Earth’s ocean currents are circulating at a rate faster than what they were over two-decades ago. What’s more, is that the scientists working on the study claim this accelerated rate of flow could be down to climate change.
According to new research published in Science Advances, the observations claim that between 1990 and 2013 the “globally integrated ocean kinetic energy” demonstrated an increase of around 15%. This increase is a cause for concern as it could have a knock-on effect on global weather patterns, jet streams, and the ocean’s natural heat storage system.
The magnitude and extent of the acceleration in ocean currents we detected throughout the global ocean and to 2000-meter (6,560 foot) depth was quite surprising. While we expected some response to the increased winds over the past two decades, that the acceleration was above and beyond that was an unexpected response that is likely due to global climate change.
Janet Sprintall, Co-author of the paper and Oceanographer, The Scripps Institution of Oceanography, University of California, San Diego
Winds of Change
Leading the study was Shijian Hu, an oceanographer at the Institute of Oceanology in Qingdao, China. Hu and his colleagues wanted to understand shifts and pattern changes across global ocean currents because previous research had generated conflicting conclusions. There was a conflict in the rate of acceleration between currents in the subtropics that shift kinetic energy towards the poles compared with regional currents such as the Kuroshio in the western North Pacific - the former demonstrating an increase while the latter showed almost no change.
Furthermore, wind speeds have been climbing at a rate of 1.9% every ten years over the past two decades and by the same token ocean speeds have increased by around 5% per decade. As wind speeds intensify the energy transfers to the ocean’s surface. Hu and his team believe that the increased speed and strength of winds is a consequence of human activity and its environmental impact.
A case in point for this argument is in the southern hemisphere where increases in greenhouse warming and a deficiency in the ozone layer coincide with a surge in the ocean’s westerly winds which has intensified the flow of the Antarctic Circumpolar Current (ACC). This current is particularly important as it is the only current to completely circumnavigate the planet and it is also what keeps Antarctica cool and frozen: a vital component in the Earth’s ocean circulatory system, the ACC is influenced mainly by the westerly winds so any significant changes will have a natural consequence.
Argo Observational Data
To gather a more accurate picture the team went over previous data and combine this with newer information from the Argo programme. The data compiled by Argo is generated by 4000 robotic floats scattered around the globe which have been sitting in the surface layer (upper 2000 meters) for 15 years. Argo’s data illustrates where ocean winds have a significant impact on the waters and consequently, how changes in pressure drive the currents.
However, as the observational data of Argo doesn’t track the flow of water through the water column by velocity the team must combine the data with the current-borne trajectories of the individual robotic floats. Once this phase has been completed the scientists were able to calculate an accurate model which demonstrates ocean current strength and velocity. Additionally, five other “assimilation products” and “12 model simulations” were also used in constructing an accurate model.
Hu and his team state in their paper that an “accurate assessment” of the fluctuations in ocean currents and overall circulation across the planet is “key to understanding global climate change.”
While climate change is thought to be a major factor, natural changes could also play a part in the acceleration of ocean currents over the past two-decades. This could be due to long-term cooling near the American coast of the Pacific which causes winds to quicken, or from the effects of other known phenomena such as El Niño.
However, whether driven by climate change or natural forces, continual acceleration in ocean currents can impact the entire planet. As well as influencing the jet streams, intense, swirling ocean currents could trap more heat from the atmosphere. How this trapped heat is then redistributed is what could lead to an increase in extreme weather events. Furthermore, warming oceans would most definitely affect marine life such as altering fish migration patterns and damaging underwater kelp forests.
Thus, understanding the changes in the ocean currents and how trends such as those observed by Hu and his colleagues, is important to making future forecasts. Yet, it could be another decade of data collection from resources such as Argo that the real picture starts to emerge.