The Messinian salinity crisis--the desiccation of the Mediterranean Sea between 5.96 and 5.33 million years (Myr) ago--was one of the most dramatic events on Earth during the Cenozoic era. It resulted from the closure of marine gateways between the Atlantic Ocean and the Mediterranean Sea, the causes of which remain enigmatic. Here we use the age and composition of volcanic rocks to reconstruct the geodynamic evolution of the westernmost Mediterranean from the Middle Miocene epoch to the Pleistocene epoch (about 12.1-0.65 Myr ago). Our data show that a marked shift in the geochemistry of mantle-derived volcanic rocks, reflecting a change from subduction-related to intraplate-type volcanism, occurred between 6.3 and 4.8 Myr ago, largely synchronous with the Messinian salinity crisis. Using a thermomechanical model, we show that westward roll back of subducted Tethys oceanic lithosphere and associated asthenospheric upwelling provides a plausible mechanism for producing the shift in magma chemistry and the necessary uplift (approximately 1 km) along the African and Iberian continental margins to close the Miocene marine gateways, thereby causing the Messinian salinity crisis.

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[1] Volcanoes confront Earth scientists with new fundamental questions: Can airborne volcanic ash release nutrients on contact with seawater, thereby excite the marine primary productivity (MPP); and, most notably, can volcanoes through oceanic fertilization affect the global climate in a way that is so far poorly understood? Here we present results from biogeochemical experiments showing that 1) volcanic ash from subduction zone volcanoes rapidly release an array of nutrients (co-)limiting algal growth in vast oceanic areas, 2) at a speed much faster (minute-scale) than hitherto known and that marine phytoplankton from low-iron oceanic areas can swiftly, within days, utilize iron from volcanic sources. We further present satellite data possibly indicating an increase of the MPP due to the seaward deposition of volcanic particulate matter. Our study supports the hypothesis that oceanic (iron) fertilization with volcanic ash may play a vital role for the development of the global climate. Citation: Duggen, S., P. Croot, U. Schacht, and L. Hoffmann (2007), Subduction zone volcanic ash can fertilize the surface ocean and stimulate phytoplankton growth: Evidence from biogeochemical experiments and satellite data,

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