LAUSR

16 A decline in global ocean oxygen concentrations has been observed over the 20 century 17 and is predicted to continue under future climate change. Here, we use a unique modeling 18 framework to understand how the perturbed ocean circulation influences the rate of ocean de19 oxygenation in response to a doubling of atmospheric CO2 and associated global warming. 20 In our simulations, the ocean circulation response to CO2 doubling slows the pace of future 21 oxygen loss by 20%. This stabilizing effect on oxygen is principally due to the perturbed cir22 culation helping to maintain dense water formation in the Southern Ocean, which ventilates 23 a large volume of the ocean, and, secondarily, by reducing export productivity and associ24 ated respiration in the ocean interior. A slowdown of the Atlantic Meridional Overturning 25 Circulation increases the residence time of the deep Atlantic Ocean, but on the decadal time 26 scale analyzed here, this aging of the water column does not result in a major oxygen decline 27 because the respiration rate is slow at these depths. The simulations show that the decrease 28 in O2 solubility associated with ocean warming is slightly greater than the actual realized 29 decrease in preformed O2 concentrations, particularly at high latitudes, where ocean warm30 ing is associated with circulation changes that alter the proportion of undersaturated waters 31 sinking into the ocean interior. Finally, in the tropical Pacific oxygen minimum zone, a pre32 dicted weakening of the Walker Circulation slows the regional upwelling of nutrients and the 33 associated export productivity and respiration, thereby preventing the intensification of low 34 oxygen concentrations there. 35