Chapter 6.2 Englacial tephras of East Antarctica

2021 ◽  
pp. M55-2018-86
Author(s):  
Biancamaria Narcisi ◽  
Jean Robert Petit

AbstractDriven by successful achievements in recovering high-resolution ice records of climate and atmospheric composition through the Late Quaternary, new ice–tephra sequences from various sites of the East Antarctic Ice Sheet (EAIS) have been studied in the last two decades spanning an age range of a few centuries to 800 kyr. The tephrostratigraphic framework for the inner EAIS, based on ash occurrence in three multi-kilometre-deep ice cores, shows that the South Sandwich Islands represent a major source for tephra, highlighting the major role in the ash dispersal played by clockwise circum-Antarctic atmospheric circulation penetrating the Antarctic continent. Tephra records from the eastern periphery of the EAIS, however, are obviously influenced by explosive activity sourced in nearby Antarctic rift provinces. These tephra inventories have provided a fundamental complement to the near-vent volcanic record, in terms of both frequency/chronology of explosive volcanism and of magma chemical evolution through time. Despite recent progress, current data are still sparse. There is a need for further tephra studies to collect data from unexplored EAIS sectors, along with extending the tephra inventory back in time. Ongoing international palaeoclimatic initiatives of ice-core drilling could represent a significant motivation for the tephra community and for Quaternary Antarctic volcanologists.

2020 ◽  
Author(s):  
Rachael Rhodes ◽  
Xin Yang ◽  
Eric Wolff

<p>It is important to understand the magnitude and rate of past sea ice changes, as well as their timing relative to abrupt shifts in other components of Earth’s climate system. Furthermore, records of past sea ice over the last few centuries are urgently needed to assess the scale of natural (internal) variability over decadal timescales. By continuously recording past atmospheric composition, polar ice cores have the potential to document changing sea ice conditions if atmospheric chemistry is altered.  Sea salt aerosol, specifically sodium (Na), and bromine enrichment (Br<sub>enr</sub>, Br/Na enriched relative to seawater ratio) are two ice core sea ice proxies suggested following this premise.</p><p>Here we aim to move beyond a conceptual understanding of the controls on Na and Br<sub>enr</sub> in ice cores by using process-based modelling to test hypotheses. We present results of experiments using a 3D global chemical transport model (p-TOMCAT) that represents marine aerosol emission, transport and deposition. Critically, the complex atmospheric chemistry of bromine is also included. Three fundamental issues will be examined: 1) the partitioning of Br between gas and aerosol phases, 2) sea salt aerosol production from first-year versus multi-year sea ice, and 3) the impact of increased acidity in the atmosphere due to human activity in the Arctic.</p>


1994 ◽  
Vol 20 ◽  
pp. 73-79
Author(s):  
Akira Higashi ◽  
Yoshiyuki Fujii

SEM observations of microparticles in ice-core samples retrieved by the Japanese Antarctic Research Expedition in east Dronning Maud Land have been carried out since 1987. Morphology and elemental composition by EDS of many microparticles taken from various depths of the 700 m Mizuho ice core were compared with each other and with those of stratospheric microparticles in NASA Cosmic Dust Catalogs and microparticles hitherto found in deep ice cores retrieved in Antarctica. Number concentrations of microparticles were measured on all samples throughout the 700 m Mizuho ice core. Remarkable fluctuations found in the depth profile of the concentration seem to coincide with cold climates indicated by δ18O of the same core. Compositional analysis of volcanic ash at a depth of 500.7 m in the Mizuho ice core, dated at approximately 6000 years BP, indicates that the ash originated from the South Sandwich Islands.


2016 ◽  
Vol 12 (4) ◽  
pp. 1061-1077 ◽  
Author(s):  
Rachael H. Rhodes ◽  
Xavier Faïn ◽  
Edward J. Brook ◽  
Joseph R. McConnell ◽  
Olivia J. Maselli ◽  
...  

