Abstract: Deposition of organic carbon forms the final net effect of the ocean carbon sink at a certain time scale. Organic carbon deposition on the Arctic shelves plays a particularly important role in the global carbon cycle because of the broad shelf area and rich nutrient concentration. To determine the organic carbon deposition flux at the northern margin of the Chukchi Sea shelf, the ²¹⁰Pb dating method was used to analyze the age and deposition rate of sediment samples from station R17 of the third Chinese National Arctic Research Expedition. The results showed that the deposition rate was 0.6 mm?a-1, the apparent deposition mass flux was 0.72 kg?m-2?a-1, and the organic carbon deposition flux was 517 mmol C?m-2?a-1. It was estimated that at least 16% of the export organic carbon flux out of the euphotic zone was transferred and chronically buried into the sediment, a value which was much higher than the average ratio (~10%) for low- to mid-latitude regions, indicating a highly effective carbon sink at the northern margin of the Chukchi Sea shelf. With the decrease of sea ice coverage caused by warming in the Arctic Ocean, it could be inferred that the Arctic shelves will play an increasingly important role in the global carbon cycle.

Key words: organic carbon deposition, ²¹⁰Pb dating, Chukchi Sea shelf