Ice core evidence for secular variability and 200-year dipolar oscillations in atmospheric circulation over East Antarctica during the Holocene |
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Authors: | Barbara Delmonte Jean Robert Petit Gerhard Krinner Valter Maggi Jean Jouzel Roberto Udisti |
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Institution: | (1) Laboratoire de Glaciologie et de Géophysique de l’Environnement (LGGE-CNRS), BP96, 38402 Saint Martin d’Hères, France;(2) Department of Environmental Sciences, University Milano-Bicocca - DISAT, Piazza della Scienza 1, 20126 Milano, Italy;(3) Department of geological sciences, University of Siena, Via del Laterino 8, 53100 Siena, Italy;(4) Laboratoire des Sciences du Climat et de l’Environnement, Institut Pierre Simon Laplace, UMR CEA-CNRS 1572, CE Saclay, Orme des Merisiers, 91191 Gif-sur-Yvette, France;(5) Chemistry Department, Analytical Chemistry Sect., Scientific Pole, University of Florence, Via della Lastruccia 3, 50019 Sesto Fiorentino (Florence), Italy |
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Abstract: | Two Holocene ice core records from East Antarctica (Vostok and EPICA-Dome C) were analysed for dust concentration and size
distribution at a temporal resolution of 1 sample per ~50 years. A series of volcanic markers randomly distributed over the
common part of the ice cores (from 9.8 to 3.5 kyear BP) ensures accurate relative dating (±33 years). Dust-size records from
the two sites display oscillations structured in cycles with sub-millennial and secular scale frequencies that are apparently
asynchronous. The power spectra of the composite sum (Σ) of the two dust-size records display spectral energy mostly for 150-
to 500-year periodicities. On the other hand, the 200-year band is common to both records and the 200 year components of the
two sites are out-of-phase (100-year lead or lag) over ~5.5 kyear, a phenomenon also reflected by a significant (>99% conf.
lev.) band in the power spectra of the composite difference (Δ) of the two size records. During long-range transport, mineral
dust originating from the Southern Hemisphere continents is graded to a variable extent depending on the altitude and duration
of atmospheric transport. Relatively coarse dust is associated with air mass penetration from the middle–lower troposphere
and conversely relatively fine dust with upper troposphere air masses or the influence of subsidence over the Antarctic plateau,
a hypothesis already proposed for the changes that occurred during the Last Glacial Maximum to Holocene transition (Delmonte
et al. 2004b). Moreover, we assume that the overall fluctuation of air mass advection over Antarctica depends on the meridional pressure
gradient with respect to low latitudes, i.e. the Antarctic Oscillation (AAO). We therefore suggest a regional variability
in atmospheric circulation over East Antarctica. The 150–500 year power spectrum of the composite (Σ) parameter represents
the long term variability of the AAO, imprinted by secular internal oscillations probably related to the southern ocean-climatic
system. On the other hand, the Δ dust composite parameter suggests a persistent atmospheric dipole over East Antarctica delivering
coarser (finer) dust particles alternatively to Vostok and Dome C regions with a bi-centennial periodicity. Indeed, a seesaw
phenomenon in dust size distribution was already observed at three East Antarctic sites during the last deglaciation (Delmonte
et al. 2004b) and was interpreted as a progressive reduction of the eccentricity of the polar vortex with respect to the geographic south
pole. Interestingly, the Δ parameter shows a pronounced 200-year oscillation mode, throwing new light on the unresolved question
of a possible relationship between climate and solar activity. |
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