Abrupt changes (Heinrich events) in late Quaternary North Atlantic marine environments: a history and review of data and concepts

Abstract

In the last several years evidence has mounted that a series of abrupt changes in sediment delivery and palaeoceanography effected the North Atlantic; they are recorded in a variety of proxy records but most dramatically in changes of grain-size and mineralogy associated with postulated iceberg rafting events, specifically Heinrich (H) events. This review paper examines the evidence for such evidence prior to the development of the ‘Heinrich event’ concept (1988–1992), and then examines the explosion of data and correlations that stemmed from the acceptance and use of this paradigm. Specific attention is focused on ideas pertaining to the cause(s) of glaciological mechanisms, sediment delivery, and sediment source, and major gaps in our understanding of the underlying glaciological, glacial geological, and glacial marine processes are stressed. Abrupt changes across boundaries associated with H-2 in the Labrador Sea are illustrated from core HU87033-009LCF. The case is made that correlations between records need to be more rigorous, especially within the range of radiocarbon dating, but it appears that abrupt changes in the delivery of iceberg rafted debris, which characterize these intervals, are multisourced. It is unclear how global ‘climate’ can simultaneously influence the abrupt behaviour of ice margins in different parts of the world—for marine-based margins, changes in relative sea-level are one possibility. A qualitative model is presented for triggering H events, which includes global changes in mass balance, changes in relative sea-level at ice margins due to glacial isostasy, and changes in the basal thermal regime of tidewater ice-streams. © 1998 John Wiley & Sons, Ltd.