Year‐round precipitation in coastal East Antarctica and Antarctic Peninsula was used to investigate the seasonal patterns in sources of atmospheric perchlorate (ClO4− ${{\text{ClO}}_{4}}^{-}$). ...Although featuring distinct climates, the two locations exhibit similar annual mean and seasonal cycles of ClO4− ${{\text{ClO}}_{4}}^{-}$ concentration, with higher values in autumn and lower concentrations in winter and spring. Tropospheric formation dominates atmospheric ClO4− ${{\text{ClO}}_{4}}^{-}$ in spring and summer, which is influenced by both oxidants levels and environmental conditions (e.g., air humidity). Tropospheric ClO4− ${{\text{ClO}}_{4}}^{-}$ production may also be promoted by elevated levels of oxidants brought by air mass from the interior Antarctic ice sheet in spring and summer. The autumn concentration maximum may originate from ClO4− ${{\text{ClO}}_{4}}^{-}$ produced in the stratosphere through reactions between reactive chlorine and ozone during spring and summer. In winter, the stratospheric input may contribute to ClO4− ${{\text{ClO}}_{4}}^{-}$ via polar stratospheric clouds sedimentation.
Plain Language Summary
Perchlorate (ClO4− ${{\text{ClO}}_{4}}^{-}$) is an inorganic anion with a persistent presence in the environment, where its exposure can pose a significant health risk to humans. Environmental ClO4− ${{\text{ClO}}_{4}}^{-}$ is derived from both man‐made and natural sources. Natural ClO4− ${{\text{ClO}}_{4}}^{-}$, widespread in the environment, is thought to be formed in the atmosphere. However, knowledge on the sources and, in particular, the formation mechanisms of natural ClO4− ${{\text{ClO}}_{4}}^{-}$ is quite limited. Antarctica, with negligible man‐made sources, is one of the best regions for investigations on natural ClO4− ${{\text{ClO}}_{4}}^{-}$. Year‐round precipitation samples were collected at China Zhongshan Station located in coastal East Antarctica and China Great Wall Station on King George Island, Antarctic Peninsula. Results show that atmospheric ClO4− ${{\text{ClO}}_{4}}^{-}$ concentration presents obvious seasonal cycles, which are related to variations in sources. A significant amount of ClO4− ${{\text{ClO}}_{4}}^{-}$ is associated with tropospheric chemistry in spring and summer. Precursor levels, environmental conditions, and air mass from the interior Antarctica may influence tropospheric ClO4− ${{\text{ClO}}_{4}}^{-}$ formation. The maximum concentration in autumn may originate from ClO4− ${{\text{ClO}}_{4}}^{-}$ formed in the stratosphere during spring and summer, and the stratospheric input may also contribute to atmospheric ClO4− ${{\text{ClO}}_{4}}^{-}$ in winter.
Key Points
Antarctic atmospheric perchlorate (ClO4− ${{\text{ClO}}_{4}}^{-}$) concentration at different locations exhibits a clear seasonal cycle
The highest concentration in autumn is likely related to ClO4− ${{\text{ClO}}_{4}}^{-}$ produced in the stratosphere in spring and summer
Major source of ClO4− ${{\text{ClO}}_{4}}^{-}$ in spring and summer is tropospheric formation influenced by both oxidants and environmental conditions
The Arctic is warming at almost four times the global rate. An estimated sixty percent of greenhouse‐gas‐induced Arctic warming has been offset by anthropogenic aerosols, but the contribution of ...aerosols to radiative forcing (RF) represents the largest uncertainty in estimating total RF, largely due to unknown preindustrial aerosol abundance. Here, sulfur isotope measurements in a Greenland ice core show that passive volcanic degassing contributes up to 66 ± 10% of preindustrial ice core sulfate in years without major eruptions. A state‐of‐the‐art model indicates passive volcanic sulfur emissions influencing the Arctic are underestimated by up to a factor of three, possibly because many volcanic inventories do not include hydrogen sulfide emissions. Higher preindustrial volcanic sulfur emissions reduce modeled anthropogenic Arctic aerosol cooling by up to a factor of two (+0.11 to +0.29 W m−2), suggesting that underestimating passive volcanic sulfur emissions has significant implications for anthropogenic‐induced Arctic climate change.
