A Method for Continuous (239)Pu Determinations in Arctic and Antarctic Ice Cores

Canadian high arctic ice core records of organophosphate flame retardants and plasticizers

Organophosphate esters (OPEs) have been used as flame retardants, plasticizers, and anti-foaming agents over the past several decades. Of particular interest is the long range transport potential of OPEs given their ubiquitous detection in Arctic marine air. Here we report 19 OPE congeners in ice cores drilled on remote icefields and ice caps in the Canadian high Arctic. A multi-decadal temporal profile was constructed in the sectioned ice cores representing a time scale spanning the 1970s to 2014-16. In the Devon Ice Cap record, the annual total OPE (∑OPEs) depositional flux for all of 2014 was 81 μg m-2, with the profile dominated by triphenylphosphate (TPP, 9.4 μg m-2) and tris(2-chloroisopropyl) phosphate (TCPP, 42 μg m-2). Here, many OPEs displayed an exponentially increasing depositional flux including TCPP which had a doubling time of 4.1 ± 0.44 years. At the more northern site on Mt. Oxford icefield, the OPE fluxes were lower. Here, the annual ∑OPEs flux in 2016 was 5.3 μg m-2, dominated by TCPP (1.5 μg m-2) but also tris(2-butoxyethyl) phosphate (1.5 μg m-2 TBOEP). The temporal trend for halogenated OPEs in the Mt. Oxford icefield is bell-shaped, peaking in the mid-2000s. The observation of OPEs in remote Arctic ice cores demonstrates the cryosphere as a repository for these substances, and supports the potential for long-range transport of OPEs, likely associated with aerosol transport.

The 239Pu nuclear fallout as recorded in an Antarctic ice core drilled at Dome C (East Antarctica)

Starting from 1952 C.E. more than 540 atmospheric nuclear weapons tests (NWT) were conducted in different locations of the Earth. This lead to the injection of about 2.8 t of ²³⁹Pu in the environment, roughly corresponding to a total ²³⁹Pu radioactivity of 6.5 PBq. A semiquantitative ICP-MS method was used to measure this isotope in an ice core drilled in Dome C (East Antarctica). The age scale for the ice core studied in this work was built by searching for well-known volcanic signatures and synchronising these sulfate spikes with established ice core chronologies. The reconstructed plutonium deposition history was compared with previously published NWT records, pointing out an overall agreement. The geographical location of the tests was found to be an important parameter strongly affecting the concentration of ²³⁹Pu on the Antarctic ice sheet. Despite the low yield of the tests conducted in the 1970s, we highlight their important role in the deposition of radioactivity in Antarctica due to the relative closeness of the testing sites.

Assessment of internal radiation exposure to Antarctic biota due to selected natural radionuclides in terrestrial and marine environment

The present article introduces data on natural radioactivity (⁴⁰K, ^230,232Th, ^234,238U) in the Antarctic marine and terrestrial environment. Various biota samples were analysed due to internal exposure to ⁴⁰K, ^230,232Th, ^234,238U. Activity concentration of ⁴⁰K was the highest in both marine and terrestrial samples. Mean values of ⁴⁰K activity concentration are 1340 Bq/kg and 370 Bq/kg for the marine and terrestrial samples respectively. ²³⁴U/²³⁸U ratios analysis revealed that sea waters and sea spray are the main source of the uranium in the terrestrial samples. Average ^230,232Th, ^234,238U activity concentrations in the Antarctic biota do not exceed 6 Bq/kg. Weighted internal dose rates are relatively low; they range from approximately 0.1 to 0.6 μGy/h. Statistically significant differences in radionuclide accumulation were discovered between the mosses and lichens. It may point to various mechanisms of the nutrient absorption from the environment by these organisms.

Hemispheric black carbon increase after the 13th-century Māori arrival in New Zealand

