Non‐saturation of the defect moment of goethite and fine‐grained hematite up to 57 Teslas

Rochette, P.; Mathé, P.-E.; Esteban, Lionel; Rakoto, H.; Bouchez, Jean‐Luc; Liu, Qingsong; Torrent, J.

doi:10.1029/2005gl024196

Cited by 77 publications

(61 citation statements)

References 17 publications

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“…Since magnetite and maghemite are usually completely saturated above 0.3 T, HIRM is a measure of the amount of high-coercivity, antiferromagnetic phases (hematite and goethite) and the S 300 -ratio is a measure of the relative amounts of low-coercivity (magnetite/maghemite) to highcoercivity (hematite/goethite) phases. However, since goethite is extremely hard to magnetize at room temperature in fields below 2.0 T (Maher et al, 2004;Rochette et al, 2005) it may contribute a negligible amount to HIRM or the S 300 -ratio value even though it may be the abundant phase. Furthermore, depending on particle sizes and cation impurity, the magnetic ordering temperature for goethite may be below room-temperature and thus be invisible to remanence measurements at room-temperature [Liu et al, 2006].…”

Section: Magnetic Methodsmentioning

confidence: 99%

Iron oxide minerals in dust-source sediments from the Bodélé Depression, Chad: Implications for radiative properties and Fe bioavailability of dust plumes from the Sahara

et al. 2016

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Atmospheric mineral dust can influence climate and biogeochemical cycles. An important component of mineral dust is ferric oxide minerals (hematite and goethite) which have been shown to influence strongly the optical properties of dust plumes and thus affect the radiative forcing of global dust. Here we report on the iron mineralogy of dust-source samples from the Bodélé Depression (Chad, north-central Africa), which is estimated to be Earth's most prolific dust producer and may be a key contributor to the global radiative budget of the atmosphere as well as to long-range nutrient transport to the Amazon Basin. By using a combination of magnetic property measurements, Mössbauer spectroscopy, reflectance spectroscopy, chemical analysis, and scanning electron microscopy, we document the abundance and relative amounts of goethite, hematite, and magnetite in dust-source samples from the Bodélé Depression. The partition between hematite and goethite is important to know to improve models for the radiative effects of ferric oxide minerals in mineral dust aerosols. The combination of methods shows (1) the dominance of goethite over hematite in the source sediments, (2) the abundance and occurrences of their nanosize components, and (3) the ubiquity of magnetite, albeit in small amounts. Dominant goethite and subordinate hematite together compose about 2% of yellowreddish dust-source sediments from the Bodélé Depression and contribute strongly to diminution of reflectance in bulk samples. These observations imply that dust plumes from the Bodélé Depression that are derived from goethite-dominated sediments strongly absorb solar radiation. The presence of ubiquitous magnetite (0.002-0.57 wt. %) is also noteworthy for its potentially higher solubility relative to ferric oxide and for its small sizes, including PM<0.1m. For all examined samples, the average iron apportionment is estimated at about 33% in ferric oxide minerals, 1.4 % in magnetite, and 65% in ferric silicates. Structural iron in clay minerals may account for much of the iron in the ferric silicates. We estimate that the mean ferric oxides flux exported from the Bodélé Depression is 0.9 Tg/yr with greater than 50% exported as ferric oxide nanoparticles (<0.1m). The high surface-to-volume ratios of ferric oxide nanoparticles once entrained into dust plumes may facilitate increased atmospheric chemical and physical processing and affect iron solubility and bioavailability to marine and terrestrial ecosystems.

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Section: Magnetic Methodsmentioning

confidence: 99%

Iron oxide minerals in dust-source sediments from the Bodélé Depression, Chad: Implications for radiative properties and Fe bioavailability of dust plumes from the Sahara

et al. 2016

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“…Besides, SIRM is influenced by the pedogenic ferrimagnetic grains to a larger extent [17]. Because goethite is far from saturation at 1000 mT [23], hematite plays a leading role in the antiferromagnetic signal involved in the above parameters. The significance of HIRM/(SIRM-IRM 100 mT ) will be stated in the discussion part.…”

Section: Sampling and Methodsmentioning

confidence: 99%

A rock magnetic record of Asian cooling and aridification processes during 1.95-0.40 Ma in the southeastern Chinese Loess Plateau

Zhu

Qiu

et al. 2013

Chin. Sci. Bull.

