Holocene palaeomagnetic secular variation at Lake Biwa, central Japan

Abstract

We have conducted a palaeomagnetic study on three sediment cores obtained from a single site in Lake Biwa, central Japan. A total of 1430 discrete samples from three cores show strong and stable remanence, which is carried by pseudo‐single‐domain magnetite. Palaeomagnetic records from individual cores show little scatter of directions, and there is excellent correlation among the records from the site. A composite palaeomagnetic secular variation (PSV) record for the Holocene was constructed after fine‐scale adjustment and stacking of the three records. The age model is based on two wide‐spread tephra layers: Kawagodaira (3150 yr BP, calendar years) and Kikai‐Akahoya (7250 yr BP). Our results show that the declinations and inclinations are strikingly similar to archaeomagnetic data from southwest Japan for the last 2000 years. The PSV record from Lake Biwa shows good correlation in directions with that of Beppu Bay, located about 500 km west of Lake Biwa, although the Beppu Bay record shows relatively smaller amplitudes of both inclination and declination, probably due to heavy smoothing of the initial results. When the Lake Biwa record is compared with the proposed type curve for southwest Japan, there is considerable disagreement throughout the Holocene. A re‐analysis of the data sets and other information used to construct the type curve revealed that the discrepancy in the results was due to inadequate age determination for the cores used in previous studies. We conclude that the stacked PSV record from Lake Biwa meets the criteria required for a reliable curve. Moreover, our results resolve the complications found in the correlation of PSV records in southwest Japan and thereby contribute to a better understanding of Holocene PSV.

Rock-magnetic changes with reduction diagenesis in Japan Sea sediments and preservation of geomagnetic secular variation in inclination during the last 30,000 years

“…Inclinations are relatively steep around 6-14 ka, and decrease with increasing age. Concerning the variations during the last 10 kyr, lows at about 5 and 8 ka are commonly observed among available records in Japan (Yamazaki et al, 1985;Hyodo et al, 1993;Ali et al, 1999), although resolution of our core is relatively low because of slow sedimentation. Please note the difference in the time scales of Fig.…”

“…Selective dissolution of finer magnetic grains caused the decrease of the coercivity of remanent Correlation of inclination variations of Core GH98-1232 with the record of a sediment core off southwest Japan (Ohno et al, 1993) and the stacked record of three cores from the Lake Biwa (Ali et al, 1999). Note the difference of time scale: radiocarbon ages (Ohno et al, 1993, and this study) and calendar age (Ali et al, 1999). magnetization within and below the dissolution zone (Fig.…”

Applications of paleomagnetism in the volcanic field: A case study of the Unzen Volcano, Japan

“…• was observed in the SV curves from lake sediments in Japan for the last 10 thousand years (Hyodo et al, 1993;Ali et al, 1999).…”

Limitations in paleomagnetic data and modelling techniques and their impact on Holocene geomagnetic field models

“…Therefore, this part of the Lake Pepin record was discarded before carrying out the modelling. The Lake Biwa record (BIW) (Ali et al 1999) has been replaced with a new record from the same lake (BI2) (Hayashida et al 2007), while both records were used in the models CALS10k.1b ) and pfm9k (Nilsson et al 2014). To avoid the problems of heterogeneous sediment data set in building the pfm9k models, Nilsson et al (2014) resampled all sedimentary records in 50-yr bins and obtained uncertainty estimates based on the dispersion of the data within each bin.…”