Non-steady state magnetic mineral reduction, chemical lock-in, and delayed remanence acquisition in pelagic sediments

Magnetic hysteresis data collected from pelagic sediment sites in the western equatorial Pacific Ocean define a progressive deepening of modern redox boundaries with decreased organic carbon input. Paleomagnetic data from the site with the highest organic carbon shows marked changes in the natural remanent magnetization at the modern Fe-redox boundary, suggesting a type of chemical lock-in process in which some magnetic grains form in situ above the boundary and freely orient in the field. The depth of chemical lock-in suggests paleomagnetic data will be smoothed on time scales ranging from less than 40 kyr to more than 425 kyr. The higher values are compatible with models calling for a delayed remanence acquisition to account for the ‘saw-tooth’ pattern observed in some sedimentary paleointensity records.