Irreversibly broken: Arctic Ocean crosses point of no return
Scientists have discovered a hidden change beneath melting Arctic ice that could reshape ecosystems far beyond the polar region.
Something has irreversibly broken in the Arctic Ocean, and is expected to have consequences that stretch far beyond the polar ice.
A new study by researchers at the University of Edinburgh has found that the Arctic Ocean crossed a critical threshold around 2009, triggering a chain of changes that is now unravelling its food web from the bottom up.
DISAPPEARING NUTRIENTS IN THE ARCTIC
The culprit behind the shifting ecosystem is the loss of sea ice, which has been shrinking steadily for decades as global temperatures rise.
But the knock-on effect that scientists have now identified goes deeper than most people realise.
As ice disappears, vast shallow stretches of the Arctic seabed, which underlie nearly half the ocean, are exposed to sunlight for the first time. That sunlight accelerates a chemical process that converts nitrate, a key nutrient, into nitrogen gas, effectively stripping it out of the water.
Nitrate is the foundation on which plankton grows, and plankton is the foundation on which a big chunk of marine life depends. Meaning the impacts are felt by fish, seabirds, whales, seals, and many others underwater.
"For years, sea-ice loss in the Arctic Ocean was expected to increase phytoplankton growth because more sunlight could reach surface waters," said Marta Santos-Garca, a PhD student at Edinburgh's School of GeoSciences who co-led the study. "Our findings suggest that this relationship has changed: the Arctic Ocean appears to have shifted from a system mainly limited by light to one increasingly limited by nitrate availability, with far-reaching consequences for marine ecosystems, food chains and the role of the Arctic in the Earth's climate."
TWO DECADES OF DATA, ONE TIPPING POINT
The researchers arrived at these conclusions by analysing over 20 years of ocean sampling data from Arctic waters.
The data showed a consistent downward trend in nitrate levels beginning in 2009, coinciding exactly with an accelerated collapse of sea ice around the same period.
The implications are clear and ignorable.
With less nitrate in the water, only smaller species of plankton can survive, meaning less food is available for the animals that depend on them. The ocean also loses some of its ability to absorb carbon from the atmosphere, since plankton play a central role in that process.
"The changes we report suggest that the Arctic Ocean ecosystem passed a tipping point around 2009. How this change cascades through the food chain needs to be closely monitored as this has profound implications for us, including on commercial fishing in the North Atlantic Ocean," said Professor Raja Ganeshram, who has led the research over the past two decades.
IRREVERSIBLE CHANGE
What makes this finding especially troubling is its permanence.
The nitrate loss is driven by ongoing sea ice melt, which shows no sign of reversing.
That means, it is now very unlikely the Arctic Ocean will ever return to its previous state, and is diagnosed with a condition with no cure.
Climate change is not slowing down, meaning the best case scenario means an unchanged situation, as the only way from here is further down.
Something has irreversibly broken in the Arctic Ocean, and is expected to have consequences that stretch far beyond the polar ice.
A new study by researchers at the University of Edinburgh has found that the Arctic Ocean crossed a critical threshold around 2009, triggering a chain of changes that is now unravelling its food web from the bottom up.
DISAPPEARING NUTRIENTS IN THE ARCTIC
The culprit behind the shifting ecosystem is the loss of sea ice, which has been shrinking steadily for decades as global temperatures rise.
But the knock-on effect that scientists have now identified goes deeper than most people realise.
As ice disappears, vast shallow stretches of the Arctic seabed, which underlie nearly half the ocean, are exposed to sunlight for the first time. That sunlight accelerates a chemical process that converts nitrate, a key nutrient, into nitrogen gas, effectively stripping it out of the water.
Nitrate is the foundation on which plankton grows, and plankton is the foundation on which a big chunk of marine life depends. Meaning the impacts are felt by fish, seabirds, whales, seals, and many others underwater.
"For years, sea-ice loss in the Arctic Ocean was expected to increase phytoplankton growth because more sunlight could reach surface waters," said Marta Santos-Garca, a PhD student at Edinburgh's School of GeoSciences who co-led the study. "Our findings suggest that this relationship has changed: the Arctic Ocean appears to have shifted from a system mainly limited by light to one increasingly limited by nitrate availability, with far-reaching consequences for marine ecosystems, food chains and the role of the Arctic in the Earth's climate."
TWO DECADES OF DATA, ONE TIPPING POINT
The researchers arrived at these conclusions by analysing over 20 years of ocean sampling data from Arctic waters.
The data showed a consistent downward trend in nitrate levels beginning in 2009, coinciding exactly with an accelerated collapse of sea ice around the same period.
The implications are clear and ignorable.
With less nitrate in the water, only smaller species of plankton can survive, meaning less food is available for the animals that depend on them. The ocean also loses some of its ability to absorb carbon from the atmosphere, since plankton play a central role in that process.
"The changes we report suggest that the Arctic Ocean ecosystem passed a tipping point around 2009. How this change cascades through the food chain needs to be closely monitored as this has profound implications for us, including on commercial fishing in the North Atlantic Ocean," said Professor Raja Ganeshram, who has led the research over the past two decades.
IRREVERSIBLE CHANGE
What makes this finding especially troubling is its permanence.
The nitrate loss is driven by ongoing sea ice melt, which shows no sign of reversing.
That means, it is now very unlikely the Arctic Ocean will ever return to its previous state, and is diagnosed with a condition with no cure.
Climate change is not slowing down, meaning the best case scenario means an unchanged situation, as the only way from here is further down.
