scholarly journals Spatiotemporal Distributions of Ocean Color Elements in Response to Tropical Cyclone: A Case Study of Typhoon Mangkhut (2018) Past over the Northern South China Sea

2021 ◽  
Vol 13 (4) ◽  
pp. 687
Author(s):  
Junyi Li ◽  
Quanan Zheng ◽  
Min Li ◽  
Qiang Li ◽  
Lingling Xie
Keyword(s):  
Tropical Cyclone ◽  
South China Sea ◽  
South China ◽  
Northern South China Sea ◽  
Ocean Color ◽  
Shelf Area ◽  
Offshore Area ◽  
Chl A ◽  
The Mean ◽  
Basin Area

The ocean color elements refer to total suspended sediment (TSS) and chlorophyll-a (Chl-a), which are important parameters for the marine ecological environment. This study aims to examine the behavior of ocean color elements in response to a tropical cyclone in the case of typhoon Mangkhut (2018), which passed over the northern South China Sea (NSCS) on 16 September 2018, using satellite multi-sensor observations, Argo float profiles, and tidal gauge sea level data. The results indicate that typhoon Mangkhut (2018) resulted in TSS and Chl-a concentrations increasing, with the spatial and timing behavior different in the offshore, shelf, and basin areas. In the offshore area from the coast to isobath 50 m, the mean TSS concentration, i.e., CTSS, reached 13.9 mg/L on 18 September 2018, two days after typhoon landfall, against about 3.5 mg/L before typhoon landfall. In the shelf area with depths from 50 m to 100 m, the mean CTSS reached 2.5 mg/L, against about 0.8 mg/L before typhoon landfall. In the basin area with depths of 100 m and beyond, the mean CTSS had only a little fluctuation. On the other hand, in the offshore area, the mean Chl-a concentration, i.e., CChl-a, was 7.3 mg/m3 on 21 September, five days after typhoon landfall, against 2.4 mg/m3 as the monthly mean value. Furthermore, TSS concentrations favorable for Chl-a bloom range from 6 to 7 mg/L in this area. In the shelf area, the mean CChl-a increased from 0.2 mg/m3 to 0.6 mg/m3 in two days. In the basin area, the CChl-a increased from 0.1 mg/m3 to 0.2 mg/m3 during typhoon passage. Concurrent dynamic condition analysis results indicate that, in the offshore area, typhoon-induced solitary continental waves may play a dominant role in determining the spatial distribution features of the TSS originating from the Pearl River runoff. The Chl-a bloom delayed rather than concurrently occurred with the terrigenous nutrient peak, which is attributed to the nonlinear relation between CChl-a and CTSS. In the shelf and basin areas, typhoon-enhanced vertical mixing and upwelling may play dominant roles in determining the spatiotemporal behavior of the TSS and the Chl-a.

scholarly journals Response of Total Suspended Sediment and Chlorophyll-a Concentration to Late Autumn Typhoon Events in the Northwestern South China Sea

2021 ◽  
Vol 13 (15) ◽  
pp. 2863
Author(s):  
Junyi Li ◽  
Huiyuan Zheng ◽  
Lingling Xie ◽  
Quanan Zheng ◽  
Zheng Ling ◽  
...  
Keyword(s):  
South China Sea ◽  
Continental Shelf ◽  
Suspended Sediment ◽  
Chlorophyll A ◽  
South China ◽  
Total Suspended Sediment ◽  
Offshore Area ◽  
Chl A ◽  
Late Autumn ◽  
China Sea

Strong typhoon winds enhance turbulent mixing, which induces sediment to resuspend and to promote chlorophyll-a (Chl-a) blooms in the continental shelf areas. In this study, we find limited Chl-a responses to three late autumn typhoons (typhoon Nesat, Mujigae and Khanun) in the northwestern South China Sea (NWSCS) using satellite observations. In climatology, the Chl-a and total suspended sediment (TSS) concentrations are high all year round with higher value in autumn in the offshore area of the NWSCS. After the typhoon passage, the Chl-a concentration increases slightly (23%), while even TSS enhances by 280% on the wide continental shelf of the NWSCS. However, in the southern area, located approximately 100 km from the typhoon tracks, both TSS and Chl-a concentrations increase 160% and 150% after typhoon passage, respectively. In the deeper area, the increased TSS concentration is responsible for the considerable increase of the Chl-a. An empirical analysis is applied to the data, which reveals the TSS and Chl-a processes during typhoon events. The results of this study suggest a different mechanism for Chl-a concentration increase and thus contribute toward further evaluation of typhoon-induced biological responses.

