Orbital, ice-sheet, and possible solar forcing of Holocene lake-level fluctuations in west-central Europe: A comment on Bleicher

Abstract

Bleicher (2013) discussed interpretations proposed by Magny (2004) that Holocene lake-level fluctuations in west-central Europe suggest possible solar forcing of climate. He pointed out that the method used by Magny (2004) is a variant of a cumulative probability function (CPF) and cannot prove solar forcing of central European lake-level changes. He concluded that only few episodes of lake-level changes are climatically driven and that non-climatic factors were dominating. While Bleicher’s paper offers a stimulating contribution to the general debate on CPFs, the present comment is based on an approach which, in contrast to CPFs, excludes any consideration of variations in the probabilities over the time intervals given by calibration of 14C dates, as well as any distinction between types of dates (radiocarbon versus tree ring). It produces a revised pattern of the mid-European high lake-level events for the whole Holocene, supporting the hypothesis proposed in Magny (2004). Comparisons with other regional and North Atlantic palaeoclimatic records suggest that, without excluding other forcing factors, the successive high lake-level events recognised in west-central Europe reflect a combination of three main forcing factors acting on millennial and centennial scales, i.e. orbitally driven changes in insolation, impacts of deglacial outbursts and, possibly, variations in solar activity. Finally, it is clear that further investigations are still needed in order to improve the chronological data set for mid-European lake-level fluctuations, with particular attention to better defining the beginning and end of events.