[Show abstract][Hide abstract] ABSTRACT: Arsenic variability records are preserved in snow and ice cores and can be utilized to reconstruct air pollution history. The Mount Johns ice core (79°55'S; 94°23'W and 91.2 m depth) was collected from the West Antarctic Ice Sheet in the 2008/09 austral summer. Here, we report the As concentration variability as determined by 2137 samples from the upper 45 m of this core using ICP-SFMS (CCI, University of Maine, USA). The record covers approximately 125 years (1883-2008) showing a mean concentration of 4.32 pg g-1. The arsenic concentration in the core follows global copper mining evolution, particularly in Chile (the largest producer of Cu). From 1940 to 1990, copper-mining production increased along with arsenic concentrations in the MJ core, from 1.92 pg g-1 (before 1900) to 7.94 pg g-1 (1950). In the last two decades, environmental regulations for As emissions have been implemented, forcing smelters to treat their gases to conform to national and international environmental standards. In Chile, decontamination plants required by the government started operating from 1993 to 2000. Thereafter, Chilean copper production more than doubled while As emission levels declined, and the same reduction was observed in the Mount Johns ice core. After 1999, arsenic concentrations in our samples decreased to levels comparable to the period before 1900.
Full-text · Article · Jan 2016 · Atmospheric Environment
[Show abstract][Hide abstract] ABSTRACT: High-resolution major and trace element (Al, As, Ca, Cd, Co, Cr, Cu, Fe, Li, Mn, Na, Pb, S, Ti, and V) ice core records from Inilchek glacier (5,120 m above sea level) on the northwestern margin of the Tibetan Plateau provide the first multi-decadal ice core record spanning the period 1908–1995 AD in central Tien Shan. The trace element records reveal pronounced temporal baseline trends and concentration maxima characteristic of post-1950 anthropogenic emissions. Examination of Pb, Cd and Cu concentrations, along with non-crustal calculation estimates (i.e. excess (ex) and enrichment factor (EF)), reveal that discernable anthropogenic inputs began during the 1950s and rapidly increased to the late-1970s and early 1980s, by factors up to of 5, 6 and 3, respectively, relative to a 1910-1950 means. Pb, Cd and Cu concentrations between the 1950s-1980s are reflective of large-scale Soviet industrial and agricultural development, including the growth of production and/or consumption of the non-ferrous metals, coal and phosphate fertilizers. NOAA HYSPLIT back-trajectory frequency analysis suggests pollutant sources originating primarily from southern Kazakhstan (e.g. Shymkent and Balkhash) and the Fergana Valley (located in Kazakhstan, Uzbekistan and Kyrgyzstan). Inilchek ice core Pb, Cd and Cu reveals declines during the 1980s concurrent with Soviet economic declines, however, due to the rapid industrial and agricultural growth of western China, Pb, Cd and Cu trends increase during the 1990s reflecting a transition from primarily central Asian sources to emission sources from western China (e.g. Xinjiang Province).
[Show abstract][Hide abstract] ABSTRACT: High-resolution δ18O records from a Geladaindong mountain ice core spanning the period 1477-1982 were used to investigate past temperature variations in the Yangtze River source region of the central Tibetan Plateau (TP). Annual ice-core δ18O records were positively correlated with temperature data from nearby meteorological stations, suggesting that the δ18O record represented the air temperature in the region. A generally increasing temperature trend over the past 500 years was identified, with amplified warming during the 20th century. A colder stage, spanning before the 1850s, was found to represent the Little Ice Age with colder periods occurring during the 1470s-1500s, 1580s- 1660s, 1700s-20s and 1770s-1840s. Compared with other temperature records from the TP and the Northern Hemisphere, the Geladaindong ice-core record suggested that the regional climate of the central TP experienced a stronger warming trend during the 20th century than other regions. In addition, a positive relationship between the Geladaindong δ18O values and the North Atlantic Oscillation index, combined with a wavelet analysis of δ18O records, indicated that there was a potential atmospheric teleconnection between the North Atlantic and the central TP.
No preview · Article · Jan 2016 · Annals of Glaciology
[Show abstract][Hide abstract] ABSTRACT: A 147-m ice core was retrieved from Guoqu Glacier (33.58°N, 91.18°E, 5750 m a.s.l.) during the Sino–US cooperation expedition on Mt. Geladaindong in the central Tibetan Plateau (TP). In this study, we investigated the high-resolution of atmospheric dust records by using the insoluble particles and crustal ions (Ca2 + and Mg2 +) from the upper 109.93 m segments, covering the period of 1477 to 1982 AD. There existed positive correlations among the ice core dust records themselves and with the dust days from the nearby meteorological stations during the recent decades, indicating that the insoluble particles and crustal ions in the ice core can be used to reconstruct the past atmospheric dust variability. During the past 500 years, the insoluble particles and crustal ions showed high concentrations in the 18th to 19th centuries and low concentrations in the 20th century, corresponding to low and high precipitation in the potential dust source regions. The ice core dust records were positively correlated with the zonal wind and the winter North Atlantic Oscillation (NAO) index, suggesting that NAO may be teleconnected to dust entrainment over the inland TP. This long-term ice core provided an approach to understand the atmospheric dust variability in the central TP during the last 500 years.
