Lord-Commander Arete wants you to deal with Grand Admiral Westwind. Return to the lord-commander upon Death's Rise after you have done so.
When High General Abbendis was confronted at New Hearthglen, the grand admiral protected himself within an impenetrable sphere of magic before making his escape.
I am particularly adept at nullifying magic.
Take this to use against him inside The Hidden Hollow when he puts the sphere up. I wish that I could be there to see the look on his face when you do it.
Deal with him.