Environmental magnetism: Principles and applications

Abstract

In environmental magnetism, rock and mineral magnetic techniques are used to investigate the formation, transportation, deposition, and postdepositional alterations of magnetic minerals under the influences of a wide range of environmental processes. All materials respond in some way to an applied magnetic field, and iron‐bearing minerals are sensitive to a range of environmental processes, which makes magnetic measurements extremely useful for detecting signals associated with environmental processes. Environmental magnetism has grown considerably since the mid 1970s and now contributes to research in the geosciences and in branches of physics, chemistry, and biology and environmental science, including research on climate change, pollution, iron biomineralization, and depositional and diagenetic processes in sediments to name a few applications. Magnetic parameters are used to routinely scan sediments, but interpretation is often difficult and requires understanding of the underlying physics and chemistry. Thorough examination of magnetic properties and of the environmental processes that give rise to the measured magnetic signal is needed to avoid ambiguities, complexities, and limitations to interpretations. In this review, we evaluate environmental magnetic parameters based on theory and empirical results. We describe how ambiguities can be resolved by use of combined techniques and demonstrate the power of environmental magnetism in enabling quantitative environmental interpretations. We also review recent developments that demonstrate the mutual benefit of environmental magnetism from close collaborations with biology, chemistry, and physics. Finally, we discuss directions in which environmental magnetism is likely to develop in the future.

Enhanced primary productivity and magnetotactic bacterial production in response to middle Eocene warming in the Neo-Tethys Ocean

“…Maher et al, 2010;Roberts et al, 2011;Larrasoaña et al, 2012;Liu et al, 2012). Roberts et al (2011) reported enhanced iron supply by aeolian dust in Eocene sediments (ODP Hole 738B) of the southern Kerguelen Plateau (Indian Ocean), where a marked increase in hematite concentrations coincided with a switch from oligotrophic to eutrophic conditions.…”

“…Evans and Heller, 2003;Liu et al, 2012). Fine-grained terrigenous inputs that reached the deep, carbonate-dominated MCA site were most likely transported by suspended plumes or wind.…”

Quantifying paleoprecipitation of the Luochuan and Sanmenxia Loess on the Chinese Loess Plateau

“…In both LC and SMX, reconstructed MAPs correlate well with corresponding maximum χ FD and ARM (Fig. 9), indicating that precipitation is essential for magnetic enhancement in loess/paleosols (Balsam et al, 2004(Balsam et al, , 2011Liu et al, 2012;Maher, 1998).…”

“…2. For both sections, χ, χ FD , SIRM and ARM, which are generally sensitive to concentration of ferrimagnetic minerals (Dekkers, 1997;Liu et al, 2012;Verosub and Roberts, 1995), exhibit high values in paleosol horizons and low values in loess horizons, respectively. This is consistent with previous studies that more fine-grained ferrimagnets are formed in paleosols.…”

“…are closely related with soil forming factors during pedogenesis, especially precipitation. Magnetic parameters, which are fast, inexpensive, non-destructive, and sensitive, have been commonly used as indicators of paleoprecipitation for decades, especially the mass-specific susceptibility (χ) (Balsam et al, 2004;Balsam et al, 2011;Liu et al, 2007;Liu et al, 2012;Maher, 1998;Maher et al, 2002;Maher and Possolo, 2013;Maher et al, 1994;Orgeira and Compagnucci, 2006). Maher and Thompson (1995) reported that pedogenic χ (defined as χ-χ C , where χ C represents the χ of the parent material) rises to a peak until MAP reaches about to reductive dissolution or alteration of the iron oxides.…”