Long-term study tracks shifting currents in Fram Straight
Intensive monitoring along the Fram Straight, between Greenland Svalbard, shows that even a short-term influx of warm water into the Arctic Ocean would be likely to have long-lasting effects on regional ecosystems.
Even small changes in surface water temperatures could quickly spread to affect life in the depths of the Arctic Ocean, a team of scientists concluded in a new study published in the journal Ecological Indicators.
The researchers reached their conclusions after studying a massive set of data collected from the HAUSGARTEN observatory in the Fram Strait, a network of 21 individual research stations.
Some of the stations feature 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,” said Alfred Wegener Institute biologist Thomas Soltwedel.
The observations showed, for example, that, between 2005 and 2008, water temperatures flowing out of the Atlantic north through the Fram Straight were 1 to 2 degrees Celsius warmer than the long-term average.
“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 said.
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. One major change 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,” Soltwedel said.
The researchers also tracked 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.
“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,” Soltwedel explained.
Although there’s no telling exactly how the changes will affect the overall arctic food web in the future, Soltwedel said the researchers are troubled by the “simple fact that the changes have been so rapid, and so far-reaching.”
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 the changes in the ecosystem have partly become lasting realities. For example, the number of diatoms remains very small. And the conchs from the lower latitudes seem to have made a home for themselves in the Fram Strait.
“At the moment we can’t say whether the warm-water influx we’ve monitored is due to climate change, as there are also natural climate fluctuations that, for instance, occur every ten years. They overlap with the anthropogenically caused effects of climate change, as a result of which, after 15 years, we still don’t exactly know whether this flow of warm water was the result of strictly natural causes,” he said.
The research efforts at HAUSGARTEN will continue. “We’ll only be able to say for sure whether changes are natural or manmade once we have data covering several decades,” Soltwedel said.