Plain Language Summary
Sulfate aerosols are particles in the atmosphere that have a net cooling effect on the climate. One of the most uncertain aspects of climate modeling is the abundance of sulfate aerosols during the preindustrial era. Without knowing the amount of sulfate aerosols during the preindustrial, it is difficult to estimate how much anthropogenic sulfate aerosols have offset warming from anthropogenic greenhouse gases. In this study, we examine preindustrial sulfate aerosols in a Greenland ice core. We find that sulfate aerosols from passive (i.e., non‐eruptive) volcanic degassing contribute almost two thirds of preindustrial Arctic sulfate aerosols in years without major volcanic eruptions. We compare this result to a state‐of‐the‐art global model and find that most climate models use a volcanic emissions inventory that underestimates preindustrial passive volcanic sulfur emissions. That volcanic inventory only includes one type of sulfur emission (sulfur dioxide), but studies have shown that volcanoes emit hydrogen sulfide, which can also form sulfate aerosols. We show that higher emissions of volcanic sulfur during the preindustrial era decrease the estimated cooling effect of anthropogenic aerosols during the industrial era. Thus, the underestimate of preindustrial volcanic emissions in current climate models has significant implications for anthropogenic climate change in the Arctic.
Key Points
Sulfur isotopes in a Greenland ice core show that passive volcanic degassing contributes 66% of preindustrial Arctic sulfate
The volcanic inventory used by most climate models underestimates passive degassing, possibly due to missing hydrogen sulfide emissions
Elevated preindustrial passive volcanic degassing reduces the estimated cooling effect of anthropogenic sulfate in the Arctic
Sulfuric acid aerosols produced in the stratosphere following massive volcanic eruptions possess a mass‐independent sulfur isotopic signature, acquired when volcanic SO2 experiences UV ...photooxidation. The volcanic data are consistent with laboratory SO2 photooxidation experiments using UV light at 248 nm (maximum absorption of ozone), whereas sulfur isotopic anomalies previously observed in Archean samples are consistent with photodissociation at 190–220 nm. A mechanism of SO2 photooxidation, occurring in the early stage of a stratospheric volcanic plume, in the range of 220–320 nm (weak band absorption of SO2), is also proposed. Since mass‐independent sulfur isotope anomalies in stratospheric volcanic sulfate appear to depend on the exposure of SO2 to UV radiation, their measurements might therefore offer the possibility to determine the degree of UV penetration in the ozone‐absorption window for the present and past atmospheres. They can also be used to determine the stratospheric or tropospheric nature of volcanic eruptions preserved in glaciological records, offering the possibility to reassess the climatic impact of past volcanic eruptions.
An ice core record from the Guliya ice cap on the Qinghai-Tibetan Plateau provides evidence of regional climatic conditions over the last glacial cycle. $^{36}$Cl data suggest that the deepest 20 ...meters of the core may be more than 500,000 years old. The $\delta^{18}$O change across Termination I is ∼5.4 per mil, similar to that in the Huascarán (Peru) and polar ice cores. Three Guliya interstadials (Stages 3, 5a, and 5c) are marked by increases in $\delta^{18}$O values similar to that of the Holocene and Eemian (∼124,000 years ago). The similarity of this pattern to that of CH$_4$ records from polar ice cores indicates that global CH$_4$ levels and the tropical hydrological cycle are linked. The Late Glacial Stage record contains numerous 200-year oscillations in $\delta^{18}$O values and in dust, NH$_4^+$, and NO$_3^-$ levels.
Two ice cores from the col of Huascarán in the north-central Andes of Peru contain a paleoclimatic history extending well into the Wisconsinan (Würm) Glacial Stage and include evidence of the Younger ...Dryas cool phase. Glacial stage conditions at high elevations in the tropics appear to have been as much as 8° to 12°C cooler than today, the atmosphere contained about 200 times as much dust, and the Amazon Basin forest cover may have been much less extensive. Differences in both the oxygen isotope ratio $\delta^{18}$O (8 per mil) and the deuterium excess (4.5 per mil) from the Late Glacial Stage to the Holocene are comparable with polar ice core records. These data imply that the tropical Atlantic was possibly 5° to 6°C cooler during the Late Glacial Stage, that the climate was warmest from 8400 to 5200 years before present, and that it cooled gradually, culminating with the Little Ice Age (200 to 500 years before present). A strong warming has dominated the last two centuries.
A primary goal of the SCAR (Scientific Committee for Antarctic Research) initiated AntClim21 (Antarctic Climate in the 21st Century) Scientific Research Programme is to develop analogs for ...understanding past, present and future climates for the Antarctic and Southern Hemisphere. In this contribution to AntClim21 we provide a framework for achieving this goal that includes: a description of basic climate parameters; comparison of existing climate reanalyses; and ice core sodium records as proxies for the frequencies of marine air mass intrusion spanning the past ∼2000 years. The resulting analog examples include: natural variability, a continuation of the current trend in Antarctic and Southern Ocean climate characterized by some regions of warming and some cooling at the surface of the Southern Ocean, Antarctic ozone healing, a generally warming climate and separate increases in the meridional and zonal winds. We emphasize changes in atmospheric circulation because the atmosphere rapidly transports heat, moisture, momentum, and pollutants, throughout the middle to high latitudes. In addition, atmospheric circulation interacts with temporal variations (synoptic to monthly scales, inter-annual, decadal, etc.) of sea ice extent and concentration. We also investigate associations between Antarctic atmospheric circulation features, notably the Amundsen Sea Low (ASL), and primary climate teleconnections including the SAM (Southern Annular Mode), ENSO (El Nîno Southern Oscillation), the Pacific Decadal Oscillation (PDO), the AMO (Atlantic Multidecadal Oscillation), and solar irradiance variations.
