Volcanic sulfate deposition to Greenland and Antarctica: A modeling sensitivity study

Reconstructions of the atmospheric sulfate aerosol burdens resulting from past volcanic eruptions are based on ice core-derived estimates of volcanic sulfate deposition and the assumption that the two quantities are directly proportional. We test this assumption within simulations of tropical volcanic stratospheric sulfur injections with the MAECHAM5-HAM aerosol-climate model. An ensemble of 70 simulations is analyzed, with SO2 injections ranging from 8.5 to 700 Tg, with eruptions in January and July. Modeled sulfate deposition flux to Antarctica shows excellent spatial correlation with ice core-derived estimates for Pinatubo and Tambora, although the comparison suggests the modeled flux to the ice sheets is 4–5 times too large. We find that Greenland and Antarctic deposition efficiencies (the ratio of sulfate flux to each ice sheet to the maximum hemispheric stratospheric sulfate aerosol burden) vary as a function of the magnitude and season of stratospheric sulfur injection. Changes in simulated sulfate deposition for large SO2 injections are connected to increases in aerosol particle size, which impact aerosol sedimentation velocity and radiative properties, the latter leading to strong dynamical changes including strengthening of the winter polar vortices, which inhibits the transport of stratospheric aerosols to high latitudes. The resulting relationship between Antarctic and Greenland volcanic sulfate deposition is nonlinear for very large eruptions, with significantly less sulfate deposition to Antarctica than to Greenland. These model results suggest that variability of deposition efficiency may be an important consideration in the interpretation of ice core sulfate signals for eruptions of Tambora-magnitude and larger

Snow Chemistry Across Antarctica

An updated compilation of published and new data of major-ion (Ca, Cl, K, Mg, Na, NO3, SO4) and methylsulfonate (MS) concentrations in snow from 520 Antarctic sites is provided by the national ITASE (International Trans-Antarctic Scientific Expedition) programmes of Australia, Brazil, China, Germany, Italy, Japan, Korea, New Zealand, Norway, the United Kingdom, the United States and the national Antarctic programme of Finland. The comparison shows that snow chemistry concentrations vary by up to four orders of magnitude across Antarctica and exhibit distinct geographical patterns. The Antarctic-wide comparison of glaciochemical records provides a unique opportunity to improve our understanding of the fundamental factors that ultimately control the chemistry of snow or ice samples. This paper aims to initiate data compilation and administration in order to provide a framework for facilitation of Antarctic-wide snow chemistry discussions across all ITASE nations and other contributing groups. The data are made available through the ITASE web page (http:// www2.umaine.edu/itase/content/syngroups/snowchem.html) and will be updated with new data as they are provided. In addition, recommendations for future research efforts are summarized

Tephrochronology and its application: A review

Tephrochronology (from tephra, Gk ‘ashes’) is a unique stratigraphic method for linking, dating, and synchronizing geological, palaeoenvironmental, or archaeological sequences or events. As well as utilising the Law of Superposition, tephrochronology in practise requires tephra deposits to be characterized (or ‘fingerprinted’) using physical properties evident in the field together with those obtained from laboratory analyses. Such analyses include mineralogical examination (petrography) or geochemical analysis of glass shards or crystals using an electron microprobe or other analytical tools including laser-ablation-based mass spectrometry or the ion microprobe. The palaeoenvironmental or archaeological context in which a tephra occurs may also be useful for correlational purposes. Tephrochronology provides greatest utility when a numerical age obtained for a tephra or cryptotephra is transferrable from one site to another using stratigraphy and by comparing and matching inherent compositional features of the deposits with a high degree of likelihood. Used this way, tephrochronology is an age-equivalent dating method that provides an exceptionally precise volcanic-event stratigraphy. Such age transfers are valid because the primary tephra deposits from an eruption essentially have the same short-lived age everywhere they occur, forming isochrons very soon after the eruption (normally within a year). As well as providing isochrons for palaeoenvironmental and archaeological reconstructions, tephras through their geochemical analysis allow insight into volcanic and magmatic processes, and provide a comprehensive record of explosive volcanism and recurrence rates in the Quaternary (or earlier) that can be used to establish time-space relationships of relevance to volcanic hazard analysis. The basis and application of tephrochronology as a central stratigraphic and geochronological tool for Quaternary studies are presented and discussed in this review. Topics covered include principles of tephrochronology, defining isochrons, tephra nomenclature, mapping and correlating tephras from proximal to distal locations at metre- through to sub-millimetre-scale, cryptotephras, mineralogical and geochemical fingerprinting methods, numerical and statistical correlation techniques, and developments and applications in dating including the use of flexible depositional age-modelling techniques based on Bayesian statistics. Along with reference to wide-ranging examples and the identification of important recent advances in tephrochronology, such as the development of new geoanalytical approaches that enable individual small glass shards to be analysed near-routinely for major, trace, and rare-earth elements, potential problems such as miscorrelation, erroneous-age transfer, and tephra reworking and taphonomy (especially relating to cryptotephras) are also examined. Some of the challenges for future tephrochronological studies include refining geochemical analytical methods further, improving understanding of cryptotephra distribution and preservation patterns, improving age modelling including via new or enhanced radiometric or incremental techniques and Bayesian-derived models, evaluating and quantifying uncertainty in tephrochronology to a greater degree than at present, constructing comprehensive regional databases, and integrating tephrochronology with spatially referenced environmental and archaeometric data into 3-D reconstructions using GIS and geostatistics

