As you might have known our oceans have great currents moving across them, with each of these currents moving as much as water as all the rivers of the world combined. New research on these continent-wrapping current suggest that they have been speeding up rapidly and global warming might be reason for this.
The research that was published in Science Advances notes the occurence of this acceleration based on observations combined with models. The authors of the study claims that these currents has seen an energy increase of 15% per decade in the 1990-2013 time period.
The lead author of the study, Hu Shijian, an oceanographer at the Chinese Academy of Sciences’s Institute of Oceanology says that oceanographers have suspected that climate warming is affecting ocean circulation, but so far, observations haven’t shown a trend. But individually these currents behave differently as some have slowed down. While the others have sped up. Beacuse of this Hu decided only a global analysis could reveal an overall trend, if there was one.
The team used something called reanalyses, a method that combines observations of the ocean and atmosphere with computer models to fill in the gaps and produce a global picture. The gaps exist because there are no sustained direct measurements available fo currents all over the world.
The method comes with the problem of unknown biases as observations can change over long time spans due to changes in the technology or devices used. To overcome this, the team combined five different reanalyses of ocean circulation. After analysing the ocean’s kinetic energy month by month they have found a distinct rise starting around 1990.
To compare the modelled results with experimental data they relied on the dataset created by oceanographer Alison Gray of the University of Washington, Seattle using Argo array. Argo array is a fleet of nearly 4000 robotic floats deployed around the world to measure ocean’s temparature and salinity for the last 15 years.
Though its data doesn’t directly determine the water column velocity, it can be used to determine wind pressure above water regions.It is the difference is wind pressures that drive large-scale flows. Using it the researchers were able to reconstruct currents and their velocities.
Although the Argo data covers only 6 years from 2005 to 2010, Hu says that it reveals an even clearer global speed-up of these currents. It is noted by Gray that ocean winds a major driver of the currents have steadily increased over the past 3 decades. Hu believes human activity has contributed to these conditions. Green house warming and ozone depletion has altered atmoshperic circulation patterns which inturn strengthens some of these currents.
Some scientists think the wind acceleration could be because of natural factors such as oscillations in ocean’s state. But Hu, thinks oscillations could be responsible for at most one-third of the wind speed-up.
In any case the increase in speed of ocean currents have large-scale implications. It could slow down uptake pf carbon dioxide by the oceans and also cause shift in weather patterns. “At the same time, by reaching deep into the ocean, the acceleration could boost the storage of heat in the depths, helping slow the warming on land,” says Hu.
This is the first ever global study made towards the speed of ocean currents. The researchers believe their work will stimulate more research into the fields to get a better picture of what exactly is happening to our oceans.