The Arctic Ocean crossed a tipping point around 2009, according to a new study showing that sea ice loss has sharply reduced nitrate levels in the water.
Researchers from the University of Edinburgh analyzed more than 20 years of data from Fram Strait. They found that the decline in nitrate began as sea ice retreated rapidly, exposing shallow waters to more sunlight and accelerating a process called benthic denitrification that removes the nutrient from seawater.