821 / 2024-09-19 15:04:29

Neodymium isotope variations in the South China Sea: implications for water mass exchange and particle dissolution

Neodymium isotope; South China Sea;water mass; particle dissolution

Session 10 - The biogeochemistry of trace metals in a changing ocean

Neodymium isotopic composition (εNd) has been used as a quasi-conservative proxy for tracking changes of ocean circulation in the past. However, εNd distributions in the ocean and underlying controlling mechanisms are still not well understood. As the largest marginal sea in the western Pacific Ocean, the South China Sea (SCS) is an ideal region to study the processes that potentially influence dissolved εNd variations and its marine cycling. Here we present εNd obtained from six stations spread across the SCS. The results show large variations of εNd (−6.7 to −2.8) and high Nd concentrations in the surface water, indicating the influence of dissolution of riverine and marine particles. The SCS deep water shows a narrow εNd range from −4.3 to −3.4, showing the presence of the North Pacific Deep Water in the deep SCS. The intermediate water in the SCS is characterized by a more negative εNd signal (–4.2 to –3.4) than its counterpart in the West Pacific (–3.5 to –2.8), implying alterations by deep water through three-dimensional overturning circulation from the northern to southern SCS below ~500 m. In addition, the Nd contributions of external sources were quantitatively estimated for the SCS. The dissolution of particles from the SCS surrounding rivers and continental margins may play an important role in providing additional Nd to the SCS surface water.