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.
Highlights
Establishing a robust and detailed sediment core chronostratigraphy is a major prerequisite for paleoceanographic interpretation and global stratigraphic correlation
This study investigates the Plio-Pleistocene North Pacific reversal and Relative Paleointensity (RPI) records of five newly studied abyssal sediment cores (Table 1) collected during North Pacific R/V SONNE cruises SO202 INOPEX (Subarctic Pacific W–E transect in 2009) and SO264 EMPEROR (Emperor Seamount Chain N–S transect in 2018)
As the paleo- and rock magnetic studies of Korff et al (2016) showed cyclic Late Pleistocene glacial magnetite depletion at Northwest Pacific core SO202-39-3, we investigate two Northeast Pacific abyssopelagic cores SO202-33-4 (Chinook Trough, 6,133 m) and SO202-35-1 (Emperor Trough, 5,507 m) to determine if such cyclic or episodic magnetite dissolution layers are present on either side of the EmperorHawaiian seamount chain (ESC)
Summary
Establishing a robust and detailed sediment core chronostratigraphy is a major prerequisite for paleoceanographic interpretation and global stratigraphic correlation. Dating abyssal North Pacific sediments is a difficult task, as many of these were deposited below the carbonate compensation depth (CCD), which today is at ∼4,700 m water depth (Lyle, 2003) (Figure 1). Since the pioneer studies of Ninkovich et al (1966), Opdyke and Foster (1970) and Kent and Lowrie (1974), reversal magnetostratigraphy has been the primary method to date North Pacific abyssal sediments. The temporal resolution of the Neogene geomagnetic polarity timescale is limited by the occurrence of only 3-5 geomagnetic polarity reversals per million years (Valet et al, 2005; Ogg, 2020). This resolution does not permit to capture orbital scale climate dynamics
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