Abstract. Advances in trace gas analysis allow localised, non-atmospheric features to be resolved in ice cores, superimposed on the coherent atmospheric signal. These high-frequency signals could not have survived the low-pass filter effect that gas diffusion in the firn exerts on the atmospheric history and therefore do not result from changes in the atmospheric composition at the ice sheet surface. Using continuous methane (CH4) records obtained from five polar ice cores, we characterise these non-atmospheric signals and explore their origin. Isolated samples, enriched in CH4 in the Tunu13 (Greenland) record are linked to the presence of melt layers. Melting can enrich the methane concentration due to a solubility effect, but we find that an additional in situ process is required to generate the full magnitude of these anomalies. Furthermore, in all the ice cores studied there is evidence of reproducible, decimetre-scale CH4 variability. Through a series of tests, we demonstrate that this is an artifact of layered bubble trapping in a heterogeneous-density firn column; we use the term “trapping signal” for this phenomenon. The peak-to-peak amplitude of the trapping signal is typically 5 ppb, but may exceed 40 ppb. Signal magnitude increases with atmospheric CH4 growth rate and seasonal density contrast, and decreases with accumulation rate. Significant annual periodicity is present in the CH4 variability of two Greenland ice cores, suggesting that layered gas trapping at these sites is controlled by regular, seasonal variations in the physical properties of the firn. Future analytical campaigns should anticipate high-frequency artifacts at high-melt ice core sites or during time periods with high atmospheric CH4 growth rate in order to avoid misinterpretation of such features as past changes in atmospheric composition.


1985 ◽  
Vol 7 ◽  
pp. 125-129 ◽  
Author(s):  
C.U. Hammer

Polar ice cores offer datable past snow deposits in the form of annual ice layers, which reflect the past atmospheric composition. Trace substances in the cores are related to the past mid-tropospheric impurity load, this being due to the vast extent of the polar ice sheets (or ice caps), their surface elevations and remoteness from most aerosol sources. Volcanic eruptions add to the rather low background impurity load via their eruptive products. This paper concentrates on the widespread influence on atmospheric impurity loads caused by the acid gas products from volcanic eruptions. In particular the following subjects are discussed: acid volcanic signals in ice cores, latitude of eruptions as derived by ice-core analysis, inter-hemispheric dating of the two polar ice sheets by equatorial eruptions, volcanic deposits in ice cores during the last glacial period and climatic implications.


1988 ◽  
Vol 10 ◽  
pp. 209-209
Author(s):  
C.C. Langway ◽  
K. Goto-Azuma

Measurements of the chemical constituents in polar-snow deposits translate into chronological records representing a history of atmospheric composition for the periods involved. The 2037 m deep continuous and undisturbed ice core recovered at Dye 3, Greenland between 1979 and 1981 contains a temporal record of sequential snow deposits for the past 9 × 104 a B.P. (Dansgaard and others 1985). The upper 90 m of the deep core were unsuitable for chemistry studies, but stratigraphic continuity with present-day accumulation was obtained by hand-excavating a 5.4 m deep pit and augering two shallow cores to 138 and 113 m depths. The pit and shallow cores represent the last two centuries of snow precipitation.To date, over 6000 individual samples of the pit, shallow and deep ice cores have been measured by ion chromatography for Cl−, NO3−, and SO42− in the field and laboratory (Herron and Langway 1985, Finkel and Langway 1985, Finkel and others 1986), under clean-room conditions. All pit and shallow-core samples were prepared in a continuous sequence of eight samples per year, as identified by other stable and radioactive isotope-dating methods. The deep ice-core samples were selected and prepared from core intervals spaced over the 2037 m profile from time units which showed evidence of abrupt or transitory periods in climate change or volcanic disturbances, as defined by stable isotopes (Dansgaard and others 1985), atmospheric gases (Oeschger and others 1985) and dust (Hammer and others 1985).Approximately 1700 new measurements from the Dye 3 samples are included in this study. Variability in the chemical constituents and their concentration levels is present and meaningful on a short-term and long-term basis. The time units measured represent seasons, years, decades, centuries and longer geological periods. Particular attention is given to two new high- and low-frequency detailed chronological data sets from (1) a continuous 26 m core profile, representing 3000 years, extending from the Holocene/Wisconsin boundary back into the late Wisconsin and (2) measurements made on 106 samples spaced every 2 m over the Wisconsin-age ice from 1786 to 2008 m.


1985 ◽  
Vol 7 ◽  
pp. 125-129 ◽  
Author(s):  
C.U. Hammer

Polar ice cores offer datable past snow deposits in the form of annual ice layers, which reflect the past atmospheric composition. Trace substances in the cores are related to the past mid-tropospheric impurity load, this being due to the vast extent of the polar ice sheets (or ice caps), their surface elevations and remoteness from most aerosol sources. Volcanic eruptions add to the rather low background impurity load via their eruptive products. This paper concentrates on the widespread influence on atmospheric impurity loads caused by the acid gas products from volcanic eruptions. In particular the following subjects are discussed: acid volcanic signals in ice cores, latitude of eruptions as derived by ice-core analysis, inter-hemispheric dating of the two polar ice sheets by equatorial eruptions, volcanic deposits in ice cores during the last glacial period and climatic implications.


