Number : MARGO 3741 Title : Oxygen and carbon isotopes of detrital carbonate in North Atlantic

9 We report oxygen and carbon isotope results of bulk and detrital carbonate grains 10 from the last glaciation at IODP Site U1308 (re-occupation of DSDP Site 609). Oxygen 11 isotopic values of individual detrital carbonate grains from Heinrich events average 12 -5.4‰±1.3‰, presumably reflecting values of limestone and dolomite derived from 13 lower Paleozoic basins in northern Canada and northwestern Greenland. The O of bulk 14 carbonate records the proportion of detrital to biogenic carbonate and O values 15 decrease to -5 ‰ during Heinrich (H) events 1, 2, 4 and 5 relative to a background value 16 of ~1 to 2‰ for biogenic carbonate. Bulk O values also decrease during H3 and H6 17 but only attain values of -1‰, indicating a greater proportion of biogenic-to-detrital 18 carbonate. Carbon isotope values of detrital carbonate in Heinrich events average 0.2 19 ±1.2‰, and are not significantly different from biogenic carbonate. We suggest that 20 oxygen isotope ratios of bulk carbonate are a sensitive proxy for recognizing detrital 21 carbonate layers and should have widespread application for tracing Heinrich events 22 throughout the North Atlantic ice-rafted-detritus (IRD) belt between ~40 and 55 N. 23 24