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Guo W.,State Key Laboratory of Estuarine and Coastal ResearchEast China Normal UniversityShanghai China | Song D.,Key Laboratory of Physical Oceanography | Wang X.H.,South China Normal University | Ding P.,State Key Laboratory of Estuarine and Coastal ResearchEast China Normal UniversityShanghai China | Ge J.,State Key Laboratory of Estuarine and Coastal ResearchEast China Normal UniversityShanghai China
Journal of Geophysical Research: Oceans | Year: 2016

The general framework for identifying tidal duration asymmetry proposed by Song et al. (2011) is extended to express fortnightly variability in duration asymmetry. The extended metrics are verified and studied using observed sea level data at 481 stations worldwide. The results reveal that fortnightly variability is universal and that duration asymmetry can be stronger during neap tide than during spring tide. The fortnightly variability in duration asymmetry is primarily induced by three types of tidal interactions: interactions within the principal tidal constituents, interactions between high-frequency and principal tidal constituents, and interactions between long-period and principal tidal constituents. Among these interactions, the first type is most important at most of the stations and is related to the form number F. The contributions of different interactions can be quantified using their frequencies, amplitudes and phases. Global patterns of the fortnightly variation are illustrated using TOPEX/Poseidon altimetry data. The findings show that remarkable fortnightly variation in the tidal duration asymmetry occurs in most open oceans and is significant around an amphidromic point. The metrics derived in this study can be used to examine any time-varying characteristics in tidal asymmetry (not limited to duration asymmetry) by selecting a suitable frequency threshold. © 2016. American Geophysical Union. All Rights Reserved.


Song D.,Key Laboratory of Physical Oceanography | Yan Y.,Ministry of EducationOcean University of ChinaQingdao China | Diao X.,Ministry of EducationOcean University of ChinaQingdao China | Ding Y.,Key Laboratory of Physical Oceanography | Bao X.,Ministry of EducationOcean University of ChinaQingdao China
Journal of Geophysical Research: Oceans | Year: 2016

Double high water and double-peak flood current were observed in Daya Bay (DYB), China, which is a shallow, mixed, mainly semidiurnal-tide dominated bay with a micro to mesotidal range. Harmonic analysis reveals that the quarter and especially the sexta-diurnal constituents are getting much stronger as tides propagating into the bay. The astronomical tides-induced tidal asymmetry is yet dominant at the bay entrance but overtaken by the sexta-diurnal tides at the end of the bay. Both the M4 and M6 tide meet the requirement proposed in previous studies but still unable to produce a double high water alone. Therefore, the conditions to produce a double high water between a fundamental tide and its higher harmonics need to be revisited. Analytical solutions were obtained in this paper, which fit the numerical solutions very well. Modeling result indicates M6 alone with M2 can produce the double high water in DYB but limited in some regions, while the combination of M2, M4, and M6 tides would enhance the capability. The amplification of sexta-diurnal tides in DYB is dominated by resonance and followed by shoaling effect. Bottom friction damped M6 a lot and largely confined its amplification. However, the quadratic friction and other nonlinear processes are just responsible for about 10% of the total M6 increase. © 2016. American Geophysical Union.


Yuan Y.,Ocean University of China | Song D.,Key Laboratory of Physical Oceanography | Wu W.,Ocean University of China | Liang S.,Ocean University of China | And 2 more authors.
Regional Studies in Marine Science | Year: 2016

In this study, marine environmental issues that occurred during the socio-economic development of Qingdao City and the exploitation and utilization of Jiaozhou Bay (JB) are reviewed. Its environmental condition has been dominated by intensive anthropogenic activities, i.e. increased wastewater discharge and rapid coastline evolution, which have reduced the ecosystem's ability to sustain itself. Efforts have been taken in scientific research and coastal management to protect and restore the environment in JB since 1990s. But lack of holistic views of JB system generates knowledge gaps in different research disciplines as well as the linkage between science and management. A case study is given to illustrate that different pollutant indicators respond to the coastline evolution differently, which cannot be explained by physics sole. The integrated research by knowledge sharing through community-benefit research projects is therefore called for on the systematic biogeochemical dynamics in JB. The integrated coastal zone management is also needed to cope with the complicated and complex systems of JB by an interdisciplinary problem-solving mechanism. © 2016 Elsevier B.V.


