Physical Forcing-Driven Productivity and Sediment Flux to the Deep Basin of Northern South China Sea: A Decadal Time Series Study

Abstract

Abstract:Understanding the driving forces of absorption of anthropogenic CO 2 by the oceans is critical for a sustainable ocean carbon cycle. Decadal sinking particle flux data collected at 1000 m, 2000 m, and 3500 m at the South East Asia Time Series Study (SEATS) Station (18 • N, 116 • E), which was located in the northern South China Sea (nSCS), show that the fluxes undergo strong seasonal and interannual variability. Changes in the flux data are correlated with the satellite-derived chlorophyll-a concentration, indicating that the mass fluxes of the sinking particles are largely controlled by the export production at or near the SEATS station. The cooling of seawater and the strengthening of wind in winter increase the nutrient inventories in the euphotic zone, thus also increasing export production in the nSCS. This study reveals that the intrusion of low-nutrient seawater from the West Philippine Sea into the nSCS significantly reduces the productivity, and hence the flux, of sinking particles.

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

“…At SM18, the S max and its corresponding temperature showed the same result, where a gradual increase in DO min corresponded to a gradual increase in the WPS seawater proportions in 2003-2004, and vice versa in 2005-2011 ( Figure 8B). Lui et al (2018) showed that, similar to that in 2003-2004, there was a strong interannual WPS seawater intrusion between 2014 and 2016 ( Figure 8C). Consequently, the SSS at SEATS gradually increased from 33.19 in 2013/9 to the third highest of 34.46 in 2016/1 (Figure 4B).…”

“…Indeed, the potential temperature (θ) vs. salinity plot provides information on such proportions. We differentiated the WPS and SCS seawaters using θ and salinity, as the WPS and SCS seawaters have distinctive θ and salinity distributions from the surface to the bottom (Chen et al, 2016;Lui et al, 2018). Generally speaking, the surface and subsurface waters of the WPS are notably saltier than that of the SCS.…”

“…That is, the degree of intrusion of the surface layer of the WPS seawater as a Kuroshio branch is one of the main factors governing the changes in nutrient inventories and, hence, productivity in the euphotic zone of the SCS (Du et al, 2013;Lui et al, 2018). Lui et al (2018) showed that the increase in the WPS seawater proportions at the SEATS station between 2014 and 2016 reflects the Kuroshio intrusion into the SCS. Consequently, the satellitederived Chl.-a concentration and the fluxes of sinking particles collected at 2000 and 3500 m depths decreased significantly.…”

“…The WPS and South China Sea (SCS) seawaters have distinctive vertical salinity, DO, and nutrient distributions (Chen et al, 2001). The intruded Kuroshio exerts inter-annual influences on the biogeochemical cycles in the nSCS (Lui et al, 2018), and possibly the hypoxic condition in the coastal regions therein. A related incidence occurred in the almost enclosed Baltic Sea, where the strong inflow of the DO-rich North Sea seawater in 2014 turned the Baltic deep water from anoxic to oxic conditions (Mohrholz et al, 2015).…”

Organic Carbon Concentrations in High- and Low-Productivity Areas of the Sulu Sea

“…The variability of the marine organic carbon cycle in a changing climate has been discussed by several papers in this issue [64][65][66][67]; the dynamics of which are related to temporal (seasonal, inter-annual) variations in hydrodynamics, nutrient cycling, and other biogeochemical processes. Continuous monitoring efforts and modelling studies are essential in predicting future changes organic carbon distributions with respect to identified factors.…”