2021 ◽  
Vol 15 (12) ◽  
pp. 5529-5555
Author(s):  
Ikumi Oyabu ◽  
Kenji Kawamura ◽  
Tsutomu Uchida ◽  
Shuji Fujita ◽  
Kyotaro Kitamura ◽  
...  

Abstract. The variations of δO2/N2 and δAr/N2 in the Dome Fuji ice core were measured from 112 m (bubbly ice) to 2001 m (clathrate hydrate ice). Our method, combined with the low storage temperature of the samples (−50 ∘C), successfully excludes post-coring gas-loss fractionation signals from our data. From the bubbly ice to the middle of the bubble–clathrate transition zone (BCTZ) (112–800 m) and below the BCTZ (>1200 m), the δO2/N2 and δAr/N2 data exhibit orbital-scale variations similar to local summer insolation. The data in the lower BCTZ (800–1200 m) have large scatter, which may be caused by millimeter-scale inhomogeneity of air composition combined with finite sample lengths. The insolation signal originally recorded at the bubble close-off remains through the BCTZ, and the insolation signal may be reconstructed by analyzing long ice samples (more than 50 cm for the Dome Fuji core). In the clathrate hydrate zone, the scatter around the orbital-scale variability decreases with depth, indicating diffusive smoothing of δO2/N2 and δAr/N2. A simple gas diffusion model was used to reproduce the smoothing and thus constrain their permeation coefficients. The relationship between δAr/N2 and δO2/N2 is markedly different for the datasets representing bubble close-off (slope ∼ 0.5), bubble–clathrate hydrate transformation (∼1), and post-coring gas loss (∼0.2), suggesting that the contributions of the mass-independent and mass-dependent fractionation processes are different for those cases. The method and data presented here may be useful for improving the orbital dating of deep ice cores over the multiple glacial cycles and further studying non-insolation-driven signals (e.g., atmospheric composition) of these gases.


2021 ◽  
Author(s):  
Rachael Rhodes ◽  
Xin Yang ◽  
Eric Wolff

<p>It is important to understand the magnitude and rate of past sea ice changes, as well as their timing relative to abrupt shifts in other components of Earth’s climate system. Furthermore, records of past sea ice over the last few centuries are urgently needed to assess the scale of natural (internal) variability over decadal timescales. By continuously recording past atmospheric composition, polar ice cores have the potential to document changing sea ice conditions if atmospheric chemistry is altered.  Sea salt aerosol, specifically sodium (Na), and bromine enrichment (Br<sub>enr</sub>, Br/Na enriched relative to seawater ratio) are two ice core sea ice proxies suggested following this premise.</p><p>Here we aim to move beyond a conceptual understanding of the controls on Na and Br<sub>enr</sub> in ice cores by using process-based modelling to test hypotheses. We present results of experiments using a 3D global chemical transport model (p-TOMCAT) that represents marine aerosol emission, transport and deposition. Critically, the complex atmospheric chemistry of bromine is also included allowing us to explore the partitioning of Br between gas and aerosol phases.  </p>


2020 ◽  
Author(s):  
Francis Ludlow ◽  
Conor Kostick ◽  
Rhonda McGovern ◽  
Laura Farrelly

