scholarly journals The Wind Effect on Biogeochemistry in Eddy Cores in the Northern South China Sea

2021 ◽  
Vol 8 ◽  
Author(s):  
Chun Hoe Chow ◽  
Yung-Yen Shih ◽  
Ya-Tang Chien ◽  
Jing Yi Chen ◽  
Ning Fan ◽  
...  
Keyword(s):  
South China Sea ◽  
South China ◽  
Northern South China Sea ◽  
Euphotic Zone ◽  
Wind Effect ◽  
Ocean Stratification ◽  
China Sea ◽  
Poc Flux ◽  
Anticyclonic Eddies

Cyclonic and anticyclonic eddies are usually characterized by upwelling and downwelling, respectively, which are induced by eddy pumping near their core. Using a repeated expendable bathythermograph transect (XBT) and Argo floats, and by cruise experiments, we determined that not all eddies in the northern South China Sea (NSCS) were accompanied by eddy pumping. The weakening of background thermocline was attributed to the strengthening of eddy pumping, affected by (1) wind-induced meridional Sverdrup transports and (2) Kuroshio intrusion into the NSCS. Higher particulate organic carbon (POC) fluxes (> 100 mg-C m−2 day−1) were found near the eddy cores with significant eddy pumping (defined by a depth change of 22°C isotherm near the thermocline for over 10 m), although the satellite-estimated POC fluxes were inconsistent with the in-situ POC fluxes. nitrogen limitation transition and high POC flux were even found near the core of a smaller mesoscale (diameter < 100 km) cyclonic eddy in May 2014, during the weakening of the background thermocline in the NSCS. This finding provides evidence that small mesoscale eddies can efficiently provide nutrients to the subsurface, and that they can remove carbon from the euphotic zone. This is important for global warming, which generally strengthens upper ocean stratification.

scholarly journals The Impact of Eddies on Nutrient Supply, Diatom Biomass and Carbon Export in the Northern South China Sea

2020 ◽  
Vol 8 ◽  
Author(s):  
Yung‐Yen Shih ◽  
Chin‐Chang Hung ◽  
Sing‐how Tuo ◽  
Huan‐Jie Shao ◽  
Chun Hoe Chow ◽  
...  
Keyword(s):  
Organic Carbon ◽  
South China Sea ◽  
Water Column ◽  
South China ◽  
Northern South China Sea ◽  
Euphotic Zone ◽  
Nutrient Supply ◽  
Carbon Export ◽  
China Sea ◽  
Poc Flux

We have investigated the effect of eddies (cold and warm eddies, CEs and WEs) on the nutrient supply to the euphotic zone and the organic carbon export from the euphotic zone to deeper parts of the water column in the northern South China Sea. Besides basic hydrographic and biogeochemical parameters, the flux of particulate organic carbon (POC), a critical index of the strength of the oceanic biological pump, was also measured at several locations within two CEs and one WE using floating sediment traps deployed below the euphotic zone. The POC flux associated with the CEs (85 ± 55 mg-C m−2 d−1) was significantly higher than that associated with the WE (20 ± 7 mg-C m−2 d−1). This was related to differences in the density structure of the water column between the two types of eddies. Within the core of the WE, downwelling created intense stratification which hindered the upward mixing of nutrients and favored the growth of small phytoplankton species. Near the periphery of the WE, nutrient replenishment from below did take place, but only to a limited extent. By far the strongest upwelling was associated with the CEs, bringing nutrients into the lower portion (∼50 m) of the euphotic zone and fueling the growth of larger-cell phytoplankton such as centric diatoms (e.g., Chaetoceros, Coscinodiscus) and dinoflagellates (e.g., Ceratium). A significant finding that emerged from all the results was the positive relationship between the phytoplankton carbon content in the subsurface layer (where the chlorophyll a maximum occurs) and the POC flux to the deep sea.

scholarly journals Eddy characteristics in the northern South China Sea as inferred from Lagrangian drifter data

