Description: Volcanic ash layers preserved within the geologic record represent precise time markers that correlate disparate depositional environments and enable the investigation of synchronous and/or asynchronous behaviors in Earth system and archaeological sciences. However, it is generally assumed that only exceptionally powerful events, such as supereruptions (≥450 km3 of ejecta as dense-rock equivalent; recurrence interval of ∼105 yr), distribute ash broadly enough to have an impact on human society, or allow us to address geologic, climatic, and cultural questions on an intercontinental scale. Here we use geochemical, age, and morphological evidence to show that the Alaskan White River Ash (eastern lobe; A.D. 833–850) correlates to the “AD860B” ash (A.D. 846–848) found in Greenland and northern Europe. These occurrences represent the distribution of an ash over 7000 km, linking marine, terrestrial, and ice-core records. Our results indicate that tephra from more moderate-size eruptions, with recurrence intervals of ∼100 yr, can have substantially greater distributions than previously thought, with direct implications for volcanic dispersal studies, correlation of widely distributed proxy records, and volcanic hazard assessment.

Description: A remarkably long period of Northern Hemispheric cooling in the 6 th century CE, which disrupted human societies across large parts of the globe, has been attributed to volcanic forcing of climate. A major tropical eruption in 540 CE is thought to have played a key role, but there is no consensus about the source volcano to date. Here, we present evidence for El Chichón in southern Mexico as the most likely candidate, based on a refined reconstruction of the volcano’s eruption history. A new chronological framework, derived from distal tephra deposits and the world’s largest Holocene beach ridge plain along the Gulf of Mexico, enabled us to positively link a major explosive event to a prominent volcanic sulfur spike in bipolar ice core records, dated at 540 CE. We speculate that voluminous tephra fall from the eruption had a severe environmental impact on Maya societies, leading to temporary cultural decline, site abandonment, and migration within the core area of Maya civilization.

Description: Volcanic ash layers preserved within the geologic record represent precise time markers that correlate disparate depositional environments and enable the investigation of synchronous and/or asynchronous behaviors in Earth system and archaeological sciences. However, it is generally assumed that only exceptionally powerful events, such as supereruptions (≥450 km 3 of ejecta as dense-rock equivalent; recurrence interval of ~10 5 yr), distribute ash broadly enough to have an impact on human society, or allow us to address geologic, climatic, and cultural questions on an intercontinental scale. Here we use geochemical, age, and morphological evidence to show that the Alaskan White River Ash (eastern lobe; A.D. 833–850) correlates to the "AD860B" ash (A.D. 846–848) found in Greenland and northern Europe. These occurrences represent the distribution of an ash over 7000 km, linking marine, terrestrial, and ice-core records. Our results indicate that tephra from more moderate-size eruptions, with recurrence intervals of ~100 yr, can have substantially greater distributions than previously thought, with direct implications for volcanic dispersal studies, correlation of widely distributed proxy records, and volcanic hazard assessment.

Description: From paleoproxy reconstructions and climate model simulations of the Northern Hemisphere (NH) climate during the Common Era (CE), we know that strong volcanic eruptions have induced cold periods like the Little Ice Age (LIA) and the mid-6th century cooling. However, less is known about such cold periods during the Holocene. Here, we study the Max Planck Institute Earth System Model Holocene simulations (6000 BCE to 1850 CE). One of the runs is forced with orbital forcing, land cover, greenhouse gas concentrations, solar forcing, stratospheric ozone, and volcanic forcing. The other run includes only orbital forcing and greenhouse gas concentrations. We simulate a large number of extremely cold years in the all-forcing run, which is primarily explained by volcanic eruptions. Applying a 200-year filter reveals 11 long-lasting cold periods similar to the LIA during the mid to late-Holocene, occurring every once or twice per millennium. These long-lasting cold periods correspond to increased volcanic activity, where the clustering of volcanic eruptions leads to an integrated cooling effect through the slow ocean-sea ice response. Eight of the eleven multi-centennial cold periods in our simulation correspond to previously identified phases of glacier advances throughout the NH, as well as reduced ring widths in tree ring records from Northern Finland. Whereas previous studies used mostly local proxy reconstructions, we identify NH annual mean multi-centennial cold periods. Finding several more such cold periods highlights the importance of understanding volcanic-induced long-lasting cold periods and the impact they could have had on society in the past.