Spatio-temporal variability in volcanic sulphate deposition over the past 2 kyr in snow pits and firn cores from Amundsenisen, Dronning Maud Land, Antarctica

In the framework of the European Project for Ice Coring in Antarctica (EPICA), a comprehensive glaciological pre-site survey has been carried out on Amundsenisen, Dronning Maud Land, East Antarctica, in the past decade. Within this survey four intermediate-depth ice cores and 13 snow pits were analysed for their ionic composition and interpreted with respect to the spatial and temporal variability of volcanic sulphate deposition. The comparison of the non-sea-salt (nss)-sulphate peaks that are related to the well-known eruptions of Mt. Pinatubo and Cerro Hudson in AD 1991 revealed sulphate depositions of comparable size (15.8±3.4 kg km-2) in 11 snow pits. There is a tendency to higher annual concentrations for smaller snow accumulation rates. The combination of seasonal sodium and annually resolved nss-sulphate records allowed the establishment of a time-scale derived by annual layer counting over the last 2000 years and thus a detailed chronology of annual volcanic sulphate deposition. Using a robust outlier detection algorithm, 49 volcanic eruptions were identified between AD 165 and 1997. The dating uncertainty is ±3 years between AD 1997 and 1601, around ±5 years between AD 1601 and 1258, and increasing to ±24 years at AD 165, improving the accuracy of the volcanic chronology during the penultimate millenium considerably

Influence of large-scale teleconnection patterns on methane sulfonate ice core records in Dronning Maud Land

Records of methane sulfonate (MS) in ice cores from the high plateau of DronningMaud Land (DML), Antarctica, drilled in the framework of the European Project for IceCoring in Antarctica, are investigated for their potential as an environmental andclimate archive for the Atlantic sector of the Southern Ocean. Despite postdepositionalchanges, years of extraordinary MS concentrations can be clearly detected in the icecore records. We use composite anomaly maps of atmospheric parameters from theNational Centers for Environmental Prediction/National Center for Atmospheric Researchreanalysis fields for years of extreme MS concentration to detect atmospheric patternscausing MS variability. Changing atmospheric transport is shown to be an important,but not exclusive, parameter being conserved in the MS record in DML. The oftenhypothesized direct link between high MS concentrations and El Nino events is notsupported for the observed region whereas the Antarctic Dipole (ADP), which ismodulated by El Nino Southern Oscillation conditions, exerts significant influence. Aclear 13.9-year cycle can be found throughout a 2000-year MS record that can be relatedto variations in the ADP. Over the last 300 years a 4.6-year cycle is revealed in theMS (and sea-salt record), which vanishes in the deeper part of the ice core as aconsequence of diffusion processes. From the long-term perspective, periods of high MSconcentrations are connected to, on average, higher sea-salt aerosol as well, reflecting aseasonally independent influence of transport on both species. A distinctive period ofefficient atmospheric transport, probably due to a pronounced ADP, could be foundfrom 1200 to 1600 A.D

Age model of firn core DML05C98_32 (B32)

In the framework of the European Project for Ice Coring in Antarctica (EPICA), a comprehensive glaciological pre-site survey has been carried out on Amundsenisen, Dronning Maud Land, East Antarctica, in the past decade. Within this survey, four intermediate-depth ice cores and 13 snow pits were analyzed for their ionic composition and interpreted with respect to the spatial and temporal variability of volcanic sulphate deposition. The comparison of the non-sea-salt (nss)-sulphate peaks that are related to the well-known eruptions of Pinatubo and Cerro Hudson in AD 1991 revealed sulphate depositions of comparable size (15.8 ± 3.4 kg/km**2) in 11 snow pits. There is a tendency to higher annual concentrations for smaller snow-accumulation rates. The combination of seasonal sodium and annually resolved nss-sulphate records allowed the establishment of a time-scale derived by annual-layer counting over the last 2000 years and thus a detailed chronology of annual volcanic sulphate deposition. Using a robust outlier detection algorithm, 49 volcanic eruptions were identified between AD 165 and 1997. The dating uncertainty is ±3 years between AD 1997 and 1601, around ±5 years between AD 1601 and 1257, and increasing to ±24 years at AD 165, improving the accuracy of the volcanic chronology during the penultimate millennium considerably