Increasing deep-water overflow from the Pacific into the South China Sea revealed by mooring observations

Abstract

Cold and dense water from the North Pacific Ocean that spills through the Luzon Strait, the only deep conduit between the South China Sea (SCS) and the Pacific Ocean, renews deep-water mass, modulates hydrographic and biogeochemical cycles, and drives abyssal and overturning circulations in the SCS. The variability of this key oceanic process, however, has been poorly studied, mainly due to a lack of sustained observations. A comprehensive observational program that started in 2009 has provided 12 years of continuous time series of velocity and volume transport within the Luzon Strait. Here we show the observation-based assessment of decadal trends of deep-water transport through this vital passage. With the estimated 12-year mean volume transport of the deep-water overflow into the SCS of 0.84 ± 0.39 Sv (1 Sv = 106 m3 s−1), a significant linear upward trend of 9% is revealed during this period. This is consistent with long-term changes in satellite-observed ocean bottom pressure. The results of this study may have broad implications for the overturning circulations and biogeochemical processes, including carbon cycles in this region.

Wind‐Driven Seasonal Variability of Deep‐Water Overflow From the Pacific Ocean to the South China Sea

“…Our analyses showed that the monthly overflow transport variability from ECCO, including the seasonal cycle, is highly consistent with observations from Zhou et al. (2023) in overlap period from October 2009 to December 2017. The correlation coefficient for monthly variability is about 0.6 with p ‐value less than 0.01.…”

“…Wang, 1986;Yang et al, 2010;Zhao et al, 2014Zhao et al, , 2016Zhou et al, 2014). In a more recent study, Zhou et al (2023) analyzed observations from two deep mooring sites within Luzon Strait and estimated that the mean transport between 2009 and 2021 is about 0.84 Sv.…”

“…(2018) estimated that Fr is only about 0.01 at the Luzon Strait sill, far smaller than 1. In addition, the observed mean transport was about 0.84 Sv (Zhou et al., 2023)—much weaker than 2.5 Sv from a hydraulics model (Qu et al., 2006). Together they indicate strongly that the overflow is subcritical in terms of rotational hydraulics.…”

Coherent Interannual–Decadal Potential Temperature Variability in the Tropical–North Pacific Ocean and Deep South China Sea

“…∆OBP contains barotropic components associated with sea level differences in the upper layer and baroclinic components related to cross‐strait density differences in the lower layer. Previous studies have confirmed that both the barotropic and baroclinic components of pressure contribute to the variability of the deep‐layer LST (Cai et al., 2023; Song, 2006; Zhou et al., 2023; Zhu, Sun, Wei, et al., 2017; Zhu, Yao, et al., 2022). The detrending ∆SLA between the two sides of the Luzon Strait moderately correlates ( r = 0.48) with the ∆OBP, implying remote modulation from upper‐layer processes.…”

Global Warming Weakens the Ocean Front and Phytoplankton Blooms in the Luzon Strait Over the Past 40 years

“…The Luzon Strait is the only deep conduit between the Pacific Ocean and the South China Sea (SCS). Owing to the difference in pressure between the Pacific Ocean and SCS (Qu et al., 2006), exchange flows through the Luzon Strait play a key role in transporting salt, heat, and biogenic elements (e.g., nutrients and carbon) between these two regions, which greatly impacts local and global ocean circulation and biogeochemical cycles (Du et al., 2013; Liu et al., 2020; Nan et al., 2015; Wang et al., 2017; Wu et al., 2018; Xu et al., 2018; Zhou et al., 2023; Zhu et al., 2022). In the upper layer (0–200 m), the intrusion of the warmer and saltier Kuroshio into the SCS from the Pacific Ocean can form an ocean front in the Luzon Strait, which significantly impacts the local marine ecology (Guo et al., 2017; Lévy et al., 2018).…”