Ocean Science ◽  
2011 ◽  
Vol 7 (5) ◽  
pp. 661-669 ◽  
Author(s):  
◽  
◽  
Keyword(s):  
South China Sea ◽  
South China ◽  
Large Scale ◽  
Northern South China Sea ◽  
Temporal Distribution ◽  
Height Anomaly ◽  
Spatial And Temporal Patterns ◽  
China Sea ◽  
Eddy Characteristics ◽  
Anticyclonic Eddies

Abstract. Cyclonic and anticyclonic eddies from large scale to submesoscale in the northern South China Sea (NSCS) have been statistically characterized based on the satellite-tracked Lagrangian drifters using our developed geometric eddy identification method. There are in total 2208 eddies identified, 70% of which are anticyclonic eddies. If the submesoscale eddies are eliminated, the other eddies in the NSCS will show a 1.2:1 ratio of the number of anticyclones (210) to the number of cyclones (171). The spatial distribution of the eddies is regional: in southwest of Taiwan, the number of anticyclones dominates the number of cyclones, and most of them are the submesoscale anticyclones with small radii; in contrast, the large and medium cyclonic eddies are a little more than the same scale anticyclonic eddies in northwest of Luzon. The temporal distribution of eddy number in the NSCS has a close relation with the Asian monsoon. The number of the large and medium eddies peaks during the winter monsoon, while the submesoscale eddies are apt to generate in the summer monsoon. The spatial and temporal patterns have a good agreement with the results of the sea surface height anomaly (SSHA). The maximum and mean tangential velocities of anticyclones (cyclones) are 40 (30) cm s−1 and 25 (15) cm s−1, respectively. The calculated normalized vorticities from drifters suggest that although the mesoscale eddies may be considered in geostrophic balance, ageostrophic dynamics and centrifugal effects may play an important role for the growth and decay of the mesoscale cores.

Formation and Dynamics of a Long-Lived Eddy Train in the South China Sea: A Modeling Study

2017 ◽  
Vol 47 (11) ◽  
pp. 2793-2810 ◽  
Author(s):  
Zhongya Cai ◽  
Jianping Gan
Keyword(s):  
South China Sea ◽  
Wind Stress ◽  
South China ◽  
Northern South China Sea ◽  
Anticyclonic Eddy ◽  
The South China Sea ◽  
The South ◽  
Wind Stress Curl ◽  
China Sea ◽  
Anticyclonic Eddies

AbstractA process-oriented numerical modeling study was conducted to investigate the formation and underlying forcing of an anticyclonic eddy train observed in the northern South China Sea. Observations showed that long-lived anticyclonic eddies formed an eddy train along an eastward separated jet across the northern South China Sea in summer. The eddy train plays a critical role in regulating ocean circulation in the region. Forced by the southwesterly monsoon and prevailing dipole wind stress curl in the summer, the northward coastal jet separates from the west boundary of the South China Sea basin and overshoots northeastward into the basin. The anticyclonic recirculation of the separated jet forms the first anticyclonic eddy in the eddy train. The jet meanders downstream with a strong negative shear vorticity that forms a second and a third anticyclonic eddy along the jet’s path. These three eddies form the eddy train. These eddies weaken gradually with depth from surface, but they can extend to approximately 500 m deep. The inherent stratification in the region regulates the three-dimensional scale of the anticyclonic eddies and constrains their intensity vertical extension by weakening the geostrophic balance within these eddies. Analyses of the vorticity balance indicate that the eddy train’s negative vorticity originates from the beta effect of northward western boundary current and from the subsequent downstream vorticity advection in the jet. The jet separation is a necessary condition for the formation of the eddy train, and the enhanced stratification, increased summer wind stress, and associated negative wind stress curl are favorable conditions for the formation of the anticyclonic eddies.

scholarly journals Oxygen isotopes of individual planktic foraminifers reveal Pliocene-Pleistocene change of seasonal upper ocean stratification in the northern South China Sea