<p>This paper capitalizes upon the recent availability of much-improved ice-core chronologies of explosive volcanism for the first millennium BCE in combination with the remarkable record of meteorological data preserved in Babylonian astronomical diaries, written on cuneiform tablets spanning 652-61BC and now housed in the British Museum. These diaries comprise systematic economic data on agricultural prices, weather observations at an hourly resolution, river heights for the Euphrates and other phenomena. Our initial results reveal strong correspondences between multiple previously unrecognized accounts of solar dimming, extreme cold weather and major ice-core volcanic signals. We also observe anomalously high spring floods of the Euphrates at Babylon, following major tropical eruptions, which is consistent with climate modelling of anomalously elevated winter precipitation in the headwaters of the Euphrates and Tigris in northeastern Turkey. With the astronomical diaries also providing systematic meteorological information (unparalleled in resolution and scope until at least the Early Modern period) ranging from wind direction and intensity, to the level of cloud cover and references to atmospheric clarity (clear vs. dusty skies), to the general conditions (temperature and precipitation) for all seasons, these sources can in combination with natural archives such as ice-cores open an unprecedented window into the Middle Eastern climate of the first millennium BCE.</p><p>Nor are these or other written sources from the region silent on the societal consequences of extreme weather and other climatic shocks. We will thus finish our paper with a brief case study of responses to the climatic impacts of explosive volcanism during the reign of Esarhaddon, ruler of Assyria, who's reign from 672 BCE suddenly became a troubled one. Contemporary prophecies indicated a loss of cattle, the failure of dates and sesame and the arrival of locusts. Such prophecies were often descriptions of events already occurring and along with predictions dated to 671 of 'darkness in the land', crop failure and famine, there is definite evidence that Esarhaddon resorted to the ritual of placing a substitute (sacrificial) ruler on the throne for 100 days. This did not, however, resolve the dangers perceived by the Assyrian ruler and he repeated the ritual in 670, along with apotropaic rituals against malaria and plague. That year, nevertheless, saw revolt. Herdsmen refused to supply oxen and sheep to the government officials, who could not travel the land without armed escort. Regional governors appropriated revenues and construction workers halted brick production. Esarhaddon acted decisively in late 670, early 669, executing a large number of rebellious Assyrian nobles. 669 and 668 remained troubled, however, with prophecies of locusts and plague among cattle and humans, while in 667 Egypt revolted against Assyria in the context of possible shortages of barely and straw.</p><p>This paper is a contribution to the Irish Research Council-funded “Climates of Conflict in Ancient Babylonia” (CLICAB) project.</p>


2020 ◽  
Author(s):  
Jochen Schmitt ◽  
James Lee ◽  
Jon Edwards ◽  
Edward Brook ◽  
Thomas Blunier ◽  
...  

<p>Air inclusions trapped in polar ice provide unique records of the past atmospheric composition ranging from key greenhouse gases to short-lived trace gases like ethane and propane. Provided the analyzed species concentrations and their isotopic fingerprints accurately reflect past atmospheric composition, valuable constraints can be put onto biogeochemical cycles. However, it is already known that not all drill sites or specific time intervals are equally suitable to derive artefact-free gas records; e.g., CO<sub>2</sub> data from Greenland ice is overprinted by CO<sub>2</sub> ‘in situ’ production due to impurities in the ice, and only the cleaner Antarctic ice allows to reconstruct past atmospheric CO<sub>2</sub>.</p><p>Until recently, CH<sub>4</sub> artefacts in polar ice were only detected on melt affected samples or for short spikes related to exceptional impurity deposition events (Rhodes et al 2013). However, careful comparison of CH<sub>4</sub> records obtained using different extraction methods revealed disagreements among Greenland CH<sub>4</sub> records and initiated targeted experiments.</p><p>Here, we report experimental findings of CH<sub>4</sub> artefacts occurring in dust-rich sections of Greenland ice cores. The artefact production happens during the melt extraction step (‘in extractu’) of the classic wet extraction technique and typically reaches 20 ppb in dusty stadial ice which causes erroneous reconstructions of the interhemispheric CH<sub>4</sub> difference and strongly affects the hydrogen isotopic signature of CH<sub>4</sub> (Lee et al. 2020). The measured CH4 excess is proportional to the amount of mineral dust in the ice. Knowing the empirical relation between produced CH4 and the dust concentration of a sample allows a first-order correction of existing CH4 data sets and to revise previous interpretations.</p><p>To shed light on the underlying mechanism, we analyzed samples for other short-chain alkanes ethane (C<sub>2</sub>H<sub>6</sub>) and propane (C<sub>3</sub>H<sub>8</sub>). The production of CH<sub>4</sub> was always tightly accompanied with C<sub>2</sub>H<sub>6</sub> and C<sub>3</sub>H<sub>8</sub> production at amounts exceeding the past atmospheric background levels derived from low-dust samples. Independent of the produced amounts, CH<sub>4</sub>, C<sub>2</sub>H<sub>6</sub>, and C<sub>3</sub>H<sub>8</sub> were produced in molar ratios of roughly 16:2:1, respectively. The simultaneous production at these ratios does not point to an anaerobic methanogenic origin which typically exhibits methane-to-ethane ratios of >>100. Such alkane patterns are indicative of abiotic degradation of organic matter as found in sediments.</p><p>We found this specific alkane pattern not only for dust-rich samples but also for samples that were affected by surface melting from the last interglacial (NEEM ice core) with low dust concentrations. This implies that the necessary precursor is an impurity also present in low-dust ice and the step leading to the production of the alkanes could then be activated when a sufficient boundary condition is met for the production, e.g. by melt/refreeze of surface snow.</p>


Sign in / Sign up

Export Citation Format

Share Document