Increase of total alkalinity due to shoaling of aragonite saturation horizon in the Pacific and Indian Oceans: Influence of anthropogenic carbon inputs

Aragonite saturation horizon (ASH) shallowed significantly by 25 to 155 m and 16 to 124 m in the Pacific and Indian Ocean respectively in two decades. Apparent oxygen utilization (AOU) increased by 3 to 34 and 0.5 to 31.5 μmol kg −1 in the Pacific and Indian Ocean respectively at the depth of ASH during this period. DIC increased by 12.5 to 36.8 and 5.5 to 32 μmol kg −1 in the vicinity of ASH in the Pacific and Indian Ocean respectively due to combined effect of increased anthropogenic CO 2 and change in AOU. TA increased significantly by 5 to 10 and 4 to 9.2 μmol kg −1 in the Pacific and Indian Oceans respectively at the ASH most likely as a result of aragonite dissolution. The upward migration of ASH solely due to anthropogenic CO 2 amounted to 6 to 58 m in the Pacific and 4 to 44 m in the Indian Ocean.