Decadal variability of Subtropical Mode Water subduction and its impact on biogeochemistry

Long-term change and variation of salinity in the western North Pacific subtropical gyre revealed by 50-year long observations along 137°E

“…Assuming the θ-S relation in the main pycnocline in the western subtropical gyre, the trends of winter mixed layer θ and S yield those on isopycnals of about −0.009 and 0.001 year trend and decadal S variation observed at 137°E originated in the KE region and was transmitted to 137°E 1-2 years later in association with the subduction and advection of STMW (Suga et al 1989;Oka 2009;Oka et al 2015).…”

“…The 25.5 and 25.0 kg m −3 isopycnals correspond to the denser and lighter varieties of the subtropical mode water (STMW; Masuzawa 1969) formed in the eastern and western parts, respectively, of its formation region that extends zonally south of the Kuroshio and the Kuroshio Extension (KE) and north of 28°N (Suga and Hanawa 1990;. STMW, which ventilates the upper halocline in the 137°E section as far south as ~18°N (Suga et al 1989;Oka 2009;Oka et al 2015), seemed to contribute greatly to the observed changes and variations of subtropical S.…”

“…It has been revealed during the last decade that the KE jet and its associated eddy field exhibit decadal variability (Qiu and Chen 2005;Qiu et al 2007) in association with the Pacific Decadal Oscillation (Mantua et al 1997) and that the winter mixed layer depth in the STMW formation region decreases (increases) during the unstable (stable) KE period (Oka et al 2015), likely because high (low) eddy activity transports more (less) high potentialvorticity water north of the KE to the STMW formation region to hinder (facilitate) mixed layer deepening (Qiu and Chen 2006). Such eddy activity, at the same time, is expected to transport more (less) fresher water north of the KE to the STMW formation region to decrease (increase) the mixed layer S. When we look at the relation to the KE index (Fig.…”

Physical oceanographic conditions around the S1 mooring site

“…Qiu et al (2014) and Oka et al (2015) indicated (Kalnay et al 1996), b potential temperature, θ (°C), c salinity, and d log 10 value of potential vorticity (PV, m −1 s −1 ) at the S1 mooring site from July 2009 to June 2014 from MOAA GPV (Hosoda et al 2008). Negative values of PV were removed.…”

Four-dimensional variational ocean reanalysis: a 30-year high-resolution dataset in the western North Pacific (FORA-WNP30)

“…The differences may partly come from temporal and spatial inhomogeneity of the observational data. Previous studies indicated that the decadal variability of STMW is closely related to that of the Kuroshio Extension (KE) state (e.g., Oka et al 2015). Therefore, the good reproduction of the KE state in the present high-resolution system as described later (Sect.…”