AZORELLA-SELAGO HOOK - USED TO ESTIMATE GLACIER FLUCTUATIONS AND CLIMATIC HISTORY IN THE KERGUELEN ISLANDS OVER THE LAST 2 CENTURIES

Climatic variations over the two last centuries are well known for the northern hemisphere, but very little information is available for sub antarctic islands. In this paper, we combined geomorphological observa tions and a new biological dating technique to propose a reconstructio n of the cool and warm events in the Kerguelen Islands during the last two centuries. The usual dating methods, such as dendrochonology or C -14 dating, are not applicable on Kerguelen. Therefore, the radial gro wth of Azorella selago Hook., a cushion-forming Umbelliferae species, was used to estimate the absolute age of deglaciated areas. Glacial ma rgins in the vicinity of the Glacier Ampere constitute the most comple te chronosequence studied in this part of the world and illustrate sev en warming-cooling cycles. This new dating technique is validated by t he close relationship between the calculated ages of these climatic ev ents and the results of several studies in other circumantarctic regio ns. The Glacier Ampere reached its maximum extent at the end of the ei ghteenth century. Since 1799, two discrete phases may be distinguished : the first period (1799-1965) is characterized by small glacier fluct uations (1 km retreat overall) whereas in the second period (1966 to t he present), the retreat is much more rapid (about 3 km). It seems tha t the current dramatic glacial retreat on Kerguelen is related to a ma jor change in the climate and could illustrate a more general southern hemispheric pattern of glacial fluctuations.