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6 Impact on lower trophic levels 50 N subsurface nitrate and Chl-a. 50 N North N During unstable phase: CHIBA Year ET AL.: ZOOPLANKTON BIOG South (a) Chl-a and EKE N South of KE: higher nitrate/chl-a X (km) E 152 E and 31.5 N 34.5 N (c) Densities at 100m 3 σchl a θ (minimum) mg m 3kg m 30 N of KE: lower nitrate/chl-a North 120 W N 150 W EKE (m2 s 2) Stability of KE could change 120 W 150 E N transport of mesoscale eddies 20 N 150 E W and curr 6spec 0.09 Mur area0.07 The cies total EKESSHA (m2 s 2 ) (cm) 60 N Kouketsu et al. (2016): 150 W 60 N σθ (maximum) kg) m 3 Nitrate (µmol kg Y (km) 150 E Fig. 5 Same as Fig. 2, but for (a) Cyclonic ( standard errors (mg m 3) for Ni = 44 (Nt = 14 monthly mean Chl-a composites north of the Kuroshio Exten143 E 152 E and 36.5 N 39.5 N sion in April (see Fig. 4b,(a) f). Chl-a and EKE 100 Standard errors were calculated 0.63 that the degrees of assuming freedom were the number of 0.54 identical eddies (Ni) 0.08 Chl a mg m 3 Mesoscale eddy effects on temporal variability cale eddy effects on temporal variability 2.2. Circ 120 W 150 E W 120 W (e) Surface fluxes unstable unstable (c) Densities at 100m [8] CHIBA ET AL.: ZOOPLANKTON BIOGEOGRAPHY IN THE KOE main [Shim forcing can be separated into tworecirculation dominant modes of variboxes arebetween focus areas in this study: the anomaly southern part of the Correlation between SSHA and Chl-a anomaly correspondboxes are focus areas st Fig. 1 Correlation SSHA and Chl-a correspond25.5 in this KES 24.5 et al., 2007]: the first mode is associated with ability [Taguchi dept (sign inverses) southward/northward shift in the of axis of thegyre KE (KE Axis gyre (142 E 152 E 28.5 N 31.5 N), the region south the main eddies from 1998 to SSHA are high-pass-filtered 7 (142 E 152 E25.4and 28.5 ing to eddies from 1998 toand SSHA areaindex), high-pass-filtered which is defined by the zonal mean of the midlatitude whe between the northern and southern fronts, and second(142 E 152 E 120 stream (142 E 152 E 31.5 N 34.5 N), and theare region north ofthethe days) to remove long-term changes. Chl-a anomalies are(<logastream and 0horiz days) to remove long-termand changes. Chl-a anomalies loga-ke mode is associated with a strengthening and weakening of (KE Strength the mean KE Index), which diagonal is defined by differmain stream and 36.5 N 39.5 N). TheGray green deviations from weekly climatology from 1998 to 2012.rithmic Gray deviations main stream (143 E 152 E an from (143 E 152 E weekly climatology from 1998 to ocea 90 ence in sea surface height (SSH) between 34.5 and 37 N ] The correlations between the KE Indices and zooplank[ horiz cross denotes the location ofats1 (145 E, 30 N) (color figure online) denote insignificant correlations at a 90 % confidence level. areas Whitedenote 24.2 denotes insignificant correlations a 90 % confidence White 1998computed the values the 2012 location of S1 ton time serieslevel. were using KE cross indices Year the several averaged over the months of March June assuming in th Negative correlation between 2002 is transported month timescale1998 when the2000 zooplankton from the plan southern source region toward the northern sampling region [Noto and Yasuda, 1999]. Because(e) the Surface PDO and NPGO are fluxes and Fig. 8 Same asaxis Fig.Index 6, but forstrength the region KE Strength and abundance of closely related to the KE and KE Index, north of the main stream. The su respectively [Taguchi et al., 2007], we also compared these inwarm 160 dices2012 and zooplankton time series to the March June average In this study, we focused on the to upstream regions south and Argo profiling float data from 2001 to 2012 (Hosoda using Argo profiling float data from 2001 (Hosoda In this study, we focuse Hida PDO index and NPGO index. As the NPGO signal reaches the warm-species-zooplankton KE with a delay of about 2.5 years [Ceballos et al., 2009], [ 9] Whereas south Kuroshio Extension, the140variability north of the Kuroshio Extension (Fig. 1), where the cyclonic 2008) et al. 2008). north of the Kuroshio Ext NPGO time series was plottedof withthe a lead time of 2.5 years. All time series are normalized by their standard deviations. rivat in Chl-a concentrations in the cyclonic eddy cores was a in the north of KE (anticyclonic) environment was expected tocontributor be favorable (anticyclonic) environmen 120 the s substantial to concentrations throughout the 3. Results and Discussion (0 5 transport of mesoscale eddies (unfavorable) for phytoplankton growth. However, a weak (unfavorable) area0.119(fig. 6b), the variability in the southernfor partphytopl of the Advection Transport and Impact on Zooplankton the g gyre could notabundance, be explained by variability in The observed warm-water zooplankton [13]recirculation correlation was found between SSHA and Chl-a in the southorrelation of SSHA and Chl-a 3 Correlation of SSHA and Chl-a whichthepeakededdies correlation for t in 1998 the late s, early and mid-1990s, s, was 2012 found betw (Fig.with 7b). the was significantly correlated thebecause KE Strength Indexpatterns around both the Year [Sas (R = 0.62, p < 0.05; KE Index was reversed in Figure 2),part indi- of the recirculation ern part of the recirculation gyre, around 30 N, where the role ern anticyclonic and cyclonic eddies in this area of the gyre cating1.more(a) warm-water years withsea a weak KE. Figure Mapspecies of inmean surface height (SSH) the Figure 2. Time series abundance of warm-water zooplank- Similar high correlations were found between the NPGO corresponded to the eddy advection mechanism (Fig. 3), SSHA (cm) Net Heat Flux (W m2) σθ (maximum) kg m 3 Net Heat Flux (W m2) MomentumkgFlux σθ (minimum) m 3(N m2) Year Momentum Flux (N m2) Chiba et al. (2013) 2

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