There have been hints that there's more biological productivity in the Arctic Ocean than once suspected (perhaps helped along by climate change): In 2012, scientists reported seeing massive blooms of algae proliferating under the sea ice. (sciencemag.org)
Azolla, like most algae, can form massive blooms, as it did 49 million years ago in the Arctic, choking out life below. (scientificamerican.com)
I could go on — but it is one of the major nutrient sources that makes algae very happy — and when they outgrow the animals that eat them they form massive blooms. (dotearth.blogs.nytimes.com)