Interannual variability of summertime cross-isobath exchanges in the northern South China Sea: ENSO and riverine influences

Yunping Song, Yunxin Lin, Peng Zhan, Zhiqiang Liu, Zhongya Cai

Abstract: Yunping Song, Yunxin Lin, Peng Zhan, Zhiqiang Liu, and Zhongya Cai Abstract. This study investigates the interannual variability of summer shelf circulation in the Northern South China Sea (NSCS) from 2000 to 2022, combining long-term observations and high-resolution simulations. We elucidate the responses of NSCS shelf circulation to ENSO and Pearl River Estuary (PRE) freshwater runoff, revealing distinct spatial and mechanistic signatures. During El Niño years, a pronounced sea level anomaly dipole forms between the central and southern South China Sea, intensifying northward geostrophic currents in the southern basin and modulating Kuroshio intrusion. Simultaneously, an amplified PRE plume extends eastward to the 100 m isobath, markedly reducing nearshore salinity. Analysis of depth-integrated vorticity equations indicates that the pressure gradient force—driven by the joint effect of baroclinicity and bottom relief (JEBAR) and bottom pressure gradients—governs NSCS circulation variability. In coastal regions, cross-isobath velocity anomalies are primarily controlled by bottom stress curl and nonlinear vorticity advection, whereas JEBAR dominates offshore dynamics beyond the 100 m isobath. During El Niño summers, bottom density anomalies generate positive cross-isobath velocity anomalies through JEBAR, partially offset by negative anomalies from altered vertical stratification, sustaining a meandering shelf current. These results highlight the interplay of regional and remote forcings, advancing understanding of NSCS hydrographic dynamics. How to cite. Song, Y., Lin, Y., Zhan, P., Liu, Z., and Cai, Z.: Interannual variability of summertime cross-isobath exchanges in the northern South China Sea: ENSO and riverine influences, EGUsphere [preprint], https://doi.org/10.5194/egusphere-2025-2712, 2025. Received: 08 Jun 2025 – Discussion started: 30 Jun 2025 Publisher's note: Copernicus Publications remains neutral with regard to jurisdictional claims made in the text, published maps, institutional affiliations, or any other geographical representation in this paper. While Copernicus Publications makes every effort to include appropriate place names, the final responsibility lies with the authors. Views expressed in the text are those of the authors and do not necessarily reflect the views of the publisher. Download & links Preprint (PDF, 6198 KB) Download & links Preprint (6198 KB) Metadata XML BibTeX EndNote Share document.addEventListener("DOMContentLoaded", function () { const mobileShareElement = document.querySelector(".mobile-native-share"); if (navigator.share) { // Native sharing is available if (mobileShareElement) { mobileShareElement.style.display = "block"; } } else { // Native sharing is NOT available if (mobileShareElement) { mobileShareElement.style.display = "none"; } } });

External IDs:doi:10.5194/egusphere-2025-2712