Magnetic Signature of Glacial/Interglacial & Paleo-Redox Variations at IODP Site U1543 from the Eastern Pacific Sector of the Southern Ocean: Evolving System Dynamics Across the Mid-Pleistocene Transition

We present a u-channel magnetic study of the upper 100 m of IODP Site U1543 (54° 35.06ʹ S, 76° 40.59ʹ W) from the Eastern Pacific sector of the Southern Ocean spanning 0-1.7 Ma. Alternating field demagnetization of the natural remanent magnetization and anhysteretic remanent magnetization (ARM) indicates a well resolved, high fidelity, low coercivity magnetization carried by a magnetite-dominated magnetic mineral assemblage. Inclination values are centered on ±70°, consistent with geocentric axial dipole predictions for both polarities. An age model with uncertainty is based upon well resolved reversal boundaries and one-to-one correlations of physical properties to glacial-interglacial variations indicated in the benthic oxygen isotope stack. We observe a repeating sequence of rock magnetic variability associated with glacial/interglacial variations that on longer trends likely reflect Mid-Pleistocene Transition (MPT; ~800-1200 ka) dynamics. Glacials are generally associated with high magnetic susceptibility (k) reflecting increased lithogenics, likely from the proximal Patagonian ice cap, while interglacials are associated with low k values. Interpreted interglacial intervals commonly begin with an initial sharp decrease in the median destructive field of the ARM as k decreases, followed by a sharp increase in kARM/k. This suggests late stages of interglacials are characterized by low magnetic concentrations and preservation of significantly finer magnetic grain sizes. We hypothesize that the magnetically finer-grained assemblage is biogenic magnetite and that the pattern of variability suggests a combination of alternating glacial/interglacial depositional processes and non-steady state, suboxic diagenesis that allows repetitive preservation of paleo-redox conditions during interglaciations. Furthermore, the amplitude and frequency of these rock magnetic features evolve throughout the Pleistocene, especially the kARM/k peaks. The character of these features appears similar to observations made between the 40 kyr and 100 kyr worlds separated by the MPT. This suggests that rock magnetic parameters at Site U1543 have recorded a signature of evolving paleoenvironmental processes in an understudied region across this key climate transition.