What is that drain east of newfoundland
It is an artifact of the processing software when it processes Multibeam Bathymetric Survey data. 
You can get the lines of the different surveys from NGBC at NOAA (https://maps.ngdc.noaa.gov/viewers/bathymetry/). As you can see in the image below both lines you see in your example correspond to multibeam data. In the area there is a fair amount of single-beam bathymetry, but the multibeam bathy is often weighted differently creating artifacts in some cases.
The GEBCO bathymetry does not contain the artifact.