Along rocky coastlines of the Arctic Ocean, a radical change is taking place, perhaps as profound as vanishing sea ice but less evident to the eye. Ecological foundations are shifting, with existing algae replaced by warmth- and light-loving species. It might not seem like much, but algae form the base of ocean food chains, and the change is happening fast.

"The abrupt character of these extensive changes, confirmed by our statistical analyses, provides a convincing case for tipping points being crossed," wrote researchers led by marine biologist Susanne Kortsch of Norway's University of Tromsø in an email to Wired.

For scientists, tipping points aren't just pop-culture shorthand, but refer to a specific type of transition: sudden and non-linear, with one set of conditions snapping into another. In marine settings, that's been seen in the western Mediterranean, now dominated by jellyfish and invertebrates, and Caribbean coral reefs now overrun by algae. As for the Arctic, they've been detected, but mostly on land or in freshwater lakes and swamps.

Kortsch and her University of Tromsø colleagues, including marine biologists Bjørn Gulliksen and Paul Renaud, went to sea, examining the rocky-bottomed subtidal zones of two Arctic fjords in the western Svalbard islands. Researchers have studied those fjords for more than three decades. As Kortsch's group described August 13 in Proceedings of the National Academy of Sciences, they've become a very different place.

Seafloor communities in Smeerenburgfjord in 1984 (left) and 2006 (right). Image: Kortsch et al./PNAS

Between 1980 and 2010, the region's summer ice-free season lengthened by an average of 3.3 days per year. Sea surface temperatures rose by one degree Fahrenheit. By Arctic standards, the heater is on blast.

In Kongsfjord, the westernmost of the fjords studied, algae composition remained stable for 15 years. Then, between 1995 and 1996, brown algae – a group that includes many types of seaweed and kelp – went from covering 8 percent of the seafloor to a whopping 80 percent.

They've since stabilized at 40 percent, or five times more than was there before. Sea anemones, previously the fjord's dominant species, have declined by 80 percent.

In Smeerenburgfjord, the jump occurred in 2000, and saw brown algae cover rise from 3 percent to 26 percent. That fjord's ecosystem had been dominated by barnacles and sea squirts. These were replaced by invertebrates called bryozoans.

Such changes aren't simple, local tweaks, say Kortsch's group. They're what ecologists call "regime shifts," in which one set of plants and animals is almost entirely replaced by another. They're also not limited to two fjords. Reports of increasing algae south of Svalbard and in western Greenland hint at regime shifts across much of the Arctic Ocean's shores.

How these changes will ripple up food chains remains to be seen. It stands to reason that some changes will occur, and anecdotal observation suggests an increase in traditionally sub-Arctic fish species, but hard data is needed. "At present, we simply don't know the answers," Kortsch said.

The researchers do speculate that these new coastline ecosystems could be more productive than before, as measured in the total weight of everything that lives there, and more biodiverse. Whether they'll be resilient to further change, however, is unknown, and the change is just starting.

Warming in the Arctic is accelerating at twice the average global rate. By 2050 the Arctic Ocean may be completely ice-free in summer. For these new coastline ecosystems, only one thing can be said with certainty: It's not going to be like it was.

Citation: "Climate-driven regime shifts in Arctic marine benthos." By Susanne Kortsch, Raul Primicerio, Frank Beuchel, Paul E. Renaud, João Rodrigues, Ole Jørgen Lønne, and Bjørn Gulliksen. Proceedings of the National Academy of Sciences, August 13, 2012.

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