Shallow firn cores, in addition to a near-basal ice core, were recovered in 2018 from the Quelccaya ice cap (5470 m a.s.l) in the Cordillera Vilcanota, Peru, and in 2017 from the Nevado Illimani glacier (6350 m a.s.l) in the Cordillera Real, Bolivia. The two sites are ~450 km apart. Despite meltwater percolation resulting from warming, particle-based trace element records (e.g. Fe, Mg, K) in the Quelccaya and Illimani shallow cores retain well-preserved signals. The firn core chronologies, established independently by annual layer counting, show a convincing overlap indicating the two records contain comparable signals and therefore capture similar regional scale climatology. Trace element records at a ~1–4 cm resolution provide past records of anthropogenic emissions, dust sources, volcanic emissions, evaporite salts and marine-sourced air masses. Using novel ultra-high-resolution (120 μm) laser technology, we identify annual layer thicknesses ranging from 0.3 to 0.8 cm in a section of 2000-year-old radiocarbon-dated near-basal ice which compared to the previous annual layer estimates suggests that Quelccaya ice cores drilled to bedrock may be older than previously suggested by depth-age models. With the information collected from this study in combination with past studies, we emphasize the importance of collecting new surface-to-bedrock ice cores from at least the Quelccaya ice cap, in particular, due to its projected disappearance as soon as the 2050s.

High-resolution analysis of the ice core from Colle Gnifetti, Switzerland, allows yearly and sub-annual measurement of pollution for the period of highest lead production in the European Middle Ages, c. AD 1170–1220. Here, the authors use atmospheric circulation analysis and other geoarchaeological records to establish that Britain was the principal source of that lead pollution. The comparison of annual lead deposition at Colle Gnifetti displays a strong similarity to trends in lead production documented in the English historical accounts. This research provides unique new insight into the yearly political economy and environmental impact of the Angevin Empire of Kings Henry II, Richard the Lionheart and John.

The seventh-century AD switch from gold to silver currencies transformed the socio-economic landscape of North-west Europe. The source of silver, however, has proven elusive. Recent research, integrating ice-core data from the Colle Gnifetti drill site in the Swiss Alps, geoarchaeological records and numismatic and historical data, has provided new evidence for this transformation. Annual ice-core resolution data are combined with lead pollution analysis to demonstrate that significant new silver mining facilitated the change to silver coinage, and dates the introduction of such coinage to c. AD 660. Archaeological evidence and atmospheric modelling of lead pollution locates the probable source of the silver to mines at Melle, in France.

Isochronal layers in firn detected with ground-penetrating radar (GPR) and dated using results from ice-core analyses are used to calculate accumulation rates along a 100 km across-flow profile in West Antarctica. Accumulation rates are shown to be highly variable over short distances. Elevation measurements from global positioning system surveys show that accumulation rates derived from shallow horizons correlate well with surface undulations, which implies that wind redistribution of snow is the leading cause of this variability. Temporal changes in accumulation rate over 25–185 year intervals are smoothed to along-track length scales comparable to surface undulations in order to identify trends in accumulation that are likely related to changes in climate. Results show that accumulation rates along this profile have decreased in recent decades, which is consistent with core-derived time series of annual accumulation rates measured at the two ends of the radar profile. These results suggest that temporal variability observed in accumulation-rate records from ice cores and GPR profiles can be obscured by spatial influences, although it is possible to resolve temporal signals if the effects of local topography and ice flow are quantified and removed.

A 40.9 m ice core was recovered from Far East Rongbuk Glacier (FER), Qomolangma (Mount Everest), Himalaya, and an 80.4 m core from neighboring East Rongbuk Glacier (ER). Both are dated by seasonal variations of δ18O and major-ionic profiles, together with references of β-activity peaks. In this paper we compare the chemical records of these two cores to show post-depositional modification processes. The smoothed β18O profiles of the two cores show a similar trend. However, the mean β18O value of the FER core for the period 1954—96 is 3.12%o less than that of the corresponding part of the ER core, and the major-ionic profiles of the two cores differ considerably. We suggest that melting-away of the snow layer deposited during the pre-monsoon season may account for lower β18O values of the FER than of the ER core, and higher terrestrial ion concentrations in the FER core for the period 1957-63 may contribute to changes by chemical reactions in the presence of snowmelting. The significantly decreased NH4 and, to a lesser degree, SO42 concentrations in the FER core could be caused by the ion elution process that moved most chemicals away with runoff.

