Arctic residents in hot water

Melting ice in Alaska (I.Quaile)

At the swimming club last weekend, one of my fellow swimmers complained the water was too warm. She said she couldn’t swim at her usual speed when the temperature in the pool rose even a little bit. It left her feeling tired and lethargic. So how much more dramatic must it be for the tiny creatures at home in cold Arctic waters, when a warm influx changes their surroundings and living conditions.?

The warming of Arctic waters with climate change is likely to produce radical changes in the marine habitats of the High North. Data from long-term observations in the Fram Strait, which researchers from the Alfred Wegener Institute (AWI) have now analysed and published in the journal “Ecological Indicators”, confirms that even a short-term influx of warm water into the Arctic Ocean would suffice to fundamentally impact the local symbiotic communities, from the water’s surface down to the deep seas. They found that this happened between 2005 and 2008.

Arctic residents like it cool (Pic: I.Quaile, Svalbard)

The deep sea observatory

Over the past 15 years, researchers from Germany’s Alfred Wegener Institute for polar and marine science (AWI) have been keeping an eye on the sensitive marine ecosystem in the Fram Strait, the sea lane between Greenland and Svalbard .The institute operates a deep-sea observatory there, known as “HAUSGARTEN”, which translates literally as house garden. It is actually a network of 21 individual mini research stations. Every summer, scientists pay them a visit and collect water and soil samples. Some of the stations have anchored systems that operate year-round, recording the water temperature and tides, collecting water and soil samples at regular intervals, and capturing the sediments that drift down to the seafloor from the upper water layers.

“This is the only observatory of its kind in the world. There’s no other project in which readings from the surface down to the ocean floor were taken in fixed positions over such a long time – let alone in the polar regions,” says AWI biologist Thomas Soltwedel.

For the current publication, the AWI researcher and his team analysed the first 15 years of the HAUSGARTEN dataset. The Fram Strait is especially interesting for Soltwedel and his colleagues because it represents the only deep juncture in the Arctic Ocean, allowing water masses from the Atlantic to flow into the Arctic to the west of Svalbard. In turn, water and ice floes find their way back out of the Arctic Ocean on the strait’s Greenland side.

Warmer water, melting ice, warmer water…melting ice (I.Quaile, Alaska)

Too warm for comfort

Until now, the scientists say it was unclear just how polar marine organisms were responding to the warming of the ocean and shrinking sea-ice cover. Now, the long-term observations show that arctic marine habitats could change radically if subjected to a sustained rise in temperature. The AWI researchers say their most surprising finding is that the thermally induced changes at the ocean surface can rapidly spread to affect life in the deep seas.

Normally the water near the surface, which flows north out of the Atlantic through the Fram Strait, has an average temperature of three degrees Celsius. With the help of their observatory, the AWI researchers were able to establish that from 2005 to 2008 the average temperature of the inflowing water was one to two degrees higher: “In that time, large quantities of warmer water poured into the Arctic Ocean. Since polar organisms have adapted to living in constant cold, this extra heat input hit them like a temperature shock,” Soltwedel explains.

He says the reactions in the ecosystem were correspondingly extreme: “We were able to identify serious changes in various symbiotic communities, from microorganisms and algae to zooplankton.”

Migrating sea creatures

One major change described in the article was the increase in free-swimming conchs and amphipods, which are normally found in the more temperate and subpolar regions of the Atlantic. In contrast, the number of conchs and amphipods in the Arctic dropped significantly.

The researchers also noted a decline in small, hard-shelled diatoms. Prior to the unexpected influx of warm water, they made up roughly 70 per cent of the vegetable plankton in the Fram Strait. But during the warm phase, the foam algae Phaeocystis took their place. A change with consequences, Soltweder explains: “Unlike diatoms, foam algae tend to clump and sink to the ocean floor, where they become a food source. But the sudden rise in available food led to major changes in deep-sea life, including a noticeable increase in the settlement density of benthic organisms.”

If you are not a marine biologist, you may be wondering what that means for the future of the Arctic and why we should be concerned about it. The problem is that all of this affects the Arctic food web.

The scientists can’t say exactly how at this point. But, as with so many other aspects of climate change: “Above all, we’re troubled by the simple fact that the changes have been so rapid, and so far-reaching.”

Melting ice in the waters off Spitsbergen. Already too hot for some? (I.Quaile)

New residents here to stay

Since the flow of warm water has subsided, the water temperature in the Fram Strait has stabilised – though it is still slightly above the average value from before 2005. Yet some of the changes appear to be there to stay. The conchs from the lower latitudes seem to have made a home for themselves in the Fram Strait.
As usual, the scientists are reluctant to say whether the warm-water influx they monitored is due to climate change or could be part of natural climate fluctuations. They say they need data covering several decades to be more certain.
But either way, the results of the ecological long-term studies clearly show that even short-term changes in ocean temperature can drastically impact life in the Arctic. So it looks like there will certainly be more to come, as the world continues to heat up.