Synchronous volcanic eruptions and abrupt climate change ∼17.7 ka plausibly linked by stratospheric ozone depletion.

Glacial-state greenhouse gas concentrations and Southern Hemisphere climate conditions persisted until ∼17.7 ka, when a nearly synchronous acceleration in deglaciation was recorded in paleoclimate proxies in large parts of the Southern Hemisphere, with many changes ascribed to a sudden poleward shift in the Southern Hemisphere westerlies and subsequent climate impacts. We used high-resolution chemical measurements in the West Antarctic Ice Sheet Divide, Byrd, and other ice cores to document a unique, ∼192-y series of halogen-rich volcanic eruptions exactly at the start of accelerated deglaciation, with tephra identifying the nearby Mount Takahe volcano as the source. Extensive fallout from these massive eruptions has been found >2,800 km from Mount Takahe. Sulfur isotope anomalies and marked decreases in ice core bromine consistent with increased surface UV radiation indicate that the eruptions led to stratospheric ozone depletion. Rather than a highly improbable coincidence, circulation and climate changes extending from the Antarctic Peninsula to the subtropics-similar to those associated with modern stratospheric ozone depletion over Antarctica-plausibly link the Mount Takahe eruptions to the onset of accelerated Southern Hemisphere deglaciation ∼17.7 ka.

Spatial pattern of reinfestation by Triatoma infestans in Chancanif, Argentina.

We examined the environmental correlates and the spatial pattern of infestation by Triatoma infestans, a vector of Chagas disease, in a rural area of Argentina five years following an insecticidal campaign. Patterns of infestation were identified in an entomological survey, as mapped with high-resolution satellite imagery and analyzed in a geographic information system. Logistic regression was used to relate infestation to observed household characteristics as well as the location and density of households. Location was the most significant predictor of infestation for domiciles. For peridomestic structures surrounding the domiciles, the combination of location and the presence/absence of goat pens was most significant. In considering any infestation, whether domiciliary or peridomestic, the combination of location, presence/absence of animal pens, and the type of household construction were found to be most significant. Using these statistical relationships to back-classify the field data resulted in accuracies between 85% and 87%. A map of infestation probability for the town of Chancaní was developed from the logistic regression.

Infection dynamics of Sin Nombre virus after a widespread decline in host populations.

Many researchers have speculated that infection dynamics of Sin Nombre virus are driven by density patterns of its major host, Peromyscus maniculatus. Few, if any, studies have examined this question systematically at a realistically large spatial scale, however. We collected data from 159 independent field sites within a 1 million-hectare study area in Nevada and California, from 1995-1998. In 1997, there was a widespread and substantial reduction in host density. This reduction in host density did not reduce seroprevalence of antibody to Sin Nombre virus within host populations. During this period, however, there was a significant reduction in the likelihood that antibody-positive mice had detectable virus in their blood, as determined by reverse-transcriptase polymerase chain reaction. Our findings suggest 2 possible causal mechanisms for this reduction: an apparent change in the age structure of host populations and landscape-scale patterns of host density. This study indicates that a relationship does exist between host density and infection dynamics and that this relationship concurrently operates at different spatial scales. It also highlights the limitations of antibody seroprevalence as a metric of infections, especially during transient host-density fluctuations.