Geomagnetic field variations during the last 400 kyr in the western equatorial Pacific: Paleointensity‐inclination correlation revisited

Abstract

A paleomagnetic study was conducted on four piston cores newly obtained from the West Caroline Basin in the western equatorial Pacific in order to investigate variations in paleointensity and inclination during the last 400 kyr. An inclination‐intensity correlation was previously reported in this region using giant piston cores, but the quality of the paleomagnetic data of the younger end, the last ca. 300 kyr, was needed to be checked because the upper part of the giant piston cores could suffer from perturbation by oversampling. Age control is based on the oxygen‐isotope ratios for one core and inter‐core correlation using relative paleointensity for other cores. Stacked curves of paleointensity and inclination were constructed from the four cores. It was confirmed that variations on the order of 104 to 105 years occur in inclination as well as paleointensity. A cross‐correlation analysis showed that significant in‐phase correlation occurs between intensity and inclination for periods longer than about 25 kyr, and power spectra of both paleointensity and inclination variations have peaks at ∼100 kyr periods. The regional paleointensity stack with higher resolution than the Sint‐800 stack (Guyodo and Valet, 1999) should be useful for paleointensity‐assisted chronostratigraphy.

Paleomagnetic inclination variations during the last 200 kyr in the Okhotsk Sea and their relation to persistent non-axial-dipole field

“…The western equatorial Pacific is known to have a large ∆I associated with a quadrupole component, and the sign of ∆I flips with polarity reversals (Johnson and Constable 1997). From sediment cores in the West Caroline Basin, ∆I of −6.5° ± 2.8° (N = 13) in the Brunhes Chron was reported (Yamazaki et al 2008). The phase of the paleointensity-inclination correlation also flipped with polarity reversals, in-phase in the Brunhes Chron and anti-phase in the Matuyama Chron (Yamazaki and Oda 2002).…”

“…5b). Long-term inclination variations are visible on the stacked record; intervals of shallower inclinations occur at about 25-45, 75-90, 110-135, and 185-200 Yamazaki and Ioka (1994), black Yamazaki et al (2008), note that the average inclination of each core was set to zero for stacking] and a inclination record of Yamazaki and Oda (2002) (red) from the West Caroline Basin in the western equatorial Pacific, and d relative paleointensity stacks of Yamazaki et al (2008) from the West Caroline Basin (blue) and the PISO-1500 paleointensity stack of Channell et al (2009) (red). Light green bands indicate periods of shallower inclinations in the Okhotsk Sea and coeval steeper negative inclinations in the West Caroline Basin in the western equatorial Pacific of paleointensity low around 100 ka contradictorily has steeper, but not shallower, inclinations in the Okhotsk Sea.…”

“…Light green bands indicate periods of shallower inclinations in the Okhotsk Sea and coeval steeper negative inclinations in the West Caroline Basin in the western equatorial Pacific of paleointensity low around 100 ka contradictorily has steeper, but not shallower, inclinations in the Okhotsk Sea. Yamazaki andOda (2002, 2004) and Yamazaki et al (2008) explained the inclination and paleointensity variations observed in the western equatorial Pacific that relative contribution of a persistent quadrupole component increased when the strength of the GAD field decreased. The western equatorial Pacific is known to have a large ∆I associated with a quadrupole component, and the sign of ∆I flips with polarity reversals (Johnson and Constable 1997).…”

“…Occurrence of inclination variations with timescales of 10 4 years and longer was previously reported using sediment cores from the western equatorial Pacific (Yamazaki and Ioka 1994;Yamazaki and Oda 2002;Yamazaki et al 2008). Using a continuous inclination record for the last 2 m.y., a possibility of orbital influence on inclination variations was argued (Yamazaki and Oda 2002;Roberts et al 2003).…”

The chaotic solar cycle

“…Several major long-term changes seem to exist s due to these processes: 400-350, 350-250, 250-175, and 175-10 Ma (Biggin & Thomas 2003), but all these are beyond the scope of our data sets, of course. Power spectra of both paleointensity and inclination variations have peaks at about 100 kyr periods, which is still far above the length of the time series considered (Yamazaki et al 2008). The data used here have been corrected for palaeomagnetic variations (Solanki et al 2004).…”