Other language confidence: 0.8200584969366479
Paleointensity versus age of all the sedimentary sequences of the present study, of the synthetic curve resulting from its compilation from other curves, and of the reference curve from ODP Site 984 (Channell, 1999). For the compilation, data have been averaged using a sliding window of 2 ka (the variance is marked by the grey shadow). Dashed lines show some of the correlations. The grey lines show the location of the low paleointensities related to geomagnetic excursions. Note that the lowest paleointensities in the time span of Blake are at c. 129 ka. (see Fig.11)
No significant HIRM change is observed at the transition between oxidising and reducing conditions in the sediment (Fig. 9A). This implies that HIRM is not affected by redox conditions and further confirms that the “hard” magnetic mineral content is the best tracer of detrital input (Peck et al., 1994). On the other hand, the S-ratio seems to be related to the redox conditions in the sediment (see Section 7.2). The ARM has also to be considered with caution as it is mainly influenced by the ferrimagnetic contribution, which is itself influenced by post depositional processes. This is seen in Fig. 9 where ARM variations are partly influenced by S-ratio variations.
Higher abundance of greigite during glacial intervals also coincides with small increases of the S content (Fig. 11B). Greigite levels in glacial sediments cannot be correlated between cores (Fig. 12), which suggests that greigite concentrations are driven by local processes. We suggest that faecal pellets could be a suitable microenvironment for sulphate reduction. And while greigite could potentially act as proxy for faecal pellets in glacial sediments, unfortunately, we cannot rely on this possible indicator since the greigite is very sensitive to onshore alterations after sampling (Snowball and Thompson, 1990).
Dashed lines mark some correlation levels of the cores from Lake Baikal with the dated δ18O record from ODP 677 (Shackleton et al., 1990), see also Fig. 3. Diagenetic features such as dissolution of magnetite and mineralization of greigite are marked according to Fig. 4. Laschamp and Iceland Basin excursions are indicated as La. and Ic., respectively. Inclination and declination records could provide information on paleosecular variations (periodicity ≤105 years and directional variability <20°, according to Butler, 1992). In the present study, we did not interpret inclination and declination records in terms of paleosecular variations since slight sediment disturbances could produce slight deviations of ChRM declinations and inclinations. (see Fig.7)
The day plot (Fig. 6B; Day et al., 1977) indicates that samples with S-ratios >0.95 plot rather in the single-domain (SD) to pseudosingle-domain (PSD) range. Samples with S-ratios between 0.9 and 0.95 instead, plot rather in the PSD to the multidomain (MD) range. Low S-ratio samples are not greatly dispersed and have ratios of Bcr/Bc and Mrs/Ms of 3.5 and 0.1, respectively.
It shows a loss of a part of the signal at temperatures between 350 and 400 °C, typical disintegration temperatures for greigite. The remaining signal disappears above a temperature of 590 °C, typical for magnetite.
It shows a loss of a part of the signal at temperatures between 350 and 400 °C, typical disintegration temperatures for greigite. The remaining signal disappears above a temperature of 590 °C, typical for magnetite.
Downcore variations of rock magnetic parameters and simplified lithological description for the sedimentary sequence VER 98-1-14. Here, MIS are denoted by numbers in the lithological column. The black squares filled intervals mark occurrences of greigite characterised by a high magnetic susceptibility (κLF) in parts, with a low coercive mineral dominating the magnetic signal (S-ratio close to 1), a high SIRM/κLF, a strong loss of ARM intensity between the demagnetisations steps 50 and 65 mT and finally a deviation of the inclination of ARM. The dark grey intervals mark occurrences of magnetite dissolution, with a low S-ratio resulting from relative higher hematite content in the ferromagnetic components. The assignment of greigite and dissolved magnetite is based on subsequent interpretation. Magnetic susceptibility (κLF) vs. S-ratio for the sedimentary sequence VER 98-1-14 showing S-ratio gathered around 0.95 in glacial sediments and scattered from 0.7 to 1 in interglac
Greigite levels in glacial sediments cannot be correlated between cores (Fig. 12), which suggests that greigite concentrations are driven by local processes. We suggest that faecal pellets could be a suitable microenvironment for sulphate reduction. And while greigite could potentially act as proxy for faecal pellets in glacial sediments, unfortunately, we cannot rely on this possible indicator since the greigite is very sensitive to onshore alterations after sampling (Snowball and Thompson, 1990).
Down-core variations of normalised relative paleointensity after removal of intervals affected by diagenesis (magnetite dissolution and/or greigite formation) and correlation to the relative paleointensity record from ODP Site 984 (Channell, 1999). In addition to AMS 14C dating and the geomagnetic excursions, the age model was completed and refined by tuning the relative paleointensity records to the equivalent record from ODP Site 984 (Channell, 1999; Fig. 8). The relative paleointensity variations in Lake Baikal and ODP Site 984 are well correlated. This confirms the global geomagnetic field origin of the relative paleointensity variations documented in the present study. In addition, it shows that local sedimentary variations have no effect on the paleomagnetic records.