Ocean Circulation and Climate Dynamics

Heinrich Events

Figure 1. Iceberg, ice-rafted detritus (IRD) from a sediment core, the IRD belt in the north Atlantic, and the location of core MD95-2040.
Figure 2. Heinrich layers H1 to H6 in core MD95-2040 from the northern Portuguese Margin (after de Abreu et al., 2003).

Heinrich Events are intermittent periods of iceberg surges and meltweater flow mainly from the Laurentide ice sheet that occurred during glacial times. Iceberg drift and meltwater influx was largest in a belt between 40° and 50°N (Bond et al., 1992; Bond and Lotti, 1995). Enhanced meltwater flux caused a significant decrease in sea surface temperatures and salinities, and it destabilized or even stopped thermohaline circulation in the glacial North Atlantic (Zahn et al., 1997). Heinrich Events are characterized by massive, short-term occurrences of the polar planktonic foraminifer Neogloboquadrina pachyderma (sinistral) and coarse lithic grains of North American origin (Baas et al., 1997, de Abreu et al., 2003). These levels are denominated as Heinrich layers may be used to establish a chronostratigraphic framework for sediment cores (Lebreiro et al., 1996; Schönfeld and Zahn, 2000). 



Baas, J.H.; Mienert, J.; Abrantes, F., and Prins, M.A., 1997. Late Quaternary sedimentation on the Portuguese continental margin: climate-related processes and products. Palaeogeography, Palaeoclimatology, Palaeoecology, 130: 1-23.
Bond, G., and Lotti, R., 1995. Iceberg discharges into the North Atlantic on millennial time scales during the last glaciation. Science, 267: 1005-1010. 
Bond, G.; Heinrich, H.; Broecker, W.; Labeyrie, L.; McManus, J.; Andrews, J.; Huon, S., Jantschik, R.; Clasen, S., Simet, C.; Tedesco, K.; Klas, M.; Bonani, G., and Ivy, S., 1992. Evidence for massive discharges of icebergs into the North Atlantic Ocean during the last glacial period. Nature, 360: 245-249.
Lebreiro, S.M.; Moreno, J.C.; McCave, I.N., and Weaver, P.P.E., 1996. Evidence for Heinrich layers off Portugal (Tore Seamount: 39° N, 12° W). Marine Geology, 131: 47-56. 
Schönfeld, J. and Zahn, R., 2000. Late Glacial to Holocene history of the Mediterranean Outflow. Evidence from benthic foraminiferal assemblages and stable isotopes at the Portuguese Margin. Palaeogeography, Palaeoclimatology, Palaeoecology, 159: 85-111.
Zahn, R.; Schönfeld, J.; Kudrass, H.-R.; Pflaumann, U.; Sinha, D.K.; Park, M.-H., and Erlenkeuser, H., 1997. Thermohaline instability in the North Atlantic during Heinrich Events: stable isotope and faunal records from core SO75-26KL. Portuguese margin. Paleoceanography, 12: 696-710.
Abreu, L. de, Shackleton, N.J., Schönfeld, J., Hall, M., and Chapman, M., 2003. Millennial-scale oceanic climate variability off the Western Iberian margin during the last two glacial periods. Marine Geology, 196: 1-20.