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The southeastern Chinese Loess Plateau is the terminal deposition area of dusts transported by the East Asian winter monsoon and the frontal area penetrated by the East Asian summer monsoon, and thus a climate sensitive region. This paper reports a rock magnetic study of a Quaternary loess-paleosol section in such a region. We tried to reconstruct the paleoclimate evolution history in the region during 1.95-0.40 Ma with magnetic parameters. The results show a general up-section decreasing trend of the ratio of HIRM/(SIRM-IRM 100 mT ), indicating a long-term decreasing trend of hematite coercivities in the deposits, which can be mainly related to the cooling and aridification trend of the environment in interglacial depositional area and glacial dust source region.The ratio,  lf / ARM , widely used to reflect the variations of magnetic mineral grain size, manifests a long-term increasing trend of the magnetic mineral grain size and tends to indicate an overall weakening trend of the East Asian summer monsoon that controlled the pedogenic intensity. Although the regional multi-segmented paleoclimatic records revealed by several magnetic parameters in our study, the long-term Asian cooling and aridification trend inferred here is of global correlation significance. As an important carrier of paleoclimate and paleoenvironment information, the East Asian eolian deposits have been extensively studied over the past thirty years [1][2][3][4][5][6][7]. Particularly, a good correlation between the events extracted from the eolian deposits and global sedimentary and tectonic events [2,[5][6][7][8][9][10][11] renders the loess-paleosol sequence an important proxy of the late Cenozoic climate and environments. The thick eolian deposits in East Asian interior can be dated back to at least Oligocene-Miocene boundary [10,12,13], providing strong evidence for the existence of a vast Asian interior desert. Recently, Hao et al. [14,15] applied rock magnetic parameters of eolian deposits since late Miocene to interpret paleoenvironment changes. The long-term trend of the magnetic signals are similar to the long-term changes of the deep-sea oxygen isotope values [16]. The studies of Deng et al. on the north Jingbian section [17] and the central Jiaodao section [18] in the Chinese Loess Plateau are only limited to the Quaternary loess-paleosol sequence, but they systematically extracted a relatively complete record of the East Asian monsoon climate evolution in the entire Quaternary period. In this study, we focus on the southeastern Chinese Loess Plateau, report the environmental magnetic signatures extracted from the eolian deposits in the Lantian Basin and a reconstruction of paleoclimate changes during 1.95-0.40 Ma. We found that the long-term trend of cooling and aridification in Asia is well correlated with global climate changes in the same period.

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“…3E and G) exhibited scatter similar to the respective uninoculated media. Similarly high levels of noise have been reported for goethite (␣-FeOOH), and this has been attributed to the high coercivity (H c ) and low-saturation magnetization (M s ) of goethite (51,54).…”

Section: Growth and Activities Ofmentioning

confidence: 99%

Iron Transformations Induced by an Acid-Tolerant Desulfosporosinus Species

Bertel

Peck

Quick

et al. 2012

Appl Environ Microbiol

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The mineralogical transformations of Fe phases induced by an acid-tolerant, Fe(III)-and sulfate-reducing bacterium, Desulfosporosinus sp. strain GBSRB4.2 were evaluated under geochemical conditions associated with acid mine drainage-impacted systems (i.e., low pH and high Fe concentrations). X-ray powder diffractometry coupled with magnetic analysis by first-order reversal curve diagrams were used to evaluate mineral phases produced by GBSRB4.2 in media containing different ratios of

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Non‐saturation of the defect moment of goethite and fine‐grained hematite up to 57 Teslas

Cited by 77 publications

References 17 publications

Iron oxide minerals in dust-source sediments from the Bodélé Depression, Chad: Implications for radiative properties and Fe bioavailability of dust plumes from the Sahara

Iron oxide minerals in dust-source sediments from the Bodélé Depression, Chad: Implications for radiative properties and Fe bioavailability of dust plumes from the Sahara

A rock magnetic record of Asian cooling and aridification processes during 1.95-0.40 Ma in the southeastern Chinese Loess Plateau

Iron Transformations Induced by an Acid-Tolerant Desulfosporosinus Species

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