Hemispheric-scale heavy metal pollution from South American and Australian mining and metallurgy during the Common Era.

Records from polar and alpine ice reflect past changes in background and industrial toxic heavy metal emissions. While Northern Hemisphere records have been used to evaluate environmental effects and linkages to historical events such as foreign conquests, plagues, economic downturns, and technological developments during the past three millennia, little is known about the magnitude and environmental effects of such emissions in the Southern Hemisphere or their historical linkages, especially prior to late 19th century industrialization. Here we used detailed measurements of the toxic heavy metals lead, cadmium, and thallium, as well as non-toxic bismuth, cerium, and sulfur in an array of five East Antarctic ice cores to investigate hemispheric-scale pollution during the Common Era. While thallium showed no anthropogenic increases, the other three metals increased by orders of magnitude in recent centuries after accounting for crustal and volcanic components. These first detailed records indicate that East Antarctic lead pollution started in the 13th century coincident with Late Intermediate Period metallurgy in the Andes and was pervasive during the Spanish Colonial period in parallel with large-scale exploitation of Andean silver and other ore deposits. Lead isotopic variations suggest that 19th-century increases in lead, cadmium, and bismuth resulted from Australian lead and Bolivian tin mining emissions, with 20th century pollution largely the result of the latter. As in the Northern Hemisphere, variations in heavy metal pollution coincided with plagues, cultural and technological developments, as well as global economic and political events including the Great Depression and the World Wars. Estimated atmospheric heavy metal emissions from Spanish Colonial-era mining and smelting during the late 16th and early 17th century were comparable to estimated European emissions during the 1st-century apex of the Roman Empire, with atmospheric model simulations suggesting hemispheric-scale toxic heavy metal pollution during the past five centuries as a result.

Hemispheric black carbon increase after the 13th-century Maori 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 Maori settlement2, but the precise timing and magnitude of associated biomass-burning emissions are unknown1,3, 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 Maori 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 Patagonia6,7, 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.

Extreme climate after massive eruption of Alaska's Okmok volcano in 43 BCE and effects on the late Roman Republic and Ptolemaic Kingdom.

The assassination of Julius Caesar in 44 BCE triggered a power struggle that ultimately ended the Roman Republic and, eventually, the Ptolemaic Kingdom, leading to the rise of the Roman Empire. Climate proxies and written documents indicate that this struggle occurred during a period of unusually inclement weather, famine, and disease in the Mediterranean region; historians have previously speculated that a large volcanic eruption of unknown origin was the most likely cause. Here we show using well-dated volcanic fallout records in six Arctic ice cores that one of the largest volcanic eruptions of the past 2,500 y occurred in early 43 BCE, with distinct geochemistry of tephra deposited during the event identifying the Okmok volcano in Alaska as the source. Climate proxy records show that 43 and 42 BCE were among the coldest years of recent millennia in the Northern Hemisphere at the start of one of the coldest decades. Earth system modeling suggests that radiative forcing from this massive, high-latitude eruption led to pronounced changes in hydroclimate, including seasonal temperatures in specific Mediterranean regions as much as 7 °C below normal during the 2 y period following the eruption and unusually wet conditions. While it is difficult to establish direct causal linkages to thinly documented historical events, the wet and very cold conditions from this massive eruption on the opposite side of Earth probably resulted in crop failures, famine, and disease, exacerbating social unrest and contributing to political realignments throughout the Mediterranean region at this critical juncture of Western civilization.

Interstellar

Earth is constantly bombarded with extraterrestrial dust containing invaluable information about extraterrestrial processes, such as structure formation by stellar explosions or nucleosynthesis, which could be traced back by long-lived radionuclides. Here, we report the very first detection of a recent ^{60}Fe influx onto Earth by analyzing 500 kg of snow from Antarctica by accelerator mass spectrometry. By the measurement of the cosmogenically produced radionuclide ^{53}Mn, an atomic ratio of ^{60}Fe/^{53}Mn=0.017 was found, significantly above cosmogenic production. After elimination of possible terrestrial sources, such as global fallout, the excess of ^{60}Fe could only be attributed to interstellar ^{60}Fe which might originate from the solar neighborhood.

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.

Industrial-era decline in subarctic Atlantic productivity.

Marine phytoplankton have a crucial role in the modulation of marine-based food webs1, fishery yields2 and the global drawdown of atmospheric carbon dioxide3. However, owing to sparse measurements before satellite monitoring in the twenty-first century, the long-term response of planktonic stocks to climate forcing is unknown. Here, using a continuous, multi-century record of subarctic Atlantic marine productivity, we show that a marked 10 ± 7% decline in net primary productivity has occurred across this highly productive ocean basin over the past two centuries. We support this conclusion by the application of a marine-productivity proxy, established using the signal of the planktonic-derived aerosol methanesulfonic acid, which is commonly identified across an array of Greenlandic ice cores. Using contemporaneous satellite-era observations, we demonstrate the use of this signal as a robust and high-resolution proxy for past variations in spatially integrated marine productivity. We show that the initiation of declining subarctic Atlantic productivity broadly coincides with the onset of Arctic surface warming4, and that productivity strongly covaries with regional sea-surface temperatures and basin-wide gyre circulation strength over recent decades. Taken together, our results suggest that the decline in industrial-era productivity may be evidence of the predicted5 collapse of northern Atlantic planktonic stocks in response to a weakened Atlantic Meridional Overturning Circulation6-8. Continued weakening of this Atlantic Meridional Overturning Circulation, as projected for the twenty-first century9,10, may therefore result in further productivity declines across this globally relevant region.

