UPDATED RECONSTRUCTION OF THE LATE PLEISTOCENE ICE-RAFTING HISTORY OF THE NORTH PACIFIC OCEAN USING ICE-RAFTED DEBRIS FROM THE PATTON-MURRAY SEAMOUNTS

Analysis of IRD in cores from ODP Site 887 contribute to the reconstruction of Pleistocene-Holocene climate in the North Pacific. Early work by St. John & Krissek (1999) described the temporal pattern of IRD accumulation in Hole 887A over the last 180 kyr using a low-resolution magnetostratigraphic age model. An updated age model was developed (Galbraith, 2008) using planktonic foraminiferal ¹⁴C data from Galbraith (2007) and benthic foraminiferal δ¹⁸O data from McDonald (1997). The purpose of this study is to re-examine the last two glacial cycles at Site 877 using this higher resolution age model and additional sediment samples to 1) understand the temporal relationships between ice rafting and climate change and 2) determine the feasibility of grain size analysis as an estimator for IRD abundance. 121 samples from Holes 887A & C were wet sieved to separate the coarse sand fraction (250μm-2mm) to calculate IRD wt% and IRD MAR and were analyzed for grain size using a laser diffraction particle size analyzer (LDPSA). A composite depth scale was constructed based on magnetic susceptibility to use the updated age model. The new IRD dataset is generally consistent with earlier work for marine isotope stages (MIS) 1-3 but shows some variations in MIS 4 & 5. A positive relationship between the coarse fraction calculated from LDPSA and from wet sieving (high IRD events) was seen but grain size analysis was also influenced by biogenic input. The LDPSA is not a suitable method for the very coarsest samples (sand and dropstones) based on comparison to the wet-sieved IRD record. The majority of IRD pulses occurred at rapid cooling events, or at rapid warming events near the end of a glacial cycle. IRD pulses are synchronous with most of the major North Atlantic Heinrich Stadial events which suggests hemispheric control on iceberg discharges. Large IRD MARs have a periodicity consistent with obliquity forcing. IRD fluxes in the last glacial period (MIS 2; ~18-24 ka) behaved as expected with high IRD throughout the period including, especially during the last glacial maximum (MIS 2a); in contrast the penultimate glacial period (MIS 6; ~138-190 ka) showed the highest IRD MARs before the penultimate glacial maximum (MIS 6a), which may indicate regional differences in source ice in response to the orbital climate cycles, but age model errors also need to be considered.