From its original formulation in 1990 the International Trans-Antarctic Scientific Expedition (ITASE) has had as its primary aim the collection and interpretation of a continent-wide array of environmental parameters assembled through the coordinated efforts of scientists from several nations. ITASE offers the ground-based opportunities of traditional-style traverse travel coupled with the modern technology of GPS, crevasse detecting radar, satellite communications and multidisciplinary research. By operating predominantly in the mode of an oversnow traverse, ITASE offers scientists the opportunity to experience the dynamic range of the Antarctic environment. ITASE also offers an important interactive venue for research similar to that afforded by oceanographic research vessels and large polar field camps, without the cost of the former or the lack of mobility of the latter. More importantly, the combination of disciplines represented by ITASE provides a unique, multidimensional (space and time) view of the ice sheet and its history. ITASE has now collected >20 000km of snow radar, recovered more than 240 firn/ice cores (total length 7000 m), remotely penetrated to ~4000m into the ice sheet, and sampled the atmosphere to heights of >20 km.

Using results stemming from the International Trans-Antarctic Scientific Expedition (ITASE) ice-core array plus data from ice cores from the South Pole and Siple Dome we investigate the use of sodium (Na+), non-sea-salt sulfate (nssSO42–) and methylsulfonate (MS–) as proxies for Antarctic sea-ice extent (SIE). Maximum and mean annual chemistry concentrations for these three species correlate significantly with maximum, mean and minimum annual SIE, offering more information and clarification than single ice-core and single species approaches. Significant correlations greater than 90% exist between Na+ and maximum SIE; nssSO42– with minimum and mean SIE; and MS– with mean SIE. Correlations with SIE within large geographic regions are in the same direction for all ice-core sites for Na+ and nssSO42– but not MS–. All ice cores display an SIE correlation with nssSO42– and MS–, but not all correlate with Na+. This multi-core multi-parameter study provides the initial step in determining which chemical species can be used reliably and in which regions as a building block for embedding other ice-core records. Once established, the resulting temporal and spatial matrix can be used to relate ice extents, atmospheric patterns, biological productivity and site conditions.

Thirteen annually resolved accumulation-rate records covering the last ~200 years from the Pine Island–Thwaites and Ross drainage systems and the South Pole are used to examine climate variability over West Antarctica. Accumulation is controlled spatially by the topography of the ice sheet, and temporally by changes in moisture transport and cyclonic activity. A comparison of mean accumulation since 1970 at each site to the long-term mean indicates an increase in accumulation for sites located in the western sector of the Pine Island–Thwaites drainage system. Accumulation is negatively associated with the Southern Oscillation Index (SOI) for sites near the ice divide, and periods of sustained negative SOI (1940–42, 1991–95) correspond to above-mean accumulation at most sites. Correlations of the accumulation-rate records with sea-level pressure (SLP) and the SOI suggest that accumulation near the ice divide and in the Ross drainage system may be associated with the mid-latitudes. The post-1970 increase in accumulation coupled with strong SLP–accumulation-rate correlations near the coast suggests recent intensification of cyclonic activity in the Pine Island– Thwaites drainage system.

