formation of some types of ore deposits that include copper, gold, and molybdenum. However, this conclusion is controversial. In this paper, K.A. Evans and colleagues used new analyses of mantle-derived material in oceanic crust and model calculations to explore the plausibility of different proposed fates for subducted oxidized material.

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The offshore export of sand during exceptional discharge from California rivers

Jonathan A. Warrick and Patrick L. Barnard, U.S. Geological Survey, Pacific Coastal and Marine Science Center, 400 Natural Bridges Drive, Santa Cruz, California 95060, USA. Posted online 29 June 2012; doi: 10.1130/G33115.1.

Having an accurate accounting of how much sand is available to build beaches is important for understanding and dealing with coastal erosion. Coastal rivers on the U.S. west coast are the primary sources of sand to this region's popular beaches, and the majority of this sand is discharged during floods on these rivers. Warrick and Barnard found that rivers with high rates of sediment discharge, like the Santa Clara River of southern California, discharge sand far offshore of the littoral cell -- the nearshore area that provides sand for beaches. Thus, a significant amount of the sand discharg
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Contact: Kea Giles kgiles@geosociety.org Geological Society of America Source:Eurekalert

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