Hi Warren,

That's a very good question.  There likely are several factors responsible for the late freeze-up in the Chukchi Sea, including the long-term warming trend, but ENSO may have been a factor as well.  I would expect a tendency for La Nina to be associated with reduced sea ice in the Chukchi Sea - specifically, I am thinking of Fig. 2b in this article: https://pubs.giss.nasa.gov/docs/2004/2004_Liu_li03200f.pdf.  However, I believe that other factors must be at play to explain such an extreme occurrence.  This article provides more insight on this topic: https://insideclimatenews.org/news/30112017/arctic-sea-ice-extent-recor….