Temporal variations in internal tide multimodal structure on the continental shelf, South China Sea

Temporal variations in multimodal structures of diurnal( D_1) and semidiurnal( D_2) internal tides were investigated on the continental slope of the Dongsha Plateau, based on 2-month moored acoustic Doppler current profiler observations. Harmonic analysis indicated that the D_1 components( K_1 and O_1) dominated the internal tide field. The vertical structure of the K_1 constituent presented a first-mode structure while the M_2 constituent seemed to exhibit a high-mode structure. Amplitude spectra analysis of the current data revealed differences in baroclinic current amplitudes between different water depths. Temporal variations in modal structures ware analyzed, based on the D_1 and D_2 baroclinic tides extracted from the baroclinic velocity field with band-pass filters. Analysis showed that the magnitude of the D_1 internal tide current was much larger than the D_2 current, and temporal variations in the modal structure of the D_1 internal tide occurred on an approximately fortnightly cycle. The EOF analyses revealed temporal transformation of multimodal structures for D_1 and D_2 internal tides. The enhancement of the D_1 internal tide was mainly due to the superposition of K_1 and O_1, according to the temporal variation of coherent kinetic energy.

Background Concentration of Copper and Cadmium in Water from a High Industrialized and Urban Coastal System (Baixada Santista, Brazil)—Contribution to a Monitoring Program

The Baixada Santista coastal region is well known in the context of the high atmospheric, soil and aquatic pollution levels derived from port, industrial, domestic and urban activities existent there, mainly in function of the Cubatão industrial pole and port of Santos. The contamination by trace metals in this region is rarely measured in water column when compared with metal determinations in sediment studies. This study aims to evidence the levels of dissolved copper and total cadmium concentrations in estuarine and seawater waters using electrochemical analysis as a chronopotentiometric stripping polarography, which could improve the environmental monitoring program. The study was performed in the Bay of Santos reaching two estuarine channels (Santos and São Vicente Channels) in two tide periods in summer 2001. This region is influenced by terrestrial and anthropogenic inputs of trace metals to seawater. The results showed that dissolved copper and total cadmium in water presented the maxima concentrations of 45.4 nM and 2.6 nM respectively. They not reached the limits proposed by Brazilian Environmental Law (CONAMA), that indicate, as reference, a maximum of 123 nM and 350 nM for dissolved copper and total cadmium, respectively and, considering seawater coastal system (salinity > 30, class 2) and also brackish water (class 2). Although the values were under the maximum recommended for each metal, the concentrations were not negligible in relation to the other polluted areas in the world. The values distribution along the system showed a progressive increase in direction to the inner part of the system that naturally compromises the local biota whose is more exposed to the bioaccumulation processes, and this data corresponds to an important reference preterit value to the monitoring program. The trace metal bioaccumulation by mangrove vegetation and by the biota in the internal part of the estuarine channels increase the risk of the poorly population that living in the internal part of the estuary, used to the seafood consumption. The contribution of this study is important to guide the protective policies destined to recuperate the natural conditions of this system, mainly considering that in the decade 1980, there was a case of toxic contamination, causing hydrocephaly in newborns. It proves the existence of risks to the human health and to the balance of the ecosystem, even with the decrease of pollution after that, the environmental evaluation needs to know the background values to guide environmental protection.