Temperature increases cause changes in marine communities
In the future, as the waters in the Arctic warm up due to climate change, there is likely to be a drastic change in the marine habitats in the Arctic. This scenario has been proposed by the researchers of the Alfred Wegener Institute, Helmholtz Centre for Polar and Marine Research after analysing the data from long-term observations in the Fram Strait.
In fact, their most significant discovery indicates that a short-term influx of warm water into the Arctic Ocean is sufficient to fundamentally impact the local symbiotic communities at all levels of the sea, from the surface down to the deep sea realms.
The Arctic is a remote and extreme habitat. Despite its isolation, the accelerated effects of global climate change will cause massive changes in the future. Over the years, the greenhouse effect has been shrinking the sea-ice cover in the Arctic and causing the ocean's temperatures to increase. However, it's been unclear how the polar marine organisms would respond.
Using a set of long-term observations, AWI scientists can show how arctic marine habitats might radically change if subjected to a sustained rise in temperatures. Publishing their findings in the journal Ecologial Indicators, they revealed the most surprising finding that the thermally-induced changes at the ocean surface can swiftly affect life in the deep seas.
To investigate the changes within the ecosystems in the Arctic waters, AWI has operated the HAUSGARTEN (= cottage garden) deep-sea observatory in the Fram Strait, the sea lane between Greenland and Spitsbergen. The Hausgarten comprises a network of 21 individual research stations which AWI staff visit every summer to collect water and soil samples. At selected stations, there are anchored systems that operate throughout the year, recording water temperatures and tides, collecting water and soil samples at regular intervals and capturing the sediments that trickle down from the top layers to the seafloor.
For the current publication, AWI biologist Thomas Soltwedel and his team analysed the first 15 years of the data collected at Hausgarten. The Fram Strait is of particular interest for them because it is the only deep juncture in the Arctic Ocean where water masses from the Atlantic flow into the Arctic to the west of Svalbard. Then, on the strait's Greenland side, water and ice floes flow out of the Arctic Ocean.
Normally, the temperature of the waters near the surface, which flows north out of the Atlantic through the Fram Strait to the north, averages three degrees Celsius. Using the observatory facilities, the scientists discovered that from 2005 to 2008, the average temperature of the inflowing water was actually one to two degrees higher.
During that time, large quantities of warm water moved into the Arctic Ocean. Since polar organisms have adapted to living in constant cold, this extra heat hit them like a temperature shock, said Soltwedel.
The reactions within the ecosystem were similarly severe. The scientists managed to identify serious changes in various symbiotic communities, from microorganisms and algae to zooplankton. ”A major change was the increase in the number of free-swimming conchs and amphipods, which were normally found in the more temperate and subpolar regions of the Atlantic. In contrast, the number of conchs and amphipods in the Arctic dropped drastically,” said Soltwedel.
Another aspect of the changes is seen in the decline of small, hard-shelled diatoms. Before the entry of warm water into the Arctic Ocean, they comprised about 70 percent of the vegetable plankton in the Fram Strait. However, when the warm water entered the picture, the diatoms were overtaken by the foam algae Phaeocystis. The consequence was a noticeable increase in the density of benthic organisms. This was because unlike diatoms, foam algae tend to clump together and sink to the seafloor, where they became a food source for the benthic organisms.
For the moment, Soltwedel is unable to predict how these changes will affect the overall Arctic food web. “Above all, we're troubled by the simple fact that the changes have been so rapid, and so far-reaching,” he said.
After the inflow of warm water has subsided, the water temperature in the Fram Strait has stabilised, though it still remains at a slightly higher temperature than the pre-2005 levels. Yet, other noticeable changes in the ecosystem persist to this day, in the form of the low quantity of diatoms and the presence of the conchs from the southernly latitudes that seem to have made themselves at home in the Fram Strait.
Link to the study: www.sciencedirect.com/../S1470160X15005361