Warming at the Agulhas region during the global surface warming acceleration and slow-down

Abstract

This study investigates the interannual to decadal ocean heat content evolution of the upper 700m in the last three decades at the Agulhas region and emphases on exploring its difference between the global surface warming acceleration and slowdown periods. The Agulhas region is a stagnation point of three circulation systems, the South Atlantic Ocean subtropical gyre, the Indian Ocean subtropical gyre, and the Subtropical Front of the Antarctic Circumpolar Current in the Southern Ocean, and it’s the linkage between two ocean basins, the Indian Ocean and the Atlantic Ocean. At this region, the ocean never stops or slows its warming even during the global surface warming slowdown. Besides the warming surface, the deeper layer (200-700m) gains more heat primarily as a result of the deepening isopycnals (heaving), possibly induced by the saltier upper layer water, also with a relatively small contribution of the changes along the isopycnals (spice). The most pronounced isopycnal sinking locates at the Return Current and the neighboring Subtropical Front region, while the isopycnals shoal at the upper layer of the Agulhas Current. Due to the altered wind pattern at the Indian Ocean and Southern Ocean, less heat comes along the Agulhas Current during the slowdown period, and the broadening Return Current moves the warm and saline subtropical water southward, which is subducted into the deeper layer by the reclining isopycnals.