Even the currents in the depths of the ocean cannot escape the effects of climate change

We know global warming affects ocean currents in a variety of ways, but questions remain as to how exactly this relationship works. A new study attempts to answer some of these questions.

Pondering data going back 66 million years in 293 locations, scientists studied gaps in sediment layers, known as hiatus, to find out the varying strength of ocean currents over the millennia and how this is related to temperature changes.

This provided a wealth of additional data beyond the 30 or so years of satellite imagery that researchers have traditionally used to study how ocean current activity changes as Earth’s temperature continues to rise.

“The satellite data typically used to inform ocean models cover only a few decades, resulting in a poor understanding of longer-term ocean variability,” says the sedimentologist Adriana Dutkiewicz from the University of Sydney in Australia.

“This prompted us to look at the deep sea geological record to decipher these changes.”

The team found that the gaps in the sediment record became rarer over the past 13 million years as the Earth gradually cooled. This suggests that the current speed in the deepest parts of the ocean has slowed overall.

By comparison, deep-sea circulation appeared to be much more active during the “greenhouse climate” period that preceded the 13-million-year cooling. At that time, global temperatures would have been 3-4°C (5.4-7.2°F) warmer than today.

You don’t have to live on the ocean floor to be affected by fluctuations in ocean currents: these deep eddies affect everything from main weather conditions to the distribution of marine life.

“An interruption in sedimentation indicates strong deep-sea currents, while continuous sediment accumulation indicates calmer conditions.” says geophysicist Dietmar Müller from the University of Sydney.

“By combining this data with ocean basin reconstructions, geologists were able to track where and when these sedimentary fractures occurred.”

The more we know about the past, the better our predictions become when it comes to modeling global warming change the oceans in the future. The ocean has already absorbed a huge amount of excess carbon and heat.

previous studies point out that in times of global warming, the oceans can capture more carbon, mainly via plankton, which use dissolved carbon to build their shells and then after death drift to the sea floor and capture the captured carbon.

What is also clear now is that there is likely to be more activity in the deep oceans as temperatures on Earth continue to rise. Future research will be required to estimate exactly how this will affect the balance of life and the atmosphere.

“Fast forward to today: Independent studies using satellite data suggest that large-scale ocean circulation and ocean eddies have become more intense over the past two to three decades of global warming, supporting our findings.” says Mueller.

The research was published in geology.

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