Interpretation of Anhysteretic Remanent Magnetization Carriers in Magnetofossil‐Rich Marine Sediments

Zhang, Qiang; Roberts, Andrew P.; Ge, Shulan; Liu, Yanguang; Liu, Jianxing; Liu, Shuangchi; Tang, Xu; Wang, Haosen; Wang, Dunfan; Li, Jinhua; Liu, Qingsong

doi:10.1029/2022jb024432

Cited by 6 publications

(7 citation statements)

References 114 publications

(247 reference statements)

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“…Thus, we consider that RPI from NRM/IRM _20-40mT is carried by magnetofossils, and RPI from NRM/ IRM _70-160mT is carried mainly by partially oxidized unprotected magnetites of detrital origin. The observation that ARM little carries a coercivity component higher than 70 mT even for ARM acquired at AF of 160 mT supports the interpretation that the middle-coercivity component of the IRM decomposition is mainly of detrital origin and magnetofossils little contribute to this component (Zhang et al, 2022).…”

Section: Relative Paleointensitysupporting

confidence: 66%

“…The lower RPI recording efficiency of magnetofossils when normalized by ARM can be partly explained by that higher ARM acquisition efficiency of magnetofossils causes underestimation of RPI (Li et al., 2022; Yamazaki, 2008; Zhang et al., 2022). This study confirmed that lower RPI recording efficiency of magnetofossils occurs also for RPI normalized by IRM, which was previously suggested from calculating RPI separately from different coercivity ranges like this study (Li et al., 2022) or inverse correlation with k ARM /SIRM (Inoue et al., 2021; Sakuramoto et al., 2017; Yamazaki et al., 2013).…”

Section: Discussionmentioning

confidence: 99%

“…Some previous studies using Pacific marine sediments proposed that RPI recording efficiency of the magnetofossil component is lower than that of the detrital component, and that increasing proportion of the magnetofossil component causes underestimation of RPI (Gai et al, 2021;Inoue et al, 2021;Li et al, 2022). This explains frequently reported anti-correlation between RPI and the ratio of ARM susceptibility to saturation IRM (k ARM /SIRM) (Hofmann & Fabian, 2009;Inoue et al, 2021;Li et al, 2022;Sakuramoto et al, 2017;, as k ARM / SIRM is a proxy for the proportion of the magnetofossil to detrital components (Egli, 2004;Yamazaki, 2008;Zhang et al, 2022) as well as magnetic grain size (Banerjee et al, 1981;King et al, 1982). The conclusion of lower RPI recording efficiency for magnetofossil by Li et al (2022) is derived from the observations that RPI calculated from a higher-coercivity fraction is smaller than that from a lower-coercivity fraction and that the higher-coercivity fraction in their studied sediments is mainly carried by magnetofossil whereas the proportion of the detrital component is larger in the low-coercivity fraction.…”

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confidence: 98%

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Difference in Relative Paleointensity Recording Efficiency of Magnetic Mineral Constituents in a Sediment Core Off Chile

Yamazaki

Shimono

et al. 2023

JGR Solid Earth

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Progress of relative paleointensity (RPI) estimations using marine sediments has greatly contributed to better understanding of the behavior of the past geomagnetic field. To enhance further the reliability of RPI estimations, we must overcome the problem that climatically induced variations of magnetic‐mineral assemblages in sediments may influence RPI records. Two major constituents of magnetic‐mineral assemblages in marine sediments are magnetofossils and detrital magnetic minerals, and the latter consists of silicate‐hosted magnetic inclusions and unprotected magnetic minerals. It is necessary to understand different RPI recording efficiencies among those constituents to tackle the problem, but previous evaluations were inconclusive. We studied this issue using a sediment core taken from the southeast Pacific Ocean. Rock‐magnetic investigations revealed that the magnetic mineral assemblage of this core during the last ∼900 ka is a mixture of low‐coercivity magnetofossils and middle‐coercivity detrital unprotected partially oxidized magnetite. Natural remanent magnetization (NRM) vs. isothermal remanent magnetization (IRM) demagnetization diagram showed strong convex curvature, and RPI signals carried by the two components could be separated by calculating RPI from the gradients of 20–40 and 70–160 mT segments. We confirmed that RPI recording efficiency of magnetofossils is lower than that of detrital unprotected magnetites/maghemites. Because of the marginal overlap between the coercivity ranges of the two components, changes in their relative abundance do not influence RPI estimations. This condition is ideal for RPI estimations, and the resulted RPI curve closely coincides with that of the PISO‐1500 stack despite changes in the relative abundance of the two components.