2020 ◽  
Author(s):  
Ning Zhao ◽  
Hubert Vonhof ◽  
Liviu Giosan ◽  
Ralf Schiebel ◽  
Gerald Haug
Keyword(s):  
South China Sea ◽  
Tropical Cyclones ◽  
South China ◽  
Northern South China Sea ◽  
Early Pleistocene ◽  
Upper Ocean ◽  
Planktic Foraminifera ◽  
Ocean Stratification ◽  
China Sea ◽  
Seasonal Signals

<p>Most paleoceanographic studies using planktic foraminifera focus on annual means, but seasonal signals buried by the analyses of lumped specimens could be very valuable. Surface ocean feedbacks on climate change may be more significant in the seasonal realm than annual mean in the northern South China Sea, a region being strongly affected by Asian monsoons and tropical cyclones. Here we use oxygen isotope measurements on individual specimens of surface and subsurface planktic foraminiferal species to reconstruct surface seasonality and seasonal upper ocean stratification in this region. Many studies have shown that the thermocline was deeper in the tropical Pacific during the Pliocene than the Pleistocene, but the mechanism remains unclear. Several processes could lead to changes in the upper ocean stratification, such as changes in sea surface temperature and upper ocean mixing by tropical cyclones. Our results show that the upper ocean stratification was weaker during the Late Pliocene than the Early Pleistocene, with the change more significant in summer than winter, while no systematic offset is observed in the surface seasonality. The observations suggest that enhanced mixing by tropical cyclones might be the major cause of the deeper thermocline during the Pliocene.</p>

scholarly journals Active and passive fluxes of carbon, nitrogen, and phosphorus in the northern South China Sea

2021 ◽  
Vol 18 (18) ◽  
pp. 5141-5162
Author(s):  
Jia-Jang Hung ◽  
Ching-Han Tung ◽  
Zong-Ying Lin ◽  
Yuh-ling Lee Chen ◽  
Shao-Hung Peng ◽  
...  
Keyword(s):  
South China Sea ◽  
South China ◽  
Nutrient Availability ◽  
Northern South China Sea ◽  
Euphotic Zone ◽  
Organic C ◽  
China Sea ◽  
Vertical Fluxes ◽  
Event Driven ◽  
The Impact

Abstract. This paper presents the measured active and passive fluxes of carbon (C), nitrogen (N), and phosphorus (P) and their response to seasonal and event-driven oceanographic changes in the northern South China Sea (NSCS). The total vertical flux of carbon (TFC) is defined as the sum of active and passive fluxes of biogenic carbon in the surface layer, which may be considered as the central part of marine carbon cycle. These active and passive fluxes of N and P were also considered to understand stoichiometric flux patterns and the roles of nutrients involved in the TFC. The magnitudes of total C, N, and P fluxes were, respectively, estimated to be 71.9–347 (mean ± SD, 163 ± 70) mgCm-2d-1, 13.0–30.5 (21.2.± 4.9) mgNm-2d-1, and 1.02–2.97 (1.94 ± 0.44) mgPm-2d-1, which were higher than most previously reported vertical fluxes in open oceans, likely because a quarter of the fluxes was contributed from active fluxes that were unaccounted for in vertical fluxes previously. Moreover, the passive fluxes dominated the total vertical fluxes and were estimated to be 65.3–255 (125 ± 64.9) mgCm-2d-1 (77 ± 52 % of total C flux), 11.9–23.2 (17.6 ± 4.2) mgNm-2d-1 (83 ± 28 % of total N flux), and 0.89–1.98 (1.44 ± 0.33) mgPm-2d-1 (74 ± 24 % of total P flux). Vertical fluxes of dissolved organic C, N, and P were small (< 5 %) relative to passive fluxes. The contrasting patterns of active and passive fluxes found between summer and winter could mainly be attributed to surface warming and stratification in summer and cooling and wind-induced turbulence for pumping nutrients into the euphotic zone in winter. In addition to seasonal variations, the impact of anticyclonic eddies and internal-wave events on enhancing active and passive fluxes was apparent in the NSCS. Both active and passive fluxes were likely driven by nutrient availability within the euphotic zone, which was ultimately controlled by the changes in internal and external forcings. The nutrient availability also determined the inventory of chlorophyll a and new production, thereby allowing the estimates of active and passive fluxes for unmeasured events. To a first approximation, the South China Sea (SCS) may effectively transfer 0.208 ± 0.089 Gt C yr−1 into the ocean's interior, accounting for approximately 1.89 ± 0.81 % of the global C flux. The internal forcing and climatic conditions are likely critical factors in determining the seasonal and event-driven variability of total vertical fluxes in the NSCS.

