33N, 19N: Atlantic Explorer ae1623

This cruise shows two small (40km) deep (550m to over 750m) eddies at similar latitudes, just north of Bermuda (33N), and another larger (100km) deep (550m-750m) eddy just north of Bermuda (19N).

Big eddy north of Bermuda

The Atlantic Explorer left Bermuda and sailed 350km north crossing through the center of a large, strong eddy. The eddy’s vertical extent was greater than the 750m range of the shipboard ADCP. Zonal velocities were 0.35-0.4m/s and meridional velocities were 0.6m/s.

The northbound leg sliced through the center of the eddy. The southbound leg was offset to the east and the velocities were smaller, but the eddy was still visible.

northbound leg (click image to enlarge)

As the ship passed into deep water just north of Bowditch Seamount, the ADCP picked up the signal of a small deep eddy, visible from about 550m down to the 750m range of the instrument. The core could have been 600-650m deep; we cannot know the actual vertical extent of the eddy. It was about 40km across.

The eddy is circled in the lower left corner of the following figure. Also visible is a scar at about 500m in the ‘v’ component, due to side-lobe interference and/or beam spreading and the existence of a strong scattering layer at about 500m. It is not uncommon for ADCP data to have an along-track bias at the shallow side of a deep scattering layer. It is only visible when the ship is moving. This diagram illustrates the phenomenon.


small eddy #1 (click image to enlarge)

Below is a zoomed in view of the small eddy north of Bowditch Seamount.


southbound leg (click image to enlarge)

The southbound leg included CTDs. Ship speed is included in the figure. At about 33N, there was a nother deep eddy, also about 40km across, at a similar latitude to the first one. This second eddy is circled in the bottom right of the velocities.


two cross-sections of the big eddy

The following figure shows the averaged velocities from 265m-410m for the northbound and southbound legs.


little eddy #2

The second eddy is shown below in the box. A brief stop took place in the middle of the eddy.


The scar at 500m is visible as a negative (because the ship is heading sought) bias in the otherwise northward flow, resulting in a light stripe (shown below).


Both eddies are shown together in the plot below


Just as the ship as pulling into Puerto Rico, the ADCP picked up the signal for a third eddy. This one was larger, measuring more like 100km across.

The next three figures show (1) the eddy as the ship passed through it from north to south, (2) a vector plot with the average velocity from 560m-660m, amd (3) the velocities from 560m-660m plotted as a function of latitue.