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Section: Relative Paleointensitysupporting

confidence: 66%

Section: Discussionmentioning

confidence: 99%

mentioning

confidence: 98%

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Difference in Relative Paleointensity Recording Efficiency of Magnetic Mineral Constituents in a Sediment Core Off Chile

Yamazaki

Shimono

et al. 2023

JGR Solid Earth

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“…Our FORC‐PCA results show that biogenic magnetite was abundant during the MH and LH at higher sea level (Figure 7a). χ ARM /SIRM has recently been used to determine the relative abundance of magnetofossils in sediments (Wang, Xu, et al., 2022; Yamazaki et al., 2020; Zhang et al., 2022), which showed that the relative abundance of magnetofossils increased gradually during the last deglaciation and reached a stable state during the MH and LH (Figures 7a and 7b). The relative variation in magnetofossil abundance in the Qiongdongnan basin was consistent with that in the northwest sub‐basin of the SCS (Figure 7c) (Wang, Xu, et al., 2022).…”

Section: Discussionmentioning

confidence: 99%

Magnetic Fingerprints for the Paleoenvironmental Evolutions Since the Last Deglaciation: Evidence From the Northwestern South China Sea Sediments

Sun,

Jiang,

Xiao

et al. 2024

Paleoceanog and Paleoclimatol

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Rapid global changes since the last deglaciation can be well documented in marginal sea sediments, while isolating individual paleoenvironmental signals is still challenging. Here, we identified magnetic minerals and unmixed their variations in sediments from the northwestern South China Sea to decipher environmental variations since the last deglaciation. The variation in the hematite to goethite ratio indicates a relatively drier mid‐Holocene and a wetter early and late Holocene in the Red River catchment. The position shift and intensity variation of Western Pacific Subtropical High may account for the Holocene precipitation changes. A higher chemical weathering intensity accompanied by a relatively more fine‐grained magnetite input during the last deglaciation suggests decoupling of the Asian Summer Monsoon and chemical weathering in the catchment, which might have been caused by the shelf exposure during the deglaciation. In addition, the relative abundance of biogenic magnetite increased with the sea level and possible deep‐water temperature rise. Therefore, magnetic minerals such as hematite, goethite, detrital and biogenic magnetite are markedly potential fingerprints for continent‐ocean environmental changes.

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“…Saturation isothermal remanent magnetization (SIRM) was measured using an AGICO JR‐6A spinner magnetometer after applying a 1 T field using a pulse coil. χ ARM /SIRM was obtained to reflect the abundance of fine magnetite particles, also as a proxy for the proportion of magnetofossils in magnetic mineral assemblages (Egli, 2004b; Yamazaki et al., 2013; Zhang et al., 2022). All paleomagnetic measurements of the 87 samples were conducted at the Institute of Geology and Geophysics, Chinese Academy of Sciences (IGGCAS).…”

Section: Samples and Methodsmentioning

confidence: 99%

Paleoenvironmental Controls on the Abundances of Magnetofossils in the Southwestern Iberian Margin

He,

Zhao,

Jiang

et al. 2024

JGR Solid Earth

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Magnetofossils are nanosized magnetic fossil remnants of magnetotactic bacteria (MTB) that are widely distributed in marine and freshwater sediments. Past studies have revealed that changes in the morphology and abundance of magnetofossils are linked with diverse paleoenvironmental changes, such as glacial‐interglacial variation, redox conditions associated with primary productivity and organic matter supply, chemical weathering and diagenesis. Besides, it has long been speculated that changes in geomagnetic field intensity could also affect the abundance of magnetofossils. However, it is not yet clear, how these environmental factors controlled past MTB populations in combination. To answer this question, we studied magnetofossils‐rich sediments from cores MD01‐2443 and 2444 off the Southwest Iberian Margin. The paleomagnetic records of our samples reveal geomagnetic excursions corresponding to the Laschamp, Blake, Iceland Basin, and Pringle Falls events. We estimated the relative abundance of magnetofossils in the samples based on isothermal remanent magnetization unmixing and found it to increase during warmer periods and decrease during colder periods, while not covary with changes in the geomagnetic field intensity. To further distinguish the role of different paleoenvironmental factors, we compared magnetofossil abundance with planktonic δ18O, δ13C of organic matter, K/Al and Si/Al, which indicate continental ice volume (paleotemperature), organic matter origin, run‐off intensity and productivity, respectively. The results indicate that less continental ice volume (higher paleotemperature), enhanced productivity and run‐off intensity are closely related and jointly promoted magnetofossil production and preservation. Our study offers a comprehensive approach to understanding how magnetofossil assemblages relate to paleoenvironmental changes off the SW Iberian Margin.

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Interpretation of Anhysteretic Remanent Magnetization Carriers in Magnetofossil‐Rich Marine Sediments

Cited by 6 publications

References 114 publications

Difference in Relative Paleointensity Recording Efficiency of Magnetic Mineral Constituents in a Sediment Core Off Chile

Difference in Relative Paleointensity Recording Efficiency of Magnetic Mineral Constituents in a Sediment Core Off Chile

Magnetic Fingerprints for the Paleoenvironmental Evolutions Since the Last Deglaciation: Evidence From the Northwestern South China Sea Sediments

Paleoenvironmental Controls on the Abundances of Magnetofossils in the Southwestern Iberian Margin

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