Polarity Variations of Internal Solitary Waves over the Continental Shelf of the Northern South China Sea: Impacts of Seasonal Stratification, Mesoscale Eddies, and Internal Tides

2018 ◽  
Vol 48 (6) ◽  
pp. 1349-1365 ◽  
Author(s):  
Xiaojiang Zhang ◽  
Xiaodong Huang ◽  
Zhiwei Zhang ◽  
Chun Zhou ◽  
Jiwei Tian ◽  
...  
Keyword(s):  
South China Sea ◽  
Continental Shelf ◽  
South China ◽  
Northern South China Sea ◽  
Internal Tides ◽  
Thermocline Depth ◽  
China Sea ◽  
Seasonal Stratification ◽  
Anticyclonic Eddies ◽  
The Impact

AbstractSpatiotemporal variations in internal solitary wave (ISW) polarity over the continental shelf of the northern South China Sea (SCS) were examined based on mooring-array observations from October 2013 to June 2014. Depression ISWs were observed at the easternmost mooring, where the water depth is 323 m. Then, they evolved into elevation ISWs at the westernmost mooring, with a depth of 149 m. At the central mooring, with a depth of 250 m, the ISWs generally appeared as depression waves in autumn and spring but were elevation waves in winter. Seasonal variations in stratification caused this seasonality in polarity. On the intraseasonal time scales, anticyclonic eddies can modulate ISW polarity at the central mooring by deepening the thermocline depth for periods of approximately 8 days. During some days in autumn and spring, depression ISWs and ISWs in the process of changing polarity from depression to elevation appeared at time intervals of 10–12 h because of the thermocline deepening caused by internal tides. Isotherm anomalies associated with eddies and internal tides have a more significant contribution to determining the polarity of ISWs than do the background currents. The observational results reported here highlight the impact of multiscale processes on the evolution of ISWs.

Effects of coastal upwelling on picophytoplankton distribution off the coast of Zhanjiang in South China Sea

2014 ◽  
Vol 43 (3) ◽  
Author(s):  
Mei-Lin Wu ◽  
You-Shao Wang ◽  
Dong-Xiao Wang ◽  
Jun-De Dong
Keyword(s):  
South China Sea ◽  
South China ◽  
Coastal Upwelling ◽  
Northern South China Sea ◽  
Euphotic Zone ◽  
Horizontal Gradient ◽  
Vertical Temperature ◽  
The West ◽  
Factors Affecting ◽  
China Sea

AbstractCoastal upwelling occurred along the west coast of Guangdong in the northern South China Sea during the summer of 2006. The effects of upwelling on the vertical and horizontal distributions of Prochlorococcus and Synechococcus were investigated. A distinct vertical temperature difference between the surface water and water at a depth of 30 m was observed in the coastal upwelling region. There was a clear spatial variability of temperature, and an increasingly obvious horizontal gradient was created from the coast to offshore waters. Picophytoplankton communities observed from the coast to offshore waters were significantly different. In the coastal upwelling waters, the picophytoplankton community was dominated by Synechococcus within the euphotic zone. Prochlorococcus dominated the picophytoplankton community in the euphotic zone in the non-upwelling region. This difference in the picophytoplankton community structure was due to different hydrodynamics. The results of canonical correspondence analysis demonstrate that temperature, salinity, and phosphate concentration may be important factors affecting the distribution of Prochlorococcus and Synechococcus.

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