Inverse Magnetic Fabrics Caused by Magnetofossils in the Northwestern South China Sea Since End of the Last Glacial. Issue 14 (22nd July 2022)

• Record Type: Journal Article
• Authors: Wang, Haosen; Xu, Xing; Gai, Congcong; Liu, Jiabo; Zhong, Yi; Jiang, Xiaodong; Zhang, Yanan; Ferré, Eric C.; He, Kuang; Liu, Qingsong
• Is Part Of: Geophysical research letters. Volume 49:Issue 14(2022)
• Page Start: n/a
• Page End: n/a
• Publication Date: 2022-07-22
• Subjects: magnetic fabrics -- magnetofossils -- South China Sea -- East Asian monsoon -- rock magnetism; Geophysics -- Periodicals; Planets -- Periodicals; Lunar geology -- Periodicals; 550
• DOI: 10.1029/2022GL098507
• Languages: English
• ISSNs: 0094-8276

Abstract

Abstract: The relationships among the abundance of magnetofossils, the ensuing magnetic properties, and the controlling paleoenvironmental factors in marine sediments remain broadly unexplored. Here, we identify magnetofossils in core XB1 from the northwestern South China Sea (SCS) since end of the Last Glacial. Using rock magnetic and electron microscopic data, we propose a model that links the anisotropy of magnetic susceptibility fabric and the abundance of magnetofossils. The magnetofossil concentration in sediments increases significantly during the 14.7–4.7 ka period, which in turns leads to inverse magnetic fabrics and near‐horizontal of the minimum magnetic susceptibility axes. Further, we show that the abundance of magnetofossils is linked to paleoenvironmental changes in the northwestern SCS. The production and preservation of magnetofossils during the 14.7–4.7 ka period are promoted by an intensified East Asian summer monsoon and sluggish deep‐water ventilation, while the paucity of magnetofossils after 4.7 ka is attributed to high oxygen content. Plain Language Summary: The anisotropy of magnetic susceptibility (AMS) is a useful magnetic property of rocks for a wide range of scientific questions. Typically, the sedimentary AMS fabric carried by coarser‐grained magnetic particles ( i.e., multi‐domain, MD) exhibits an oblate shape with a horizontal maximum magnetic susceptibility axis. However, single‐domain (SD) magnetic particles (e.g., nano‐sized magnetofossil magnetites) complicate the AMS fabric, through their intrinsic inverse magnetic fabric with the minimum magnetic susceptibility axis aligned along the horizontal plane. For natural samples, quantification of the contributions of SD and MD particles to AMS is essential for accurate interpretation of the AMS. This paper puts forward a novel approach that links the AMS and the abundance of magnetofossils. By applying this new method to sediments from the South China Sea, we found that the inverse magnetic fabrics in the studied sediments are associated with high magnetofossils concentration, which can be affected by various factors including the East Asian monsoon, nutrient supply or deep‐water ventilation. Key Points: Values of the minimum susceptibility axis inclination are associated with the abundance of magnetofossils The magnetofossils can be quantified by the proportion of inverse component in sediments The strong deep‐water ventilation hinders the production and preservation of magnetofossils in the South China Sea