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The specific goal of this project was to develop a more complete and quantitative understanding of natural and anthropogenic drivers of biomass burning over the Common Era. To do so, new high-resolution measurements of a broad range of chemical, elemental, and isotopic species were analyzed on the archived HT95 core using the continuous flow analysis system at the Desert Research Institute in 2023. These new measurements of the Hans Tausen 1995 (HT95) ice core, which was provided by collaborators at the University of Copenhagen, were used along with existing ice-core datasets to underpin atmospheric modeling to understand past emissions of black carbon from biomass burning and anthropogenic activities over the past 250 years (Zhang et al., 2024). The HT95 ice core was collected in 1995 and extends to ~3670 BCE. 

The specific goals of this project were to (1) investigate the rate and timing of temperature-dependent in situ biological production of carbon monoxide and methane in an Arctic ice core, (2) develop records of atmospheric carbon monoxide and methane spanning recent centuries, and (3) determine the roles that ice impurities may play in any observed in situ gas production. The collection and analysis of a ~150 meter (m) long ice core from Summit Station, Greenland in 2023 was used for these investigations and analysis of the ice core was conducted both in the field and in the Ice Core Laboratory at the Desert Research Institute (Reno, NV). This ice core was drilled within Summit Station near the cargo line, so ice deposited after camp establishment in the late 1980s was not analyzed because of contamination. 

Aerosol radiative forcing is an important but often poorly understood component of regional climate. While glacier ice contains the most detailed archives of past atmospheric aerosol composition and temperature, no well-preserved ice records extending into the last climatic transition have been reported for the historically important European region. Here, we use an Alpine ice core to document changes in European aerosols and climate from the end of the last glacial age (LGA) through the Holocene. The core was drilled on a glacier dome in the French Alps called the Dôme du Goûter (DDG), and it provides a stratigraphically intact record of aerosol and climate extending to at least 12 kyears (ky) before present. Although dating near the base of the glacier is not well constrained, the oldest DDG ice layers reflect glacial conditions in western Europe during the LGA. In addition to changes in atmospheric transport, increased sea-salt and dust deposition in western Europe recorded in the LGA ice suggest enhanced westerly winds and more active dust sources, possibly including North Africa. Deposition of terrestrial biogenic indicators during the cold LGA climate was lower, however, consistent with strongly reduced European vegetation. The DDG record of terrestrial biogenic emissions also suggests a decline of European forests throughout the Holocene, resulting from deterioration of climatic conditions and more recently from establishment of the first agricultural societies. The pronounced changes in atmospheric aerosol recorded in Alpine ice imply large variations in aerosol radiative forcing in western Europe during the last 12 ky. 

Ancient texts and archaeological evidence indicate substantial lead exposure during antiquity that potentially impacted human health. Although lead exposure routes were many and included the use of glazed tablewares, paints, cosmetics, and even intentional ingestion, the most significant for the nonelite, rural majority of the population may have been through background air pollution from mining and smelting of silver and lead ores that underpinned the Roman economy. Here, we determined potential health effects of this air pollution using Arctic ice core measurements of Roman-era lead pollution, atmospheric modeling, and modern epidemiology-based relationships between air concentrations, blood lead levels (BLLs), and cognitive decline. Findings suggest air lead concentrations exceeded 150 ng/m³near metallurgical emission sources, with average enhancements of >1.0 ng/m³over Europe during the Pax Romana apogee of the Roman Empire. The result was blood lead enhancements in young children of about 2.4 µg/dl above an estimated Neolithic background of 1.0 µg/dl, leading to widespread cognitive decline including a 2.5-to-3 point reduction in intelligence quotient throughout the Roman Empire. 

Refractory black carbon (rBC) aerosols in air and precipitation result from incomplete combustion. Prior to 18th century industrialization, the primary emission sources were wildfires and agricultural fires. After industrialization, fossil fuel burning has become an important emission source as well. Because these aerosols are import contributors to Earth’s radiative forcing both in the air and when deposited to bright surfaces such as fresh snow, quantifying past rBC emissions is critical to accurate Earth System Modeling. This data set contains 1750 to 2010 annual rBC depositional fluxes measured in a global array of 31, mostly polar ice cores. They were used (Zhang et al., Nature Communications, 2024) to reconstruct atmospheric rBC emissions using the atmospheric chemical transport GEOS-Chem. Details on the rBC measurement methods and chronology development are provided in the associated references for the individual ice core records. 

The original goal of the proposed research was to develop accurately dated, high-resolution, ice-core records of a broad range of elements and chemical species to expand and extend recently identified, causal linkages between (1) ancient societies; (2) volcanism and hydroclimate; and (3) wars, plagues, social unrest, and economic activity--while engaging ancient and pre-modern historians, economists, and students in consilient ice core research and interpretation. Underpinning these efforts was the proposed collection and analysis of a ~440 meter (m) ice core (Tunu2020 but delayed by COVID until 2022) from the northeastern flank of the Greenland ice sheet that was to be used to develop accurately dated, sub-annually resolved, multi-parameter records during the past 4k years of volcanism, heavy-metal pollution from ancient mining and smelting activities, as well as other indicators of climate and human activities. Because core quality and the drill penetration rate decreased very dramatically below ~165 m, however, two cores were collected instead of a single longer core. The Tunu2022a and Tunu2022b cores were located 50 m apart and about 5 kilometer (km) from the Tunu2013 core site. 

The overall objective of this research was to develop and interpret detailed records of Arctic lead pollution during the past ~8000 years to better understand the development, history, and impacts of mining and metallurgy from the late Neolithic period to present. The dataset contains high-resolution (30 millimeters [mm] average) measurements of elements, chemical species, and water isotopic ratios in the upper ~520 meters [m] of the archived REnland ice CAP (RECAP) ice core. Included are lead and other parameters such as the rare-earth-element cerium, non-sea-salt calcium, sulfur and sodium used for chronology development and interpretation of the lead record. The core was collected in 2015 from the Renland Ice Cap in east-central Greenland. No archive was available for the upper 99.6 m so the most recent part of the record corresponds to 116 years before 1950 (yb1950) or 1833 current era (CE).