Extreme temperature events in the Agulhas Current

Climate change is generally seen as a gradual warming in centennial global mean surface temperatures, but the associated increase in the frequency and severity of extreme events are increasingly recognized. Western boundary currents (WBCs) have the highest kinetic energy, carry the greatest amounts of heat, and express the fastest rates of warming in the world’s oceans. Past analyses have been too coarse-grained to reveal regional nuances and mechanistic underpinnings of warming trends. We apply a marine heatwave (MHW) analysis to daily Optimally Interpolated Sea Surface Temperature (dOISST) data, and provide an analysis of warming trends in the mean and extreme temperatures of WBC regions. Contextualised by the spatial patterns in mean and eddy kinetic energy (MKE and EKE) and the meandering properties of the WBCs, we show that the boundary current jets, eddy fields, and meanders are not equal in their potential to drive trends in heat transport. The jets and the eddy fields minimally influence warming trends in the mean SST and the extremes, but the lateral meandering of the currents into the cooler, poleward water masses cause MHW-like phenomena.

Below is an animation that shows the meandering of the Agulhas Current and the formation of marine heatwaves (MHW). The MHW are usually associated with the region where the current retroflects back towards the South West Indian Ocean.

Here is another animation showing the Gulf Stream of the eastern USA. MHW are also associated with this current’s trajectory.