Redeposition experiments with natural sediments from the SE Black Sea in magnetic fields between about 2 and 114 µT

Abstract

Summary Diluted slurry with an initial density of 1.30 gcm−3 prepared from natural glacial Black Sea sediments was deposited under controlled field conditions between 1.72 and 114.21 µT. Compaction was achieved by evaporation of a portion of the pore water from the open sample boxes over 4 to 7 days until a density of about 1.44 to 1.55 gcm−3 was reached. Magnetizations M acquired in a magnetic field B follow a slightly non-linear function with M ∼ B0.82. Similar relationships were also obtained for palaeointensity estimates for the artificial samples by using normalisation by low-field susceptibility, anhysteretic remanent magnetization, and saturation magnetization. All samples are characterized by a magnetic fabric typical for natural sediments as checked by determining the anisotropy of magnetic susceptibility. The sediments’ anisotropy is in the range of 6 to 7 per cent and it is characterized by an oblate anisotropy ellipsoid with its small axis perpendicular to the deposition plane. According to scanning electron microscope imaging low-Ti magnetite particles present in the used sediments are in the range of 1 to 30 µm with the majority of particles 2 to 5 µm in size. Obtained results confirm the conclusion from other magnetostratigraphic studies that the Laschamps geomagnetic polarity excursion in the Black Sea area exhibited field values as low as 2.8 µT in its transitional phase between normal and reversed polarity.

A High‐Resolution Paleosecular Variation Record for Marine Isotope Stage 6 From Southeastern Black Sea Sediments

“…In contrast to this, greigite‐dominated samples (SIRM/k LF >> 10 kAm −1 ) exhibit partly a massive acquisition of a gyro‐remanent magnetization (GRM) during AF demagnetization, starting at an AF level of 50 mT, with vector endpoints passing by the origin (Figures 4d and 4f). For such samples only AF steps lying on a straight line pointing toward the origin were used tentatively for ChRM determination (see also Nowaczyk et al., 2020a). Note that greigite‐dominated samples (Figures 4d and 4f) have NRMs about 50 times higher than magnetite‐dominated samples.…”

“…While reconstructed lake surface temperature (LST) trends and oxygen isotopes are likely related to the long‐lasting discharge of colder meltwater into the Black Sea “Lake” from the retreating Eurasian Ice Sheet (EIS), millennial‐scale variability in LST and IRD proxy records clearly point to subdued Dansgaard‐Oeschger (DO)‐type cycles (Dansgaard et al., 1993), particularly during the first part of MIS 6. After ∼160 ka BP, the Black Sea was more “locked” in a stable colder condition due to the expansion of the EIS and the southward migration of the atmospheric polar front over the Black Sea region (Wegwerth et al., 2019, 2020). But, these climatic expression are less pronounced when compared to the sequence of DO‐events from the last glacial (MIS 2‐4; Nowaczyk et al., 2012).…”

“…The protocol and calculation of irregular FORC (irFORC) and transient hysteresis FORC (tFORC) diagrams were performed following Zhao et al (2017). More detailed descriptions of applied paleo-and mineral magnetic methods are provided by Liu et al (2018Liu et al ( , 2019Liu et al ( , 2020 and Nowaczyk et al (2012Nowaczyk et al ( , 2018Nowaczyk et al ( , 2020.…”

“…(2020) performed a first investigation of the cosmogenic radioisotope 10Be in Black sea sediments during Greenland‐interstadial 10. Paleo‐ and rock magnetic investigations focusing on sediments from the last glacial, marine isotope stages (MIS) 2–4 were published by Nowaczyk (2020), Nowaczyk et al. (2012, 2013, 2018, 2021a) and Liu et al.…”

“…Czymzik et al (2020) performed a first investigation of the cosmogenic radioisotope 10Be in Black sea sediments during Greenland-interstadial 10. Paleo-and rock magnetic investigations focusing on sediments from the last glacial, marine isotope stages (MIS) 2-4 were published by Nowaczyk (2020), Nowaczyk et al (2012Nowaczyk et al ( , 2018Nowaczyk et al ( , 2021a and Liu et al (2018Liu et al ( , 2019Liu et al ( , 2020. Here we present the final paleo-and rock magnetic study summarizing data from the pen-ultimate glacial, MIS 6, providing a high-resolution full-vector PSV curve (inclination, declination, and relative paleointensity) from 130 ka back to 180 ka, based on 12 of the 18 cores from the Arkhangelsky Ridge, SE Black Sea.…”