Sources of new nitrogen in the Vietnamese upwelling region of the South China Sea

Bombar, Deniz; Dippner, Joachim W.; Doan, Hai Nhu; Nguyen-Ngoc, Lam; Liskow, Iris; Loick‐Wilde, Natalie; Voß, Maren

doi:10.1029/2008jc005154

Cited by 36 publications

(28 citation statements)

References 66 publications

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“…However, the nitracline depth of the central NSCS during the summer was about 60 m, which was only 10–20 m shallower than that in the KC (Figures a and e). High rates of N 2 ‐fixation with nitracline shallower than 50 m had been observed in the offshore extension zones of the Vietnamese upwelling in the southern South China Sea [ Bombar et al ., ]. Our results suggested that the low diazotroph biomass and nitrogen fixation rate in the central NSCS was caused by its high nitrate fluxes from subsurface (Figure ), which have supplied plenty of nutrients for new production and thus the energy‐costing N 2 ‐fixation became disadvantaged when diazotrophs competing for nutrients with the fast growing nondiazotroph phytoplankton.…”

Section: Resultsmentioning

confidence: 99%

Modeling long‐term change of planktonic ecosystems in the northern South China Sea and the upstream Kuroshio Current

Wang

Dong

et al. 2015

JGR Oceans

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Field studies suggested that the biogeochemical settings and community structures are substantial different between the central Northern South China Sea (NSCS) and the upstream Kuroshio Current (KC). In particular, the water column of KC is characterized by substantially lower nutrients and productivity but higher Trichodesmium abundance and nitrogen fixation compared to the NSCS. The mechanism driving the difference of the two marine ecosystems, however, remains inadequately understood. Here, a onedimensional biogeochemical model was developed to simulate the long-term variability of lower-trophic planktonic ecosystem for two pelagic stations in the NSCS and the KC near the Luzon Strait. The physical model included the vertical mixing driven by air-sea interaction and the Ekman pumping induced by wind stress curl. The biological model was constructed by modifying a nitrogen-based NPZD model with the incorporation of phosphorus cycle and diazotroph nitrogen fixation. After validation by several field data sets, the model was used to study the impact of long-term physical forcing on ecosystem variability in the two distinct stations. Our results suggested that nutrient transport above nitracline during summer was largely controlled by vertical turbulent mixing, while Ekman pumping was important for nutrient transport below the nitracline. Our results also indicated that diazotroph community structure and N 2 fixation in the NSCS and the KC could be strongly influenced by physical processes through the impacts on vertical nutrient fluxes. The disadvantage of diazotroph in the NSCS in compared to the KC during the summer could be attributed to its high nitrate fluxes from subsurface leading to outcompete of diazotrophs by faster growing nondiazotroph phytoplankton.

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Section: Resultsmentioning

confidence: 99%

Modeling long‐term change of planktonic ecosystems in the northern South China Sea and the upstream Kuroshio Current

Wang

Dong

et al. 2015

JGR Oceans

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“…In the framework of VG research cooperation since 2003, seven cruises with different research vessels took place during different seasons. [ Bombar et al , , , Dippner et al , , , Dippner and Loick‐Wilde , , Doan‐Nhu et al , , Loick et al , , Voss et al , ]. The overall objective of these expeditions was the understanding of the nitrogen cycle in an upwelling and river influenced area during monsoon and inter‐monsoon.…”

Section: Observationsmentioning

confidence: 99%

Comment on “Current separation and upwelling over the southeast shelf of Vietnam in the South China Sea” by Chen et al.

et al. 2013

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[1] In a recent paper, Chen et al. (2012) showed that the offshore current in front of the Vietnamese upwelling area in the South China Sea (SCS) is caused by an encounter of southward buoyancy-driven coastal current and tidal rectified currents from the southwest. These findings seem not in agreement with in-situ observations. The mechanism for the formation of the offshore current has its origin in the inter-annual variability of atmospheric forcing. El Niño Southern Oscillation events modulate the northern position of Inter-Tropical Convergence Zone and the intensity of both, SW monsoon and upwelling. Strong upwelling influences the spatial distribution of characteristic water masses which results in a blocking of the near coastal northward propagation of the plume of River Mekong and the formation of an offshore current.

