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1] Abstract: Isotopic and trace element analyses of basalts dredged from across the Galápagos Platform confirm the previously established east facing horseshoe pattern of depleted geochemical signatures at the center of the archipelago and more enriched signatures along the periphery. Statistical analysis of the isotopic data indicates that geochemical variations in the Galápagos cannot be explained by mixing between only the plume and the depleted asthenosphere. Instead, four isotopically distinct end-members must be interacting to account for the subtleties of the Sr, Nd, Pb, and He isotopic data. Three of the components are geographically restricted: one in the south, one in the central region, and one in the north. These three plume components then mix with the fourth component, depleted mantle, which is indistinguishable from the MORB source. The central component resembles the high 3 He/ 4 He mantle reservoir that may be common to many plumes and has variously been called PHEM, FOZO, and C by others. Whereas this mantle reservoir appears to make a minor contribution to the composition of most hot spot systems, it may constitute the main body of the Galápagos plume. Geographic distribution of the end-members suggests that the plume is centered near Fernandina $928N but may be significantly diluted by depleted mantle even near the main conduit. The geochemically distinct end-members trace an eastward mantle flow, manifested as decreasing contributions of the plume in the direction of plate motion. The plume may be tilted by shear in the asthenosphere from plate motion and ambient mantle flow. As it is bent, the plume thermally entrains surrounding upper mantle, resulting in the horseshoe-shaped distribution of depleted and enriched material. The end-members may also outline a deep, strong lateral flow of mantle toward the Galápagos Spreading Center, supplying plume material to the ridge system. Overall, our results suggest that the Galápagos hot spot is both compositionally and dynamically complex owing to its tectonic setting adjacent to a mid-ocean ridge.

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This article provides an overview of the Reanalysis Study of the Harvard Six Cities and the American Cancer Society (ACS) studies of particulate air pollution and mortality. The previous findings of the studies have been subject to debate. In response, a reanalysis team, comprised of Canadian and American researchers, was invited to participate in an independent reanalysis project to address the concerns. Phase I of the reanalysis involved the design of data audits to determine whether each study conformed to the consistency and accuracy of their data. Phase II of the reanalysis involved conducting a series of comprehensive analyses using alternative statistical methods. Alternative models were also used to identify covariates that may confound or modify the association of particulate air pollution as well as identify sensitive population subgroups. The audit demonstrated that the data in the original analyses were of high quality, as were the risk estimates reported by the original investigators. The sensitivity analysis illustrated that the mortality risk estimates reported in both studies were found to be robust against alternative Cox models. Detailed investigation of the covariate effects found a significant modifying effect of education and a relative risk of mortality associated with fine particles and declining education levels. The study team applied spatial analytic methods to the ACS data, resulting in various levels of spatial autocorrelations supporting the reported association for fine particles mortality of the original investigators as well as demonstrating a significant association between sulfur dioxide and mortality. Collectively, our reanalysis suggest that mortality may be attributable to more than one component of the complex mixture of ambient air pollutants for U.S. urban areas.

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