Origin and Consequences of Cyclic Ice Rafting in the Northeast Atlantic Ocean During the Past 130,000 Years

Abstract

Deep-sea sediment cores recovered from the Northeast Atlantic Ocean were examined in order to elucidate the influence of the Earth's orbital parameters on major ice rafting. Analyses of coarse-grained ice-rafted debris and planktonic foraminifers revealed a strong reaction to the precession signal. Since 130,000 yr B.P., dropstone layers have been deposited each half period of a precessional cycle (11,000 ± 1000 yr). Ice rafting occurs during times of winter minimum/summer maximum insolation and summer minimum/winter maximum insolation. In the first case, high summer insolation forces meltwater discharge from the ice sheets into the polar seas which subsequently enhances formation of sea ice during the winter. In the second case, growth of continental ice enhances iceberg production which also leads to a salinity reduction of surface seawater. Both situations result in a southward penetration of polar water. Thus, the marine record of dropstones documents ice rafting not only during Weichselian stades but also during cold events within interstades. The regularity of ice rafting yields a useful framework to calibrate and elucidate climatic changes, not only in the region of the North Atlantic Ocean but also in remote areas such as the Pacific Ocean and the Antarctic.

On the reconstruction of palaeo-ice sheets: Recent advances and future challenges

“…The marine geological record also preserves evidence of palaeo-ice streaming in the form of episodic layers of ice-rafted detritus (IRD), the most conspicuous of which were deposited during Heinrich events (Heinrich, 1988;Hemming, 2004; Section 2.7). Andrews and Tedesco (1992) attributed the carbonate-rich IRD layers associated with the two most recent Heinrich events (H1 and H2) to a source area eroded by an ice stream in Hudson Strait (Andrews and MacLean, 2003).…”

“…Glacial intervals are characterised by Heinrich events that, sensu stricto, are identified by a sudden increase in the coarse lithic fraction, a dominance of the polar planktonic foraminifera Neogloboquadrina pachyderma(s), and a lowering of inferred sea-surface salinity (Heinrich, 1988;Bond et al, 1993). For the past two decades, these events have highlighted the limits of our understanding with respect to reconstructing ice sheet dynamics and their links to the ocean-climate system (Hemming, 2004).…”

“…The original definition of Heinrich layers was based on IRD in the central North Atlantic (Ruddiman 1977;Heinrich, 1988) (Hesse and Khodabakhsh, 1998) and are similar to seasonal cycles recognised in the Bay of Biscay by Zaragosi et al (2006). Dispersed drop clasts and pellets within the turbidite layers suggest that ice calving occurred at the same time as meltwater supply.…”

Prospecting Glacial Ages and Paleoclimatic Reconstructions Northeastward of Nevado Coropuna (16° S, 73° W, 6377 m), Arid Tropical Andes

“…Therefore, after the LGM-RSL, the Central Andes deglaciation onset could have happened earlier or later, depending on the temperature evolution in both terrestrial hemispheres ( Figure 12): (a) First, between~19 and~9 ka, the Surface Sea Temperature (SST) westward of the Iberian Peninsula (SSTN; [109]) got warmer by 6 • C in 10 ka. However, it was not a gradual trend, because it was broken by abrupt cold episodes due to AMOC shutdowns: H1 (e.g., [110,111]) and YD (e.g., [112]), which appear reflected in the SST N curve,~18 and~12 ka ago, respectively. (b) Secondly, the humidity increases due to cold boreal events, which is well recorded in the Andean Altiplano lacustrine evidence; e.g., -At the Coropuna latitude (~16 • S), one clear evidence of moister conditions is the strong decrease in the Titicaca salinity~21-10 ka ago, as shown by the great abundance (>80%) of freshwater plankton, nowadays extinct, in the lake sediments [113].…”

The role of North Brazil Current transport in the paleoclimate of the Brazilian Nordeste margin and paleoceanography of the western tropical Atlantic during the late Quaternary

“…Greenland ice cores (e.g., Dansgaard et al, 1993 andGrootes et al, 1993) and North Atlantic sediment cores (e.g., Heinrich, 1988 andLotti, 1995) distinguish the late Quaternary as a period of abrupt, large amplitude oceanic and atmospheric reorganizations, the Dansgaard-Oeschger and Heinrich events. These events seem to have strongly impacted South and Central American paleoclimate.…”