Wind perturbation experiments to simulate the 1970s drop in the sea ice extent in the Southern Ocean

The sea ice extent (SIE) in the Southern Ocean experienced a drop in the late 1970s, though less pronounced compared to the one post-2016. Though several studies explain the drop since 2016, the 1970s decline is critical in understanding the long-term variability of SIE. To investigate the underlying mechanisms for this decline, we conducted wind perturbation experiments using the general circulation model EC-Earth3. We perturb the model by adding wind stress anomalies derived from ERA5 to the model winds. Using this technique, we simulate the evolution of SIE over the period 1958-2023. Our analyses show that the perturbation induces a drop in the 1970s despite the control (no-perturbation) run showing no such trend. This strongly indicates the important role of winds in driving the drop, though ocean processes and other feedback mechanisms may also contribute to the decline. The SIE shows spatial heterogeneity in the variations driven by the wind. Presently, we are conducting multiple ensemble simulations to evaluate the influence of initial conditions on the results.