Traces of tephra and increased sulfate (SO42−) concentrations were identified in the 1992–1994 snow layers in 2 firn cores from South Pole. The deposition of the Pinatubo SO42− aerosol was delayed ...due to the long transport to the high south latitudes and its initial existence at high altitudes in the Antarctic atmosphere. Electron microscopic analyses show that the element composition of the tephra is identical to that of volcanic ash found near the Pinatubo volcano in Philippines. Detailed stratigraphic snow sampling resolved the Pinatubo signal from that of Cerro Hudson eruption during August 1991 in Chile. The South Pole sulfate flux from Pinatubo is calculated to be (10.9±1.1) kg·km−2, while the Hudson sulfate flux is (3.2±1.1) kg·km−2. This information will be useful to estimating the magnitudes of the past volcanic eruptions recorded in Antarctic ice core.
Variability in sea ice is a critical climate feedback, yet the seasonal behavior of Southern Hemisphere sea ice and climate across multiple timescales remains unclear. Here, we develop a seasonally ...resolved Holocene sea salt record using major ion measurements of the South Pole Ice Core (SPC14). We combine the SPC14 data with the GEOS‐Chem chemical transport model to demonstrate that the primary sea salt source switches seasonally from open water (summer) to sea ice (winter), with wintertime variations disproportionately responsible for the centennial to millennial scale structure in the record. We interpret increasing SPC14 and circum‐Antarctic Holocene sea salt concentrations, particularly between 8 and 10 ka, as reflecting a period of winter sea ice expansion. Between 5 and 6 ka, an anomalous drop in South Atlantic sector sea salt indicates a temporary sea ice reduction that may be coupled with Northern Hemisphere cooling and associated ocean circulation changes.
Plain Language Summary
Sea ice variability has a dramatic effect on regional and global climate. Because sea ice extent has such a large summer to winter difference, seasonally specific records of past sea ice conditions are necessary to properly interpret sea ice/climate relationships. Here, we present a sea salt record from the South Pole Ice Core, which represents Southern Hemisphere sea ice changes during the last 11,400 years. We use an atmospheric chemistry model to show that wintertime sea salt in the South Pole Ice Core comes mostly from salty snow originating from sea ice. Wintertime sea ice variations are responsible for most of the long‐term variability in the South Pole sea salt record. Ice core data across Antarctica show increasing sea salt concentrations since 11,400 years ago, representing cooling and sea ice expansion, particularly between 8,000 and 10,000 years ago. Between 5,000 and 6,000 years ago, a drop in sea salt indicates an abrupt reduction in sea ice cover in the South Atlantic. Interestingly, paleoclimate data suggest that sea ice was more extensive in the North Atlantic at this time, indicating a linked and opposing sea ice signal in the North and South Atlantic most likely due to changing ocean circulation.
Key Points
Millennial‐scale Holocene variations in sea salt sodium at the South Pole primarily originate from changes in winter sea ice extent
Antarctic Holocene sea salt values increased, especially from 8,000 to 10,000 years ago, reflecting a zonally symmetric change in sea ice
We infer reduced Atlantic sector winter sea ice from 5,000 to 6,000 years ago, possibly related to North‐South Atlantic Ocean heat redistribution
A 36C1 peak has been found at about 37 ka BP in the Guliya ice core, drilled from the Qinghai-Tibetan Plateau. This peak is indicative of enhanced cosmogenic isotope production in the atmosphere, ...rather than a change in accumulation rate. Comparison with the records of 10Be and 36C1 in ice cores from Antarctica and Greenland indicates that peaks of the cosmogenic isotopes are global, and that they can be used as time markers for dating ice cores. Interestingly, the 37 ka BP global event coincided with a cold period.
A comprehensive record (WHV2020) of explosive volcanic eruptions in the last 11,000 years is reconstructed from the West Antarctica Ice Sheet Divide deep ice core (WDC). The chronological list of 426 ...large volcanic eruptions in the Southern Hemisphere and the low latitudes during the Holocene are of the highest quality of all volcanic records from ice cores, owing to the high‐resolution chemical measurement of the ice core and the exceptionally accurate WDC timescale. No apparent trend is found in the frequency (number of eruptions per millennium) of volcanic eruptions, and the number of eruptions in the most recent millennium (1,000–2,000 CE) is only slightly higher than the average in the last 11 millennia. The atmospheric aerosol mass loading of climate‐impacting sulfur, estimated from measured volcanic sulfate deposition, is dominated by explosive eruptions with extraordinarily high sulfur mass loading. Signals of three major volcanic eruptions are detected in the second half of the 17th century (1700–1600) BCE when the Thera volcano in the eastern Mediterranean was suspected to have erupted; the fact that these signals are synchronous with three volcanic eruptions detected in Greenland ice cores suggests that these are likely eruptions in the low latitudes and none should be attributed exclusively to Thera. A number of eruptions with very high sulfur mass loading took place shortly before and during an early Holocene climatic episode, the so‐called 8.2 ka event, and are speculated to have contributed to the initiation and magnitude of the cold event.
