Diapycnal Fluxes of Nutrients in an Oligotrophic Oceanic Regime: The South China Sea

Du, Chuanjun; Liu, Zhiyu; Kao, Shuh‐Ji; Dai, Minhan

doi:10.1002/2017gl074921

Cited by 75 publications

(72 citation statements)

References 45 publications

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“…These conditions intensified upper layer stratification, resulting in the shallowest MLD of the study period (<15 m; Figure a). This MLD would have been shallower than the upper nutricline (~50 m; Du et al, ; Wong et al, )—so unable to supply nutrients from subsurface waters. Mesoscale eddies are another potential driver, but the positive SLA values of this time (Figure d) indicate that such eddies were not present.…”

Section: Discussionmentioning

confidence: 99%

“…The South China Sea (SCS), located between the Tibetan Plateau and the Western Pacific Warm Pool (i.e., within the East Asian Monsoon system), is one of the world's largest semienclosed marginal seas. Except for its coastal areas, the SCS is a typical well‐stratified oligotrophic sea with depleted surface nutrients, thereby manifesting low primary production in the surface layer (Du et al, ; Wong et al, ). The biogeochemistry of the SCS is responsive to multiscale physical forcings such as intraseasonal upwelling and mesoscale eddies (Liu et al, ; Ning et al, ), the seasonally reversing monsoon, and interannual El Ninõ–Southern Oscillation (ENSO) events (H. Liu, Hu, et al, ).…”

Section: Introductionmentioning

confidence: 99%

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Enhancement of Mesopelagic Sinking Particle Fluxes Due to Upwelling, Aerosol Deposition, and Monsoonal Influences in the Northwestern South China Sea

Zhang

Xuan

et al. 2019

JGR Oceans

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Time series data from a sediment trap at approximately 1,000-m depth in the northwestern South China Sea, July 2012 to April 2013, were used in combination with remote sensing and shipboard physical and biogeochemical data to quantify the effects of multiscale physical processes on sinking particle fluxes and the function of the local biological carbon pump. Total mass flux and the fluxes of its primary components-particulate organic carbon, calcium carbonate, opal, and lithogenic matter-exhibited similar temporal trends, with three conspicuous high-flux events. These events occurred in the summer, autumn, and winter, attributable to upwelling, aerosol deposition, and the northeast monsoon, respectively. Together, these events accounted for only 40% of the total time but approximately 80% of the 10-month total mass flux (21% during the upwelling event, 23% during the aerosol event, and 36% during the northeast monsoon event). Each event contributed its own unique biogeochemical overprint. For example, Calcareous phytoplankton benefited from both the upwelling and aerosol deposition events, but siliceous phytoplankton benefited more than calcifiers during the upwelling conditions. The biogenic sinking particles were primarily marine authigenic, while the lithogenic matter was mainly resuspended sediment from the neighboring slope. The high flux of lithogenic matter was due to scavenging by sinking organic matter and the ballasting effect, especially during the high-flux periods. This study illustrates that episodic intraseasonal physical processes are as important as the most common major seasonal event-the northeast monsoon-in modulating the strength of the South China Sea biological carbon pump.Plain Language Summary Sinking particles are the most important carriers of matter and energy within the marine biological carbon pump, which largely determines the ocean's capacity to sequester atmospheric carbon dioxide (CO 2 ) over century timescales. Multiscale physical processes are important in modulating the strength and efficiency of the biological carbon pump, but the mechanisms and contributions of different physical forcings on mesopelagic sinking particle fluxes in the South China Sea (SCS) are still poorly known. Based on time series data from a sediment trap at approximately 1,000-m depth as well as upper layer physical and biogeochemical data, we have found that three discrete high-flux events in the northwestern SCS were driven by upwelling, aerosol deposition and the northeast monsoon. Together, the three events accounted for nearly 80% of the total mass flux and nearly 75% of the total particulate organic carbon flux. Each event contributed nearly equal to the total particulate organic carbon flux, but each also contributed its own unique biogeochemical overprint. Our findings confirm the importance of multiscale physical processes on SCS biogeochemistry and in particular highlight the roles of upwelling and aerosol deposition, which are as important as the northeast monsoon in modulating the strength of...

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Section: Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Enhancement of Mesopelagic Sinking Particle Fluxes Due to Upwelling, Aerosol Deposition, and Monsoonal Influences in the Northwestern South China Sea

Zhang

Xuan

et al. 2019

JGR Oceans

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“…Two 1D physical-biological models were constructed with one located in the northern SCS (116°E, 18°N; SEATS) and the other in the central SCS (114°E, 13°N; SCS2; Figure 1a). The two sites selected for modeling are located in the SCS deep basin, far from the continental shelf, with a bottom depth of >3,800 m. In these regions, horizontal advection and diffusion are thought to be less important for chlorophyll dynamics than vertical mixing (Du et al, 2017;Li et al, 2015;Lu et al, 2015). The physical model is based on the Princeton Ocean Model (Blumberg & Mellor, 1987).…”

Section: One-dimensional Coupled Modelmentioning

confidence: 99%

“…driven by local processes, especially on a seasonal time scale (e.g., Du et al, 2017;Li et al, 2015;Tseng et al, 2009). Previous 1D modeling studies conducted for the SCS basin have been able to simulate the vertical structures of biogeochemical variables reasonably well (e.g., Geng et al, 2012;Gong et al, 2014;Li et al, 2015).…”

