Oxygen and carbon isotopes of detrital carbonate in North Atlantic Heinrich Events

We report oxygen and carbon isotope results of detrital carbonate grains from Heinrich layers at three sites in the North Atlantic located along a transect from the Labrador Sea to the eastern North Atlantic. Oxygen isotopic values of individual detrital carbonate grains from six Heinrich layers at all sites average -5.6 parts per thousand +/- 1.5 parts per thousand (1 sigma: n=166), reflecting values of dolomitic limestone derived from source areas in northeastern Canada. The delta O-18 of bulk carbonate at Integrated Ocean Drilling Program (IODP) Site U1308 (re-occupation of Deep Sea Drilling Project (DSDP) Site 609) in the eastern North Atlantic records the proportion of detrital to biogenic carbonate and delta O-18 decreases to -5 parts per thousand during Heinrich (H) events 1, 2,4 and 5 relative to a background value of similar to 1 to 2 parts per thousand for biogenic carbonate. Bulk delta O-18 also decreases during H3 and H6 but only attains values of -1 parts per thousand, indicating either a greater proportion of biogenic-to-detrital carbonate or a different source. Because the delta O-18 of detrital carbonate is similar to 9 parts per thousand lower than foraminifer carbonate, any fine-grained detrital carbonate not removed from the inner test chambers will lower foraminifer delta O-18. We conclude bulk carbonate delta O-18 is a sensitive proxy for detrital carbonate and may be useful for identifying Heinrich layers in cores within and near the margins of the North Atlantic ice-rafted detritus (IRD) belt. (C) 2008 Elsevier B.V. All rights reserved.