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

Geng, Bingxu; Xiu, Peng; Shu, Chan; Zhang, Wenzhou; Chai, Fei; Li, Shiyu; Wang, Dongxiao

doi:10.1029/2018jc014170

Cited by 17 publications

(17 citation statements)

References 49 publications

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“…Coastal hypoxia has been increasingly exacerbated near the mouths of large rivers as a consequence of anthropogenic nutrient inputs (Gilbert et al, 2010;Rabalais et al, 2014;Breitburg et al, 2018). The rise in the size, intensity and frequency of eutrophication-induced hypoxia exposes coastal oceans to a higher risk of elevated N 2 O and CH 4 production; enhanced ocean acidification; and associated reductions in biodiversity, shifts in community structures, and negative impacts on food security and livelihoods (Diaz and Rosenberg, 2008;Vaquer-Sunyer and Duarte, 2008;Naqvi et al, 2010).…”

Section: Introductionmentioning

confidence: 99%

Destruction and reinstatement of coastal hypoxia in the South China Sea off the Pearl River estuary

Zhao

Uthaipan

et al. 2021

Biogeosciences

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Abstract. We examined the evolution of intermittent hypoxia off the Pearl River estuary based on three cruise legs conducted in July 2018: one during severe hypoxic conditions before the passage of a typhoon and two post-typhoon legs showing destruction of the hypoxia and its reinstatement. The lowest ever recorded regional dissolved oxygen (DO) concentration of 3.5 µmol kg−1 (∼ 0.1 mg L−1) was observed in bottom waters during leg 1, with an ∼ 660 km2 area experiencing hypoxic conditions (DO < 63 µmol kg−1). Hypoxia was completely destroyed by the typhoon passage but was quickly restored ∼ 6 d later, resulting primarily from high biochemical oxygen consumption in bottom waters that averaged 14.6 ± 4.8 µmol O2 kg−1 d−1. The shoreward intrusion of offshore subsurface waters contributed to an additional 8.6 ± 1.7 % of oxygen loss during the reinstatement of hypoxia. Freshwater inputs suppressed wind-driven turbulent mixing, stabilizing the water column and facilitating the hypoxia formation. The rapid reinstatement of summer hypoxia has a shorter timescale than the water residence time, which is however comparable with that of its initial disturbance from frequent tropical cyclones that occur throughout the wet season. This has important implications for better understanding the intermittent nature of hypoxia and predicting coastal hypoxia in a changing climate.

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Section: Introductionmentioning

confidence: 99%

Destruction and reinstatement of coastal hypoxia in the South China Sea off the Pearl River estuary

Zhao

Uthaipan

et al. 2021

Biogeosciences

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“…The South China Sea (SCS; Figure 1a), located in the (sub)tropical western North Pacific Ocean, is one of the world's largest marginal seas (Geng et al, 2019). Although it receives input from the Pearl and Gaoping Rivers in the north and the Mekong River in the south, the SCS is an oligotrophic ocean‐dominated marginal sea with a deep basin and a permanently stratified central gyre (Dai et al, 2013; Gong et al, 1992).…”

Section: Introductionmentioning

confidence: 99%

Laterally Transported Particles From Margins Serve as a Major Carbon and Energy Source for Dark Ocean Ecosystems

Shen

Jiao

Dai

et al. 2020

Geophysical Research Letters

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Deep ocean microorganisms consume particulate organic matter that is produced in the surface ocean and exported to deeper depths. Such consumption not only enriches inorganic carbon in the deep ocean but also transforms organic carbon into recalcitrant forms, creating an alternative type of carbon sequestration. However, estimates of deep microbial carbon demand substantially exceed the available particulate organic carbon exported from the euphotic zone, resulting in an unbalanced dark ocean carbon budget. Here, we combined field-based microbial activity parameters, integrated multiyear particle export flux data, sinking particle fluxes measured by sediment traps, and optical data from Biogeochemical-Argo floats to quantify the main sources of organic carbon to the dark ocean. Laterally transported particles (including sinking and suspended particles) serve as a major energy source, which directly provide organic carbon and enhance new organic carbon production by dark carbon fixation, reconciling the mismatch in the regional carbon budget. Plain Language Summary Particulate organic matter, produced by phytoplankton in the upper ocean, can sink through the water column and act as a source of organic matter to the deep ocean. These particles are decomposed to carbon dioxide by microorganisms, resulting in dissolved inorganic carbon and organic carbon resistant to decomposition in the deeper ocean. This process controls the biological sequestration of CO 2 by the oceans. However, there is an imbalance between the low amount of organic carbon exported from the photic zone and the high microbial demand for carbon in the dark ocean. We attempted to explain how the deep ocean carbon and energy supply can meet the microbial metabolic demand. Four main organic carbon sources were measured and quantified in the South China Sea: particles that come from the photic zone, particles that move laterally through the ocean, dark carbon fixation, and dissolved organic carbon. We found that laterally transported particles from the surrounding margins provide a direct source of organic carbon and also allow for much new organic carbon production through dark carbon fixation. These particles, which provide a major energy source to dark ocean ecosystems, help resolve the mismatch in the regional carbon budget.