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“…It stands out from the SCS sea surface temperature (SST) map in August as a large area with waters 1–2 °C cooler than the surrounding areas (Figure ). The SVU is associated with a high bio‐productivity (Bombar et al, ; Loick et al, ; Lu et al, ; Tang et al, ) and is a major area for the halieutic industry in Vietnam (Levadoux et al, ). It can also cause blooms of haptophyte algae, which are harmful for local coastal ecosystems and aquaculture (Dippner et al, ; Hai et al, ).…”

Section: Introductionmentioning

confidence: 99%

Contributions of Wind, Ocean Intrinsic Variability, and ENSO to the Interannual Variability of the South Vietnam Upwelling: A Modeling Study

Herrmann

Morrow

et al. 2019

JGR Oceans

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The summer South Vietnam Upwelling (SVU) is a major component of the South China Sea circulation where it also influences ecosystems. Here we revisit the existing knowledge of the SVU interannual variability. Based on a set of 15-year eddy-resolving sensitivity simulations, we quantify the respective contributions from different factors (atmospheric, river, and oceanic forcings; ocean intrinsic variability; and El Niño Southern Oscillation) to this interannual variability and explore the underlying mechanisms. Our sea surface temperature upwelling indices allow us to quantify the strong SVU interannual variability in terms of strength and spatial distribution. Strong SVU years are offshore dominant with SVU centers located within 11-12°N and 110-112°E, whereas weak SVU years are coastal dominant with SVU centers located near the coast and spanning a larger 10-14°N latitude range. Our study confirms the leading influence of the summer wind and further reveals that coastal SVU variability is related to the variability of the eastward jet that develops from the coast, whereas offshore SVU variability is strongly driven by the spatiotemporal collocation of wind stress curl with cyclonic eddies. Ocean intrinsic variability, and to a lesser extent perturbations induced by river discharge and lateral oceanic conditions, strongly triggers interannual variability of background eddy circulation, thus of the SVU. El Niño Southern Oscillation influences the SVU mainly through its direct influence on summer winds. Plain Language SummaryThe coastal seas along Southern Vietnam are rich in nutrients during the summer, and fish find an abundant supply of food in the region. The summer wind blows the surface waters offshore and pumps up deep, cold, nutrient-rich water in this "upwelling" region, allowing plankton to thrive at the surface where sunlight is available. Three factors strengthen the upwelling strength: stronger wind speed, wind blowing counterclockwise, and the presence of counterclockwise rotating eddies, which all contribute to pump up deep, nutrient-rich waters to the surface. Based on numerical modeling studies of ocean circulation, we found that when those three factors occur simultaneously, they pump up much more deep water than each of them alone. On the other hand, wind blowing clockwise or clockwise rotating eddies tend to pump water downward. While it is possible to predict upwelling produced by the wind, the ocean eddies whose radius ranges from tens to hundreds of kilometers move more randomly, and it is difficult to predict their contribution to the upwelling strength. We also found that El Niño weakens the wind and favors clockwise eddy circulation in the upwelling area. Thus, in strong El Niño years, upwelling is weaker in the seas off Southern Vietnam.

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Sources of new nitrogen in the Vietnamese upwelling region of the South China Sea

Cited by 36 publications

References 66 publications

Modeling long‐term change of planktonic ecosystems in the northern South China Sea and the upstream Kuroshio Current

Modeling long‐term change of planktonic ecosystems in the northern South China Sea and the upstream Kuroshio Current

Comment on “Current separation and upwelling over the southeast shelf of Vietnam in the South China Sea” by Chen et al.

Contributions of Wind, Ocean Intrinsic Variability, and ENSO to the Interannual Variability of the South Vietnam Upwelling: A Modeling Study

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