Measuring oxygen concentrations to improve the detection capabilities of an ocean circulation observation array

[1] The North Atlantic meridional overturning circulation (MOC) may weaken or even collapse in response to anthropogenic climate forcing, with potentially nontrivial socioeconomic impacts. One currently implemented MOC observation system uses temperature and salinity (as well as other) observations along a zonal transect in the North Atlantic. The resulting MOC estimate has, however, a relatively low signal-to-noise ratio due to large internal variability and observation errors. Observations of hydrographic tracers that are mechanistically linked to MOC changes may increase the signal-to-noise ratio. A MOC slowdown is associated in model simulations with a shoaling of the boundary between North Atlantic Deep Water and Antarctic Bottom Water. This shoaling results in detectable trends in water mass tracers. Here we deploy a virtual observation array into a numerical model starting in model year 2006 to test whether observing the apparent oxygen utilization (AOU) in addition to the MOC estimate improves detection capabilities. Our detection method accounts for observation errors, autocorrelated variability, and uncertainty about the initial conditions. Neglecting the effects of observation errors and the uncertainty about the initial conditions results in artificially early detection times. The MOC signal alone enables reliable detection in roughly five decades. Adding AOU observations reduces this detection time by approximately 40%.