EVIDENCE FOR HEINRICH LAYERS OFF PORTUGAL (TORE SEAMOUNT - 39-DEGREES-N, 12-DEGREES-W)

The Tore Seamount is a circular, volcano-like feature 100 km in diamet er with its summit at 2200 m water depth and a small, 5000 m deep basi n in its interior. It is situated approximately 300 km west of Lisbon and is surrounded by deep abyssal plains. This site with a standard pe lagic stratigraphy is the southernmost point where the so-called Heinr ich events have so far been recorded. A succession of alternating inte rglacial/glacial periods reveals a stratigraphic record back to the be ginning of isotopic stage 7 (225 kyr). Climatic changes are identifiab le by coherent variations in colour, carbonate content and distributio n of ice-rafted detritus in the carbonate-free fraction. Inputs of ice -rafted quartz are well defined. Characteristics in common with other sites showing Heinrich layers include a high terrigenous to biogenic r atio, a dramatic decrease in the accumulation rate of foraminifera she lls, an increase in dolomite abundance and the occurrence of polar for aminiferal species indicating southwards penetration of cold waters wh ich lead us to consider a wider southeastern extent of the North Atlan tic ice-rafted detritus belt than hitherto. If the presently accepted position of the Polar Front is maintained, icebergs must have been swe pt southwards from the southern boundary of the pack ice in a current merging into the ancestral Canary Current, bringing ice-rafted materia l to the Tore Seamount. The coincidence of reddish-feldspar, probably derived from the northern Appalachian Triassic red facies, with the tr ansparent quartz suggests at least a partial Labrador source for all t he Heinrich layers here, including HL 3. In comparison to other sites in the entire North Atlantic, two exceptions stand out: the absence of HL 5 and the low detritus to biogenics ratio for HL 3. The simultaneo us occurrence of these two types of ice-rafted minerals is a new piece in the puzzle of the origin of Heinrich layers.