Section: Uncertainties In the Modelmentioning

confidence: 99%

Evaluating the Roles of Wind‐ and Buoyancy Flux‐Induced Mixing on Phytoplankton Dynamics in the Northern and Central South China Sea

et al. 2019

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Observations from two Bio-Argo floats deployed in the northern and central South China Sea (SCS) show distinct seasonal patterns of vertical chlorophyll distribution. There is a permanent subsurface chlorophyll maximum (SCM) located between 60 and 80 m throughout the year and a weak seasonality of surface chlorophyll in the central SCS. In the northern SCS, the SCM shoals to the upper mixed layer in winter and surface phytoplankton shows a clear winter bloom pattern. The mechanism driving the spatial and seasonal differences in phytoplankton dynamics in the euphotic zone remains unclear. Here a coupled physical-biological model is developed and applied to the northern and central SCS. With model and satellite data, we show that the contrasting patterns in chlorophyll are induced by the spatial variability in winter mixing dynamics. In the northern SCS, the buoyancy flux-induced mixing plays a dominant role in controlling the seasonal variability of vertical nutrient transport and phytoplankton production, which leads to the peak of surface chlorophyll and the significant shoaling of the SCM in winter. In the central SCS, the intensity of the buoyancy flux is reduced and both buoyancy fluxand wind-induced mixing control the winter mixing dynamics. However, the combination of these two mixing processes is weaker than in the northern SCS and the vertical nutrient transport is limited to the layer above the SCM, resulting in the reduced seasonality of surface chlorophyll and the relatively stable SCM all year round in the central SCS.Plain Language Summary Both satellite and Bio-Argo floats show a significant increase of surface chlorophyll concentration in winter in the northern South China Sea (SCS) but a very weak seasonal change in the central SCS. We used a coupled physical-biological model to systematically study the mechanism driving these spatial and seasonal differences. The model can reasonably simulate the different chlorophyll distribution patterns identified by observations. We found that the buoyancy flux-induced mixing plays a dominant role in controlling the seasonal change of chlorophyll in the northern SCS. In the central SCS, both buoyancy fluxand wind-induced mixing control the winter mixing dynamics. However, the combination of these two mixing dynamics is not as strong as that in the northern SCS and the vertical nutrient transport is only limited to the layer above the SCM, resulting in the reduced seasonality of surface chlorophyll and the relatively stable SCM all year round in the central SCS.

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“…e). Although the temperature anomaly decreases by about 0.66°C at 50 m from El Niño to La Niña, the anomaly of ~ 1.33°C (~ 2.4 mmol m −3 of nutrient) in La Niña is still sufficient to induce phytoplankton growth when mixed into the euphotic zone, given the general oligotrophic condition at the surface in the NSCS (Du et al ). During El Niño, the MLD is about 13 m shallower, which may reduce the vertical transport efficiency of eddy‐induced anomaly.…”

Section: Resultsmentioning

confidence: 99%

On contributions by wind‐induced mixing and eddy pumping to interannual chlorophyll variability during different ENSO phases in the northern South China Sea

Xiu

Dai

Chai

et al. 2018

Limnology & Oceanography

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The chlorophyll in the northern South China Sea (NSCS) shows strong interannual variability between different phases of the El Niño‐Southern Oscillation (ENSO), primarily due to the influence from Kuroshio intrusion. Chlorophyll observations also reveal that significant year‐to‐year variation remains in the same ENSO phase, but its controlling mechanism is unknown. In this study, we examined driving mechanisms for such regional ecosystem variability on a year‐to‐year timescale. Using observational data and modeling results, we found that both cyclonic eddies (CEs) and wind‐induced mixing affect phytoplankton variability, but the former is the dominant factor regulating the interannual variability of chlorophyll during La Niña years, while the latter becomes the dominant one during El Niño years. The underlying mechanisms leading to the contrast in biological responses are attributable to changes in background nutricline depth and mixed‐layer depth (MLD) during different ENSO phases. During La Niña, both thermocline and nutricline are deepened in the NSCS. Thus, wind mixing is less effective in non‐eddy areas due to the deepened nutricline, while the CE‐induced subsurface nutrient anomaly associated with increased MLD is able to control the interannual variability of chlorophyll. During El Niño, wind‐induced mixing is more effective than CEs because the surface wind can influence a larger area.

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Diapycnal Fluxes of Nutrients in an Oligotrophic Oceanic Regime: The South China Sea

Cited by 75 publications

References 45 publications

Enhancement of Mesopelagic Sinking Particle Fluxes Due to Upwelling, Aerosol Deposition, and Monsoonal Influences in the Northwestern South China Sea

Enhancement of Mesopelagic Sinking Particle Fluxes Due to Upwelling, Aerosol Deposition, and Monsoonal Influences in the Northwestern South China Sea

Evaluating the Roles of Wind‐ and Buoyancy Flux‐Induced Mixing on Phytoplankton Dynamics in the Northern and Central South China Sea

On contributions by wind‐induced mixing and eddy pumping to interannual chlorophyll variability during different ENSO phases in the northern South China Sea

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