•Antarctic climate change based on ice cores and climate reanalyses.•Past and present analogs yield plausible scenarios for near-term future climate.•Antarctic – Southern Hemisphere plausible scenarios for near-term climate change.
Ice cores that were recovered from the summit of Sajama mountain in Bolivia provide carbon-14-dated tropical records and extend to the Late Glacial Stage (LGS). Oxygen isotopic ratios of the ice ...decreased 5.4 per mil between the early Holocene and the Last Glacial Maximum, which is consistent with values from other ice cores. The abrupt onset and termination of a Younger Dryas-type event suggest atmospheric processes as the probable drivers. Regional accumulation increased during the LGS, during deglaciation, and over the past 3000 years, which is concurrent with higher water levels in regional paleolakes. Unlike polar cores, Sajama glacial ice contains eight times less dust than the Holocene ice, which reflects wetter conditions and extensive snow cover.
The injection of sulfur into the stratosphere by volcanic eruptions is the dominant driver of natural climate variability on interannual to multidecadal timescales. Based on a set of continuous ...sulfate and sulfur records from a suite of ice cores from Greenland and Antarctica, the HolVol v.1.0 database includes estimates of the magnitudes and approximate source latitudes of major volcanic stratospheric sulfur injection (VSSI) events for the Holocene (from 9500 BCE or 11 500 years BP to 1900 CE), constituting an extension of the previous record by 7000 years. The database incorporates new-generation ice-core aerosol records with a sub-annual temporal resolution and a demonstrated sub-decadal dating accuracy and precision. By tightly aligning and stacking the ice-core records on the WD2014 chronology from Antarctica, we resolve long-standing inconsistencies in the dating of ancient volcanic eruptions that arise from biased (i.e., dated too old) ice-core chronologies over the Holocene for Greenland. We reconstruct a total of 850 volcanic eruptions with injections in excess of 1 teragram of sulfur (Tg S); of these eruptions, 329 (39 %) are located in the low latitudes with bipolar sulfate deposition, 426 (50 %) are located in the Northern Hemisphere extratropics (NHET) and 88 (10 %) are located in the Southern Hemisphere extratropics (SHET). The spatial distribution of the reconstructed eruption locations is in agreement with prior reconstructions for the past 2500 years. In total, these eruptions injected 7410 Tg S into the stratosphere: 70 % from tropical eruptions and 25 % from NH extratropical eruptions. A long-term latitudinally and monthly resolved stratospheric aerosol optical depth (SAOD) time series is reconstructed from the HolVol VSSI estimates, representing the first Holocene-scale reconstruction constrained by Greenland and Antarctica ice cores. These new long-term reconstructions of past VSSI and SAOD variability confirm evidence from regional volcanic eruption chronologies (e.g., from Iceland) in showing that the Early Holocene (9500–7000 BCE) experienced a higher number of volcanic eruptions (+16 %) and cumulative VSSI (+86 %) compared with the past 2500 years. This increase coincides with the rapid retreat of ice sheets during deglaciation, providing context for potential future increases in volcanic activity in regions under projected glacier melting in the 21st century. The reconstructed VSSI and SAOD data are available at https://doi.org/10.1594/PANGAEA.928646 (Sigl et al., 2021).
Oxygen isotopic ratio measurements (δ17O and δ18O) of background and volcanic sulfate preserved in South Pole snow and ice were used to investigate the impact on the oxidation state of the atmosphere ...by explosive volcanic eruptions. By comparing different paleovolcanic events, we observe a difference in the SO2 oxidation pathway between moderate (tens of teragrams (Tg) of SO2) and massive (hundreds of Tg) eruptions. Both isotopic data and numerical simulations suggest the shutdown of stratospheric OH chemistry and the opening of unaccounted oxidation channels for SO2, such as the reaction with O(3P) atoms when hundreds of Tg of SO2 are injected into the stratosphere. It is very likely that oxidation rates and pathways and concentrations of most traces gases are also dramatically affected, with potentially important implications for climate forcing.
PDF
