Ocean boundary pressures link Atlantic-Pacific sea level difference to Indo-Pacific Overturning.

Diagnostics from a 1/12 degree resolution ocean model simulation have confirmed that depth-integrated upper-ocean boundary pressure anomalies can be predicted from a simple theory involving wind stress and net meridional flows through the southern boundaries of the Atlantic and Indo-Pacific basins. In particular, the difference between eastern Atlantic and eastern Pacific boundary pressures is mainly determined by wind stress in this model, with the Indo-Pacific overturning playing a significant secondary role. We apply this framework to the analysis of CMIP-6 simulations and find that, for centennial changes, the dominant factor becomes the changing Indo-Pacific overturning (itself related to AMOC changes), and that the resulting boundary pressure changes predict an important proportion of the change in Pacific-Atlantic sea level difference. We also find an amplification mechanism, whereby small changes in deep ocean pressures result in larger sea level changes than would be expected from a simple hydrostatic balance argument.