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.

Resolving the controls of water vapour isotopes in the Atlantic sector.

Stable water isotopes are employed as hydrological tracers to quantify the diverse implications of atmospheric moisture for climate. They are widely used as proxies for studying past climate changes, e.g., in isotope records from ice cores and speleothems. Here, we present a new isotopic dataset of both near-surface vapour and ocean surface water from the North Pole to Antarctica, continuously measured from a research vessel throughout the Atlantic and Arctic Oceans during a period of two years. Our observations contribute to a better understanding and modelling of water isotopic composition. The observations reveal that the vapour deuterium excess within the atmospheric boundary layer is not modulated by wind speed, contrary to the commonly used theory, but controlled by relative humidity and sea surface temperature only. In sea ice covered regions, the sublimation of deposited snow on sea ice is a key process controlling the local water vapour isotopic composition.

Growth suppression of ice crystal basal face in the presence of a moderate ice-binding protein does not confer hyperactivity.

Ice-binding proteins (IBPs) affect ice crystal growth by attaching to crystal faces. We present the effects on the growth of an ice single crystal caused by an ice-binding protein from the sea ice microalga Fragilariopsis cylindrus (fcIBP) that is characterized by the widespread domain of unknown function 3494 (DUF3494) and known to cause a moderate freezing point depression (below 1 °C). By the application of interferometry, bright-field microscopy, and fluorescence microscopy, we observed that the fcIBP attaches to the basal faces of ice crystals, thereby inhibiting their growth in the c direction and resulting in an increase in the effective supercooling with increasing fcIBP concentration. In addition, we observed that the fcIBP attaches to prism faces and inhibits their growth. In the event that the effective supercooling is small and crystals are faceted, this process causes an emergence of prism faces and suppresses crystal growth in the a direction. When the effective supercooling is large and ice crystals have developed into a dendritic shape, the suppression of prism face growth results in thinner dendrite branches, and growth in the a direction is accelerated due to enhanced latent heat dissipation. Our observations clearly indicate that the fcIBP occupies a separate position in the classification of IBPs due to the fact that it suppresses the growth of basal faces, despite its moderate freezing point depression.

Physical analysis of an Antarctic ice core-towards an integration of micro- and macrodynamics of polar ice.

Microstructures from deep ice cores reflect the dynamic conditions of the drill location as well as the thermodynamic history of the drill site and catchment area in great detail. Ice core parameters (crystal lattice-preferred orientation (LPO), grain size, grain shape), mesostructures (visual stratigraphy) as well as borehole deformation were measured in a deep ice core drilled at Kohnen Station, Dronning Maud Land (DML), Antarctica. These observations are used to characterize the local dynamic setting and its rheological as well as microstructural effects at the EDML ice core drilling site (European Project for Ice Coring in Antarctica in DML). The results suggest a division of the core into five distinct sections, interpreted as the effects of changing deformation boundary conditions from triaxial deformation with horizontal extension to bedrock-parallel shear. Region 1 (uppermost approx. 450 m depth) with still small macroscopic strain is dominated by compression of bubbles and strong strain and recrystallization localization. Region 2 (approx. 450-1700 m depth) shows a girdle-type LPO with the girdle plane being perpendicular to grain elongations, which indicates triaxial deformation with dominating horizontal extension. In this region (approx. 1000 m depth), the first subtle traces of shear deformation are observed in the shape-preferred orientation (SPO) by inclination of the grain elongation. Region 3 (approx. 1700-2030 m depth) represents a transitional regime between triaxial deformation and dominance of shear, which becomes apparent in the progression of the girdle to a single maximum LPO and increasing obliqueness of grain elongations. The fully developed single maximum LPO in region 4 (approx. 2030-2385 m depth) is an indicator of shear dominance. Region 5 (below approx. 2385 m depth) is marked by signs of strong shear, such as strong SPO values of grain elongation and strong kink folding of visual layers. The details of structural observations are compared with results from a numerical ice sheet model (PISM, isotropic) for comparison of strain rate trends predicted from the large-scale geometry of the ice sheet and borehole logging data. This comparison confirms the segmentation into these depth regions and in turn provides a wider view of the ice sheet.This article is part of the themed issue 'Microdynamics of ice'.

An Optical Dye Method for Continuous Determination of Acidity in Ice Cores.

The pH of polar ice is important for the stability and mobility of impurities in ice cores and can be strongly influenced by volcanic eruptions or anthropogenic emissions. We present a simple optical method for continuous determination of acidity in ice cores based on spectroscopically determined color changes of two common pH-indicator dyes, bromophenol blue, and chlorophenol red. The sealed-system method described here is not equilibrated with CO2, making it simpler than existing methods for pH determination in ice cores and offering a 10-90% peak response time of 45 s and a combined uncertainty of 9%. The method is applied to Holocene ice core sections from Greenland and Antarctica and compared to standard techniques such as electrical conductivity measurement (ECM) conducted on the solid ice, and electrolytic meltwater conductivity, EMWC. Acidity measured in the Greenland NGRIP ice core shows good agreement with acidity calculated from ion chromatography. Conductivity and dye-based acidity Hdye+ are found to be highly correlated in the Greenland NEGIS firn core (75.38° N, 35.56° W), with all signals greater than 3σ variability coinciding with either volcanic eruptions or possible wild fire activity. In contrast, the Antarctic Roosevelt Island ice core (79.36° S, 161.71° W) features an anticorrelation between conductivity and Hdye+, likely due to strong influence of marine salts.