Full-text · Article · Dec 2015 · Atmospheric Research
[Show abstract][Hide abstract] ABSTRACT: Emissions and long-range transport of toxic metals and metalloids pose a global threat to ecosystems and human health. Global industrialization occurring from the late nineteenth century releases large quantities of pollutants into the Earth's atmosphere. Despite international efforts to mitigate emissions, accumulation of metals is still observed in the most remote regions of the planet. New baseline studies are needed to determine (i) natural background concentration of pollutants, (ii) contributions of anthropogenic emissions, and (iii) potential remobilization of previously deposited metals. Constructing such records requires distinguishing source strength from transport efficiency to the recording site and accounting for local depositional effects. Here we investigate the sensitivity and representation of Southern Hemisphere atmospheric concentrations of heavy metals (Fe, Al, Mn, Pb, Tl, and As) in the Roosevelt Island Climate Evolution (RICE) ice core, a new coastal Antarctic ice core site. Concentration variability with precipitation is explored in daily surface snow samples collected over 70 days, while seasonal deposition is investigated through snow pit sampling. We find that snow sample concentrations increase with particular snow precipitation types (rime and fog) and enhanced meridional atmospheric transport to the site. Snow pit heavy metals peak in summer and also show variable intraannual peaks. Seasonal airmass modeling based on ERA Interim reanalysis data indicates a synoptic shift during the spring and summer months. We conclude that modern heavy metal concentrations are influenced by transport efficiency and scavenging behavior; and thus, time series records from RICE have the potential to provide representative data of regional changes in heavy metals.
Full-text · Article · Oct 2015 · Journal of Geophysical Research Atmospheres
[Show abstract][Hide abstract] ABSTRACT: Climate model results suggest that future climate change in Antarctica will be accompanied by continued strengthening and poleward contraction of the Southern Ocean westerly wind belt. Paleoclimate records suggest past changes in the westerly winds can be abrupt and that healing of the Antarctic ozone hole could lead to poleward contraction of the westerlies and increased meridional atmospheric transport of warm air regionally into Antarctica. An abrupt shift to more meridional circulation could lead to notable changes in moisture availability for extra-Antarctic regions, increased Antarctic ice sheet disintegration and more rapid sea-level rise.
No preview · Article · Jul 2015 · Journal of Quaternary Science
[Show abstract][Hide abstract] ABSTRACT: Two ice cores were retrieved from high elevations (~5800 m a.s.l.) at Mt. Nyainqêntanglha and Mt. Geladaindong in the southern and central Tibetan Plateau region. The combined tracer analysis of tritium (3H), 210Pb and mercury, along with other chemical records, provided multiple lines of evidence supporting that the two coring sites had not received net ice accumulation since at least the 1950s and 1980s, respectively. These results implied an annual ice loss rate of more than several hundred millimeter water equivalent over the past 30–60 years. Both mass balance modeling at the sites and in situ data from the nearby glaciers confirmed a continuously negative mass balance (or mass loss) in the region due to dramatic warming in recent decades. Along with a recent report on Naimona'nyi Glacier in the Himalayas, the findings suggest that the loss of accumulation area of glacier is a possibility from the southern to central Tibetan Plateau at high elevations, probably up to about 5800 m a.s.l. This mass loss raises concerns over the rapid rate of glacier ice loss and associated changes in surface glacier runoff, water availability, and sea levels.
[Show abstract][Hide abstract] ABSTRACT: 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 CO2 and CH4 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 CO2 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 CO2 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 CO2 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.
Full-text · Article · May 2015 · Proceedings of the National Academy of Sciences
[Show abstract][Hide abstract] 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.
No preview · Article · May 2015 · Journal of Glaciology
[Show abstract][Hide abstract] ABSTRACT: Understanding past atmospheric dust variability is necessary to put modern atmospheric dust into historical context and assess the impacts of dust on the climate. In Asia, meteorological data of atmospheric dust is temporally limited, beginning only in the 1950s. High-resolution ice cores provide the ideal archive for reconstructing pre-instrumental atmospheric dust concentrations. Using a ~500-year (1477-1982AD) annually resolved calcium (Ca) dust proxy from a Tibetan Plateau (TP) ice core, we demonstrate the lowest atmospheric dust concentrations in the past ~500 years during the latter 20th century. Declines in late 19th-20th century Ca concentrations significantly correspond with regional zonal wind trends from two reanalysis models, suggesting that the Ca record provides a proxy for the westerlies. Twentieth century warming and attendant atmospheric pressure reductions over northern Asia have potentially reduced temperature/pressure gradients resulting in lower zonal wind velocities and associated dust entrainment/transport in the past ~500 years over the TP.
