Historical reconstructions of sedimentary organic matter sources and phytoplankton evolution in the Jiaozhou Bay based on sterols and carbon isotope

Abstract

Bulk organic matter proxies including total organic carbon (TOC), total nitrogen (TN), C/N ratio and carbon stable isotopic composition (δ13C) combined with sterols in a sediment core were studied to reconstruct both organic matter (OM) sources and phytoplankton evolutions of the Jiaozhou Bay (JZB) during the past ~ 80 years. The OM source allocations were calculated based on δ13C and sterol. The results showed that the marine OM (MOM) input was the dominant OM sources, with the marine organic carbon (OCM) proportion of 54.2–78.4% and marine sterol proportion of 63.9–72.7%. The Terrestrial OM (TOM) contribution increased especially since the 1960s, mainly attributed to the increased sewage discharge and usage of fertilizer. Elevated marine primary productivity since the 1980s was mainly attributed to the increased nutrient inputs. Evolution of diatom compared with dinoflagellate in the JZB was closely related to the anthropogenic forcing and climate change.