Description: Atmospheric nuclear weapons testing (NWT) resulted in the injection of plutonium (Pu) into the atmosphere and subsequent global deposition. We present a new method for continuous semiquantitative measurement of 239Pu in ice cores, which was used to develop annual records of fallout from NWT in ten ice cores from Greenland and Antarctica. The 239Pu was measured directly using an inductively coupled plasma-sector field mass spectrometer, thereby reducing analysis time and increasing depth-resolution with respect to previous methods. To validate this method, we compared our one year averaged results to published 239Pu records and other records of NWT. The 239Pu profiles from the Arctic ice cores reflected global trends in NWT and were in agreement with discrete Pu profiles from lower latitude ice cores. The 239Pu measurements in the Antarctic ice cores tracked low latitude NWT, consistent with previously published discrete records from Antarctica. Advantages of the continuous 239Pu measurement method are (1) reduced sample preparation and analysis time; (2) no requirement for additional ice samples for NWT fallout determinations; (3) measurements are exactly coregistered with all other chemical, elemental, isotopic, and gas measurements from the continuous analytical system; and (4) the long half-life means the 239Pu record is stable through time.

Description: Volcanic eruptions contribute to climate variability, but quantifying these contributions has been limited by inconsistencies in the timing of atmospheric volcanic aerosol loading determined from ice cores and subsequent cooling from climate proxies such as tree rings. Here we resolve these inconsistencies and show that large eruptions in the tropics and high latitudes were primary drivers of interannual-to-decadal temperature variability in the Northern Hemisphere during the past 2,500 years. Our results are based on new records of atmospheric aerosol loading developed from high-resolution, multi-parameter measurements from an array of Greenland and Antarctic ice cores as well as distinctive age markers to constrain chronologies. Overall, cooling was proportional to the magnitude of volcanic forcing and persisted for up to ten years after some of the largest eruptive episodes. Our revised timescale more firmly implicates volcanic eruptions as catalysts in the major sixth-century pandemics, famines, and socioeconomic disruptions in Eurasia and Mesoamerica while allowing multi-millennium quantification of climate response to volcanic forcing.

Description: Rates of climate change in the Arctic are among the highest on Earth. Warming from increased carbon dioxide and other greenhouse gas concentrations is the long-term driver of Arctic climate change, but reductions in short-lived aerosols such as black carbon (BC) that contribute to climate warming offer the possibility of slowing Arctic climate change in the near-term. BC in snow and water is especially important to climate forcing in the Arctic because of its impact on albedo. Detailed understanding of past and present concentrations, deposition rates, sources, and transport pathways of BC to and within the Arctic is critical, however, to the design of effective mitigation policies. With their short lifetimes in the atmosphere, aerosol concentrations and deposition in the Arctic are dominated by regional, rather than global, sources, transport processes, and pathways. Such aerosols consist of continental dust, sea spray, particulates including BC and organic matter from combustion processes, sulfur and trace metals from volcanic emissions, and, during recent centuries, industrial activities. Further, intra- and inter-annual variability of aerosol deposition is large. As a result, spatially distributed measurements of historical, high-time-resolution records with a broad range of analytes are required to understand aerosol concentrations, sources, and variability while providing adequate information for evaluating global circulation, snowpack radiation, and other modeling results. Arrays of ice cores from polar and alpine glaciers and ice sheets offer the potential to provide spatially distributed historical records with very high time resolution and a broad spectrum of aerosols and source tracers, particularly when using a continuous flow analytical system. Here we present and discuss recent findings from measurements of BC and related source tracers in a developing array of ice cores from around the Arctic. We use 1850 to 2000 general circulation modeling to evaluate sources and transport pathways for BC, understand the impact of industrial and other human activities on Arctic BC, and assess the implications for climate forcing.