COARSE FRACTION ABUNDANCES AND THE PLEISTOCENE RECORD OF ICEBERG-RAFTING AT IODP SITES 1304, 1305, AND 1308, NORTH ATLANTIC OCEAN

Plio-Pleistocene orbital- and suborbital-scale climatic variability in the North Atlantic was investigated during IODP Expedition 303, which cored Sites 1304 (southern Gardar Drift, 3024 mbsl), 1305 (southwestern Eirik Drift, 3459 mbsl), and 1308 (reoccupation of DSDP Site 609, central North Atlantic, 3871 mbsl).

Sediments from these 3 sites were sampled with an average time spacing of ~2 - 3 ky to ~1 Ma or more, and analyzed for coarse fraction abundance (CFA; weight % of the 150 µm – 2 mm fraction) by sieving. Present data is the total CFA for each sample. At Sites 1305 and 1308, the CFA includes biogenic particles (mostly foraminifers) and terrigenous grains (interpreted as iceberg-rafted debris, or IRD). At Site 1304, the CFA includes biogenic particles (mostly diatoms) and IRD; however, samples taken from laminated diatomaceous oozes were observed during sieving to contain no IRD, so those samples were assigned a CFA of 0 wt%. Because IRD grains have a significantly higher weight per grain than the biogenic components, IRD variations are interpreted to drive major variations in total CFA of the non-diatomaceous samples.

As has been reported previously for Sites 1305 and 1308, the CFA record at Site 1304 does not appear to correlate directly with marine isotope stages (MIS); for example, both MIS 6 and MIS 7 at Site 1304 have relatively high CFAs. As is the case at Site 1305, many of the largest CFA peaks at Site 1304 occur at, or near, transitions between isotope stages.

The diluting influence of diatomaceous oozes at Site 1304 is most extensive in sediments older than 0.5 Ma, so the CFA records for sediments younger than ~0.5 Ma at Sites 1304, 1305, and 1308 have been compared to evaluate basin-wide vs. more localized controls on coarse fraction abundances. Age control is based on published data (mostly shipboard data), with MIS boundaries inferred from those data. The CFA records show consistent relative abundance variations at all 3 sites for MIS 12 through 7 (relatively high CFAs in MIS 11, 9, and 7; relatively low CFAs in MIS 12, 10, and 8), suggesting a stronger basin-wide control on coarse-fraction distribution at those times. The 3 CFA records are less consistent during MIS 6 through 1, suggesting increased importance of local controls (e.g., oceanographic and/or glaciological influences) in the last ~200 ky.