Subseasonal to interannual flow variability at the southern entrance of the Solomon Sea by end-point moorings and bottom pressure observations

Volume transport and mean velocity across the Solomon Sea southern entrance have been observed by end-point subsurface moorings and seafloor Pressure sensing Inverted Echo Sounders (PIES). The mean equatorward volume transport in the upper 500 m of the water column is 15.2 Sv (1 Sv ≡ 10⁶ m³ s^-1) over July 2012 – May 2017. The measurements resolve the full spectrum of the volume transport including energetic subseasonal variability that fluctuates by as much as 25 Sv over one week. Local Ekman pumping and remote wind stress curl capture about a third of the subseasonal variability. While the influence of Rossby waves is insignificant on subseasonal timescales, on longer timescales linear Rossby waves forced by Ekman pumping in the interior of the Pacific capture 66% and 46% of the observed inflow variance in the surface layer (above σ_θ = 24.0) and upper 500 m of the water column, respectively. A proxy volume transport time series based on the satellite altimetry spanning the period of 1993-2017 is constructed to examine interannual variability. Poleward transport anomalies occur during La Niña conditions and equatorward anomalies occur during El Niño conditions. Moreover, the observations indicate suppression of the seasonal cycle in both surface and subsurface (σ_θ = 24.0 to 500 m) flows from the second half of 2014, prior to the mature phase of the 2015/2016 El Niño, to September 2016.