The Spatio-temporal Variability Of Oceanic Fronts Offshore China Seas And Analysis Of Marine Observations

The oceanic front is one of the typical ocean mesoscale phenomena, and it is an importantfactor to affect the flow field structures, heat exchanges, mass transports and ocean-atmosphereinteractions, and is also the control element for biogeochemical processes which should not beignored. Most oceanic fronts own the narrow banded spatial structures and character as a highlevel of gradient with different hydrological factors. Meanwhile, front is the place with intenseperformance for the ocean energy transfer from large scales to smaller ones. It is closelyassociated with other mesoscale phenomena in the ocean. The mesoscale eddies act on thefrontogenesis, accordingly, the frontal instability could also produce frontal eddies. The strongvertical gradient such as thermocline, halocline, and pycnocline should be considered as thefronts in vertical direction, and it is the basis of the generation of internal waves.Using data analysis and theoretical methods for various types of satellite-derived data andother data resources, the studies in the following sections are mainly focused on thespatio-temporal variability of the oceanic front and its dynamic mechanism, and explore theresponse of the mesoscale phenomena in marine ecology. We also use in situ CTD data andmoored ADCP observations to confirm or modify the results.The thermal front, formed between the Kuroshio and continental shelf water in the EastChina Sea, has a significant seasonal signal, whereas the corresponding ocean color front existswithout remarkable spatio-temporal changes. This result suggests that ocean color data seemmore suitable to depict the oceanic front because it is not affected by the solar radiation andspatial heating. As to the strong thermal front in summertime off northeastern Taiwan, weconsider that it should be closely related to the upwelling of subsurface Kuroshio waters.The Argo floats, which were launched in the middle of the Luzon Strait, often drift into thestrait; and the results of temperature-salinity profile data and near-surface trajectory informationshow that there exists some high salt Kuroshio water in the upper layer around the continentalslope in the northern South China Sea. The Kuroshio warm filaments southwest of Taiwan Islandare also captured by satellite-derived remote sensing SST data during the period of Argo floatsmeasurement. The Moored ADCPs with long-term observations are also deployed northwest ofLuzon Island. The current profile data indicates that the flow field is mainly west or northwest in the upper200m layers, whereas beneath this layer, the flow is eastward. This tendency impliesthat the Kuroshio frontal intrusion in this region should not be neglected.The winter blooms with high Chlorophyll_a concentration is positive correlated with thecooling sea surface temperature index, and this phenomenon is maintained by the Luzon ColdEddy which seems to be an important vehicle for nutrient transport from depth to euphotic zone.This seasonal bloom is similar to a dissipative structure, and the Rossby wave works as theconveyor belt, which essentially changes the face of nutrient-depleted waters at a westernoffshore area of Luzon Island.