[A-OS13] Exploring Variability and Changes in Ocean Biogeochemical Cycles

[AOS13-P06] Forcings and Mechanisms of Future Pacific Basin Oxygen Change in Idealized Model Simulations

*Benjamin A Taylor¹, Yohei Takano², Yassir Eddebbar¹, Shang-Ping Xie¹, Lynne Talley¹ (1.University of California San Diego, 2.British Antarctic Survey)

Keywords:Deoxygenation, Stratification, Buoyancy Forcing, Oxygen Minimum Zones

Projections of ocean deoxygenation under global warming consistently show decreases in water mass age and apparent oxygen utilization (AOU) in the oxygen minimum zones of the subsurface tropical Pacific. Whereas previous analysis has attributed this change to a reduction in tropical upwelling of old deep waters associated with the slowing global overturning circulation, we argue that it is primarily related to the dynamical adjustment of the upper ocean circulation to increased stratification. Building on recent insights derived from separating the effects of buoyancy flux and wind stress trends on ocean circulation change, we show that the dynamical response of the Pacific thermocline to a basin-wide surface warming is a large-scale “flattening” of subsurface isopycnals associated with upward heave in the subtropics and downward heave in the tropics. In a suite of idealized biogeochemical model experiments, this buoyancy-driven circulation response explains the contrasting subtropical and tropical age/AOU subsurface ocean response to imposed warming at the surface. We further demonstrate the relevance of this dynamical adjustment to the future oxygen trends in realistic models.