Ecological Indicators (Jun 2022)
Multiple biomarkers for indicating changes of the organic matter source over the last decades in the Min-Zhe sediment zone, the East China Sea
Abstract
The temporal variation of sedimentary organic matters (SOM) in the East China Sea (ECS) is not fully assessed due to the complicated natural and anthropogenic processes. In this study, the compositions and distributions of multi-biomarker indicators (n-alkanes, n-alkanols and specific sterols) in a long sediment core collected from the Min-Zhe fined-grained sediment zone of the ECS were systematically studied to reveal variations of SOM sources and phytoplankton records over the last decades. The results of n-alkanes and sterols have demonstrated that terrestrial plants are the dominant SOM source, with the mean proportion of 67%. The temporal variation of terrestrial to marine biomarker ratios (TMBR) agree well with that of the dominant n-alkanes and terrigenous/aquatic ratios (TAR), suggesting that the multi-biomarker indicators yield a better assessment of the SOM source input. The regular variations of terrestrial OM and phytoplankton signals during the past decades record the interaction among marine ecological effects, anthropogenic activities and natural processes (i.e., extreme climate events). As a whole, the elevated productivity of marine phytoplankton since 1952 (mainly caused by enhanced nutrient inputs owing to the intensified human activities) and the decline in the period of 2005–2011 (likely influenced by the water impoundment of the Three Gorges Dam in 2003) were well reconstructed on the basis of brassicasterol (B) and dinosterol (D) indicators in this study. The B/(B + D) ratios also reveal the changes of community structure as a result of variations in the nutrient structure controlled by anthropogenic forcing. Notably, the anomalous peak in the abundance of n-alkanes with the even carbon predominance in about 1990 is identified for the first time, which may occur at that time of the first heavy rainfall after a long drought and is probably of the origin of biomass/fossil fuel combustion.
