Today, Earth's oceans absorb excess carbon dioxide from the atmosphere. Research suggests in the past the opposite was true.
In recent decades, scientists estimate the Arctic and Nordic seas absorbed as much as 40 percent of CO2 emissions. Analysis of sediment cores suggests Earth's northern seas pumped significant amounts of CO2 into the atmosphere in the past.
"Our research shows that areas in Norwegian Sea have changed their function on several occasions through the past 135,000 years," Mohamed Ezat, a geoscientist at the Arctic University of Norway, said in a news release. "Instead of absorbing CO2 from the air, they released more of the greenhouse gas into it."
Researchers were able to track changes in ocean pH and CO2 emission rates by analyzing the ratios of boron isotopes in the fossil shells of foraminifera, a single-celled marine organism. The foraminifera fossils were sourced from sediment cores representing the Norwegian Sea's biochemical history spanning the last 135,000 years.
"We saw that at the end of several of the severe cooling periods in the region, so-called Heinrich events, the ocean became more acidic and later released CO2 into the atmosphere," Ezat explained. "These episodes of CO2 pumping from the Nordic Seas coincide with times of increase in atmospheric CO2."
Analysis suggests an influx of terrestrial organic matter, as well as shifts in marine biology and ocean currents, influenced fluctuations in CO2 and pH levels on the ocean's surface. The findings were published in the journal Nature Communications.
The research also showed modern changes in CO2 and pH levels are unnatural.
"Results of our study actually show that the sea surface pH throughout the last 135,000 years has never been as low as today in our study area," Ezat said. "This is not an unexpected result. It is similar to previous studies conducted in other ocean areas. It does however add a body of evidence to the hypothesis that human activity is profoundly affecting the chemistry of our oceans."
The oceans are great at absorbing carbon dioxide (CO2) from the air, but when their deep waters are brought to the surface, the oceans themselves can be a source of this prevalent greenhouse gas.
Wind patterns together with the Earth's rotation drive deep ocean water – and the CO2 it sequesters – upward, replacing surface water moving offshore. A process known as upwelling, it occurs on th … read more
