Pascal Bohleber

Next‐generation ice core technology reveals true minimum natural levels of lead (Pb) in the atmosphere: Insights from the Black Death

Abstract Contrary to widespread assumptions, next‐generation high (annual to multiannual) and ultra‐high (subannual) resolution analyses of an Alpine glacier reveal that true historical minimum natural levels of lead in the atmosphere occurred only once in the last ~2000 years. During the Black Death pandemic, demographic and economic collapse interrupted metal production and atmospheric lead dropped to undetectable levels. This finding challenges current government and industry understanding of preindustrial lead pollution and its potential implications for human health of children and adults worldwide. Available technology and geographic location have limited previous ice core investigations. We provide new high‐ (discrete, inductively coupled plasma mass spectrometry, ICP‐MS) and ultra‐high resolution (laser ablation inductively coupled plasma mass spectrometry, LA‐ICP‐MS) records of atmospheric lead deposition extracted from the high Alpine glacier Colle Gnifetti, in the Swiss‐Italian Alps. We show that contrary to the conventional wisdom, low levels at or approaching natural background occurred only in a single 4 year period in ~2000 years documented in the new ice core, during the Black Death (~1349–1353 C.E.), the most devastating pandemic in Eurasian history. Ultra‐high chronological resolution allows for the first time detailed and decisive comparison of the new glaciochemical data with historical records. Historical evidence shows that mining activity ceased upwind of the core site from ~1349 to 1353, while concurrently on the glacier lead (Pb) concentrations—dated by layer counting confirmed by radiocarbon dating—dropped to levels below detection, an order of magnitude beneath figures deemed low in earlier studies. Previous assumptions about preindustrial “natural” background lead levels in the atmosphere—and potential impacts on humans—have been misleading, with significant implications for current environmental, industrial, and public health policy, as well as for the history of human lead exposure. Trans‐disciplinary application of this new technology opens the door to new approaches to the study of the anthropogenic impact on past and present human health.

Influence of ice crystal anisotropy on seismic velocity analysis

Abstract In 2010 a reflection seismic survey was carried out on the Alpine glacier Colle Gnifetti. The processed and depth-converted data could be compared to a nearby ice core, drilled almost to the bed. Comparisons showed that the depth of the P-wave bed reflection was too shallow, while the depth of the SH-wave bed reflection fitted the ice-core length well. We are now able to explain the major part of these differences using the existing crystal orientations of the ice at Colle Gnifetti. We calculate anisotropic velocities for P- and SH-waves that are usually picked for stacking and compare them with zero-offset velocities needed for the depth conversion. Here we take the firn pack at Colle Gnifetti into account for P- and S-wave analysis. To incorporate the S-wave analysis we first derive a new equation for the relationship between density and S-wave velocity from diving waves. We show that anisotropic fabrics observed at Colle Gnifetti introduce a difference of only 1% between stacking and depth-conversion velocities for the SH-wave, but 7% for the P-wave. We suggest that this difference in stacking and depth-conversion velocity for the P-wave can be used to derive information about the existing anisotropy by combining our seismic data with, for example, radar data.

Joint interpretation of explosive and vibroseismic surveys on cold firn for the investigation of ice properties

Abstract Two seismic surveys were carried out on the high-altitude glacier saddle, Colle Gnifetti, Monte Rosa, Italy/Switzerland. Explosive and vibroseismic sources were tested to explore the best way to generate seismic waves to deduce shallow and intermediate properties (<100 m) of firn and ice. The explosive source (SISSY) excites strong surface and diving waves, degrading data quality for processing; no englacial reflections besides the noisy bed reflector are visible. However, the strong diving waves are analyzed to derive the density distribution of the firn pack, yielding results similar to a nearby ice core. The vibrator source (ElViS), used in both P- and SH-wave modes, produces detectable laterally coherent reflections within the firn and ice column. We compare these with ice-core and radar data. The SH-wave data are particularly useful in providing detailed, high-resolution information on firn and ice stratigraphy. Our analyses demonstrate the potential of seismic methods to determine physical properties of firn and ice, particularly density and potentially also crystal-orientation fabric.

A New Multielement Method for LA-ICP-MS Data Acquisition from Glacier Ice Cores

To answer pressing new research questions about the rate and timing of abrupt climate transitions, a robust system for ultrahigh-resolution sampling of glacier ice is needed. Here, we present a multielement method of LA-ICP-MS analysis wherein an array of chemical elements is simultaneously measured from the same ablation area. Although multielement techniques are commonplace for high-concentration materials, prior to the development of this method, all LA-ICP-MS analyses of glacier ice involved a single element per ablation pass or spot. This new method, developed using the LA-ICP-MS system at the W. M. Keck Laser Ice Facility at the University of Maine Climate Change Institute, has already been used to shed light on our flawed understanding of natural levels of Pb in Earths atmosphere.

Possible Icelandic Tephra Found in European Colle Gnifetti Glacier

Volcanic ash (tephra) provides unique time markers (isochrons) that are often used as an independent age-control tool for stratigraphic correlations of paleoclimate archives from ice cores. However, little credence has been given to the notion of finding tephra in ice cores collected in the European Alps because of the relatively large distance from volcanic sources and the presumed nature of regional atmospheric circulation patterns. We filtered particles from melted ice core drilling chips gathered roughly every meter during a 2013 drilling operation at Colle Gnifetti glacier in the Swiss-Italian Alps (45°55.74N, 7°52.58E, 4450 m asl). One filter, preliminarily dated to the nineteenth century by annual layer counting, contained a group of six visually similar tephra particles. Analyzing their chemistry using a scanning electron microscope equipped with an energy-dispersive x-ray spectrometer established that the six particles were volcanic in origin and are very similar in composition (a distinctive geochemical signature), pointing to a single volcanic eruption source. We proposed that one of several massive nineteenth century Eastern Icelandic neruptions is a potential source given eruption timing, size, tephra dispersion area, and similarities in chemical composition. This first finding of tephra in an Alpine ice core contributes to a regional tephrochronological framework that can be adapted for future correlation among different paleoclimate sequences.

The Role of Historical Context in Understanding Past Climate, Pollution and Health Data in Trans‐disciplinary Studies: Reply to Comments on More et al., 2017

Abstract Understanding the context from which evidence emerges is of paramount importance in reaching robust conclusions in scientific inquiries. This is as true of the present as it is of the past. In a trans‐disciplinary study such as More et al. (2017, https://doi.org/10.1002/2017GH000064) and many others appearing in this and similar journals, a proper analysis of context demands the use of historical evidence. This includes demographic, epidemiological, and socio‐economic data—common in many studies of the impact of anthropogenic pollution on human health—and, as in this specific case, also geoarchaeological evidence. These records anchor climate and pollution data in the geographic and human circumstances of history, without which we lose a fundamental understanding of the data itself. This article addresses Hinkley (2018, https://doi.org/10.1002/2017GH000105) by highlighting the importance of context, focusing on the historical and archaeological evidence, and then discussing atmospheric deposition and circulation in the specific region of our study. Since many of the assertions in Bindler (2018, https://doi.org/10.1002/2018GH000135) are congruent with our findings and directly contradict Hinkley (2018), this reply refers to Bindler (2018), whenever appropriate, and indicates where our evidence diverges.