Construction of statistically reliable sclerochronology using subfossil shells of river pearl mussel

Sclerochronology is based on series of skeletal growth records that have been correctly aligned in time. These chronologies have so far been derived from living bivalves and corals. Here we demonstrate the possibility of constructing the sclerochronology from a suite of river pearl mussel (Margaritifera margaritifera (L.)) shells with unknown but at least partly overlapping geological age. Subsequent to measuring of the annual shell growth increments, the sample series were iteratively compared to each other and to the mean series of other samples. This comparison forms the basis of the applied procedure, termed cross-dating, in which more inter-correlative sample series can be progressively added into the mean chronology in step-wise fashion. After cross-dating, the correlation of the 16 sample series (0.52) indicated that the subfossil sclerochronology bore common growth signal that was comparable to previously recorded chronologies from modern samples. The cross-dated sclerochronology represented growth variations over a time window of 91 years. Variability in chronology was found to be statistically reliable, with sample replication in at least six series (this equalled to chronology sub-interval of 78 years). In the wider paleontological context, these results show the possibility of constructing statistically reliable sclerochronologies from fossil specimens at any given locality bearing an abundance of skeletal remains. Such chronologies will be important in their ability to provide paleolimnological records with comparable quality to recent proxy and observational series. Sclerochronologies can be numerically examined for paleolimnological variations using standard time-series analysis tools: a dominant frequency-band at inter-annual and multi-annual time-scales was found in our sample by spectral analysis.     

Evaluating direct and indirect evidence of climatic change by Hölder regularity and order pattern in time series

The several competing reconstructions of Northern Hemisphere temperature variability exists with partly conflicting evidence. Here we considered a specific problem of choosing “the best” reconstruction, in a frame of assumptions, that they are produced by smooth dynamical system as well as instrumental time series. Using some sophisticated measures of similarity, we could not match to all existing hemispheric paleoclimate reconstructions with hypothesis about any deterministic system which can produced its as typical projection of their trajectories. The results cast doubt on the conventional techniques frequently used to reconstruct past climate variability.