Atmospheric Chemistry Changes Over The Last Climatic Cycle (180 000 Years) Inferred From The Vostok (Antarctica) Ice-Core Study

Abstract

A 2 200 m-deep ice core from Vostok Station (East Antarctica) has been used for a comprehensive study of a series of ions (Na⁺ NH₄⁺, K⁺, H⁺, Ca²⁺, Mg²⁺, C1⁻, F⁻, NO₃⁻ and SO₄²⁻) originating from impurities deposited over the whole last climatic cycle (180 000 years) as depicted from the isotopic composition of the ice.

Concentration profiles confirm that both marine and terrestrial aerosol inputs were higher (up to five and 30 times the Holocene values respectively) during cold climatic conditions. Such large variations of marine and terrestrial aerosol concentrations measured in ice mainly reflect global (source strength and atmospheric transport efficiency) changes, and to a lesser extent local (deposition) changes.

As opposed to these primary aerosols, secondary aerosols or gases (HNO₃, HC1) exhibit more moderate variations. Finally, variations of other minor ions such as NH₄⁺ provide information on the capacity of ammonia to neutralize the natural acidity of the past background atmosphere.

Spectral analyses performed on our chemical profiles (200 samples) exhibit several specific periodicities (around 20 and 40 k year) close to the Earth's orbit tilt and precession frequencies which are discussed in terms of atmospheric response to climatic fluctuations.