The physics of wind-blown loess: implications for grain size proxy interpretations in Quaternary paleoclimate studies

摘要

Loess deposits are recorders of aeolian activity during past glaciations. Since the size distribution of loess depositsuddepends on distance to the dust source, and environmental conditions at the source, during transport, and at deposition,udloess particle size distributions and derived statistical measures are widely used proxies in Quaternaryudpaleoenvironmental studies. However, the interpretation of these proxies often only considers dust transportudprocesses. To move beyond such overly simplistic proxy interpretations, and toward proxy interpretations thatudconsider the range of environmental processes that determine loess particle size distribution variations we provideuda comprehensive review on the physics of dust particle mobilization and deposition. Furthermore, usingudhigh-resolution bulk loess and quartz grain size datasets from a last glacial/interglacial sequence, we showudthat, because grain size distributions are affected by multiple, often stochastic processes, changes in these distributionsudover time allow multiple interpretations for the driving processes. Consequently, simplistic interpretationsudof proxy variations in terms of only one factor (e.g. wind speed) are likely to be inaccurate. Nonethelessudusing loess proxies to understand temporal changes in the dust cycle and environmental parameters requiresud(i) a careful site selection, to minimize the effects of topography and source distance, and (ii) the joint use ofudbulk and quartz grain size proxies, together with high resolution mass accumulation rate calculations if possible.