Zoophycos cyclicity during the last 425 ka in the northeastern South China Sea: Evidence for monsoon fluctuation at the Milankovitch scale

In a deep-sea piston core, covering the last 425 ka from the northeastern South China Sea, power spectrum analysis of several core data from sediment parameters has been conducted and compared with that obtained from time-series analysis of the distribution of the trace fossil Zoophycos through the core. Power spectra show a more or less well developed cyclical pattern, with similar cyclostratigraphic patterns for sand and carbonate content, oxygen isotopes and Zoophycos distribution, but different for carbon isotopes and total organic carbon content (TOC). Temporal calibration allows the recognition of Milankovitch orbital–scale cycles, with a duration of 111–100 ka for short-term eccentricity, 63–55 ka for the combined effect of both precession and obliquity, 42–40 ka for the obliquity cycle, and 28–21 ka for the precessional cycle band. The variable Milankovitch-scale cyclicity suggests the influence of a complex interaction of variable processes. East Asian monsoon variability at the Milankovitch orbital–scale cycles could determine variations in environmental conditions, including changes in the organic material reaching the sea floor, and in turn influencing the cyclical occurrence of the Zoophycos trace makers. The cyclicity of Zoophycos is of special interest to basin analysis, where Zoophycos has the potential of being used as a proxy for cyclical monsoon fluctuations at the Milankovitch scale.