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Liao X.,University of Chinese Academy of Sciences | Zhan H.,State Key Laboratory of Tropical OceanographySouth China Sea Institute of Oceanology | Du Y.,State Key Laboratory of Tropical OceanographySouth China Sea Institute of Oceanology
Journal of Geophysical Research: Oceans | Year: 2016

Using satellite-derived and in situ data, the wind-driven potential new production (nitrate supply) for the 300 km wide coastal band in two upwelling regions of the western Arabian Sea (AS) during the southwest monsoon is estimated. The upward nitrate flux to the euphotic zone is generally based on the physical processes of coastal transport (Ekman transport and geostrophic transport) and offshore Ekman pumping. The coastal geostrophic current in the western AS influences the upwelling intensity and latitudinal distributions of nitrate supply. The Oman and Somalia upwelling regions have similar level of potential new production (nitrate supply) during the summer monsoon, while the satellite estimates of primary production off Oman are 2 times greater than those off Somalia. The much higher potential f-ratio in the Somalia upwelling region indicates that the primary production could be limited by availability of other macronutrients (e.g., silicate). The correlation analysis of the primary production and the aerosol optical thickness shows that the Oman upwelling region displays a stronger coupling between the atmospheric deposition and the phytoplankton abundance. The high summertime dust levels in the atmosphere are suggested to contribute to the high primary production in the Oman upwelling region. © 2016. American Geophysical Union. All Rights Reserved. Source


Zeng L.,State Key Laboratory of Tropical OceanographySouth China Sea Institute of Oceanology | Liu W.T.,Jet Propulsion LaboratoryCalifornia Institute of TechnologyPasadena | Xue H.,University of Chinese Academy of Sciences | Xiu P.,University of Chinese Academy of Sciences | Wang D.,State Key Laboratory of Tropical OceanographySouth China Sea Institute of Oceanology
Journal of Geophysical Research C: Oceans | Year: 2014

Newly available sea surface salinity (SSS) data from the Aquarius together with in situ hydrographic data are used to explore the spatial and temporal characteristics of SSS in the South China Sea (SCS). Using in situ observations as the reference, an evaluation of daily Aquarius data indicates that there exists a negative bias of 0.45 psu for the version 3.0 data set. The root-mean-square difference for daily Aquarius SSS is about 0.53 psu after correcting the systematic bias, and those for weekly and monthly Aquarius SSSs are 0.45 and 0.29 psu, respectively. Nevertheless, the Aquarius SSS shows a reliable freshening in the SCS in 2012, which is larger than the Aquarius uncertainty. The freshening of up to 0.4 psu in the upper-ocean of the northern SCS was confirmed by in situ observations. This freshening in 2012 was caused by a combined effect of abundant local freshwater flux and limited Kuroshio intrusion. By comparing the Kuroshio intrusion in 2012 with that in 2011, we found the reduction as a relatively important cause for the freshening over the northern SCS. In contrast to the northern SCS, reduced river discharge in 2012 played the leading role to the saltier surface in the region near the Mekong River mouth with respect to 2011. © 2014. American Geophysical Union. All Rights Reserved. Source


Xie X.,State Key Laboratory of Tropical OceanographySouth China Sea Institute of Oceanology | Liu Q.,University of the Sea | Shang X.,State Key Laboratory of Tropical OceanographySouth China Sea Institute of Oceanology | Chen G.,State Key Laboratory of Tropical OceanographySouth China Sea Institute of Oceanology | Wang D.,State Key Laboratory of Tropical OceanographySouth China Sea Institute of Oceanology
Journal of Geophysical Research: Oceans | Year: 2016

