Profiles in the East China Sea and the Okinawa Trough

Abstract

Abstract Dissolved beryllium-10 concentration profiles in sea water of the East China Sea and the Okinawa Trough in 1993 autumn and 1994 summer have been investigated. The results show that 10 Be concentrations in this area are mainly controlled by surface biological productivity, particle remineralization, and the degree of mixing with the Yangtze River and the Kuroshio waters. During the sampling periods (summer and autumn), the East China Sea was well stratified. Generally, the 10 Be water depth profiles can be divided into three layers: the surface mixed layer, the particulate 10 Be regeneration layer, and the bottom layer. Surface water 10 Be concentrations increase gradually towards the Kuroshio and increase sharply at the edge of the Kuroshio Current. Vertical distributions of 10 Be show that in the summer 10 Be is enriched in the bottom water near the Yangtze River estuary and the bottom water in the middle of the continental shelf. The two enriched areas are separated, probably by an intrusion of the Continental Coastal Water. In the autumn, 10 Be bottom enrichment only occurred in the western part of the East China Sea. This phenomenon is consistent with the seasonal circulation pattern change of currents induced by monsoon winds. The influence on 10 Be by the Kuroshio branch intrusion in the southern East China Sea northeast of Taiwan may be more significant than the Kuroshio main flow. Simple box model results indicate that 10 Be input from the Kuroshio Current is more important than Yangtze River input and atmospheric precipitation. About 81% of 10 Be input to the East China Sea is scavenged into the sediments and 19% of 10 Be flows out of the East China Sea by currents and water exchange. The 10 Be sedimentation flux in the East China Sea is nearly five times of the average global 10 Be production rate, suggesting that the East China Sea is an important sink for 10 Be .