Burial of terrestrial and marine organic carbon in Jiaozhou Bay: different responses to urbanization

Organic geochemical proxies (OC, OC/TN, delta C-13, and lignin oxidation products) were measured in a 271 cm long sediment core collected from central Jiaozhou Bay, northern China, to study the response of terrestrial and marine organic carbon burials to the surrounding urbanization. Terrestrial organic carbon content was constantly low from the bottom of the core to similar to 150 cm depth, indicating a stable and low level of terrestrial input before urbanization. Thereafter, it increased up to similar to 20 cm depth, suggesting that increased human activities and land-use changes during urbanization likely enhanced the flux of terrestrial organic carbon to the bay. Overall, 5-38% of the total organic carbon was terrigenous, which was derived from a mixture of woody and non-woody angiosperms and moderately degraded. Marine organic carbon content did not increase notably during urbanization. It increased from the bottom of the core to similar to 180 cm and stayed at high levels until it decreased in the top 20 cm. It was affected by multiple factors, including grain size and nutrient composition. These results demonstrate the different influences of urbanization on terrestrial and marine organic carbon cycles and suggest the importance of discriminating between these two organic carbon pools in the reconstruction of their historical changes.