Ice-rafted detritus

Figure 20 Nd-Sr-isotope ratios of terrigenous clastic components of Heinrich layer H3. Shown for reference are the average and 2 sigma range for the data published on Heinrich layers HI, H2, H4, and H5, and reported compositions of potential source areas of ice rafted detritus (Grousset et al., 2001, and references therein). Also included is the average of 5 unpublished analyses across H3 from V28-82, where the error bars represent the range of values measured (A. lost and S. Hemming) (somces Grousset et al., 1993 Revel et al., 1996 Snoeckx et al., 1999).

Results from studies of the ice-rafted detritus population from core V23-14 provide insights into the evolution of ice sheets of the northwest Atlantic margin since 43 ka. Between Heinrich layers H5 and H3 (MIS 3), it appears that the... 

Grousset F. E., Labeyrie L., Sinko J. A., Cremer M., Bond G., Duprat J., Cortijo E., and Huon S. (1993) Patterns of ice-rafted detritus in the glacial North-Atlantic (40-degrees-55-degrees-N). Paleoceanography 8(2), 175-192. 

Hemming S. R. and Hajdas 1. (2003) Ice-rafted detritus evidence from Ar-40/Ar-39 ages of individual hornblende grains for evolution of the eastern margin of the Laurentide ice sheet since 43 C-14ky. Quat. Int. 99, 29-43. 

Records of the percent ice-rafted detritus (% iRD) in cores from the North Atiantic. Heinrich events i-5 are iabeied on the graphs, aithough ionger cores indicate that there are more. The map shows a suite of cores in which these events are observed only two representative curves of the data are shown here. Modified from Hemming (2004). 

The oldest unequivocal evidence for ice sheets on Antarctica, ice-rafted detritus (IRD) deposited by icebergs in the ocean, places the first large ice sheet in the earliest Oligocene. Thus, it is reasonable to assume that ice sheets were small to absent and that surface and deep-water temperature changes controlled much if not all the d 0 change prior to 34 Ma. The modern Antarctic and Greenland ice sheets lock up 2% of the total water in the world s ocean. If melted, these ice sheets would raise global sea level by 70-75 m and mean ocean d O ater value would decrease to — 0.9%o PDB (see above). One can then apply eqn [2] to the benthic and planktonic foraminiferal d O records to estimate deep- and surface-ocean temperatures for the first half of the Cenozoic c. 65-34 Ma). 

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