Magnetic records of Core MD77-181 in the Bay of Bengal and their paleoenvironmental implications

Abstract

High-resolution environmental magnetic measurements were carried out on Core MD77-181 in the Bay of Bengal, including magnetic susceptibility, anhysteretic remanent magnetization, isothermal remanent magnetization of all samples, and temperature-dependence of magnetic susceptibilities and magnetic hysteresis parameters of representative samples. The results suggest that (1) the magnetic mineral assemblage of the upper 9.82 m sediments (corresponding to the last 160 ka) is dominated by pseudo-single domain magnetite, with more abundant coarse grains in glacial periods than in interglacial periods; (2) the uppermost 6.50 m of sediments (corresponding to the last 70 ka) shows significant temporal variations in grain sizes of magnetic minerals, possibly reflecting the teleconnection between variations of the Indian summer monsoon and rapid cold events of the North Atlantic (Heinrich events); (3) the sediments below 9.82 m are dominated by paramagnetic minerals (probably including pyrites), suggesting reductive diagenesis. The magnetic records of Core MD77-181 are comparable to those of Core MD77-180 in the Bay of Bengal, and ODP Hole 722B in the Arabian Sea. This study suggests that the paleoceanographic event at ~160 ka significantly changed the redox state of the northern Indian Ocean, from a reductive environment before the event to an oxic or suboxic environment after the event.

Magnetic characteristics and its environmental implications of core YSJD-86GC sediments from the southern South China Sea

“…Magnetic records were used to identify climatic cycles, sediment sources, changes of the sedimentary environment and reductive diagenesis during post-deposition [8][9][10][11][12][13]. Magnetic research of sediments for the SCS has been concerned since nearly the past 20 years.…”

Relative paleointensity of the geomagnetic field during the past 200 ka from the West Philippine Sea and its chronological significance

“…The magnetic sizes are usually coarser in glacial periods and finer in interglacial times, and this kind of magnetic response to climatic fluctuation is also found in South China Sea [28] and the Bay of Bengal [30] .…”

“…Low-frequency volume magnetic susceptibility (χ) was measured with a Bartington Instruments MS2 magnetic susceptibility meter. The natural remanent magnetization (NRM) was measured on all samples with a 2G-755 Enterprises superconducting rock magnetometer, and then progressively demagnetized using stepwise peak alternating fields (AF) of 5,10,15,20,25,30,40,50 and 60 mT to isolate the characteristic component (ChRM). An anhysteretic remanent magnetization (ARM) was imparted using an 80 mT peak AF with a 0.05 mT direct current bias field on a 2G-760 Enterprises superconducting rock magnetometer.…”

Mineral magnetic properties of surface sediments at Bei’anhe, Beijing, and its environmental significance

“…Iron oxides in sediments may be dissolved and pyritized in the reductive diagenetic environment and the terminal product is pyrite [35,36] . Pyritization is common in underwater sediments [34,36,42,43] . Iron oxide cannot transform ultimately to pyrite in fine-grained sediments with low permeability, due to the supply limit of organic matter and sulfate, and thus form the intermediate product such as pyrrhotite and greigite [35,43] .…”