[Show abstract][Hide abstract] ABSTRACT: Two ice cores were retrieved from high elevations (~ 5800 m a.s.l.) at Mt. Nyainqentanglha and Mt. Geladaindong in the southern to inland Tibetan Plateau. The combined analysis of tritium (3H), 210Pb, mercury tracers, along with other chemical records, revealed that the two coring sites had not received net ice accumulation since at least the 1950s and 1980s, respectively, implying an annual ice loss rate of more than several hundred millimeter water equivalent over these periods. Both mass balance modeling at the sites and in situ data from nearby glaciers confirmed a continuously negative mass balance (or mass loss) in the region due to the dramatic warming in the last decades. Along with a recent report on Naimona'nyi Glacier in the Himalaya, the findings suggest that glacier decapitation (i.e., the loss of the accumulation zone) is a wide-spread phenomenon from the southern to inland Tibetan Plateau even at the summit regions. This raises concerns over the rapid rate of glacier ice loss and associated changes in surface glacier runoff, water availability, and sea levels.
No preview · Article · Jan 2015 · The Cryosphere Discussions
[Show abstract][Hide abstract] ABSTRACT: Significant Arctic-wide warming over the past decade is thought to result in part from
a weakening of the equator-pole thermal gradient in the atmosphere. Francis and Vavrus
(2012) and others link Arctic amplification, or enhanced Arctic warming, to decreasing
extratropical cyclone (ETC) speeds, and increasing northward meridional heat transports.
Here, as part of the collaborative NSF award GreenTrACS, we are using the latest
high-resolution reanalysis models (ASR, JRA-55, CFSR, ERA-Interim, MERRA) to
evaluate how Arctic amplification may be impacting the mass balance of the Greenland
Ice Sheet. Our approach is to assess synoptic-scale changes in circulation as represented
by changes in storm tracks and storm intensities in the North Atlantic region. As part of
this work, we are validating the reanalysis models against existing accumulation, ablation,
and meteorological station data available across Greenland, and therefore hope to
gain insights on model performance and applicability to the problem domain.
[Show abstract][Hide abstract] ABSTRACT: Continuous, high-resolution paleoclimate records from the North Pacific region spanning the past 1500 years are rare, and the behavior of the Aleutian Low (ALow) pressure center, the dominant climatological feature in the Gulf of Alaska, remains poorly constrained. Here we present a continuous, 1500 year long, calibrated proxy record for the strength of the wintertime (December-March) ALow from the Mt. Logan summit (PR Col; 5200 m a.s.l.) ice core soluble sodium time series. We show that ice core sodium concentrations are statistically correlated with North Pacific sea level pressure and zonal wind speed. Our ALow proxy record reveals a weak ALow from ca. 900–1300 AD and 1575–1675 AD, and a comparatively stronger ALow from ca. 500–900 AD, 1300–1575 AD, and 1675 AD to present. The Mt. Logan ALow proxy record shows strong similarities with tropical paleoclimate proxy records sensitive to the El Niño-Southern Oscillation, and is consistent with the hypothesis that the MCA was characterized by more persistent La Niña-like conditions while the LIA was characterized by at least two intervals of more persistent El Niño-like conditions. The Mt. Logan ALow proxy record is significantly (p < 0.05) correlated and coherent with solar irradiance proxy records over various timescales, with stronger solar irradiance generally associated with a weaker ALow and La Niña-like tropical conditions. However, a step-like increase in ALow strength during the Dalton solar minimum ca. 1820 is associated with enhanced Walker Circulation. Furthermore, rising CO2 forcing or internal variability may be masking the 20th century rise in solar irradiance.
[Show abstract][Hide abstract] ABSTRACT: Subtropical and extratropical proxy records of wind field, sea level
pressure (SLP), temperature and hydrological anomalies from South
Africa, Australia/New Zealand, Patagonian South America and Antarctica
were used to reconstruct the Indo-Pacific extratropical southern
hemisphere sea-level pressure anomaly (SLPa) fields for the Medieval
Climate Anomaly (MCA ~700-1350 CE) and transition to the Little Ice Age
(LIA 1350-1450 CE). The multivariate array of proxy data were
simultaneously evaluated against global climate model output in order to
identify climate state analogues that are most consistent with the
majority of proxy data. The mean SLP and SLP anomaly patterns derived
from these analogues illustrate the evolution of low frequency changes
in the extratropics. The Indo-Pacific extratropical mean climate state
was dominated by a strong tropical interaction with Antarctica emanating
from: (1) the eastern Indian and south-west Pacific regions prior to
1100 CE, then, (2) the eastern Pacific evolving to the central Pacific
La Niña-like pattern interacting with a +ve SAM to 1300 CE. A
relatively abrupt shift to -ve SAM and the central Pacific El
Niño-like pattern occurred at ~1300. A poleward (equatorward)
shift in the subtropical ridge occurred during the MCA (MCA-LIA
transition). The Hadley Cell expansion in the Australian and Southwest
Pacific, region together with the poleward shift of the zonal westerlies
is contemporaneous with previously reported Hadley Cell expansion in the
North Pacific and Atlantic regions, and suggests that bipolar climate
symmetry was a feature of the MCA.