ASSESSING LOCK-IN DEPTH AND ESTABLISHING A LATE HOLOCENE PALEOMAGNETIC SECULAR VARIATION RECORD FROM THE MONGOLIAN ALTAI

Although paleomagnetic secular variations (PSV) often corroborate radiocarbon (C-14)-based lacustrine sediment chronologies, this is not the case at the high-altitude site Khar Nuur in the Mongolian Altai Mountains. Our results show that the inclination pattern resembles those from a regional reference record from Shireet Naiman Nuur and global geomagnetic field models very well, but with a constant offset of 730 +/- 90 yr. Possible reservoir effects from terrestrial pre-aging and hardwater effects can be excluded as the cause of the similar to 730-yr offset because the different dated compounds correspond very well to each other, and modern reservoir effects are negligible. Instead, the constant similar to 730-yr offset in the PSV pattern is likely the result of a constant lock-in depth of 26 +/- 2 cm below the sediment-water interface at Khar Nuur. This assumption is supported by comparison of paleoclimatological proxies from Shireet Naiman Nuur, where similarities are obvious for the C-14-based chronology of Khar Nuur without a similar to 730-yr adjustment. Therefore, the previously published C-14-based chronology of Khar Nuur provides a reliable age control. Accepting the lock-in depth of 26 +/- 2 cm, the good consistency in inclination between Khar Nuur and global geomagnetic field models highlights the reliability of the latter even in a paleomagnetically understudied area.

Automated summary

Despite the inconsistency between paleomagnetic secular variations (PSV) and radiocarbon (C-14)-based lacustrine sediment chronologies at Khar Nuur in the Mongolian Altai Mountains, the inclination pattern at the site resembles regional and global geomagnetic field models with a constant offset of 730 +/- 90 years. The offset is not caused by reservoir effects or modern factors, but rather by the constant lock-in depth of 26 +/- 2 cm below the sediment-water interface at Khar Nuur. The good consistency in inclination further highlights the reliability of global geomagnetic field models in under-studied areas.