Rockmagnetic investigations of IODP Site U1302-U1303

Integrated Ocean Drilling Program (IODP) Sites U1302-U1303, drilled on the SE flank of Orphan Knoll (Labrador Sea), preserve a record of detrital layers and other proxies of hydrographic change that extend the record of ice-sheet/ocean interactions through most of the Brunhes Chron. The age model is built by tandem matching of relative paleointensity (RPI) and oxygen isotope data (d18O) from Neogloboquadrina pachyderma (sin.) to reference records, indicating a mean Brunhes sedimentation rate of 14 cm/kyr. Sedimentation back to marine isotope stage (MIS) 18 is characterized by detrital layers that are detected by higher than background gamma-ray attenuation (GRA) density, peaks in X-ray fluorescence (XRF) indicators for detrital carbonate (Ca/Sr) and detrital silicate (Si/Sr), and an ice-rafted debris (IRD) proxy (wt.% >106 µm). The age model enables correlation of Site U1302/03 to IODP Site U1308 in the heart of the central Atlantic IRD belt where an age model and a similar set of detrital-layer proxies have already been derived. Ages of Heinrich (H) layers H1, H2, H4, H5 and H6 are within ~2 kyr at the two sites (H0, H3 and H5a are not observed at Site U1308), and agree with previous work at Orphan Knoll within ~3 kyr. At Site U1308, Brunhes detrital layers are restricted to peak glacials and glacial terminations back to marine isotope stage (MIS) 16 and have near-synchronous analogs at Site U1302/03. Detrital layers at Site U1302/03 are distributed throughout the record in both glacial and most interglacial stages. We distinguish Heinrich-like layers associated with IRD from detrital layers marked by multiple detrital-layer proxies (including Ca/Sr) but usually not associated with IRD, that may be attributed to lofted sediment derived from drainage and debris-flow events funneled down the nearby Northwest Atlantic Mid-Ocean Channel (NAMOC). The prominent detrital layers at Sites U1302/03 and U1308 can be correlated to millennial scale features in the Chinese speleothem (monsoon) record over the last 400 kyr, implying a link between monsoon precipitation and Laurentide Ice Sheet (LIS) instability. The detrital-layer stratigraphy at Site U1302/03 provides a long record of LIS dynamics against which other terrestrial and marine records can be compared