This study presents two sets of current records obtained from the South China Sea and satellite altimeter data, and it suggests that near-inertial waves induced by parametric subharmonic instability (PSI) associated with internal tides can be transported poleward beyond their critical latitude ϕc by background geostrophic flow (BGF). The two mooring locations were poleward of ϕc (≈14°N) for diurnal subharmonics (0.5D1; half diurnal frequency D1); however, both of the current records revealed clear signals at 0.5D1. The enhanced subinertial motion at 0.5D1 exhibited a fortnightly spring-neap cycle but did not agree with that of D1, indicating that it may not be generated via PSI associated with the local D1. Observations from the altimeter data and a ray-tracing simulation suggested that these nonlocally generated 0.5D1 waves may be excited near their ϕc, after which they propagated poleward under the role of the BGF to the observation site with a latitude higher than ϕc. The poleward propagation of near-inertial waves can produce elevated vertical shears; thus, it may play an important role in enhancing the local turbulent mixing. © 2016. American Geophysical Union. All Rights Reserved. Source


Jing Z.,State Key Laboratory of Tropical OceanographySouth China Sea Institute of Oceanology | Qi Y.,State Key Laboratory of Tropical OceanographySouth China Sea Institute of Oceanology | Fox-Kemper B.,Brown UniversityProvidence | Du Y.,State Key Laboratory of Tropical OceanographySouth China Sea Institute of Oceanology | Lian S.,State Key Laboratory of Tropical OceanographySouth China Sea Institute of Oceanology
Journal of Geophysical Research: Oceans | Year: 2016

Seasonal thermal fronts associated with wind-driven coastal downwelling/upwelling in the northern South China Sea are investigated using satellite measurements and three repeated fine-resolution mapping surveys in winter, spring, and summer. The results show that vigorous thermal fronts develop over the broad shelf with variable widths and intensities in different seasons, which tend to be approximately aligned with the 20-100 m isobaths. Driven by the prevailing winter/summer monsoon, the band-shaped fronts were observed with a magnitude exceeding 0.1°C/km in the subsurface, and accompanied by energetic coastal downwelling/upwelling due to shoreward/offshore Ekman transport. The downward/upward tilting of seasonal thermoclines across the shelf exceeds 20 m, significantly contributing to the development of thermal fronts over the shelf. In addition, the diagnostic analysis of Potential Vorticity (PV) suggests that the summer frontal activities induced by the coastal upwelling are more stable to convection and symmetric instabilities in comparison to the winter fronts associated with downwelling-favorable monsoon forcing. This is primarily due to their essential differences in the upper ocean stratification and horizontal buoyancy gradients arising from wind forcing. At the same time, the coastal currents are substantially regulated by the seasonal winds. An expected lag correlation between the velocity from mooring measurements and alongshore wind stress is detected near the frontal region. These results indicate that seasonal wind forcing plays an important role in the frontal activities and coastal water transport over the shelf. © 2016. American Geophysical Union. All Rights Reserved. Source


Jing Z.,State Key Laboratory of Tropical OceanographySouth China Sea Institute of Oceanology | Qi Y.,State Key Laboratory of Tropical OceanographySouth China Sea Institute of Oceanology | Du Y.,State Key Laboratory of Tropical OceanographySouth China Sea Institute of Oceanology
Journal of Geophysical Research C: Oceans | Year: 2015

Persistent coastal upwelling and upwelling-induced thermal fronts in the northwestern South China Sea are investigated using satellite measurements, two intensive mesoscale mapping surveys and three bottom-mounted ADCPs. The results indicate that pronounced surface cooling and upwelling-related fronts with a width of 20-50 km occur around Hainan Island and persist through the summer upwelling season. Driven by the prevailing southwesterly monsoon, the subsurface cooling band is ∼6°C colder than the water offshore of the East Coast, where the thermal gradients are generally more than 0.1°C/km. The cold and nutrient-rich coastal water is identified to be derived primarily from the deep water of the outer shelf. At the same time, the spatial structure of the upwelling and thermal front, as well as the upwelling-related coastal currents, is significantly regulated by wind forcing. A prominent lagged correlation between the moored temperature records and alongshore wind stress is detected in the East Coast. The correlation coefficient is -0.8 with the temperature lagging behind wind stress by 2.2 days, indicating that the cooling band off the East Coast is dominated mostly by the alongshore southwesterly monsoon during the upwelling season. © 2015. American Geophysical Union. Source

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