Bloom of algae near Wrangel Island

A bloom of algae near Wrangel Island in the Arctic Ocean, where the ocean’s levels of algae have rapidly increased. Credit: M. Kahru. Click to enlarge photo.

Carl Zimmer writes in the New York Times that scientists have reported global warming is altering the ecology of the Arctic Ocean on a huge scale. The annual production of algae, the base of the food web, increased an estimated 47 percent between 1997 and 2015, and the ocean is greening up much earlier each year.

These changes are likely to have a profound impact for animals further up the food chain, such as birds, seals, polar bears and whales.

While global warming has affected the whole planet in recent decades, nowhere has been hit harder than the Arctic. This month, temperatures in the high Arctic have been as much as 36 degrees above average, according to records kept by the Danish Meteorological Institute.

In October, the extent of sea ice was 28.5 percent below average — the lowest for the month since scientists began keeping records in 1979. The area of missing ice is the size of Alaska and Texas put together.

Since the mid-2000s, researchers like Kevin R. Arrigo, a biological oceanographer at Stanford University, have been trying to assess the effects of retreating ice on the Arctic ecosystem. Each spring the returning sun melts some of the ice that formed in winter. Algae in the open water quickly spring to life and these algae are the base of the food chain in the Arctic Ocean, grazed by krill and other invertebrates that in turn support bigger fish, mammals and birds.

Dr. Arrigo and his colleagues visited the Arctic in research ships to examine the ocean’s algae productivity. Last year he and his colleagues published their latest update, estimating that the algal productivity of the Arctic rose 30 percent between 1998 and 2012.

Not only is the Arctic Ocean producing more algae, but it’s doing so sooner each year. “These blooms are coming earlier, sometimes two months earlier,” said Mati Kahru, an oceanographer at the University of California, San Diego.

“The ice has gotten so thin that sunlight reaches through it. Now they’re not even waiting for the ice to melt,” Dr. Arrigo said of algal organisms.

If we stay on our current course, pouring more carbon dioxide into the atmosphere, the Arctic will only get warmer, perhaps becoming ice-free in the summer. If algae can find more nitrogen and other nutrients in the ocean, its productivity may continue to rise.

Scientists can’t yet say what the ecological effects of this transformation will be. “It is probable it will have an impact on the whole food web,” said Marcel Babin, an oceanographer at Université Laval in Quebec. Dr. Babin and his colleagues have been studying that impact over the past two summers on an expedition called the Green Edge Project, which has looked at the ecology in Baffin Bay off the coast of northern Canada. They hope to present the first results of the survey next year.

Some species may thrive because they can graze on the extra algae. But if the ecosystem comes to life earlier in the year, many species may be left behind. “It’s going to be a different Arctic unless we turn things around,” said Dr. Arrigo.

Read More