Song D.,Key Laboratory of Physical Oceanography | Song D.,University of New South Wales | Wang X.H.,University of New South Wales | Wang X.H.,State Key Laboratory of Satellite Ocean Environment Dynamics
Journal of Geophysical Research: Oceans | Year: 2013

A three-dimensional wave-current-sediment coupled numerical model with wetting and drying process is developed to understand hydrodynamics and sediment transport dynamics in the Deepwater Navigation Channel (DNC), the North Passage of the Yangtze River Estuary (YRE), China. The model results are in good agreement with observed data, and statistics show good model skill scores and correlation coefficients. The model well reproduces the spring-neap variation between a well-mixed estuary and a highly stratified estuary. Model results indicate that the estuarine gravitational circulation plays the most important role in the estuarine turbidity maximum (ETM) formation in the DNC. The upstream nonlocal sediment intrusion through the spillover mechanism is a major source of sediment trapping in the North Passage after the morphological changes. Numerical studies are conducted to show scenarios in the YRE under the effects of different forcings (river discharges, waves, and winds). Between these study cases, surface-wave-breaking relieves the sediment trapping and bottom-wave-current-interaction aggravates the bed erosion and elevates the SSC in the ETM; the former and the latter have the least and largest influence on the suspended sediment transport in the DNC. The wind effects have a greater influence on sediment trapping than the river discharges, and the steady northwesterly wind condition favors the siltation in the DNC most. The significance of density-driven turbidity current is also assessed, which can enhance the saline-water intrusion and suppress the turbulent mixing in the bottom boundary layer. © 2013. American Geophysical Union. All Rights Reserved.


Song D.,Key Laboratory of Physical Oceanography | Song D.,University of New South Wales | Wang X.H.,Key Laboratory of Physical Oceanography | Wang X.H.,University of New South Wales | And 2 more authors.
Journal of Geophysical Research: Oceans | Year: 2013

The in situ data in the Deepwater Navigation Channel (DNC), Yangtze River Estuary (YRE), China, in the dry season 2009, shows spring tides associated with greater maximum velocities, more mixing, less stratification, and diffused fluid mud; whereas neap tides are associated with smaller maximum velocities, greater stratification, inhibited mixing, and stratified fluid muds. The balance of salt flux indicates the seaward salt transport is dominated by fluvial flows, and the landward salt transport is generated by compensation flows during spring tides, but shear effects during neap tidal cycles. The balance of suspended sediment flux illustrates the offshore sediment transport is dominated by fluvial flows as well, but the onshore transport is induced by tidal-pumping effects on spring tides, and shear effects on neaps. The suspended sediment transport is strongly affected by the salinity distribution and salinity-gradient-induced stratification in the DNC. The spring-neap asymmetry is generated by the estuarine gravitational circulation during low-flow conditions; while the flood-ebb asymmetric stratification within a tidal cycle is due to the semidiurnal tidally movement of the salt front. © 2013. American Geophysical Union. All Rights Reserved.


Shi J.,Key Laboratory of Physical Oceanography | Shi J.,Ocean University of China | Cheng Y.,Ocean University of China | Jiao Y.,Ocean University of China | Hou J.,Ocean University of China
Chinese Journal of Oceanology and Limnology | Year: 2011

Supercooled water with temperatures below freezing point, was identified from hydrographic data obtained by Chinese and Australian expeditions to Prydz Bay, Antarctica, during the austral summer. The study shows that most supercooled waters occurred at depths of 63-271 m in the region north of the Amery Ice Shelf (AIS) front. The maximum supercooling was 0. 16°C below the in-situ freezing point. In temperature and salinity ranges of -2. 14-1. 96°C and 34. 39-34. 46, respectively, the water was colder and fresher than peripheral shelf water. The supercooled water had less variability in the vertical profiles compared to shelf water. Based on analysis of their thermohaline features and spatial distribution, as well as the circulation pattern in Prydz Bay, we conclude that these supercooled waters originated from a cavity beneath the AIS and resulted from upwelling just outside of the AIS front. Water emerging from the ice shelf cools to an extremely low temperature (about -2. 0°C) by additional cooling from the ice shelf, and becomes buoyant with the addition of melt water from the ice shelf base. When this water flows out of the ice shelf front, its upper boundary is removed, and thus it rises abruptly. Once the temperature of this water reaches below the freezing point, supercooling takes place. In summer, the seasonal pycnocline at ~100 m water depth acts as a barrier to upwelling and supercooling. The upwelling of ice shelf outflow water illuminates a unique mid-depth convection of the polar ocean. © 2011 Chinese Society for Oceanology and Limnology, Science Press and Springer Berlin Heidelberg.


