Three‐dimensional pathways of water masses in the South China Sea: A modeling study

Abstract

We conduct a numerical Eulerian analysis on the Lagrangian characteristics of South China Sea (SCS) water masses. This is the first study to investigate the water pathway and residence time in response to time‐dependent, three‐dimensional basin circulation in the SCS. The circulation of the SCS is largely determined by westward intrusions of the northwestern Pacific waters in the upper layer (0–750 m) and deep layer (>1500 m), and by an eastward extrusion in the intermediate layer (750–1500 m) through Luzon Strait (LS). The waters in these three layers are interlinked to sustain the three‐dimensional circulation in the SCS. The upper intrusive waters flow cyclonically and have a residence time of ∼3 years before they subduct into a deeper layer or exit the SCS through surrounding straits. The intrusive denser waters in the deep layer flow along the northern slope and reside for ∼25 years in the northern basin (north of 13°N), where a strong subduction occurs. A cyclonic circulation exists in the deep layer in the southern basin (south of 13°N), where a subduction of intermediate waters occurs over its eastern side and a deep upwelling exists over its western side. The water in the deep southern basin has a residence time of ∼40 years. The upwelled deep waters and the subducted waters from the upper layer form the intermediate water, where waters circulate anti‐cyclonically toward LS and have a longest residence time (∼42 years). These findings are supported by the spatial variation in the observed potential density variance.

Dissolved Organic Nitrogen Cycling in the South China Sea From an Isotopic Perspective

“…While it is close to the δ 15 N of N 2 fixer biomass and the DON they produce (Carpenter et al, 1997;Macko et al, 1987;McRose et al, 2019;Minagawa & Wada, 1986;Zerkle et al, 2008), we know of no reason to expect N 2 fixers to dominate net DON production in this region. The SCS has relatively strong vertical exchange and net upwelling, with both monsoonal seasons hosting conditions that encourage vertical fluxes (Liu & Gan, 2017). This results in high vertical nitrate flux to the euphotic zone on an annual basis, which dominates new production (Liu et al, 2010;.…”

Distribution of Concentration and Stable Isotopic Composition of N2O in the Shelf and Slope of the Northern South China Sea: Implications for Production and Emission

“…Positive N* and high ambient O 2 in the deep water does not support N 2 O production by local denitrification in the water column. However, the deep water in the study region originates partly from the western North Pacific waters (Kuroshio; Liu & Gan, 2017), which may carry an isotopic signal from a remote region with water column denitrification, that is, the ETNP. In these waters, N 2 O may be produced predominantly by denitrification with partial reduction in the oxygen deficient zone (Fujii et al, 2013;Yamagishi et al, 2007).…”

“…As an ocean-dominated marginal sea, the SCS is characterized by intensive interactions with the West Philippine Sea (WPS) via the Luzon Strait (Figure 1). The Kuroshio usually intrudes westward into the upper layer (<750 m) and deep layer (>1,500 m) of the SCS, while the intermediate layer (750-1,500 m) extrudes eastward through the Luzon Strait (Liu & Gan, 2017). Overall, the SCS basin is oligotrophic Chen et al, 2016).…”

Intrusion of Kuroshio Helps to Diminish Coastal Hypoxia in the Coast of Northern South China Sea

“…Importantly, the influence of intruded Kuroshio on the seawater chemistry in the nSCS can sustain for years. Liu and Gan (2017) indicated that the intruded Kuroshio in the upper layer had a residence time of about 3 years before subducting into deeper layers or flowing out of the SCS. Restated, the intruded Kuroshio could have inter-annual influences on the biogeochemical cycles in the SCS.…”