A see-saw in Pacific Subantarctic Mode Water formation driven by atmospheric modes

Andrew Meijers, NERC British Antarctic Survey, Cambridge, United Kingdom, Ivana Cerovecki, Scripps Institute of Oceanography, La Jolla, CA, United States, Brian A. King, National Oceanography Centre, Southampton, United Kingdom and Veronica Tamsitt, University of South Florida, College of Marine Science, Saint Petersburg, United States
Subantarctic Mode Water (SAMW) in the Pacific forms in two distinct pools in the south central and southeast Pacific, which subduct into the ocean interior and impact global storage of heat and carbon. Wintertime thickness of the central and eastern SAMW pools vary predominantly out of phase with each other, by up to ±150 m between years, resulting in an interannual thickness see-saw. The thickness in the eastern (central) pool is found to be strongly positively (negatively) correlated with both the Southern Annular Mode (SAM) and El Niño Southern Oscillation (ENSO). The relative phases of the SAM and ENSO set the SAMW thickness, with in phase reinforcing modes in 2005-2008 and 2012-2017 driving strong differences between the pools. Between 2008-2012 out of phase atmospheric modes result in less coherent SAMW patterns. SAMW thickness is dominated by local formation driven by SAM and ENSO modulated wind stress and turbulent heat fluxes.