Unusual Heinrich Events
H3 and H6 do not share such a convincing suite of Heinrich event symptoms as events H1, H2, H4, and H5. This has led some researchers to suggest that they are not true Heinrich events, which would make Bond's suggestion of Heinrich events fitting into a 7,000-year cycle suspect. Several lines of evidence do suggest that H3 and H6 were somehow different from the other events.
- Lithic peaks: a far smaller proportion of lithics (3000 vs. 6000 grains per gram) is observed in H3 and H6, which means that the role of the continents in providing sediments to the oceans was relatively lower.
- Foram dissolution: Foraminifera tests appear to be more eroded during H3 and H6 (Gwiazda et al., 1996). This may indicate an influx of nutrient-rich—hence corrosive—Antarctic Bottom Water, due to a reconfiguration of oceanic circulation patterns.
- Ice provenance: Icebergs in H1, H2, H4, and H5 appear to have flowed along the Hudson Strait; H3 and H6 icebergs appear to have flowed across it (Kirby and Andrews, 1999).
- Ice rafted debris distribution: Sediment transported by ice does not extend as far East during H3/6. Hence some researchers have been moved to suggest a European origin for at least some H3/6 clasts: America and Europe were originally adjacent to one another; hence the rocks on each continent are difficult to distinguish and the source is open to interpretation (Grousset et al. 2000).
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