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Quantitative reconstruction of past plant abundance from fossil pollen data is still a challenging task for palynologists. During the last decades, mechanistic methods have been developed to convert pollen assemblages from peat and lake deposits into vegetation abundance at regional and local scale. Coastal areas are particularly sensitive to climate and environmental hazards. Thus, quantitative estimates of past vegetation are important to better understand their history and address potential effects of future environmental changes. However, assumptions of the mechanistic models of pollen dispersal and deposition originally designed for near-circular lakes and bogs located inland are violated when applied to coastal sites because of different basin shape and wind direction distribution. This study investigates how to adapt a model of pollen dispersal and deposition developed for lakes to coastal lagoons. A new geometry is defined, and it is demonstrated how some of the major formulas from previous models can be used without any modification in this singular context. [ABSTRACT FROM AUTHOR]

To better understand the long-term changes of the East Asian summer monsoon precipitation (Pjja), quantitative reconstructions and model simulations are needed. Here, we develop continental-scale pollen-based transfer functions for Pjja with weighted averaging–partial least squares (WA-PLS) regression and a Bayesian multinomial regression method. We apply these transfer functions to a set of fossil pollen data from monsoonal China for quantitatively reconstructing the Pjja changes over the last 9500 years. We compare the reconstructions with Pjja simulations from a coupled atmosphere–ocean–sea ice general circulation model (the Kiel Climate Model, KCM). The results of cross-validation tests for the transfer functions show that both the WA-PLS model (r2 = 0.83, root mean square error of prediction (RMSEP) = 112.11 mm) and the Bayesian model (r2 = 0.86, RMSEP = 107.67 mm) exhibit good predictive performance. We stack all Pjja reconstructions from northern China to a summary curve. The stacked record reveals that Pjja increased since 9500 cal. yr BP, attained its highest level during the Holocene summer monsoon maximum (HSMM) at ~7000–4000 cal. yr BP and declined to present. The KCM output and the reconstructions differ in the early-Holocene (~9500–7000 cal. yr BP) where the model suggests higher Pjja than the reconstructions. Moreover, during the HSMM, the amplitude of the Pjja changes (~20–60 mm above present) in simulations is lower than the reconstructed changes (~70–110 mm above present). The rising (declining) Pjja patterns in reconstructions before (after) the HSMM are more pronounced and fluctuating than in simulations. Other palaeohydrological data such as lake-level reconstructions indicate substantial monsoon precipitation changes throughout the Holocene. Our results therefore show that the KCM underestimates the overall amplitude of the Holocene monsoon precipitation changes. [ABSTRACT FROM AUTHOR]

Bio-chronostratigraphic observations compiled from Quai-Branly in Paris (France) and their comparison with previous studies in the Paris Basin allow documentation of the morphodynamic evolution of the River Seine during the middle and late Holocene. This history begins in the Boreal (between 9500 and 8850 cal. BP), with the deposition of tufa, expressing a stabilized river bed. During the second part of the sub-Boreal the water-table was low. At the beginning of the sub-Atlantic (towards 2800/2700 cal. BP), alluvial dynamics increase, as is recorded elsewhere throughout the Paris Basin. At the beginning of the second part of the sub-Atlantic (around 2000 cal. BP), flood dynamics persisted at a lower intensity. Human occupation occurred from the fifth century AD. Before or around the beginning of the seventeenth century AD, a natural levee was built, indicating the progressive attachment of the Quai-Branly area to the floodplain. The hydrodynamic evolution of the River Seine observed at the Quai-Branly site is similar to that recorded in other river valley floors of the Paris Basin. This evolution appears to be in response to global climatic changes rather than to variations induced by human activities. [ABSTRACT FROM AUTHOR]