High-resolution chemical records from an 80.4m ice core from the central Himalaya demonstrate climatic and environmental changes since 1844. the chronological net accumulation series shows a sharp decrease from the mid-1950s, which is coincident with the widely observed glacier retreat. A negative correlation is found between the ice-core δ18O record and the monsoon precipitation for Indian region 7. the temporal variation of the terrestrial ions (Ca2+ and Mg2+) is controlled by both the monsoon precipitation for Indian regions 3,7 and 8, located directly south and west of the Himalaya, and the dust-storm duration and frequency in the northern arid regions, such as the Taklimakan desert, China. the NH4+ profile is fairly flat until the 1940s, then substantially increases until the end of the 1980s, with a slight decrease during the 1990s which may reflect new agricultural practices. the SO42– and NO3– profiles show an apparent increasing trend, especially during the period 1940s–80s. Moreover, SO42– concentrations for the East Rongbuk Glacier core are roughly double that of the nearby Dasuopu core at Xixabangma, Himalaya, due to local human activity including that of climbing teams who use gasoline for cooking, energy and transport.

A series of ice cores from sites with different snow-accumulation rates across Law Dome, East Antarctica, was investigated for methanesulphonic acid (MSA) movement. the precipitation at these sites (up to 35 km apart) is influenced by the same air masses, the principal difference being the accumulation rate. At the low-accumulation-rate W20k site (0.17m ice equivalent), MSAwas completely relocated from the summer to winter layer. Moderate movement was observed at the intermediate-accumulation-rate site (0.7m ice equivalent), Dome Summit South (DSS), while there was no evidence of movement at the high-accumulation-rate DE08 site (1.4m ice equivalent). the main DSS record of MSA covered the epoch AD 1727–2000 and was used to investigate temporal post-depositional changes. Co-deposition of MSA and sea-salt ions was observed in the surface layers, outside of the main summer MSA peak,which complicates interpretation of these peaks as evidence of movement in deeper layers. A seasonal study of the 273 year DSS record revealed MSA migration predominantly from summer into autumn (in the up-core direction), but this migration was suppressed during the Tambora (1815) and unknown (1809) volcanic eruption period, and enhanced during an epoch (1770–1800) with high summer nitrate levels. A complex interaction between the gradients in nss-sulphate, nitrate and sea salts (which are influenced by accumulation rate) is believed to control the rate and extent of movement of MSA.

Shallow ice cores were obtained from widely distributed sites across the West Antarctic ice sheet, as part of the United States portion of the International Trans-Antarctic Scientific Expedition (US ITASE) program. The US ITASE cores have been dated by annual-layer counting, primarily through the identification of summer peaks in non-sea-salt sulfate (nssSO42–) concentration. Absolute dating accuracy of better than 2 years and relative dating accuracy better than 1 year is demonstrated by the identification of multiple volcanic marker horizons in each of the cores, Tambora, Indonesia (1815), being the most prominent. Independent validation is provided by the tracing of isochronal layers from site to site using high-frequency ice-penetrating radar observations, and by the timing of mid-winter warming events in stable-isotope ratios, which demonstrate significantly better than 1 year accuracy in the last 20 years. Dating precision to ±1 month is demonstrated by the occurrence of summer nitrate peaks and stable-isotope ratios in phase with nssSO42–, and winter-time sea-salt peaks out of phase, with phase variation of <1 month. Dating precision and accuracy are uniform with depth, for at least the last 100 years.

This paper reports the lead concentration and flux (where accumulation rate is available) along the route of the 1990 International Trans-Antarctic Expedition. The lead concentration in Larsen Ice Shelf and Antarctic Peninsula, the western part of the route, was 7.4 ± 4.1 pg g−1. The lead concentration in East Antarctic snow (South Pole to Mirny station) was 2 3 times higher than that in West Antarctica (Larsen Ice Shelf to South Pole). Taking into account the difference in site conditions, the difference between the above value over this area in 1989 and the value of 6.3 ±3.3 pg g−1 at a site within this area in 1980 (Wolff and Peel, 1985) is not significant. Because the relative contribution of soil dust, volcanoes and the oceans to lead concentration in Antarctica is about 0.5 pg g−1 under modern climatic conditions (Boutron and Patterson, 1987), it is believed that the lead in Antarctic surface snow is dominated by pollution input. The lead-concentration increase from west to east over the trans-Antarctic route suggests that remote Antarctica has been impacted by anthropogenic activities. The lowest lead flux (0.064 ng cn-2 a−1) was on the Antarctic Plateau, mainly reflecting the background global pollution. The mean flux of 0.273 ng cnT2 a−1 in the western part of the route (Larsen Ice Shelf to the Ellsworth Mountains) may result from the pollution input from the Southern Hemisphere. In addition to the influence of global and/or hemispheric pollution, local activities (notably the use of leaded gasolene) appear to have affected the region from Pionerskaya to Mirny.

