Astronomical forcing of terrestrial organic carbon burial in East Asia during the Eocene

Carbon sources and sinks are primary components of the climate system, but their response to external forcing remain unconstrained, especially for past greenhouse climates. Lakes are important carbon sinks that play a key role in the global carbon cycle. In this study, we investigate organic carbon burial processes and the possible role played by astronomical forcing in low to middle latitude lakes in China during the Eocene. Sediment noise modeling of lake level fluctuations in the three basins suggests that TOC maxima coincided with lake level maxima. We suggest that elevated lake levels likely led to stagnation of bottom waters, thereby promoting the development and preservation of organic matter. Total organic carbon (TOC) data spanning the Eocene from three borehole cores of separate basins show a common cyclicity of ∼1.2 Myr. According to the three TOC time series studied, maxima in TOC are linked to maxima in long-term 1.2 Myr obliquity modulation cycles, with long-term 2.4 Myr eccentricity cycles either at a maxima or minima. Our analysis elucidates a likely control on the burial of organic carbon by long-term astronomical climate cycles. The superposition of different orbital cycles may have driven the process of differential enrichment of organic matter by inducing perturbations in the carbon cycle through nonlinear climate effects. Overall, our chemostratigraphy results illustrate the sensitivity of the terrestrial carbon cycle to orbital forcing on geological timescales.