Multiple-scale temporal variations and fluxes near a hydrothermal vent over the Southwest Indian Ridge

Abstract

A deep-ocean mooring system was deployed 100 m away from an active hydrothermal vent over the Southwest Indian Ridge (SWIR), where the water depth is about 2,800 m. One year of data on ocean temperature 50 m away from the ocean floor and on velocities at four levels (44 m, 40 m, 36 m, and 32 m away from the ocean floor) were collected by the mooring system. Multiple-scale variations were extracted from these data: seasonal, tidal, super-tidal, and eddy scales. The semidiurnal tide was the strongest tidal signal among all the tidal constituents in both currents and temperature. With the multiple-scale variation presented in the data, a new method was developed to decompose the data into five parts in terms of temporal scales: time-mean, seasonal, tidal, super-tidal, and eddy. It was shown that both eddy and tidal heat (momentum) fluxes were characterized by variation in the bottom topography: the tidal fluxes of heat and momentum in the along-isobath direction were much stronger than those in the cross-isobath direction. For the heat flux, eddy heat flux was stronger than tidal heat flux in the cross-isobath direction, while eddy heat flux was weaker in the along-isobath direction. For the momentum flux, the eddy momentum flux was weaker than tidal momentum flux in both directions. The eddy momentum fluxes at the four levels had a good relationship with the magnitude of mean currents: it increased with the mean current in an exponential relationship.

Keywords

multiple-scale analysis / tidal flux / eddy flux

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Acknowledgements

The data used in this paper are from Chinese DY115-21 cruise. We thank all the staff for their hard work, especially our colleague Tao Ding, who brought back the mooring system successfully and acquired these invaluable observational data. We express our sincere gratitude to Weifang Jin and Tao Ding, for their help during the early-stage data processing. This study was support by the National Basic Research Program of China on hydrothermal plume characteristics and environmental effects (No. 2012CB417303), the project of global change and interaction between ocean and atmosphere (GASI-03-01-01-07). CD appreciates the support from the National Natural Science Foundation of China (Grant Nos. 41376033, 41476022, and 41490640), and the NUIST startup grants. We appreciate Jian Zhu's help to make Figure 1.

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2014 Higher Education Press and Springer-Verlag Berlin Heidelberg