Abstract
AbstractSubantarctic 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 and 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.
Highlights
SubAntarctic Mode Water (SAMW) formation is the key process in the Southern Ocean whereby surface waters are subducted into the thermocline, transporting heat, CO2, and nutrients to intermediate ocean depths where they are subsequently exported northward (Marshall & Speer, 2012)
This analysis demonstrates the clear dominance of the relative phase of the Southern Annular Mode (SAM) and El Niño–Southern Oscillation (ENSO) atmospheric modes in driving both the spatial and the temporal variability of Subantarctic Mode Water (SAMW) volume and heat content in the South Pacific
The new pressure mapping of Argo data demonstrates a dramatic see‐saw in SAMW thickness between the central and eastern Pacific SAMW pools, varying out of phase with one another by up to ±150 m on yearly timescales
Summary
SubAntarctic Mode Water (SAMW) formation is the key process in the Southern Ocean whereby surface waters are subducted into the thermocline, transporting heat, CO2, and nutrients to intermediate ocean depths where they are subsequently exported northward (Marshall & Speer, 2012). Since Argo observations began, changes in SAMW formation rates and properties have driven the most significant anthropogenic heat uptake by the global ocean anywhere on the planet, accounting for 67–98% of the net global ocean heat uptake, which itself is the dominant component of the global climate system warming (Roemmich et al, 2015; Frölicher et al, 2015). This increase in heat uptake is driven largely by increased formation rates and increases in the volume of the SAMW layer, rather than significant changes in the temperature of the SAMW itself (Gao et al, 2018).
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