Abstract
Despite numerous surface eddies are observed in the ocean, deep eddies (a type of eddies which have no footprints at the sea surface) are much less reported in the literature due to the scarcity of their observation. In this letter, from recently collected current and temperature data by mooring arrays, a deep energetic and baroclinic eddy is detected in the northwestern South China Sea (SCS) with its intensity, size, polarity and structure being characterized. It remarkably deepens isotherm at deep layers by the amplitude of ~120 m and induces a maximal velocity amplitude about 0.18 m/s, which is far larger than the median velocity (0.02 m/s). The deep eddy is generated in a wake when a steering flow in the upper layer passes a seamount, induced by a surface cyclonic eddy. More observations suggest that the deep eddy should not be an episode in the area. Deep eddies significantly increase the velocity intensity and enhance the mixing in the deep ocean, also have potential implication for deep-sea sediments transport.
Highlights
An interesting event is that two maximum velocities with the amplitude of 0.18 m/s occur between 4 April and 8 May 2012 at mooring A
It has been reported that strong surface eddies in the South China Sea (SCS) can extend vertically to thousands of meters, and induce larger velocity in deep layer[17] and transport sediments[6]
The eddy induces the maximum velocities during the observational period in deep layer with the amplitude of 0.18 m/s, which is far larger than the mean value of 3.4 cm/s
Summary
In the deeper layer (larger than 1000 m) observed at moorings A and B are less than 0.02 m/s for most of the time (Fig. 2b,f). Larger velocity amplitude in the deeper layer can be observed in Mooring B (Fig. 2f) in May 2012. It has been reported that strong surface eddies in the SCS can extend vertically to thousands of meters, and induce larger velocity in deep layer[17] and transport sediments[6].
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