Transit Time Distributions and Apparent Oxygen Utilization Rates in Northern South China Sea Using Chlorofluorocarbons and Sulfur Hexafluoride Data

Abstract

AbstractCFC‐12 and SF6 data were used in combination to estimate the mean age of water in the northern South China Sea (NSCS), to explore oceanographic processes related to “time,” including the transit time through the Luzon Strait (LS) with a three‐layer circulation structure and the apparent oxygen utilization rates (AOUR). Significant differences in mean ages of water were observed at the same density level in the water columns on both sides of the LS, presented as a westward flow in the upper layer, eastward flow in the intermediate layer, and westward flow in the deep layer with transit times of 8 ± 5, 39 ± 22, and 20 ± 18 yr, respectively. The AOUR was estimated to be 8.4 μmol kg−1 yr−1 at about 100 m and decreased to approximately 0.66 μmol kg−1 yr−1 at 1,500 m in the NSCS. The average organic carbon flux in the depth range of 100–1,500 m was 1.7 mol C m−2 yr−1 in the NSCS and 1.3 mol C m−2 yr−1 in the western Pacific Ocean (WP). The activation energy—derived using the Arrhenius equation—in the NSCS and WP (87.7–154.2 kJ mol−1) are close to those in the northern Pacific Ocean (60.8–133.5 kJ mol−1). These results suggest a conspicuous correlation between temperature and AOUR. The impact of climate change on the ocean and the feedback mechanism between ocean warming and oxygen consumption needs further investigation.