Holocene changes in biome size and tropical cyclone activity around the Northern South China Sea

2019 ◽  
Vol 215 ◽  
pp. 45-63 ◽  
Author(s):  
L.A. Contreras-Rosales ◽  
T. Jennerjahn ◽  
S. Steinke ◽  
M. Mohtadi ◽  
E. Schefuß
Keyword(s):  
Tropical Cyclone ◽  
South China Sea ◽  
South China ◽  
Northern South China Sea ◽  
Tropical Cyclone Activity ◽  
Cyclone Activity ◽  
China Sea

scholarly journals Distinct bacterial-production–DOC–primary-production relationships and implications for biogenic C cycling in the South China Sea shelf

2014 ◽  
Vol 11 (1) ◽  
pp. 147-156 ◽  
Author(s):  
C.-C. Lai ◽  
Y.-W. Fu ◽  
H.-B. Liu ◽  
H.-Y. Kuo ◽  
K.-W. Wang ◽  
...  
Keyword(s):  
South China Sea ◽  
Primary Production ◽  
South China ◽  
Bacterial Production ◽  
Northern South China Sea ◽  
Outer Shelf ◽  
Inorganic Nutrient ◽  
Shelf Area ◽  
China Sea ◽  
Spatio Temporal

Abstract. Based on two summer spatio-temporal data sets obtained from the northern South China Sea shelf and basin, this study reveals contrasting relationships among bacterial production (BP), dissolved organic (DOC) and primary production (PP) in the transition zone from the neritic to the oceanic regions. Inside the mid-shelf (bottom depth <100 m), where inorganic nutrient supplies from river discharge and internal waves were potentially abundant, BP, DOC and PP were positively intercorrelated, whereas these three measurements became uncorrelated in the oligotrophic outer shelf and slope. We suggest that the availability of limiting minerals could affect the couplings/decouplings between the source (i.e. phytoplankton) and sink (i.e. bacteria) of organic carbon, and thus DOC dynamics. DOC turnover times were homogeneously low (37–60 days) inside the mid-shelf area and then increased significantly to values >100 days in the outer shelf, indicating that riverine (Pearl River) DOC might be more labile. The actual mechanism for this is unknown, but might relate to higher inorganic nutrient supply from river/terrestrial sources. The positive correlation of the BP / PP ratios vs. phosphate (and nitrate) concentrations in the inner shelf implies that if anthropogenic mineral loading keeps increasing in the foreseeable future, the near-shore zone may become more heterotrophic, rendering the system a stronger source of CO2.

scholarly journals The Influence of Turbulent Mixing on the Subsurface Chlorophyll Maximum Layer in the Northern South China Sea

2020 ◽  
Author(s):  
Chenjing Shang ◽  
Changrong Liang ◽  
Guiying Chen ◽  
Yongli Gao
Keyword(s):  
South China Sea ◽  
Water Column ◽  
South China ◽  
Turbulent Mixing ◽  
Northern South China Sea ◽  
Luzon Strait ◽  
Nutrient Fluxes ◽  
Chl A ◽  
China Sea ◽  
Subsurface Chlorophyll Maximum

