(ORDO NEWS) — We know that global warming affects ocean currents in a variety of ways, but questions remain about exactly how this relationship works. The new study attempts to answer some of these questions.
The scientists analyzed 66 million years of data from 293 sites, looking at gaps in sedimentary layers known as hiatuses to find out how the strength of ocean currents has changed over millennia and how this is related to changes in temperature.
This provided a wealth of additional data beyond the 30 years of satellite imagery that researchers have traditionally used to study how ocean current activity changes as global temperatures rise.
“Satellite data commonly used to inform ocean models span only a few decades, leading to a poor understanding of long-term ocean variability,” says sedimentologist Adriana Dutkiewicz of the University of Sydney in Australia.
“This prompted us to look to the deep sea geological record to decipher these changes.”
The team found that over the past 13 million years, as the Earth gradually cooled, breaks in sediment records became less frequent. This suggests that the speed of currents in the deepest parts of the ocean has generally slowed down.
By comparison, during the “hothouse climate” period that preceded the 13-million-year cooling epoch, circulation in the deep layers of the ocean was much busier. At this time, global temperatures were 3-4°C (5.4-7.2°F) warmer than today.
You don’t have to live on the seafloor to be affected by fluctuating ocean currents: These deep eddies influence everything from basic weather patterns to the distribution of marine life.
“The hiatus in sedimentation indicates vigorous deep water currents, while the continuous accumulation of sediment indicates calmer conditions,” says geophysicist Dietmar Müller from the University of Sydney.
“Combining this data with the reconstruction of ocean basins allowed geologists to trace where and when these breaks in sedimentation occurred.”
The more we know about the past, the better our predictions will be when modeling how global warming will change the oceans in the future. The ocean has already absorbed a huge amount of excess carbon and heat.
Previous research suggests that oceans can retain more carbon during periods of warming, largely because plankton use dissolved carbon to build their shells and then sink to the ocean floor after death, trapping the absorbed carbon.
It is now also clear that as the temperature on Earth continues to rise, activity in the deep oceans is likely to increase. Further research will be required to assess exactly how this will affect the balance of life and atmosphere.
“Today, independent studies using satellite data show that large-scale ocean circulation and ocean eddies have become more intense over the past two to three decades of global warming, confirming our findings,” says Muller.
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