Temperature‐Modulated Ocean CO ₂ Uptake in Response to CO ₂ Increase and Decrease

Abstract We use an Earth system model to investigate climate change effect on ocean CO 2 uptake. Atmospheric CO 2 increases from 1 × CO 2 (285 ppm) to 4 × CO 2 and then returns to 1 × CO 2 at a rate of 1% per year. At 4 × CO 2 , climate change reduces cumulative CO 2 uptake by 96 PgC, with the effect of temperature‐induced changes in ocean mixing, CO 2 solubility, and biology accounting for 46%, 38%, and 16%, respectively. After CO 2 starts to decrease, climate change continues to reduce CO 2 uptake due to persistent ocean warming, and the relative role of ocean mixing and biology becomes more important. When atmospheric CO 2 returns to 1 × CO 2 , climate change reduces cumulative CO 2 uptake by 198 PgC, with changes in ocean mixing, CO 2 solubility, and biology accounting for 52%, 23%, and 25%, respectively. Temperature‐induced changes in phytoplankton growth and remineralization rates each affect CO 2 uptake more strongly than solubility, though their effects partially offset each other.