McMurdo Dry Valleys (MDV; Ross Sea region, Antarctica) precipitation exhibits extreme seasonality in ion concentration, 3–5 orders of magnitude between summer and winter precipitation. To identify aerosol sources and investigate causes for the observed amplitude in concentration variability, four snow pits were sampled along a coast–Polar Plateau transect across the MDV. The elevation of the sites ranges from 50 to 2400 m and the distance from the coast from 8 to 93 km. Average chemistry gradients along the transect indicate that most species have either a predominant marine or terrestrial source in the MDV. Empirical orthogonal function analysis on the snow-chemistry time series shows that at least 57% of aerosol deposition occurs concurrently. A conceptual climate model, based on meteorological observations, is used to explain the strong seasonality in the MDV. Our results suggest that radiative forcing of the ice-free valleys creates a surface low-pressure cell during summer which promotes air-mass flow from the Ross Sea. The associated precipitating air mass is relatively warm, humid and contains a high concentration of aerosols. During winter, the MDV are dominated by air masses draining off the East Antarctic ice sheet, that are characterized by cold, dry and low concentrations of aerosols. The strong differences between these two air-mass sources create in the MDV a polar version of the monsoonal flow, with humid, warm summers and dry, cold winters.

Annually dated ice cores from West and East Antarctica provide proxies for past changes in atmospheric circulation over Antarctica and portions of the Southern Ocean, temperature in coastal West and East Antarctica, and the frequency of South Polar penetration of El Niño events. During the period AD 1700–1850, atmospheric circulation over the Antarctic and at least portions of the Southern Hemisphere underwent a mode switch departing from the out-of-phase alternation of multi-decadal long phases of EOF1 and EOF2 modes of the 850 hPa field over the Southern Hemisphere (as defined in the recent record by Thompson and Wallace, 2000; Thompson and Solomon, 2002) that characterizes the remainder of the 700 year long record. From AD 1700 to 1850, lower-tropospheric circulation was replaced by in-phase behavior of the Amundsen Sea Low component of EOF2 and the East Antarctic High component of EOF1. During the first phase of the mode switch, both West and East Antarctic temperatures declined, potentially in response to the increased extent of sea ice surrounding both regions. At the end of the mode switch, West Antarctic coastal temperatures rose and East Antarctic coastal temperatures fell, respectively, to their second highest and lowest of the record. Polar penetration of El Niño events increased during the mode switch. The onset of the AD 1700–1850 mode switch coincides with the extreme state of the Maunder Minimum in solar variability. Late 20th-century West Antarctic coastal temperatures are the highest in the record period, and East Antarctic coastal temperatures close to the lowest. Since AD 1700, extratropical regions of the Southern Hemisphere have experienced significant climate variability coincident with changes in both solar variability and greenhouse gases.

Chemistry data from 16, 50–115m deep, sub-annually dated ice cores are used to investigate spatial and temporal concentration variability of sea-salt (ss) SO42– and excess (xs) SO42– over West Antarctica and the South Pole for the last 200 years. Low-elevation ice-core sites in western West Antarctica contain higher concentrations of SO42– as a result of cyclogenesis over the Ross Ice Shelf and proximity to the Ross Sea Polynya. Linear correlation analysis of 15 West Antarctic ice-core SO42– time series demonstrates that at several sites concentrations of ssSO42– are higher when sea-ice extent (SIE) is greater, and the inverse for xsSO42–. Concentrations of xsSO42– from the South Pole site (East Antarctica) are associated with SIE from the Weddell region, and West Antarctic xsSO42– concentrations are associated with SIE from the Bellingshausen–Amundsen–Ross region. The only notable rise of the last 200 years in xsSO42–, around 1940, is not related to SIE fluctuations and is most likely a result of increased xsSO42– production in the mid–low latitudes and/or an increase in transport efficiency from the mid–low latitudes to central West Antarctica. These high-resolution records show that the source types and source areas of ssSO42– and xsSO42– delivered to eastern and western West Antarctica and the South Pole differ from site to site but can best be resolved using records from spatial ice-core arrays such as the International Trans-Antarctic Scientific Expedition (ITASE).

