Carlo Barbante

Meteoric smoke fallout over the Holocene epoch revealed by iridium and platinum in Greenland ice

An iridium anomaly at the Cretaceous/Tertiary boundary layer has been attributed to an extraterrestrial body that struck the Earth some 65u2009million years ago. It has been suggested that, during this event, the carrier of iridium was probably a micrometre-sized silicate-enclosed aggregate or the nanophase material of the vaporized impactor. But the fate of platinum-group elements (such as iridium) that regularly enter the atmosphere via ablating meteoroids remains largely unknown. Here we report a record of iridium and platinum fluxes on a climatic-cycle timescale, back to 128,000u2009years ago, from a Greenland ice core. We find that unexpectedly constant fallout of extraterrestrial matter to Greenland occurred during the Holocene, whereas a greatly enhanced input of terrestrial iridium and platinum masked the cosmic flux in the dust-laden atmosphere of the last glacial age. We suggest that nanometre-sized meteoric smoke particles, formed from the recondensation of ablated meteoroids in the atmosphere at altitudes >70u2009kilometres, are transported into the winter polar vortices by the mesospheric meridional circulation and are preferentially deposited in the polar ice caps. This implies an average global fallout of 14 ± 5u2009kilotons per year of meteoric smoke during the Holocene.

Interglacials of the last 800,000 years

Interglacials, including the present (Holocene) period, are warm, low land ice extent (high sea level), end-members of glacial cycles. Based on a sea level definition, we identify eleven interglacials in the last 800,000u2009years, a result that is robust to alternative definitions. Data compilations suggest that despite spatial heterogeneity, Marine Isotope Stages (MIS) 5e (last interglacial) and 11c (~400u2009ka ago) were globally strong (warm), while MIS 13a (~500u2009ka ago) was cool at many locations. A step change in strength of interglacials at 450u2009ka is apparent only in atmospheric CO2 and in Antarctic and deep ocean temperature. The onset of an interglacial (glacial termination) seems to require a reducing precession parameter (increasing Northern Hemisphere summer insolation), but this condition alone is insufficient. Terminations involve rapid, nonlinear, reactions of ice volume, CO2, and temperature to external astronomical forcing. The precise timing of events may be modulated by millennial-scale climate change that can lead to a contrasting timing of maximum interglacial intensity in each hemisphere. A variety of temporal trends is observed, such that maxima in the main records are observed either early or late in different interglacials. The end of an interglacial (glacial inception) is a slower process involving a global sequence of changes. Interglacials have been typically 10–30u2009ka long. The combination of minimal reduction in northern summer insolation over the next few orbital cycles, owing to low eccentricity, and high atmospheric greenhouse gas concentrations implies that the next glacial inception is many tens of millennia in the future.

A Historical Record of Heavy Metal Pollution in Alpine Snow and Ice

Heavy metals and trace elements are ubiquitous throughout the environment, some are essential for life (e.g., Fe), others are micronutrients (e.g., Se) and others are considered as toxic elements (e.g., Hg). Levels of these elements in the environment are determined by the local geochemistry and anthropogenic emissions, with implications for human and environmental health. Records from Alpine ice cores have demonstrated to be among the best tools in paleoenvironmental studies to reconstruct past emissions of heavy metals and persistent organic pollutants. From the comparison of trace element records in the snow and ice with the emission inventories compiled in recent years it is also possible to reconstruct the past trends in the emission of these compounds. We present here some trace elements records from the European Alps and in particular from the Mont Blanc and Monte Rosa regions. The study of levels of these elements in alpine regions allows us to begin to understand their biogeochemistry and their effects on a global and regional scale. However, without advances in clean working techniques and the outstanding improvement in instrument sensitivity that have occurred over the last two decades, none of these studies would have been possible.