U-CHANNEL PALEOMAGNETIC RESULTS FROM IODP SITE U1543: DEVELOPING THE FIRST LONG, HIGH RESOLUTION PALEOINTENSITY RECORD FROM THE HIGH LATITUDE SOUTHERN HEMISPHERE AND CHRONOLOGICAL IMPLICATIONS FOR THE EVOLUTION OF THE PATAGONIAN ICE SHEET

IODP Site U1543 is located in the eastern South Pacific at 54°35.06ʹS, 76°40.59ʹW, west of the Chile Trench on a topographically elevated ridge ~300 m above the trench axis at ~3860 m water depth. Site U1543 was drilled to a depth of 340 m and magnetic polarity and bio-stratigraphies indicate that these sediments extend back over 7.2 Ma with an average accumulation rate of ~5 cm/kyr. Physical properties vary with a pacing consistent with glacial-interglacial cycles, with high (low) magnetic susceptibility (MS) and GRA-density, possibly representing advance and retreat of the Patagonian Ice Sheet. Here we present initial u-channel paleomagnetic results that refine and build on shipboard data to improve our understanding of time and the MS record. Alternating field (AF) demagnetization of u-channel samples indicates a well resolved, high fidelity, low coercivity natural remanent magnetization (NRM) with inclination values centered around +/-70°, consistent with the geocentric axial dipole (GAD) prediction for both polarities. Well defined polarity reversals and a series of excursions from both polarities are observed, providing distinct stratigraphic markers. NRM intensity normalized by anhysteretic remanent magnetization (ARM) passes most criteria for relative paleointensity (RPI), however interglaciations appear to be characterized by an extremely fine-grained magnetic assemblage. Based on changes in direction and RPI, the Brunhes-Matuyama boundary occurs at ~41 m and an excursion at ~27 m is tentatively correlated with Big Lost. MIS 11 has been placed between 20-21 m based on the MS minimum and high biogenic carbonate content. The interval of shallower inclination and decrease in intensity around 3 m has tentatively been labeled the Laschamp, assuming the MS low around 6 m represents MIS 5 and average accumulation rate apply. Here we explore comparisons with global paleointensity stacks to refine the chronology for these sediments and assist with reconstruction of changes in the Patagonian Ice Sheet.