The magnetic record of inorganic fly ash deposition in lake sediments and ombrotrophic peats

Abstract

Interest in identifying a geological marker signifying the starting point for the Anthropocene has prompted an exploration of the stratigraphic record of inorganic particulates generated by industrial activities. Magnetic measurements of recent lake sediments and ombrotrophic peats are here used to reconstruct the history of deposition of inorganic fly ash spheres resulting mainly from solid fuel combustion and metal smelting. The chronologies used have been based on moss-increment counting, radioisotope dating and pollen analysis. The sites come from the United Kingdom, Scandinavia and North America. In several cases where detailed chronologies of both fly ash deposition and local industry can be compared, the sequence of concentration-linked magnetic measurements appears to capture accurately the record of industrial development despite incontrovertible evidence from other peat based records for some selective dissolution of magnetic minerals. The dates at which magnetic concentration increases begin range from the 16 th century in the peat profiles around the head of Morecambe Bay, South Cumbria, in North-West England where early iron manufacture using charcoal-fuelled bloomery hearths is well documented, to the mid 20 th century at the remotest sites in Arctic Scandinavia. The lake sediment profiles used here come mainly from the United Kingdom and, in most cases, they date increases to the late 19 th century or the first decades of the 20 th century. Any attempt to use the magnetic record of fly ash deposition in lake sediments and/or peats to mark the date chosen as the onset of the Anthropocene would require careful choice of site location and archive, bearing in mind the issue of selective magnetic mineral dissolution.

Air pollutant contamination and acidification of surface waters in the North York Moors, UK: Multi-proxy evidence from the sediments of a moorland pool

“…In the absence of catchment inputs, the Grey Heugh Slack mineral magnetic record can be assumed to be dominated by magnetic particles deposited from the atmosphere, especially by those produced by coal combustion, iron and steel manufacture and metal smelting (Oldfield et al, 1983; Oldfield et al, this volume). However, the steep increase in χ ARM values at the top of the core (Figure 4), not reflected in any component of the IRM, probably results from early dissolution of SD grains of biogenic magnetite produced in situ by magnetotactic bacteria.…”

Variations in erosion intensity and soil maturity as revealed by mineral magnetism of sediments from an alpine lake in monsoon-dominated central east China and their implications for environmental changes over the past 5500 years

“…The approach of mineral magnetism has been proved very effective in reconstructing palaeoenvironments (e.g. Chen et al, 2013; Liu et al, 2011; Oldfield et al, 2015; Tang et al, 2015). Measurements of mineral magnetism were performed on the 56 samples from the sediment sequence, one surface-sediment sample, 12 soil-profile samples, two rock debris, one catchment surface-soil and 33 non-catchment surface-soil samples.…”

Marking the boundaries of stratigraphy: Is stratigraphy able and willing to define, describe and explain the Anthropocene?

“…First, various development trajectories of human societies across the globe mean that the anthropogenic rock record is characterised by apparently similar material that, however, varies in age from place to place (Brown, 2014;Brown et al, 2013;Edgeworth, 2014;Edgeworth et al, 2015;Gale & Hoare, 2012;Oldfield et al, 2015;Streeter et al, 2015;Wolfe et al, 2013;Zalasiewicz et al, 2014a;Zalasiewicz et al, 2012;Zalasiewicz et al, 2014c;Zalasiewicz et al, 2016a). Even though this "diachroneity" is a feature of much of the Earth's rock record (Doyle et al, 2001, p. 31), it cannot easily be resolved in the thin record of the Anthropocene (Autin & Holbrook, 2012a).…”

“…Third, and closely related to the last point, the continuing human "bioturbation", or reworking of the developing rock record, means that stratigraphers assessing this record in the future may reach different conclusions about its content and boundaries than those working today (Coughlan et al, 2015;Zalasiewicz et al, 2016a). This raised the concern that today's stratigraphic evidence may not be obtainable in the distant future; such concerns are aggravated by the often limited preservability of anthropogenic deposits used to characterise Anthropocene sediments (Ferreira et al, 2016;Gale & Hoare, 2012;Oldfield et al, 2015;Waters et al, 2014a;Wolfe et al, 2013;Zalasiewicz et al, 2014a).…”