Abstract. We present observations from deployments of a turbulent microstructure instrument and a CTD package in the northern South China Sea from April to May 2010. From these we determined the turbulent mixing (dissipation rate ε and diapycnal diffusivity κ), nutrients (phosphate, nitrate, and nitrite), nutrient fluxes, and chlorophyll a (Chl-a) in two transects (A and B). Transect A was located in region far away from the Luzon Strait where turbulent mixing in the upper 100 m was weak (κ~10−6–10−4 m2 s−1). Transect B was located in region near the Luzon Strait where the turbulent mixing in the upper 100 m was strong (κ~10−5–10−3 m2 s−1) due to the influence of the internal waves originating from the Luzon strait and the water intrusion from the western Pacific. In both transects, there was a thin subsurface chlorophyll maximum layer (SCML) (0.3–0.7 mg m−3) nested in the water column between ~50 and 100 m. The observations indicate that effects of turbulent mixing on the distributions of nutrient and Chl-a were different in different transects. In transect with weak turbulent mixing, nutrient fluxes induced by turbulent mixing transported nutrients to the SCML but not to the upper water. Nutrients were sufficient to maintain a local SCML phytoplankton population and the SCML remained compact. In transect with strong turbulent mixing, nutrient fluxes induced by turbulent mixing transported nutrients not only to the SCML but also to the upper water, which scatters the nutrients in the water column, and weakens and diffuses the SCML.

scholarly journals Photosynthetic Characteristics of Smaller and Larger Cell Size-Fractioned Phytoplankton Assemblies in the Daya Bay, Northern South China Sea

2021 ◽  
Vol 10 (1) ◽  
pp. 16
Author(s):  
Guangming Mai ◽  
Xingyu Song ◽  
Xiaomin Xia ◽  
Zengling Ma ◽  
Yehui Tan ◽  
...  
Keyword(s):  
Solar Radiation ◽  
South China Sea ◽  
Cell Size ◽  
South China ◽  
Northern South China Sea ◽  
Daya Bay ◽  
Cell Assembly ◽  
Ps Ii ◽  
Chl A ◽  
Change Pattern

Cell size of phytoplankton is known to influence their physiologies and, consequently, marine primary production. To characterize the cell size-dependent photophysiology of phytoplankton, we comparably explored the photosynthetic characteristics of piconano- (<20 µm) and micro-phytoplankton cell assemblies (>20 µm) in the Daya Bay, northern South China Sea, using a 36-h in situ high-temporal-resolution experiment. During the experimental periods, the phytoplankton biomass (Chl a) in the surface water ranged from 0.92 to 5.13 μg L−1, which was lower than that in bottom layer (i.e., 1.83–6.84 μg L−1). Piconano-Chl a accounted for 72% (mean value) of the total Chl a, with no significant difference between the surface and bottom layers. The maximum photochemical quantum yield (FV/FM) of Photosystem II (PS II) and functional absorption cross-section of PS II photochemistry (σPS II) of both piconano- and micro-cells assemblies varied inversely with solar radiation, but this occurred to a lesser extent in the former than in the latter ones. The σPS II of piconano- and micro-cell assemblies showed a similar change pattern to the FV/FM in daytime, but not in nighttime. Moreover, the fluorescence light curve (FLC)-derived light utilization efficiency (α) displayed the same daily change pattern as the FV/FM, and the saturation irradiance (EK) and maximal rETR (rETRmax) mirrored the change in the solar radiation. The FV/FM and σPS II of the piconano-cells were higher than their micro-counterparts under high solar light; while the EK and rETRmax were lower, no matter in what light regimes. In addition, our results indicate that the FV/FM of the micro-cell assembly varied quicker in regard to Chl a change than that of the piconano-cell assembly, indicating the larger phytoplankton cells are more suitable to grow than the smaller ones in the Daya Bay through timely modulating the PS II activity.

scholarly journals Poleward Propagation of Typhoon-Induced Near-Inertial Waves in the Northern South China Sea

2021 ◽  
Vol 8 ◽  
Author(s):  
Ruhui Huang ◽  
Xiaohui Xie ◽  
Jianyu Hu ◽  
Zhenyu Sun
Keyword(s):  
South China Sea ◽  
South China ◽  
Northern South China Sea ◽  
Subsurface Layer ◽  
Inertial Waves ◽  
Background Flow ◽  
China Sea ◽  
Short Period ◽  
The Mean ◽  
Baroclinic Modes

