What does the following sentence mean?

[sky753]

Hello Everyone,
Today I have read a report on YAHOO online about the future possible passage through Arctic region. Could you please explain the underlined sentence to me?
Until now, the passage has been expected to remain closed even during reduced ice cover by multiyear ice pack — sea ice that remains through one or more summers, ESA said.

Thanks and Best Regards
Richard

[Soup]

Originally Posted by sky753

Hello Everyone,
Today I have read a report on YAHOO online about the future possible passage through Arctic region. Could you please explain the underlined sentence to me?
Until now, the passage has been expected to remain closed even during reduced ice cover by multiyear ice pack — sea ice that remains through one or more summers, ESA said.

Thanks and Best Regards
Richard

The green part explains the orange part. The sea ice doesn't completely melt during the summer, and so when the winter comes and more sea ice freezes, the result is layers of ice called a multiyear ice pack--more than one year's worth of frozen layered ice.

[sky753]

Originally Posted by Soup

The green part explains the orange part. The sea ice doesn't completely melt during the summer, and so when the winter comes and more sea ice freezes, the result is layers of ice called a multiyear ice pack--more than one year's worth of frozen layered ice.

Thanks a lot . I have understood it!