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“…Oceanographic processes cause strong spatiotemporal variations of physical and biogeochemical factors, forming sharp gradients between rivers and the ocean, which eventually determine phytoplankton distribution in terms of biomass and community composition (Cullen et al, 2002;Margalef, 1978). Many studies have focused on phytoplankton dynamics in systems that are mainly controlled by riverine inputs, including the East China Sea (eg., Chen et al, 2003;Gao & Song, 2005;Zhou et al, 2017;Zhu et al, 2009), Baltic Sea (eg., Lips et al, 2014;Stipa, 2004;Tamminen & Andersen, 2007;Wasmund et al, 1998), Chesapeake Bay (eg., Adolf et al, 2006;Harding, 1994;Jiang & Xia, 2017), northern South China Sea (eg., Chen et al, 2004;Geng et al, 2012Geng et al, , 2019Pan et al, 2015), and northern Gulf of Mexico (eg., Bargu et al, 2016;Camacho et al, 2014;Lohrenz et al, 1997Lohrenz et al, , 2008. The mechanisms controlling the algal blooms can be generalized as physical and biological controls.…”

Section: Introductionmentioning

confidence: 99%

Phytoplankton Blooms off a High Turbidity Estuary: A Case Study in the Changjiang River Estuary

Wang

Lin

et al. 2019

JGR Oceans

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The occurrence of phytoplankton blooms in estuarine and coastal waters is codetermined by the export of fluvial nutrients and other water properties such as turbidity. In this study, the Changjiang River Estuary was used as an example to investigate the intrinsic link between river plume dynamics, riverine nutrient loading, suspended sediment concentration, and phytoplankton blooms with a coupled hydrodynamic-sediment-ecosystem numerical model. Suspended sediment concentration from the sediment module was used to parameterize light attenuation in waters, which, in association with river plume dynamics, was found to impact phytoplankton distribution. Data that was collected in situ, in addition to satellite data for chlorophyll, nutrients, and suspended sediments, were used to validate the model, which performed well. The surface high chlorophyll centers exhibited a patch-like pattern from the northeast to the south off the Changjiang River mouth. The high chlorophyll concentration within the river plume was mainly determined by riverine nutrient exports, and potential phosphate limitation occurred away from the river mouth. The chlorophyll concentration decreased dramatically shoreward of the sediment front, which was controlled by the bottom river plume front. The bottom plume front was an intrinsic feature of the Changjiang River plume and similar river plume systems, which set a boundary separating the well-mixed (turbid) nearshore waters and stratified (clear) offshore waters. Without considering the sediment shading effect, the model yielded an unrealistic chlorophyll distribution with artificially high values in the turbid area. This indicated that light attenuation was a key factor limiting phytoplankton blooms in turbid river estuaries.Plain Language Summary In estuaries and coastal waters, the aquatic environment is affected by both riverine nutrient input and water properties such as turbidity. The associated river plume may play an essential role in controlling water properties, thus influencing the aquatic environment such as the algal blooms. In the current study, a well-validated hydrodynamic-sediment-ecosystem model was used to simulate phytoplankton blooms and the dynamic link with the Changjiang River plume. The results showed that the surface suspended sediment front was of vital importance in determining the shoreward boundary of the phytoplankton bloom area. Light attenuation due to high turbidity became a major factor limiting phytoplankton blooms in turbid nearshore waters. In environments with a strong tidal influence, the surface suspended sediment front was closely related to the bottom river plume front, which gave rise to differences in water stabilization and thus resulted in turbid conditions on either side. The results of this study provided a good reference for understanding the phytoplankton distribution characteristics in estuaries with high turbidity.

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

Cited by 17 publications

References 49 publications

Destruction and reinstatement of coastal hypoxia in the South China Sea off the Pearl River estuary

Destruction and reinstatement of coastal hypoxia in the South China Sea off the Pearl River estuary

Laterally Transported Particles From Margins Serve as a Major Carbon and Energy Source for Dark Ocean Ecosystems

Phytoplankton Blooms off a High Turbidity Estuary: A Case Study in the Changjiang River Estuary

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