A summary of paleomagnetic secular variation and excursions for the last 380 ky of the Brunhes Normal Polarity Chron – regional results from the Bering Sea (IODP Ex. 323)

This study describes high-resolution, full-vector paleomagnetic secular variation (PSV) records recovered from Integrated Ocean Drilling Program (IODP) Expedition 323 to the Bering Sea (58° N-60° N). The PSV records come from Sites U1343, U1344, and U1345 and cover marine isotope stages (MIS) 1–10 (last 380 ky). These records identify 291 inclination features and 251 declination features that are common to all three sites. The average sedimentation rates are ∼20–45 cm/ky, which produce sampling intervals of ∼100–200 years. All three sites have been dated independently to the MIS level by oxygen-isotope stratigraphy. We have also developed relative paleointensity records for all three sites that have 34 features in common. The paleointensity features can also be correlated to the PISO-1500 global paleointensity record of Channell et al. (2009) that is itself dated by oxygen-isotope records. The relative paleointensity records provide an independent chronostratigraphy to the PSV records that is consistent with the MIS level oxygen-isotope stratigraphy but provides better constraint on the sub-MIS scale with an uncertainty of ∼ ± 2000 years. The directions have near Gaussian distributions with average inclinations about 2° higher than axial dipole expectation due to the ΔI anomaly. The intensities have a non-Gaussian distribution, with some bias to higher intensities that may be an artifact of environmental bias to the measurements. There is reproducible evidence for eight excursions in these records with good waveform detail. The excursions are, with one exception, short in duration lasting less than 1000 years. The exception is the Iceland Basin Excursion (196 ± 3 ka), which has a duration of ∼2500 years. All of the excursions are Class I excursions with out-of-phase inclination and declination variability that produces clockwise or counter-clockwise looping (circularity). We have complete full-vector PSV records that surround each of these excursions. Some of the excursions occur quickly with no distinctive pre- or post-excursion anomalous directional variability. However some of the excursions are preceded by 10–20 ky of anomalous directional variability (high angular dispersion). These features indicate a close relationship between normal PSV and the excursions themselves. Statistical PSV studies note distinctive features to the PSV over 3ky to 9 ky intervals. The most distinctive feature is that PSV angular dispersion on 3ky intervals has a bimodal distribution with high (low) values associated with low (high intensity). The high angular dispersion intervals have values ∼3 times that of the low angular dispersion intervals and all of the excursions occur within high angular dispersion intervals. The timing and number of these high angular dispersion intervals is almost exactly the same as recorded in the North Atlantic Ocean. There is evidence for three other excursions elsewhere in the world, but not in our records, that are also associated with high angular dispersions. We see no evidence for the 8α excursion (238 ± 2 ka) that is recorded in the North Atlantic Ocean.