One of the main responses of the ocean to typhoons is the generation of near-inertial waves (NIWs), whose intrinsic frequency is close to the local inertial frequency. Based on the mooring observations, we carefully investigated the spatial–temporal variations in NIWs in the northern South China Sea (SCS) after Typhoon “Haima,” which passed through the northern SCS from October 20 to 21, 2016, with its track parallel to the mooring array on its northeast side. Moorings in different locations responded differently to this typhoon, with stronger NIWs found on the continental slope to the shelf break and relatively weak NIWs found on the shallow continental shelf. Strong NIWs appeared twice within a short period and showed different characteristics and frequencies. The first NIWs were generated locally with blue-shifted (super-inertial) frequencies. These initial NIWs were dominated by the first three baroclinic modes and rapidly weakened due to their propagation away and local dissipation. However, the second NIWs mainly consisted of higher baroclinic modes with red-shifted (sub-inertial) frequencies. The analysis of the mean background flow revealed that these red-shifted NIWs were excited at low latitudes, and subsequently advected by the poleward background flow to moorings whose latitudes were higher than their critical latitudes. Higher-mode (n &gt; 3) NIWs were more easily carried away by mean background flow, and, at the same time, high-mode NIWs propagated downward to the subsurface layer, leading to the significant elevation of velocity shear therein. Given these findings, the mean background flow may provide an important route to redistributing the energy of the upper ocean imported from typhoons.

scholarly journals Using TPI to Map Spatial and Temporal Variations of Significant Coastal Upwelling in the Northern South China Sea

2021 ◽  
Vol 13 (6) ◽  
pp. 1065 ◽  
Author(s):  
Weian Shi ◽  
Zhi Huang ◽  
Jianyu Hu
Keyword(s):  
South China Sea ◽  
South China ◽  
Coastal Upwelling ◽  
Northern South China Sea ◽  
River Estuary ◽  
Temporal Variations ◽  
Mapping Method ◽  
Chl A ◽  
China Sea ◽  
Influence Area

Based on Himawari-8 Sea Surface Temperature (SST) data and the semi-automatic Topographic Position Index (TPI)-based mapping method, this study maps the significant coastal upwelling in the northern South China Sea (NSCS). The results show that the Minnan coastal upwelling mainly occurs within 100 km off the south coast of Fujian; the Yuedong coastal upwelling appears to the east of Pearl River Estuary, limited to the area shallower than 40 m; and the Qiongdong coastal upwelling occurs most frequently in the area shallower than 75 m off the east coast of Hainan Island. Based on the results, this paper quantitatively describes the temporal and spatial variations of upwelling duration, influence area, upwelling SST anomaly, and chlorophyll-a (Chl-a) increase. Different coastal upwelling regions in the NSCS are significantly different in characteristics. The Qiongdong coastal upwelling has the longest duration and occurs most frequently, the Yuedong coastal upwelling has the largest influence area and Chl-a increase, and the Minnan coastal upwelling is quite strong in the NSCS.

scholarly journals Unusual Warming in the Coastal Region of Northern South China Sea and Its Impact on the Sudden Intensification of Tropical Cyclone Tembin (2012)

2014 ◽  
Vol 2014 ◽  
pp. 1-7 ◽  
Author(s):  
Zhe-Wen Zheng
Keyword(s):  
Tropical Cyclone ◽  
South China Sea ◽  
South China ◽  
Northern South China Sea ◽  
Lower Boundary ◽  
Coastal Region ◽  
Wave Radiation ◽  
Time Interval ◽  
Lower Boundary Condition ◽  
China Sea

Tropical cyclone Tembin (2012) passed twice and made landfall over south tip of Taiwan in August 2012. During its passage, an unusual sea surface warming was generated at22.5∘N,117∘Ein the coastal region of northern South China Sea. Subsequently, Tembin passed over this extreme warming region and its intensity was enhanced drastically and suddenly from Category 1 to Category 3 within less than 1-day time interval. This unusual warming seems to largely prompt the intensification of Tembin. Next, the relationship between this extreme warming and rapid intensification of Tembin is identified by atmospheric model Weather Research and Forecast (WRF) with updated time-varying lower boundary condition. In addition, given the tight relationship between generation of unusual warming in the shore region and following possible TC intensification, a series of numerical experiments based on oceanic model Regional Oceanic Modeling System (ROMS) were designed and executed to resolve the possible generated mechanism of the extreme warming. The results indicate that a distinct positive short-wave radiation influx anomaly may dominate the generation of the unusual warming in the shore region during Tembin’s passage. This result is validated by the distributions of free cloudy coverage shown in satellite infrared images.

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