Observations of the Intermediate Water Exchange Between the South China Sea and the Pacific Ocean Deduced From Transient Tracer Measurements

Abstract

The South China Sea (SCS) is the largest semienclosed marginal sea in the western Pacific (WP) and connects to the west Pacific through the Luzon Strait (LU). In this study, we use the observation of transient tracer chlorofluorocarbon-12 (CFC-12) to calculate the ventilation time scales of the SCS, LU, and WP. The CFC-12 and oxygen data are used together to identify the sandwiched structure vertically of the flows across the LU. The CFC-12 and oxygen distributions reveal a pronounced decrease westward across the LU and a slight decrease southward in the transport of the SCS. The mean age gradient of the salinity minimum (S min ) water between the WP and the northern SCS could be a consequence of intensive mixing and entrainment of the inflow water from the WP. An expected difference in age between the LU and SSCS is verified to reflect the transit time for the given water layers in the SCS. Thus, a mean transit time of 77 ± 20 years is estimated for the intermediate water in the SCS interior.

Volume and Heat Transport in the South China Sea and Maritime Continent at Present and the End of the 21st Century

“…Due to its unique location and bathymetry, the SCS has the characteristics of both shelf seas and tropical oceans. While the Luzon Strait plays a major role in transport between the tropical Pacific and SCS (Deng et al., 2018; Qu et al., 2004; Wyrtki, 1961), other surrounding straits have significant control on the SCS climate as well. Understanding monsoon modulated SCS transports are critical for a multitude of factors such as upper ocean dynamics over the SCS (e.g., Liu et al., 2008), interaction with the western tropical Pacific Ocean (e.g., Xue et al., 2004), and Indonesian throughflow (ITF) (e.g., Tozuka et al., 2007, 2009).…”

Ventilation in the Arctic Ocean and the Role of Pacific Inflow Deduced From Transient Tracer Measurements

“…We then focus on the estimation of mean transit time from the Bering Sea to the Canada Basin. Care must be taken that the mean transit time is the difference of ideal mean age (i.e., ventilation age) between two given reference points and differ from the other terminology residence time (Deng, Huang, et al, 2018). Considering that the atmospheric CFC‐12 concentration has declined since the mid‐2000s, it cannot be used for tracking newly ventilated water.…”

“…For the filed sample, nonnegligible blanks can obviously be detected for the samples collected in the deep water (>1,500 m). These have to do with potential unforeseen contamination that might have been from Niskin bottles (Deng et al, 2018). Seawater samples with very low concentrations of SF 6 are extremely sensitive to contamination by contact with the interior spring of a Niskin bottle.…”

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

“…The time‐dependent source functions of transient tracers, such as chlorofluorocarbons (CFCs) and sulfur hexafluoride (SF 6 ) are widely used to track oceanic processes, such as currents or circulation (Rhein, 1994; Smethie et al., 2000), the rates and variability of water mass formation (Hartin et al., 2011; LeBel et al., 2008; Orsi et al., 1999; Rhein et al., 2002; Smethie & Fine, 2001), upper ocean ventilation (Deng et al., 2018; Sonnerup et al., 2008; Tanhua & Liu, 2015; Wang et al., 2020), and anthropogenic CO 2 ( C ant ) inventories (Huang & Tanhua, 2017; Tanhua et al., 2009; Waugh et al., 2004, 2006). They are also helpful in estimating biogeochemical rates, including apparent oxygen utilization rates (AOUR; Mecking et al., 2004; Sonnerup et al., 1999, 2013, 2015, 2019; Warner et al., 1996).…”

“…Based on the transit time distribution (TTD) method, Huang et al (2016) estimated the ventilation time (mean age) and C ant using the CFC-11 data. Deng et al (2018) used the new CFC-12 data set to calculate the mean transit time of intermediate water in the interior of the SCS. Based on these studies, we pay attention to the TTD age-derived AOUR, which is defined as an integrated measure of the oxygen consumption in the ocean interior reflecting oxygen consumption during remineralization of organic carbon (OC) and respiration, and closely related to primary productivity in the photic zone.…”