Sack Lunch Seminar (SLS)

Due to the larger thermal expansion coefficient at higher temperatures, more buoyancy is put into the ocean by heating than is removed by cooling at low temperatures. Even with balanced time-mean thermal and haline surface forcing of the ocean, there is a net positive buoyancy flux. As shown by McDougall and Garrett (1992), this must be compensated by interior densification by mixing due to the nonlinearity of the equation of state (cabbeling). Three issues that arise from this are addressed: the estimation of the annual input of buoyancy forcing, the effects of the seasonal cycle and the total cabbeling potential of the ocean upon complete mixing. I estimate the annual input of buoyancy forcing to a steady-state ocean driven by balanced E-P-R and Qnet as 74,000 m³/s, which would be equivalent to a sea level change of 6.3 mm/yr or approximately three times the estimated rate of sea level rise or 450% of the average Mississippi river discharge. When seasonal variations are included, this buoyancy forcing increases by 35% compared to the time-mean case to 101,000 m³/s. I establish likely bounds on these numbers by using different Qnet and E-P-R datasets and find the estimates robust to a factor of approximately two. These values compare well with the cabbeling-induced contraction inferred from independent thermal dissipation rate estimates. The potential sea level decrease upon complete vertical mixing of the ocean is estimated as 230 mm. When horizontal mixing is included, the sea level drop is estimated for diffusive and turbulent mixing end-states as 289 and 325 mm, respectively.