Global warming is accelerating currents in the ocean depths

World ocean circulation. Credit: NASA via Wikimedia Commons.

Scientists at the University of Sydney have used deep sea geological records to discover that past global warming has accelerated deep ocean circulation.

This is one of the missing links in predicting how future climate change might affect the uptake of heat and carbon by the oceans: stronger ocean currents make it easier to “mix” carbon and heat.

“So far, the ocean has absorbed a quarter of the anthropogenic CO2 and more than 90% of the associated excess heat,” said the study’s lead author, Dr. Adriana Dutkiewicz of the EarthByte group from the School of Geosciences at the University of Sydney.

Microscopic marine organisms called plankton use this dissolved carbon to build their shells. They sink to the bottom of the sea after they die, sequestering carbon. These sedimentary deposits form the largest carbon sink on Earth.

The authors note that observations and climate models have been used alternately to assert that deep ocean circulation could slow down or accelerate during global warming. This inconsistency is a problem for modeling future climate trends and the new study, published today in the benchmark journal Geologyhelps resolve this controversy.

“Satellite data typically used to inform ocean models spans only a few decades, leading to poor understanding of longer-term ocean variability. This prompted us to examine deep-sea geologic records to decipher these changes” , said Dr. Dutkiewicz.

Scientific ocean drilling data collected over half a century has generated a treasure trove from which to map deep sea currents. Dr Dutkiewicz and co-author Professor Dietmar Müller compiled data from more than 200 drill sites to map deep-sea sediment records, which can indicate current speed.

“A sedimentation break indicates vigorous deep sea currents, while a continued accumulation of sediment indicates calmer conditions,” Prof Müller said. “Combining this data with reconstructions of ocean basins has allowed geologists to track where and when these sediment breaks occurred.”

Teresa H. Sadler