Environmental magnetism of Pleistocene sediments in the North Pacific and Ontong‐Java Plateau: Temporal variations of detrital and biogenic components

Abstract

An environmental magnetic study was conducted to investigate temporal variations of the sources of magnetic minerals in the Pacific Ocean using sediment cores of Pleistocene age. The proportion of interacting (I) to noninteracting (N‐I) single‐domain components was estimated from first‐order reversal curve diagrams, and the proportion of middle‐ (M) to low‐ (L) coercivity components was determined from decomposition of isothermal remanent magnetization (IRM) acquisition curves. The I and M components are interpreted to be carried by terrigenous maghemite, while the N‐I and L components represent biogenic magnetite. An inverse correlation between the ratio of anhysteretic remanent magnetization susceptibility (χARM) to saturation IRM (SIRM) and the I/N‐I ratio was confirmed for sediments across wide expanses in the Pacific Ocean. This implies that χARM/SIRM can be used to estimate the relative abundances of biogenic and terrigenous components in sediments. In the North Pacific, the relative abundance of the I and M components increases in glacial periods. Variations of χARM/SIRM and S ratio (S−0.1T) resemble each other and decrease in the same time intervals. These variations reflect increases of terrigenous input in glacial periods as eolian dust. On the Ontong‐Java Plateau in the western equatorial Pacific, on the other hand, minima in χARM/SIRM and S−0.1T occur at glacial‐to‐interglacial transitions, and the relative abundance of the I and M components increases in these periods. Terrigenous material in this region is considered to be transported mainly from the New Guinea and Solomon Islands by the Equatorial Undercurrent. The higher proportion of the terrigenous component at glacial‐to‐interglacial transitions is coeval with carbonate preservation maxima reported from the Ontong‐Java Plateau, suggesting a linkage between the two.