Nonlinear Effects of Wind on Atlantic Ocean Circulation


Source: Journal of Geophysical Research: Oceans

The Atlantic Meridional Reversing Circulation (AMOC) is a system of ocean currents that carries warm, salty water from the tropics to the North Atlantic. As the water cools, it becomes denser and sinks, in a process known as overturning. The cold deep water then flows back to the equator. This transport process plays an essential role in the Earth’s climate.

Although scientists know that surface wind stress can affect the variability of AMOC from year to year, the impact of wind stress on decadal timescales is less clear. In a new study, Lohmann et al. fill this knowledge gap by using MPI-ESM (Max Planck Institute for Meteorology Earth System Model). They performed 250-year simulations in which the average wind stress received by the ocean was changed so that it was either half or double that of a reference simulation.

They found that under reduced forcing by the wind, the strength of AMOC decreases sharply. Reduced northward heat and salt transport and subsequently a greater extent of sea ice in winter and reduced surface density have halted the production of cold, deep water that usually forms in the area. ‘Subpolar North Atlantic and Nordic Seas.

In the case of increased wind stress forcing, the authors found that effects opposite to those of reduced wind stress forcing initially occur and the strength of AMOC increases. Over time, however, the AMOC weakens and stabilizes at a force similar to what was observed in the baseline simulation. Researchers attribute this nonlinear effect to a decrease in surface density (after the initial increase) in the North Atlantic and weakening of the subpolar formation in deep water.

The results indicate that the future intensification or weakening of jet streams in the northern hemisphere could affect the circulation and climate of the North Atlantic. Further analyzes with other climate models will provide additional support for the new findings, according to the authors. (Journal of Geophysical Research: Oceans, https://doi.org/10.1029/2021JC017902, 2021)

—Jack Lee, science writer

Quote: Lee, J. (2022), Nonlinear Effects of Wind on Atlantic Ocean Circulation, Éos, 103 years old, https://doi.org/10.1029/2022EO220013. Posted on January 11, 2022.
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