Plain Language Summary
A complete record of large volcanic eruptions during the last 11,000 years has been produced from a detailed chemical analysis of a 3,400‐m long ice core from Antarctica. The record is a chronological list of 426 explosive volcanic eruptions with the quantity of emitted volcanic materials that can impact the global climate. A number of very large eruptions some 8,200 years ago may have triggered and/or enhanced an abrupt cold episode in Earth's climate history. This record does not provide conclusive evidence that the Thera eruption occurred in the 17th century BCE.
Key Points
Record of large volcanic eruptions in the Holocene is constructed from chemical analysis of a 3,400‐m ice Core from WAIS Divide, Antarctica
Atmospheric aerosol mass loading of climate‐impacting sulfur is dominated by explosive eruptions with extraordinarily high sulfur emission
No apparent trend is found in number of volcanic eruptions per millennium; frequency in the most recent millennium is not particularly high
Nitrogen stable isotope ratio (δ ¹⁵N) in Greenland snow nitrate and in North American remote lake sediments has decreased gradually beginning as early as ∼1850 Christian Era. This decrease was ...attributed to increasing atmospheric deposition of anthropogenic nitrate, reflecting an anthropogenic impact on the global nitrogen cycle, and the impact was thought to be amplified ∼1970. However, our subannually resolved ice core records of δ ¹⁵N and major ions (e.g., Formula, Formula) over the last ∼200 y show that the decrease in δ ¹⁵N is not always associated with increasing Formula concentrations, and the decreasing trend actually leveled off ∼1970. Correlation of δ ¹⁵N with H ⁺, Formula, and HNO ₃ concentrations, combined with nitrogen isotope fractionation models, suggests that the δ ¹⁵N decrease from ∼1850–1970 was mainly caused by an anthropogenic-driven increase in atmospheric acidity through alteration of the gas−particle partitioning of atmospheric nitrate. The concentrations of Formula and Formula also leveled off ∼1970, reflecting the effect of air pollution mitigation strategies in North America on anthropogenic NO ₓ and SO ₂ emissions. The consequent atmospheric acidity change, as reflected in the ice core record of H ⁺ concentrations, is likely responsible for the leveling off of δ ¹⁵N ∼1970, which, together with the leveling off of Formula concentrations, suggests a regional mitigation of anthropogenic impact on the nitrogen cycle. Our results highlight the importance of atmospheric processes in controlling δ ¹⁵N of nitrate and should be considered when using δ ¹⁵N as a source indicator to study atmospheric flux of nitrate to land surface/ecosystems.
Abstract
Anthropogenic sulfate aerosols are estimated to have offset 60% of greenhouse-gas-induced warming in the Arctic, a region warming four times faster than the rest of the world. However, ...sulfate radiative forcing estimates remain uncertain because the relative contributions from anthropogenic versus natural sources to total sulfate aerosols are unknown. Here we measure sulfur isotopes of sulfate in a Summit, Greenland ice core from 1850 to 2006 CE to quantify the contribution of anthropogenic sulfur emissions to ice core sulfate. We use a Keeling plot to determine the anthropogenic sulfur isotopic signature (δ
34
S
anthro
= +2.9 ± 0.3 ‰), and compare this result to a compilation of sulfur isotope measurements of oil and coal. Using δ
34
S
anthro
, we quantify anthropogenic sulfate concentration separated from natural sulfate. Anthropogenic sulfate concentration increases to 67 ± 7% of non-sea-salt sulfate (65.1 ± 20.2
µ
g kg
−1
) during peak anthropogenic emissions from 1960 to 1990 and decreases to 45 ± 11% of non-sea-salt sulfate (25.4 ± 12.8
µ
g kg
−1
) from 1996 to 2006. These observations provide the first long-term record of anthropogenic sulfate distinguished from natural sources (e.g. volcanoes, dimethyl sulfide), and can be used to evaluate model characterization of anthropogenic sulfate aerosol fraction and radiative forcing over the industrial era.
A super(3) super(6) Cl peak has been found at about 37 ka BP in the Guliya ice core, drilled from the Qinghai-Tibetan Plateau. This peak is indicative of enhanced cosmogenic isotope production in the ...atmosphere, rather than a change in accumulation rate. Comparison with the records of super(1) super(0) Be and super(3) super(6) Cl in ice cores from Antarctica and Greenland indicates that peaks of the cosmogenic isotopes are global, and that they can be used as time markers for dating ice cores. Interestingly, the 37 ka BP global event coincided with a cold period.
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