The late glacial–Holocene transition as inferred from ostracod and pollen records in the Lago Piccolo di Avigliana (Northern Italy)

Abstract

Ostracod and pollen records of Lago Piccolo di Avigliana were used for the reconstruction of aquatic and terrestrial palaeoenvironments between 17 and 10 kyr cal BP. A combination of multivariate ordination techniques (PCA and RDA) made it possible to describe ostracod and pollen biostratigraphies and to evaluate whether changes in the aquatic ecosystem were associated with those in the terrestrial environments. Samples and taxa in the ordination plots were grouped into three clusters: a first cluster representing herbaceous and shrub pollen taxa (Juniperus, Chenopodiaceae, Gramineae, Artemisia, and Rubiaceae) associated with ostracods typical of oligotrophic and well oxygenated aquatic environments (Cytherissa lacustris), a second cluster containing pollen taxa representing boreal forests (Betula, Pinus sylvestris, and Pinus cembra) associated with ostracod taxa from shallow oligo-mesotrophic aquatic environments (Candona candida, Darwinula stevensoni), and a third cluster including pollen of thermophilous trees and shrubs (Corylus, Quercus ilex, Fraxinus, Quercus robur-type, and Ulmus) connected to ostracods representing warm mesotrophic aquatic conditions with aquatic vegetation (Cypria ophtalmica, Metacypris cordata). Hypothesis testing with constrained Monte Carlo permutations rejected the null hypothesis that no relationship exists between ostracod and pollen datasets at 2% level of significance. As a whole, changes in temperature and precipitation–evaporation balance that influenced terrestrial vegetation were represented by changes in trophic level and water level in the aquatic environment