Understanding oxygen in the Southern Ocean from models

Understanding oxygen in the Southern Ocean from models and observations Lauren Santi and Alison Gray

Motivation High variability of oxygen levels seasonal, interannual, regional Limited knowledge of the Southern Ocean historical observations are sparse, biased towards summer Importance of Southern Ocean in global oxygen cycle Annual mean zonally averaged oceanic uptake of oxygen for period 1990 -2000 (Matear et al. 2000) climate change control difference

Research Questions How well do current models represent the variability of oxygen in the Southern Ocean? How will oxygen concentrations in the Southern Ocean change with increased CO 2? Approach: Use observations and coupled climate models

ARGO Profiling Floats ● Floats take profile measurements of top 2000 meters every ten days A subset have oxygen sensors 17, 521 profiles Oxygen data has recently been recalibrated using World Ocean Atlas http: //aquarius. umaine. edu/images/sci_argo_float. jpg

GFDL climate model simulations CM 2 -1 deg and CM 2. 6: Pre-industrial and climate change CO 2 simulations Coupled to mini. BLING biogeochemical model Subsampling of model data Allows for more representative comparison between the models and observations http: //soccom. princeton. edu/

Zonally and time-averaged depth profiles

Zonally averaged seasonal cycle comparison (depth = 50 meters)

20 year time-mean change in oxygen (µmol/kg) (Control - climate change)

Percent change between subsampled control and climate change simulations

Summary CM 2 -1 deg tends to underpredict the amount of dissolved oxygen compared to observations Higher resolution CM 2. 6 is somewhat better at modeling oxygen concentrations but still underpredicts oxygen levels High variability in the seasonal cycle Decrease in dissolved oxygen in climate change simulation Maximum decrease between density surfaces 1026. 5 and 1027. 5 kg/m 3

Increased ventilation/ less respiration Decreased ventilation/ more respiration Water temperature increases Little or no change in water temperature