Although paleomagnetic secular variations (PSV) often corroborate radiocarbon (14C)-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 ∼730-yr offset because the different dated compounds correspond very well to each other, and modern reservoir effects are negligible. Instead, the constant ∼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 14C-based chronology of Khar Nuur without a ∼730-yr adjustment. Therefore, the previously published 14C-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.

The marine reservoir effect is the difference in radiocarbon (14C) between the atmosphere and the marine surface ocean. To overcome the dating errors induced, it is necessary to correct marine 14C ages for this effect. ΔR is the difference between the marine 14C age and the marine calibration curve based on an ocean-atmosphere box diffusion model, which accounts for the time delay in diffusion of carbon into the ocean from the atmosphere and biosphere. This global assessment, however, requires computation of a regional ∆R value for calibration to cater for studies based on a local scale. In this paper the marine reservoir effect is assessed for the southern and eastern coasts of South Africa using 14C dating on pre-1950 marine shells of known age. The resultant ∆R values enable a more complete understanding of the marine reservoir effect along the southern and eastern coastal zone of South Africa. 14C age determinations were conducted on 15 shell samples of known age and the results, combined with previously published values, were used to calculate regional marine reservoir correction values. The east coast has a weighted mean ∆R of 121±16 14C yr, while the south coast has a weighted mean ∆R of 187±18 14C yr.

Aquatic macrophytes from a lacustrine environment are highly prone to a reservoir effect, resulting in an overestimation of age. This is often caused by the incorporation of dissolved carbon (CO2 and HCO3 –) through photosynthesis from lake waters that have a different 14C activity than the atmosphere. The atmosphere-water disparity is often produced by a mixing of carbon between the water body and its terrestrial surroundings, a process highly prone to temporal variations. Thus, only a comprehensive understanding of the 14C budget over time enables a reliable chronology of lacustrine records. We studied lacustrine sediments from Lake Heihai on the northern Tibetan Plateau with a recent reservoir effect of 6465 ± 75 14C yr as estimated from accelerator mass spectrometry (AMS) dating of three living aquatic plants. Age inversions in a well-laminated composite core from the lake suggest that the reservoir effect markedly changed over the depositional period. In the lower part of the core, an excellent correlation was observed between the allochthonous input of dolomite and the inverse 14C ages, indicating the incorporation of dissolved 14C-dead carbon from a limestone catchment in the plant material. For the upper part of the core, sediment recycling of Holocene high-stand deposits may have further contributed to the reservoir effect. These findings give rise to a reliable process- and provenance-based chronology within a confidence interval supported by 137Cs measurements and magnetostratigraphic investigations. Our results highlight the need to identify the interactions of lakes with their surroundings to estimate reservoir-corrected ages in lacustrine settings.