Sea-surface temperatures near several currents like the Agulhas, called western boundary currents, have increased more rapidly over the last century compared to temperatures elsewhere in the ocean. This rise in temperature — along with increasing velocities of wind systems across the world — has led researchers to suspect that western boundary currents are gaining strength and transporting more heat poleward.
In a new study in Nature, however, researchers suggest that instead of strengthening, the Agulhas Current is actually broadening and growing more chaotic — thus potentially transporting less heat poleward.
“On a global scale, broadening of the Agulhas Current would mean that the transport of heat towards the poles may decrease, rather than increase, with climate change, leading to warmer tropics and cooler polar regions,” says Lisa Beal, an oceanographer at the University of Miami and lead author of the study.
At the local level, Beal says, it could lead to a larger exchange of pollutants and various animal larvae between the South African continental shelf and the open ocean. “This could affect nutrient flow, larvae survival, and ultimately, ocean productivity and fisheries.”
To determine whether the current has been growing stronger, Beal and her University of Miami colleague, Shane Elipot, used measurements of sea-surface height gradients as a proxy for current strength.
Many factors, such as winds, tides, currents, and differences in temperature and salinity, can lead to some parts of the ocean surface being higher or lower than others. In general, the larger the difference in sea-surface height, or the steeper the slope of the ocean surface, the stronger the current.
Read the full article here: https://www.earthmagazine.org/article/broadening-ocean-current-could-carry-less-heat-poleward-climate-change