For further clarification:

The Antarctic Peninsula(the long bit sticking out) is the furtest part away from the south pole in the antarctic and is thus the northernmost part, and is generally considered to be the "north" when using cardinal directions there. The Weddell Sea is off the coast of the peninsula.

The entire Weddell Sea is just north of Antarctica. That's where the Weddell Sea is. The problem is that everything near Antarctica is just north of Antarctica, including things on the complete opposite side of the entire continent. It's just a way of saying near Antarctica that sounds like you're giving more information than you really are.

We all probably understood that's what they meant but it's funny and not super clear. "The Weddell Sea just north of Antarctica." or "The Weddell Sea near Antarctica." work much better.

Yeah, you're right: https://en.wikipedia.org/wiki/Weddell_Sea?wprov=sfla1

Headline syntax sucks.

If you leave Antarctica, you're heading north. Is it North of Antarctica toward Australia, South Africa, Patagonia or some other northerly direction from Antarctica?

That's the ambiguity inherent to the headline.