They don't have a fucking clue what ocean currents were doing 1,500 yrs ago. Fake news.
A sucker is born everyday. They can't do much more than a guess with that info.
You obviously didn't read the article.
I understand what they claim they can know from core samples but I don't believe it, never will. This is the same voodoo science bull shit they use to perpetuate the global warming hoax. There is no doubt they can gain some information about the past but they sure as hell can't tell us exactly what the ocean currents were doing 1500 yrs ago by core samples. It's just not believable.