Phytoplankton growth and physiological responses to a plume front in the northern South China Sea

Abstract. Due to a strong river discharge during April–June 2016, a persistent salinity front, with freshwater flushing seaward on the surface but seawater moving landward at the bottom, was formed in the coastal waters west of the Pearl River Estuary (PRE) over the Northern South China Sea (NSCS) shelf. Hydrographic measurements revealed that the salinity front was influenced by both river plume and coastal upwelling. Shipboard nutrient-enrichment experiments with size-fractionation chlorophyll-a measurements were performed on both sides of the front as well as the front zone to diagnose the spatial variations of phytoplankton physiology across the frontal system. We also assessed the size-fractionated responses of phytoplankton to the treatment of plume water at the frontal zone and the seaside of the front. Biological impact of vertical mixing or upwelling was further examined by the response of surface phytoplankton to the addition of local bottom water. Our results suggested that there was a large variation of phytoplankton physiology on the seaside of the front driven by dynamic nutrient fluxes, although P-limitation was prevailing on the shore-side of the front and at the frontal zone. The spreading of plume water at the frontal zone would directly improve the growth of micro-phytoplankton, while nano- and pico-phytoplankton growths could become saturated at high percentages of plume water. Also, the mixing of bottom water would stimulate the growth of surface phytoplankton on both sides of the front by altering the surface N / P ratio closer to the Redfield stoichiometry. In summary, phytoplankton growth and physiology could be profoundly influenced by physical dynamics of the frontal system during the spring–summer of 2016.

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Phytoplankton response to a plume front in the northern South China Sea

Biogeosciences ◽

10.5194/bg-15-2551-2018 ◽

2018 ◽

Vol 15 (8) ◽

pp. 2551-2563 ◽

Cited By ~ 7

Author(s):

Qian P. Li ◽

Weiwen Zhou ◽

Yinchao Chen ◽

Zhengchao Wu

Keyword(s):

South China Sea ◽

South China ◽

Bottom Water ◽

Coastal Upwelling ◽

Frontal Zone ◽

Northern South China Sea ◽

River Estuary ◽

Frontal System ◽

China Sea ◽

Plume Water

Abstract. Due to a strong river discharge during April–June 2016, a persistent salinity front, with freshwater flushing seaward on the surface but seawater moving landward at the bottom, was formed in the coastal waters west of the Pearl River estuary (PRE) over the northern South China Sea (NSCS) shelf. Hydrographic measurements revealed that the salinity front was influenced by both the river plume and coastal upwelling. On shipboard nutrient-enrichment experiments with size-fractionation chlorophyll a measurements were taken on both sides of the front as well as in the frontal zone to diagnose the spatial variations of phytoplankton physiology across the frontal system. We also assessed the size-fractionated responses of phytoplankton to the treatment of plume water at the frontal zone and the sea side of the front. The biological impact of vertical mixing or upwelling was further examined by the response of surface phytoplankton to the addition of local bottom water. Our results suggested that there was a large variation in phytoplankton physiology on the sea side of the front, driven by dynamic nutrient fluxes, although P limitation was prevailing on the shore side of the front and at the frontal zone. The spreading of plume water at the frontal zone would directly improve the growth of microphytoplankton, while nano- and picophytoplankton growths could have become saturated at high percentages of plume water. Also, the mixing of bottom water would stimulate the growth of surface phytoplankton on both sides of the front by altering the surface N∕P ratio to make it closer to the Redfield stoichiometry. In summary, phytoplankton growth and physiology could be profoundly influenced by the physical dynamics in the frontal system during the spring–summer of 2016.

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A preliminary study on sediment records of possible typhoon in the northern South China Sea during the past 6500 yr

The Holocene ◽

10.1177/09596836211003229 ◽

2021 ◽

pp. 095968362110032

Author(s):

Pingyuan Li ◽

Mingkun Li ◽

Huayang Gan ◽

Zhen Xia

Keyword(s):

South China Sea ◽

South China ◽

Southern China ◽

Northern South China Sea ◽

River Estuary ◽

Pearl River Estuary ◽

Human Beings ◽

China Sea ◽

The Pearl River ◽

China Coast

Typhoon is an important meteorological phenomenon that affects the living and development of human beings on the southern China coast. However, there is still lack of clarity in the paleo-typhoon history and its influence on the evolution of the ancient human settlement environment since the mid-Holocene. Here, we identify six typhoon-like deposits from a core retrieved from the northern South China Sea shelf, close to the Pearl River Estuary, based on accelerated mass spectrometry 14C dating, grain size, and geochemistry. The sand fractions, CaO, Sr, SiO2/TiO2, and SiO2/Al2O3 were used to indicate the typhoon-like deposits. Results show that the ages with high-frequency typhoons are present ~200–300 cal yr BP, ~800–1000 cal yr BP, ~1500–1700 cal yr BP, ~2000–2100 cal yr BP, ~2400–2500 cal yr BP, and ~2700–3000 cal yr BP. Our results are comparable to the records from adjacent regions. Significantly, the vast tides occurred in the duration of ~2700–3000 cal yr BP in southern China, which probably caused the ancestors’ migration to the inland. Further studies are needed to deeply study the paleo-typhoon history in the southern China coast to verify our results.

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Seasonal and spatial comparisons of phytoplankton growth and mortality rates due to microzooplankton grazing in the northern South China Sea

Biogeosciences Discussions ◽

10.5194/bgd-9-16005-2012 ◽

2012 ◽

Vol 9 (11) ◽

pp. 16005-16032

Author(s):

B. Chen ◽

L. Zheng ◽

B. Huang ◽

S. Song ◽

H. Liu

Keyword(s):

South China Sea ◽

Mixed Layer ◽

South China ◽

Surface Waters ◽

Northern South China Sea ◽

Phytoplankton Growth ◽

China Sea ◽

Grazing Effect ◽

Basin Surface ◽

Microzooplankton Grazing

Abstract. We conducted a comprehensive investigation on the microzooplankton herbivory effect on phytoplankton in the northern South China Sea (SCS) using the seawater dilution technique at surface and deep chlorophyll maximum (DCM) layers in two cruises (July–August of 2009 and January of 2010). We compared vertical (surface vs. DCM), spatial (onshore vs. offshore), and seasonal (summer vs. winter) differences of phytoplankton growth (μ0) and microzooplankton grazing rates (m). During summer, both μ0 and m were significantly higher at the surface than at the layer of DCM, which was below the mixed layer. During winter, surface μ0 was significantly higher than at DCM, while m was not significantly different between the two layers, both of which were contained within the mixed layer. Surface μ0 was, on average, significantly higher in summer than in winter; while average surface m was not different between the two seasons. There were no significant cross-shelf trends of μ0 in summer or winter surface waters. In surface waters, μ0 was not correlated with ambient nitrate concentrations and the effect of nutrient enrichment on phytoplankton growth was not pronounced. There was a decreasing trend of m from shelf to basin surface waters in summer, but not in winter. Microzooplankton grazing effect on phytoplankton (m/μ0) did not increase with distance offshore, suggesting that the importance of microzooplankton as grazers of phytoplankton may not decrease in onshore waters. On average, microzooplankton grazed 73% and 65% of the daily primary production in summer and winter, respectively.

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