Abstract
Mineral dust deposition is a process often overlooked in the northern mid-latitudes, despite its potential effects on ecosystems. These areas are often rich in peat, providing ample material for reconstructing past changes in atmospheric deposition. However, the highly organic matrix (up to 99% in some cases) of atmospherically fed mires makes studying the actual dust particles (grain size, mineralogy) challenging. Here, we explore some of the potentials and problems of using geochemical data from conservative, lithogenic elements (Al, Ga, Rb, Sc, Y, Zr, Th, Ti and REE) to build detailed dust records, using an example from the 8,900-year peat sequence from Store Mosse (the “Great Bog”), which is the largest mire complex in the boreo-nemoral region of southern Sweden. The four dust events recorded at this site were elementally distinct, suggesting different dominant mineral hosts. The oldest and longest event (6385–5300 cal yr BP) shows a clear signal of clay input, with increasing contributions of mica, feldspar and middle-REE-rich phosphate minerals over time. These clays are likely transported from a long-distance source (<100 km). While dust deposition was reduced during the second event (5300–4370 cal yr BP), this is the most distinct in terms of its source character, with [Eu/Eu∗]UCC revealing the input of plagioclase feldspar from a local source, possibly active during this stormier period. The third (2380–2200 cal yr BP) and fourth (1275–1080 cal yr BP) events are much shorter in duration, and the presence of clays and heavy minerals is inferred. Elemental mass accumulation rates reflect these changes in mineralogy, where the relative importance of the four dust events varies by element. The broad changes in major mineral hosts, grain size, source location and approximated net dust deposition rates observed in the earlier, longer-duration dust events agree well with palaeoclimatic changes observed in northern Europe. The two most recent dust events are much shorter in duration, which, combined with evidence of their local and regional character, may explain why they have not been observed elsewhere.
