Characteristics of the surface mixed layer depths in the northern South China Sea in spring

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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Ocean Response to Successive Typhoons Sarika and Haima (2016) in the Northern South China Sea

10.5194/egusphere-egu2020-6882 ◽

2020 ◽

Author(s):

Han Zhang

Keyword(s):

South China Sea ◽

Mixed Layer ◽

South China ◽

Model Simulation ◽

Heat Budget ◽

Northern South China Sea ◽

Heat Content ◽

Sea Surface ◽

Surface Cooling ◽

China Sea

<p>Tropical cyclones (TCs) are natural disasters for coastal regions. TCs with maximum wind speeds higher than 32.7 m/s in the north-western Pacific are referred to as typhoons. Typhoons Sarika and Haima successively passed our moored observation array in the northern South China Sea in 2016. Based on the satellite data, the winds (clouds and rainfall) biased to the right (left) sides of the typhoon tracks. Sarika and Haima cooled the sea surface ~4 and ~2 &#176;C and increased the salinity ~1.2 and ~0.6 psu, respectively. The maximum sea surface cooling occurred nearly one day after the two typhoons. Station 2 (S2) was on left side of Sarika&#8217;s track and right side of Haima&#8217;s track, which is studied because its data was complete. Strong near-inertial currents from the ocean surface toward the bottom were generated at S2, with a maximum mixed-layer speed of ~80 cm/s. The current spectrum also shows weak signal at twice the inertial frequency (2f). Sarika deepened the mixed layer, cooled the sea surface, but warmed the subsurface by ~1 &#176;C. Haima subsequently pushed the subsurface warming anomaly into deeper ocean, causing a temperature increase of ~1.8 &#176;C therein. Sarika and Haima successively increased the heat content anomaly upper than 160 m at S2 to ~50 and ~100 m&#176;C, respectively. Model simulation of the two typhoons shows that mixing and horizontal advection caused surface ocean cooling, mixing and downwelling caused subsurface warming, while downwelling warmed the deeper ocean. It indicates that Sarika and Haima sequentially modulated warm water into deeper ocean and influenced internal ocean heat budget. Upper ocean salinity response was similar to temperature, except that rainfall refreshed sea surface and caused a successive salinity decrease of ~0.03 and ~0.1 psu during the two typhoons, changing &#160;the positive subsurface salinity anomaly to negative.</p>

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Upper vertical structures and mixed layer depth in the shelf of the northern South China Sea

Continental Shelf Research ◽

10.1016/j.csr.2019.01.004 ◽

2019 ◽

Vol 174 ◽

pp. 26-34 ◽

Cited By ~ 1

Author(s):

Chunhua Qiu ◽

Dan Huo ◽

Changjian Liu ◽

Yongsheng Cui ◽

Danyi Su ◽

...

Keyword(s):

South China Sea ◽

Mixed Layer ◽

South China ◽

Mixed Layer Depth ◽

Northern South China Sea ◽

Layer Depth ◽

China Sea

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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 ◽

10.5194/bg-10-2775-2013 ◽

2013 ◽

Vol 10 (4) ◽

pp. 2775-2785 ◽

Cited By ~ 27

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 on 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 DCM layer, which was below the mixed layer. During winter, surface μ0 was significantly higher than at the DCM, while m was not significantly different between the two layers, both of which were 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 cross-shelf gradients 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) was relatively small in the summer basin waters, indicating a decoupling of microzooplankton grazing and phytoplankton growth at this time. On average, microzooplankton grazed 73% and 65% of the daily primary production in summer and winter, respectively.

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