New Zealand was among the last habitable places on earth to be colonized by humans¹. Charcoal records indicate that wildfires were rare prior to colonization and widespread following the 13th- to 14th-century Māori settlement², but the precise timing and magnitude of associated biomass-burning emissions are unknown^1,3, as are effects on light-absorbing black carbon aerosol concentrations over the pristine Southern Ocean and Antarctica⁴. Here we used an array of well-dated Antarctic ice-core records to show that while black carbon deposition rates were stable over continental Antarctica during the past two millennia, they were approximately threefold higher over the northern Antarctic Peninsula during the past 700 years. Aerosol modelling⁵ demonstrates that the observed deposition could result only from increased emissions poleward of 40° S-implicating fires in Tasmania, New Zealand and Patagonia-but only New Zealand palaeofire records indicate coincident increases. Rapid deposition increases started in 1297 (±30 s.d.) in the northern Antarctic Peninsula, consistent with the late 13th-century Māori settlement and New Zealand black carbon emissions of 36 (±21 2 s.d.) Gg y^-1 during peak deposition in the 16th century. While charcoal and pollen records suggest earlier, climate-modulated burning in Tasmania and southern Patagonia^6,7, deposition in Antarctica shows that black carbon emissions from burning in New Zealand dwarfed other preindustrial emissions in these regions during the past 2,000 years, providing clear evidence of large-scale environmental effects associated with early human activities across the remote Southern Hemisphere.

Plutonium in coral archives: A good primary marker for an Anthropocene type section

While we officially live in the Holocene epoch, global warming and many other impacts of global change have led to the proposal and wide adoption of the Anthropocene to define the present geological epoch. The Anthropocene Working Group (AWG) established that it should be treated as a formal stratigraphic unit, demonstrated by a reference level commonly known as "golden spike", still under discussion. Here we show that the onset of bomb-derived plutonium recorded in two banded massive corals from the Caribbean Sea is consistent (1955-1956 CE), so sites far from nuclear testing grounds are potentially suitable to host a type section of the Anthropocene. Coastal coral demonstration sites are feasible, could foster economic development, and may serve as focal points for scientific dissemination and environmental education.

Anthropogenic radionuclides in Antarctic biota - dosimetrical considerations

The article presents results of the research on artificial radionuclides (¹³⁷Cs, ⁹⁰Sr, ²⁴¹Am) in the Antarctic environment. Samples of 12 species from the marine environment: Pygoscelis adeliae, Pygoscelis papua, Macronectes giganteus, Pagodroma nivea, Catharacta antarctica, Leptonychotes weddellii, Mirounga leonina, Harpagifer antarcticus, Chaenocephalus aceratus, Nacella concinna, Himantothallus grandifolius, Iridaea cordata (bones, feathers, soft tissues, eggs' shells of birds, bones, skin, fur of mammals, fish, mollusks' soft tissues and shells, algae) and samples of 4 species from the terrestrial environment: Sanionia uncinata, Usnea antarctica, Usnea aurantiaco-atra, Deschampsia antarctica (mosses, lichens, grass) were investigated. Differences in the accumulation of ¹³⁷Cs between marine and terrestrial ecosystem were shown, which are mostly due to conservatism of mosses and lichens and active removal of cesium by animal body. Furthermore discrepancy between mosses and lichens in the radioceasium accumulation was statistically proven with the additional use of Neutron Activation Analysis. Moreover, the internal weighted dose rates assessment was prepared using the ERICA Tool. The dose rates were relatively low, not exceeding several dozen nGy/h. Nonetheless, one species - Pagodroma nivea, was significantly outstanding due to the highest weighted dose rate it is burdened with.

Pervasive Arctic lead pollution suggests substantial growth in medieval silver production modulated by plague, climate, and conflict

Lead pollution in Arctic ice reflects large-scale historical changes in midlatitude industrial activities such as ancient lead/silver production and recent fossil fuel burning. Here we used measurements in a broad array of 13 accurately dated ice cores from Greenland and Severnaya Zemlya to document spatial and temporal changes in Arctic lead pollution from 200 BCE to 2010 CE, with interpretation focused on 500 to 2010 CE. Atmospheric transport modeling indicates that Arctic lead pollution was primarily from European emissions before the 19th-century Industrial Revolution. Temporal variability was surprisingly similar across the large swath of the Arctic represented by the array, with 250- to 300-fold increases in lead pollution observed from the Early Middle Ages to the 1970s industrial peak. Superimposed on these exponential changes were pronounced, multiannual to multidecadal variations, marked by increases coincident with exploitation of new mining regions, improved technologies, and periods of economic prosperity; and decreases coincident with climate disruptions, famines, major wars, and plagues. Results suggest substantial overall growth in lead/silver mining and smelting emissions-and so silver production-from the Early through High Middle Ages, particularly in northern Europe, with lower growth during the Late Middle Ages into the Early Modern Period. Near the end of the second plague pandemic (1348 to ∼1700 CE), lead pollution increased sharply through the Industrial Revolution. North American and European pollution abatement policies have reduced Arctic lead pollution by >80% since the 1970s, but recent levels remain ∼60-fold higher than at the start of the Middle Ages.

