Here, we present direct measurements of atmospheric composition and Antarctic climate from the mid-Pleistocene (∼1 Ma) from ice cores drilled in the Allan Hills blue ice area, Antarctica. The 1-Ma ice is dated from the deficit in 40 Ar relative to the modern atmosphere and is present as a stratigraphically disturbed 12-m section at the base of a 126-m ice core. The 1-Ma ice appears to represent most of the amplitude of contemporaneous climate cycles and CO 2 and CH 4 concentrations in the ice range from 221 to 277 ppm and 411 to 569 parts per billion (ppb), respectively. These concentrations, together with measured δD of the ice, are at the warm end of the field for glacial-interglacial cycles of the last 800 ky and span only about one-half of the range. The highest CO 2 values in the 1-Ma ice fall within the range of interglacial values of the last 400 ka but are up to 7 ppm higher than any interglacial values between 450 and 800 ka. The lowest CO 2 values are 30 ppm higher than during any glacial period between 450 and 800 ka. This study shows that the coupling of Antarctic temperature and atmospheric CO 2 extended into the mid-Pleistocene and demonstrates the feasibility of discontinuously extending the current ice core record beyond 800 ka by shallow coring in Antarctic blue ice areas.climate change | glacial cycles | atmospheric CO 2 | ice cores | greenhouse gases

Abstract. Among ice core drilling sites in the European Alps, Colle Gnifetti (CG) is the only non-temperate glacier to offer climate records dating back at least 1000 years. This unique long-term archive is the result of an exceptionally low net accumulation driven by wind erosion and rapid annual layer thinning. However, the full exploitation of the CG time series has been hampered by considerable dating uncertainties and the seasonal summer bias in snow preservation. Using a new core drilled in 2013 we extend annual layer counting, for the first time at CG, over the last 1000 years and add additional constraints to the resulting age scale from radiocarbon dating. Based on this improved age scale, and using a multi-core approach with a neighbouring ice core, we explore the time series of stable water isotopes and the mineral dust proxies Ca 2+ and insoluble particles. Also in our latest ice core we face the already known limitation to the quantitative use of the stable isotope variability based on a high and potentially non-stationary isotope/temperature sensitivity at CG. Decadal trends in Ca 2+ reveal substantial agreement with instrumental temperature and are explored here as a potential site-specific supplement to the isotope-based temperature reconstruction. The observed coupling between temperature and Ca 2+ trends likely results from snow preservation effects and the advection of dust-rich air masses coinciding with warm temperatures. We find that if calibrated against instrumental data, the Ca 2+ -based temperature reconstruction is in robust agreement with the latest proxy-based summer temperature reconstruction, including a "Little Ice Age" cold period as well as a medieval climate anomaly. Part of the medieval climate period around AD 1100-1200 clearly stands out through an increased occurrence of dust events, potentially resulting from a relative increase in meridional flow and/or dry conditions over the Mediterranean.

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.

ABSTRACT. Ice cores provide a robust reconstruction of past climate. However, development of timescales by annual-layer counting, essential to detailed climate reconstruction and interpretation, on ice cores collected at low-accumulation sites or in regions of compressed ice, is problematic due to closely spaced layers. Ice-core analysis by laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) provides sub-millimeter-scale sampling resolution (on the order of 100 µm in this study) and the low detection limits (ng L -1 ) necessary to measure the chemical constituents preserved in ice cores. We present a newly developed cryocell that can hold a 1 m long section of ice core, and an alternative strategy for calibration. Using ice-core samples from central Greenland, we demonstrate the repeatability of multiple ablation passes, highlight the improved sampling resolution, verify the calibration technique and identify annual layers in the chemical profile in a deep section of an ice core where annual layers have not previously been identified using chemistry. In addition, using sections of cores from the Swiss/Italian Alps we illustrate the relationship between Ca, Na and Fe and particle concentration and conductivity, and validate the LA-ICP-MS Ca profile through a direct comparison with continuous flow analysis results.

Terrestrial meteorite ages indicate that some ice at the Allan Hills blue ice area (AH BIA) may be as old as 2.2 Ma. As such, ice from the AH BIA could potentially be used to extend the ice core record of paleoclimate beyond 800 ka. We collected samples from 5 to 10 cm depth along a 5 km transect through the main icefield and drilled a 225 m ice core (S27) at the midpoint of the transect to develop the climate archive of the AH BIA. Stable water isotope measurements (δD) of the surface chips and of ice core S27 yield comparable signals, indicating that the climate record has not been significantly altered in the surface ice. Measurements of 40Aratm and δ18Oatm taken from ice core S27 and eight additional shallow ice cores constrain the age of the ice to approximately 90–250 ka. Our findings provide a framework around which future investigations of potentially older ice in the AH BIA could be based.