The isotopic and chemical signatures for ice-age and Holocene ice from Summit, Greenland, and Penny Ice Cap, Baffin Island, Canada, are compared. the usual pattern of low δ18O, high Ca2+ and high Cl– is presented in the Summit records, but Penny Ice Cap has lower than present Cl– in its ice-age ice. A simple extension of the Hansson model (Hansson, 1994) is developed and used to simulate these signatures. the low ice-age Cl– from Penny Ice Cap is explained by having the ice-age ice originating many thousands of km inland near the centre of the Laurentide ice sheet and much further from the marine sources. Summit’s flowlines all start close to the present site. the Penny Ice Cap early-Holocene δ18O’s had to be corrected to offset the Laurentide meltwater distortion. the analysis suggests that presently the Summit and Penny Ice Cap marine impurity originates about 500 km away, and that presently Penny Ice Cap receives a significant amount of local continental impurity.

Explosive volcanic eruptions can inject large quantities of sulphur dioxide into the stratosphere. the aerosols that result from oxidation of the sulphur dioxide can produce significant cooling of the troposphere by reflecting or absorbing solar radiation. It is possible to obtain an estimate of the relative stratospheric sulphur aerosol concentration produced by different volcanoes by comparing sulphuric acid fluxes determined by analysis of polar ice cores. Here,we use a non-sea-salt sulphate time series derived from three well-dated Law Dome ice cores to investigate sulphuric acid flux ratios for major eruptions over the period AD 1301–1995. We use additional data from other cores to investigate systematic spatial variability in the ratios. Only for the Kuwae eruption (Law Dome ice date AD 1459.5) was the H2SO4 flux larger than that deposited by Tambora (Law Dome ice date AD 1816.7).

Ice-core chemistry data from Victoria Lower Glacier, Antarctica, suggest, at least for the last 50 years, a direct influence of solar activity variations on the McMurdo Dry Valleys (MDV) climate system via controls on air-mass input from two competing environments: the East Antarctic ice sheet and the Ross Sea. During periods of increased solar activity, when total solar irradiance is relatively high, the MDV climate system appears to be dominated by air masses originating from the Ross Sea, leading to higher aerosol deposition. During reduced solar activity, the Antarctic interior seems to be the dominant air-mass source, leading to lower aerosol concentration in the ice-core record. We propose that the sensitivity of the MDV to variations in solar irradiance is caused by strong albedo differences between the ice-free MDV and the ice sheet.

We present highly resolved, annually dated, calibrated proxies for atmospheric circulation from several Antarctic ice cores (ITASE (International Trans-Antarctic Scientific Expedition), Siple Dome, Law Dome) that reveal decadal-scale associations with a South Pole ice-core 10Be proxy for solar variability over the last 600 years and annual-scale associations with solar variability since AD 1720. We show that increased (decreased) solar irradiance is associated with increased (decreased) zonal wind strength near the edge of the Antarctic polar vortex. The association is particularly strong in the Indian and Pacific Oceans and as such may contribute to understanding climate forcing that controls drought in Australia and other Southern Hemisphere climate events. We also include evidence suggestive of solar forcing of atmospheric circulation near the edge of the Arctic polar vortex based on ice-core records from Mount Logan, Yukon Territory, Canada, and both central and south Greenland as enticement for future investigations. Our identification of solar forcing of the polar atmosphere and its impact on lower latitudes offers a mechanism for better understanding modern climate variability and potentially the initiation of abrupt climate-change events that operate on decadal and faster scales.