Plutonium fallout reconstructed from an Antarctic Plateau snowpack using inductively coupled plasma sector field mass spectrometry

Anthropogenic plutonium (Pu) in the environment is a result of atmospheric nuclear testing during the second half of the 20th century. In this work, we analyzed a 4-meter deep Antarctic Plateau snowpack characterized by a low snow accumulation rate and negligible snow impurities. These sample conditions enabled us to measure the snowpack Pu fallout by applying inductively coupled plasma sector field mass spectrometry to a few mL of snow melt without purification or preconcentration. Pu concentrations in the reconstructed Pu fallout record for the period after 1956 CE increased and decreased in agreement with past atmospheric nuclear testing. Two peaks and two dips associable with historical events were observed, and the highest peak in 1964(±1) CE approximately coincided with the maximum concentration of non-sea-salt sulfate caused by the Mt. Agung eruption in 1963 CE. Enhanced Pu fallout in the 1970s was attributed the geographical proximity of the Southern Hemispheric nuclear test sites. Our results suggest that by improving the instrumental sensitivity and precision, the potential of the Antarctic ice sheet as an archive of Pu fallout can be further explored and utilized for understanding atmospheric dispersion and for dating ice cores.

Method for Correcting Continuous Ice-Core Elemental Measurements for Under-Recovery

Measurement of elemental concentrations in ice cores are critical for determining atmospheric aerosol variations. For such measurements, acidified ice-core meltwater typically is analyzed continuously (<5 min after acidification) or discretely (∼3 months after acidification). The reduced acidification time during continuous analysis may result in a measured elemental concentration that is lower than the concentration of discrete analysis if particulates are not fully dissolved. To evaluate this, sections of three ice cores from Greenland and Antarctica were measured both continuously (4.5 min after acidification) and discretely (repeatedly from 1 to 151 days after continuous measurements), with discrete samples collected from the meltwater sample stream prior to continuous measurement. We show that elements such as Na, Sr, and S dissolved readily and therefore were fully recovered during continuous measurements. Average recovery for other elements was between 70 to 100% for Cd, Gd, Mg, Mn, U, and Yb, 50 to 90% for Ca, Ce, Sm, and V, and less than 50% for Al, Fe, and La. Given the advantages of continuous measurements, we conclude that the preferred method for ice-core measurements is continuous analysis with simultaneous discrete sample collection, followed by adjustment of the continuous measurements based on discrete sample analysis at least 3 months after acidification.

Nonlinear rise in Greenland runoff in response to post-industrial Arctic warming

The Greenland ice sheet (GrIS) is a growing contributor to global sea-level rise¹, with recent ice mass loss dominated by surface meltwater runoff^2,3. Satellite observations reveal positive trends in GrIS surface melt extent⁴, but melt variability, intensity and runoff remain uncertain before the satellite era. Here we present the first continuous, multi-century and observationally constrained record of GrIS surface melt intensity and runoff, revealing that the magnitude of recent GrIS melting is exceptional over at least the last 350 years. We develop this record through stratigraphic analysis of central west Greenland ice cores, and demonstrate that measurements of refrozen melt layers in percolation zone ice cores can be used to quantifiably, and reproducibly, reconstruct past melt rates. We show significant (P < 0.01) and spatially extensive correlations between these ice-core-derived melt records and modelled melt rates^5,6 and satellite-derived melt duration⁴ across Greenland more broadly, enabling the reconstruction of past ice-sheet-scale surface melt intensity and runoff. We find that the initiation of increases in GrIS melting closely follow the onset of industrial-era Arctic warming in the mid-1800s, but that the magnitude of GrIS melting has only recently emerged beyond the range of natural variability. Owing to a nonlinear response of surface melting to increasing summer air temperatures, continued atmospheric warming will lead to rapid increases in GrIS runoff and sea-level contributions.

Variations of plutonium isotopic ratios in Antarctic ecosystems

The aim of the article was to verify the hypothesis concerning the diversification of plutonium sources in the natural environment of Antarctica. Plutonium activity and atom ratios were analyzed in two groups of biological samples: terrestrial and marine. Both isotopic ratios in the terrestrial set were consistent with global radioactive fallout ratios. The average activity ratio in the marine ecosystem was lower than global radioactive fallout. At the same time mass ratio values in this group turned out to be surprisingly varied. Analysis of the results showed statistically significant differences between the marine and terrestrial ecosystems.

