Pollen preservation and its potential influence on paleoenvironmental reconstruction in Chinese loess deposits

Abstract

Pollen analysis in loess sediment has long been used to reconstruct Quaternary environmental change. However, caution should be taken as the reconstructed paleovegetation may be biased if pollen preservation is ignored. This paper investigates spatio-temporal pollen preservation condition and its causal factors in Chinese loess deposits, based on studying pollen of samples in three glacial and interglacial units across a climate gradient in China. We show that pollen concentration decreases from the cool and dry North China to warmer and wetter climate in more southerly locations at the same period. Pollen concentration in loess deposits is influenced by both pollen preservation and production, and the former one becomes the overwhelming factor where climate is quite warm and wet. Climate can influence pollen preservation by enhancing conditions for oxidation and microbial attack. Increasing temperature and moisture facilitates both the oxidation process and microbial destruction, which can result in pollen deterioration in loess deposits. In addition, a high soil pH can also cause pollen damage over time. These factors favour the relative preservation of several taxa such as Artemisia, Aster, Taraxacum, Pinus and Chenopodiaceae, and this leads to them dominating pollen spectra of Chinese loess deposits. The original pollen record suffers from the differential loss of taxa, especially toward southern loess regions and the absence of broadleaf forests or forest steppe reconstructed by pollen records may be attributable to this.