Guo G.,Ocean University of China | Guo G.,Key Laboratory of Physical Oceanography | Shi J.,Ocean University of China | Shi J.,Key Laboratory of Physical Oceanography | And 2 more authors.
Acta Oceanologica Sinica | Year: 2015

Based on hydrographic data obtained at an ice camp deployed in the Makarov Basin by the 4th Chinese Arctic Research Expedition in August of 2010, temporal variability of vertical heat flux in the upper ocean of the Makarov Basin is investigated together with its impacts on sea ice melt and evolution of heat content in the remnant of winter mixed layer (rWML). The upper ocean of the Makarov Basin under sea ice is vertically stratified. Oceanic heat flux from mixed layer (ML) to ice evolves in three stages as a response to air temperature changes, fluctuating from 12.4 W/m2 to the maximum 43.6 W/m2. The heat transferred upward from ML can support (0.7±0.3) cm/d ice melt rate on average, and daily variability of melt rate agrees well with the observed results. Downward heat flux from ML across the base of ML is much less, only 0.87 W/m2, due to enhanced stratification in the seasonal halocline under ML caused by sea ice melt, indicating that increasing solar heat entering summer ML is mainly used to melt sea ice, with a small proportion transferred downward and stored in the rWML. Heat flux from ML into rWML changes in two phases caused by abrupt air cooling with a day lag. Meanwhile, upward heat flux from Atlantic water (AW) across the base of rWML, even though obstructed by the cold halocline layer (CHL), reaches 0.18 W/m2 on average with no obvious changing pattern and is also trapped by the rWML. Upward heat flux from deep AW is higher than generally supposed value near 0, as the existence of rWML enlarges the temperature gradient between surface water and CHL. Acting as a reservoir of heat transferred from both ML and AW, the increasing heat content of rWML can delay the onset of sea ice freezing. © 2015, The Chinese Society of Oceanography and Springer-Verlag Berlin Heidelberg.


Mao X.,Ocean University of China | Mao X.,Key Laboratory of Physical Oceanography | Jiang W.,Key Laboratory of Physical Oceanography | Jiang W.,Ocean University of China | And 4 more authors.
Journal of Ocean University of China | Year: 2016

Inter-tidal (subtidal) transport processes in coastal sea depend on the residual motion, turbulent dispersion and relevant sources/sinks. In Feng et al. (2008), an updated Lagrangian inter-tidal transport equation, as well as new concept of Lagrangian inter-tidal concentration (LIC), has been proposed for a general nonlinear shallow water system. In the present study, the LIC is numerically applied for the first time to passive tracers in idealized settings and salinity in the Bohai Sea, China. Circulation and tracer motion in the three idealized model seas with different topography or coastline, termed as ‘flat-bottom’, ‘stairs’ and ‘cape’ case, respectively, are simulated. The dependence of the LIC on initial tidal phase suggests that the nonlinearities in the stairs and cape cases are stronger than that in the flat-bottom case. Therefore, the ‘flat-bottom’ case still meets the convectively weakly nonlinear condition. For the Bohai Sea, the simulation results show that most parts of it still meet the weakly nonlinear condition. However, the dependence of the LIS (Lagrangian inter-tidal salinity) on initial tidal phase is significant around the southern headland of the Liaodong Peninsula and near the mouth of the Yellow River. The nonlinearity in the former region is mainly related to the complicated coastlines, and that in the latter region is due to the presence of the estuarine salinity front. © 2016, Science Press, Ocean University of China and Springer-Verlag Berlin Heidelberg.


Yang W.,Key Laboratory of Physical Oceanography | Yang W.,Ocean University of China | Zhao L.,Key Laboratory of Physical Oceanography | Zhao L.,Tianjin University of Science and Technology | And 10 more authors.
Journal of Ocean University of China | Year: 2013

During the two cruises in March and July of 2011, the tidal cycling of turbulent properties and the T/S profiles at the same location in seasonally stratified East China Sea (ECS) were measured synchronously by a bottom-mounted fast sampling ADCP (acoustic Doppler current profiler) and a RBR CTD (RBR-620) profiler. While focusing on the tide-induced and stratification's impact on mixing, the Reynolds stress and the turbulent kinetic energy (TKE) production rate were calculated using the 'variance method'. In spring, the features of mixing mainly induced by tides were clear when the water column was well-mixed. Velocity shear and turbulent parameters intensified towards the seabed due to the bottom friction. The components of the velocity shear and the Reynolds stress displayed a dominant semi-diurnal variation related to velocity changes caused by the flood and ebb of M2 tide. Stratification occurred in summer, and the water column showed a strongly stratified pycnocline with a characteristic squared buoyancy frequency of N2 ~ (1-6) × 10-3 s-2. The components of the velocity shear and the Reynolds stress penetrated upwards very fast from the bottom boundary layer to the whole water column in spring, while in summer they only penetrated to the bottom of the pycnocline with a relatively slow propagation speed. In summer, the TKE production within the pycnocline was comparable with and sometimes larger than that in the well-mixed bottom layer under the pycnocline. Considering the associated high velocity shear, it is speculated that the mixing in the pycnocline is a result of the local velocity shear. © 2013 Science Press, Ocean University of China and Springer-Verlag Berlin Heidelberg.

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