Dating North Pacific Abyssal Sediments by Geomagnetic Paleointensity: Implications of Magnetization Carriers, Plio-Pleistocene Climate Change, and Benthic Redox Conditions

Abstract

Non-carbonaceous abyssal fine-grained sediments cover vast parts of the North Pacific’s deep oceanic basins and gain increasing interests as glacial carbon traps. They are, however, difficult to date at an orbital-scale temporal resolution and still rarely used for paleoceanographic reconstructions. Here, we show that sedimentary records of past geomagnetic field intensity have high potential to improve reversal-based magnetostratigraphic age models. Five sediment cores from Central North Pacific mid-latitudes (39–47°N) and abyssal water depths ranging from 3,900 to 6,100 m were cube-sampled at 23 mm resolution and analyzed by automated standard paleo- and rock magnetic methods, XRF scanning, and electron microscopy. Relative Paleointensity (RPI) records were determined by comparing natural vs. anhysteretic remanent magnetization losses during alternating field demagnetization using a slope method within optimized coercivity windows. The paleomagnetic record delivered well interpretable geomagnetic reversal sequences back to 3 Ma. This age span covers the climate-induced transition from a biogenic magnetite prevalence in the Late Pliocene and Early Pleistocene to a dust-dominated detrital magnetic mineral assemblage since the Mid-Pleistocene. Volcaniclastic materials from concurrent eruptions and gravitational or contouritic sediment re-deposition along extinct seamount flanks provide a further important source of fine- to coarse-grained magnetic carriers. Surprisingly, higher proportions of biogenic vs. detrital magnetite in the late Pliocene correlate with systematically lowered RPI values, which seems to be a consequence of magnetofossil oxidation rather than reductive depletion. Our abyssal RPI records match the astronomically tuned stack of the mostly bathyal Pacific RPI records. While a stratigraphic correlation of rock magnetic and element ratio logs with standard oxygen isotope records was sporadically possible, the RPI minima allowed to establish further stratigraphic tie points at ∼50 kyr intervals. Thus, this RPI-enhanced magnetostratigraphy appears to be a major step forward to reliably date unaltered abyssal North Pacific sediments close to orbital-scale resolution.

A 6.2 Ma‐Long Record of Major Explosive Eruptions From the NW Pacific Volcanic Arcs Based on the Offshore Tephra Sequences on the Northern Tip of the Emperor Seamount Chain

“…Two layers originally sampled as tephra appeared to contain mostly terrigenous particles with only minor amounts of compositionally different glasses. These layers might be a result of accumulation of debris carried by sea ice or ocean currents, which is typical for the NW Pacific pelagic sedimentation (Figure 7h; McCarron et al, 2021;Wang et al, 2021). In addition to tephra layers and pods, we sampled a few sediment intervals, which seemed enriched in tephra particles.…”

Impact of Upward Oxygen Diffusion From the Oceanic Crust on the Magnetostratigraphy and Iron Biomineralization of East Pacific Ridge-Flank Sediments

“…The RPI records of our three cores were obtained by an ARMbased straight slope method and plotted in Figure 6 against an RPI record by Yamazaki and Yamamoto (2018). A discussion on alternative target records for deep pacific sites has been recently given by Wang et al (2021). The here chosen reference record relies on two Equatorial Pacific cores recovered about 7 °S and 8 °W of our coring sites.…”