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 icestreams.

Palaeo-ice streams, trough mouth fans and high-latitude continental slope sedimentation

“…This ice stream was the principal source of the ice-rafted Heinrich layers in the North Atlantic (Bond et al 1992;Dowdeswell et al 1995;Andrews 1998). -The Hudson Strait drainage basin was the largest drainage basin of the Laurentide Ice Sheet (1-2 Â 10 6 km 2 ) and fed the Hudson Strait ice stream during the Quaternary.…”

Asynchronous deposition of ice-rafted layers in the Nordic seas and North Atlantic Ocean

“…12). Thus, detailed correlations may, in some cases, be 'event matching' rather than based on a suite of bracketing AMS (accelerator mass spectrometer) radiocarbon dates 14 . In addition, several of the IRD events identified in isotope stages 3 and 4 by Baumann et al 12 do not correspond to the IRD peaks identified by Fronval et al 3 , although the cores were obtained in nearby areas of the Nordic seas.…”

“…1). Finally, it is clear that both additional dating control on IRD layers and petrographical evidence on the source areas of IRD are important in unravelling what appears an increasingly complex picture of ice-sheet variability 14 . Sympatric speciation, the origin of two or more species from a single local population, has almost certainly been involved in formation of several species flocks 1-4 , and may be fairly common in nature 5 .…”

“…Thus, multilocus models of sympatric speciation must be studied because single-locus models have very peculiar properties 6,12 . When a polygenic, quantitative trait is under disruptive selection, indirect selection favours reproductive isolation between the opposite, extreme phenotypes 7,9,[13][14][15] . If such isolation evolves as a result of fixation of alleles that cause assortative mating based on this trait 16,17 , the same variable quantitative trait will determine both fitness and mate choice of an individual.…”

Grain-size characteristics and provenance of ice-proximal glacial marine sediments

“…Heinrich events (Heinrich 1988;Andrews 1998) have provided a catalyst to develop a better understanding of the physics underlying ice sheet behaviour on 6-7 ka time scales (Clarke et al 1999;Dowdeswell & Siegert 1999). Progress is also being made on understanding the controls on iceberg trajectories and melt rates (Matsumoto 1997;Schaefer-Neth & Stattegger 1999;Clarke & Prairie in press).…”