Reply to the comment on “Geochemical gradients in soil O-horizon samples from southern Norway: Natural or anthropogenic?” by Eiliv Steinnes

Abstract

1. IntroductionIn his comment on Reimannet al. (2009a), Eiliv Steinnes consid-ers the data presented interesting but claims that the interpreta-tion is misleading and biased. The authors wish to make clearthat they do not doubt the existence of long range atmospherictransport (LRT) – the well known satellite images of Sahara dustcrossing the Atlantic or the excellent work of Posfai et al. (1999)or Buseck et al. (2000) are more than proof enough for the exis-tence of LRT, as such.The primary points of Reimann et al. (2009a) are the relativeimportance of the additional input of certain elements via atmo-spheric deposition on geochemical patterns observed in soils andthe importance of understanding these inputs in terms of the nat-ural variationsin geochemicalbackground.These pointslead to theimportance of mass balances and scale, and of knowing the geo-chemical background for any one area and sample material (Rei-mann and Garrett, 2005) before jumping to conclusions aboutthe source of elements in different compartments of the terrestrialenvironment at the continental or even global scale.2. The Chernobyl exampleSteinnes uses the Chernobyl accident as an illustrative examplefor the importance of long range transport and the visibility andpatchiness of the patterns. This comparison is, however, irrelevant,misleading, biased and circular. The Chernobyl accident was a one-time high-energy event (e.g., Hohenemser et al., 1986). Of course,such a one-time event will lead to ‘‘patchy patterns” dependingon the meteorological conditions of that day and, of course, theradionuclides emitted from such an event will travel long dis-tances. Even more important, the emitted radiocaesium does notoccur in nature, is not deposited against a high and highly variablenatural background, and is thus much easier to follow and detect.In contrast, metal emissions from human activities have persistedover a long time span, often thousands of years from the same gen-eral areas, and even traffic emissions have been going on for tens ofyears. These emissions are then deposited on a landscape with ahigh natural variation in concentration of exactly the same ele-ments as emitted. Although it is agreed that even here climateand deposition patterns will play an important role on the ob-served distribution, the two sources and processes areincomparable.Steinnes points out that LRT from Chernobyl leads to patchypatterns, thus seemingly implying that such patchy patternsshould be the norm for LRT. However, he then goes on to pointout that the observed geochemical gradient in O-horizon soils ofsouthern Norway ‘‘led to the suggestion that long-range atmo-spheric transport might be the main source of these elements inthe natural surface soils of the far north”. A key question thus iswhat type of pattern would be expected from LRT of pollutantsfrom central Europe. If it is considered that Steinnes may actuallybe correct in saying that the LRT pattern resulting from depositionof very small particles will be patchy, can it then be expected thatLRT produces a uniform gradient as seen in southern Norway?What will cause such a uniform pattern? It is actually the authors’opinion that, in contrast to singular events, persistent processes