Invited speakers

Monday 03 February - Franck Lavigne (LGP, Meudon) : Environmental impact of tropical volcanic eruptions, from local to global.

Tuesday 04 February - Hartmut Heinrich (0°E maritime consult, Allemagne) : Heinrich Events and Stadials interdependencies: A conceptual model deduced from Pleistocene eolian deposits on the Canary Island.

with contribution of Christopher Roettig and Dominik Faust (TU Dresden), Florian Ziemen and Uwe Mikolaiewicz (Max-Planck Institute of Meteorolgy, Hamburg) and  of Christoph Schmidt (University of Bayreuth)

Periodic ice shield collapses, so-called Heinrich events, were accidentally discovered in the 1980ies during an environmental impact study on the potential dumping of nuclear waste in the Northeastern Atlantic. A set of eleven partly anoxic sandy layers between Termination 2 and Termination 1, six of them during the main Weichselian Glaciation, turned out to be the cause of abrupt oceanic as well as atmospheric climatic changes all over the globe. They mostly occurred during Stadials but their relationship to Stadials remain unclear.

The Canary Islands at the southeastern corner of the North Atlantic with their eolian deposits make them an ideal and sensitive place to study in detail the succession and related climatic consequences of a glacial oceanic cycle in a terrestrial environment directly where the meltwater had exited the North Atlantic Ocean. The eolian deposits are mainly sequences of a mixture of biogenic carbonate detritus from the islands’ shelf area and variable amounts of dust from West Africa. Each sequence consists generally of three units in which the top unit has the by far highest dust content. The upper two units contain large amounts of land snail shells and Anthophora nests (earth wasps). A new assessment of published and unpublished information from Pleistocene eolian deposits of the Canary Islands Lanzarote and Fuerteventura, published model data about the behavior of the atmospheric polar jet stream during ice sheet collapses and new dates of ages from the top dust layers reveal that these layers formerly interpreted as soil formations turned out to be massive dust supplies during Heinrich Events. Thus, we conclude that each sequence is a succession of interstadial to stadial climatic conditions in which the top dust layer represents the coldest parts of a Stadial.

As it is the case in deep Northeast Atlantic sediments the change from Unit 2 to the top dust layer seems to be abrupt and thus, the deposition is not a continuous process. Unfortunately, the new results from the Canary Islands do not provide clarity on the genetic interdependence of Stadials and Heinrich Events. Since the early 1990ies, several mechanisms were proposed for the abrupt onsets of the collapses, e.g. ice sheet internal processes or ocean warming. In fact, there seems stronger evidence for an influence from (precessional) warming of the subtropical/tropical Atlantic Ocean. Such water -via the AMOC and beneath a low-density surface meltwater layer which covered the North Atlantic- approached the grounding lines of ice shields and may had triggered the collapses. The collapses then prepared ocean and atmosphere for the subsequent Interstadial. The actual anthropogenic ocean warming and its effects on marine terminations of glaciers and on ice shelves one presently observes along the Arctic and Antarctic supposedly is the same mechanism that lead to the collapses during the past Glacials. If so, collapses of the today existing polar ice shields or parts of them somewhere in the future seem already unavoidable.