Lead pollution recorded in Greenland ice indicates European emissions tracked plagues, wars, and imperial expansion during antiquity

Lead pollution in Arctic ice reflects midlatitude emissions from ancient lead-silver mining and smelting. The few reported measurements have been extrapolated to infer the performance of ancient economies, including comparisons of economic productivity and growth during the Roman Republican and Imperial periods. These studies were based on sparse sampling and inaccurate dating, limiting understanding of trends and specific linkages. Here we show, using a precisely dated record of estimated lead emissions between 1100 BCE and 800 CE derived from subannually resolved measurements in Greenland ice and detailed atmospheric transport modeling, that annual European lead emissions closely varied with historical events, including imperial expansion, wars, and major plagues. Emissions rose coeval with Phoenician expansion, accelerated during expanded Carthaginian and Roman mining primarily in the Iberian Peninsula, and reached a maximum under the Roman Empire. Emissions fluctuated synchronously with wars and political instability particularly during the Roman Republic, and plunged coincident with two major plagues in the second and third centuries, remaining low for >500 years. Bullion in silver coinage declined in parallel, reflecting the importance of lead-silver mining in ancient economies. Our results indicate sustained economic growth during the first two centuries of the Roman Empire, terminated by the second-century Antonine plague.

High-resolution 129I bomb peak profile in an ice core from SE-Dome site, Greenland

¹²⁹I in natural archives, such as ice cores, can be used as a proxy for human nuclear activities, age marker, and environmental tracer. Currently, there is only one published record of ¹²⁹I in ice core (i.e., from Fiescherhorn Glacier, Swiss Alps) and its limited time resolution (1-2 years) prevents the full use of ¹²⁹I for the mentioned applications. Here we show ¹²⁹I concentrations in an ice core from SE-Dome, Greenland, covering years 1956-1976 at a time resolution of ∼6 months, the most detailed record to date. Results revealed ¹²⁹I bomb peaks in years 1959, 1962, and 1963, associated to tests performed by the former Soviet Union, one year prior, in its Novaya Zemlya test site. All ¹²⁹I bomb peaks were observed in winter (1958.9, 1962.1, and 1963.0), while tritium bomb peaks, another prominent radionuclide associated with nuclear bomb testing, were observed in spring or summer (1959.3, and 1963.6; Iizuka et al., 2017). These results indicate that ¹²⁹I bomb peaks can be used as annual and seasonal age markers for these years. Furthermore, we found that ¹²⁹I recorded nuclear fuel reprocessing signals and that these can be potentially used to correct timing of estimated ¹²⁹I releases during years 1964-1976. Comparisons with other published records of ¹²⁹I in natural archives showed that ¹²⁹I can be used as common age marker and tracer for different types of records. Most notably, the 1963 ¹²⁹I bomb peak can be used as common age marker for ice and coral cores, providing the means to reconcile age models and associated trends from the polar and tropical regions, respectively.

Reassessment of the Upper Fremont Glacier Ice-Core Chronologies by Synchronizing of Ice-Core-Water Isotopes to a Nearby Tree-Ring Chronology

The Upper Fremont Glacier (UFG), Wyoming, is one of the few continental glaciers in the contiguous United States known to preserve environmental and climate records spanning recent centuries. A pair of ice cores taken from UFG have been studied extensively to document changes in climate and industrial pollution (most notably, mid-19th century increases in mercury pollution). Fundamental to these studies is the chronology used to map ice-core depth to age. Here, we present a revised chronology for the UFG ice cores based on new measurements and using a novel dating approach of synchronizing continuous water isotope measurements to a nearby tree-ring chronology. While consistent with the few unambiguous age controls underpinning the previous UFG chronologies, the new interpretation suggests a very different time scale for the UFG cores with changes of up to 80 years. Mercury increases previously associated with the mid-19th century Gold Rush now coincide with early-20th century industrial emissions, aligning the UFG record with other North American mercury records from ice and lake sediment cores. Additionally, new UFG records of industrial pollutants parallel changes documented in ice cores from southern Greenland, further validating the new UFG chronologies while documenting the extent of late 19th and early 20th century pollution in remote North America.