The paper by Chase et al. details the discovery of sensitive indicators of past environmental change in the stratified fecal deposits (known as middens) of rock hyraxes in the Namib Desert of Namibia. The records they have obtained, derived from stable carbon and nitrogen isotope signals, show that hyrax middens have extraordinary potential to preserve high-resolution records of rapid climate change, and that over the last 11,700 years, the Namib Desert has experienced highly variable climates, marked by abrupt shifts in moisture availability. These shifts include events such as the Little Ice Age, the Medieval Warm Period, and the 2700 B.P. event, indicating strong links with atmospheric and oceanic circulation dynamics as well as cycles of orbital and solar forcing. These data are critical to the evaluation of processes and feedbacks within the global climate system, particularly the relative importance of high- vs. low-latitude insolation forcing of tropical systems. Their findings indicate that the long-held hypothesis that the Inter-Tropical Convergence Zone has migrated southward during the Holocene following precessional variations in summer insolation cannot be applied to southern Africa. The implications of this in terms of understanding regional- to global-scale climate dynamics and developing general circulation models that can adequately predict future climate scenarios cannot be overstated.
Decoupled geochemical behavior of As and Cu in hydrothermal systems
Artur P. Deditius et al., Commonwealth Scientific and Industrial Research Organisation (CSIRO), Exploration and Mining, 26 Dick Perry Avenue, Perth, WA 6151, Australia. Pages 707-710.
Deditius et al. describe alternating zones of copper- and arsenic-rich pyrite from gold-deposits at Pueblo Viejo (Dominican Republic) and Yanacocha (Peru). Arsenic-rich zones are enriched in gold, silver, an
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Geological Society of America