Progressive reduction in NE Atlantic intermediate water ventilation prior to Heinrich events : response to NW European ice sheet instabilities? - Peck, V. L. (Cardiff University. School of Earth and Ocean Sciences) ; Hall, Ian R. (Cardiff University. School of Earth and Ocean Sciences) ; Zahn, Rainer (Institució Catalana de Recerca i Estudis Avançats) ; Scourse, J. D. (University of Wales. School of Ocean Sciences)