Wind-driven changes of current, temperature, and chlorophyll inferred from space north of New Guinea M.-H. Radenac, F. Léger, M. Messié, P. Dutrieux, G. Eldin, C. Menkes mesotrophic 0,1 mg m-3 oligotrophic 0 mg m-3 Averaged SeaWiFS chlorophyll (Sep. 1997 – Dec. 2010)

cross-track geostrophic current anomaly (Lagerloef et al., 1999) Data - method chlorophyll vent SeaWiFS, 8 days, 9 km, Sep. 1997-Dec. 2010 ERS, 7 days, 1°, Aug. 1991-Dec. 2001 SST QuikSCAT, 7 days, 0,5°, Aug. 1999-Nov. 2009 TMI, 7 days, 0,25°, since Dec. 1997 courant AVHRR – PFV5, nighttime, 4 km OSCAR, 5 days, 1° CTOH altimetric tracks, 10 days cross-track geostrophic current anomaly (Lagerloef et al., 1999) + Wavelet analysis Spectra  dominant modes of variability Band-pass filters  reconstruction of the signal Intraseasonal 20 – 120 days Seasonal 150 – 500 days Interannual > 500 days

Chlorophyll response to WWE The 20-120 day signals Sustained intraseasonal activity in summer Strong relationship between increasing chlorophyll (decreasing SST) and westerly wind in summer Running correlation of x vs. chl, x vs. SST Composite maps of chlorophyll and surface currents during WWE Local upwelling Surface current convergence Equatorial extension Eastward equatorial current Local upwelling Equatorial extension The December 2001 event West of 146°E Vertical and biological processses East of 146°E Zonal advection [Chl]/t u [Chl]/x v [Chl]/y u [Chl]/x  v [Chl]/y December 2001 2°S-0°S

x, chl, SST Seasonal variations Along coast Ua 099 023 201 SST chl Vitiaz Strait Mamberamo R. Sepik R. August February SST and wind stress chl and Ua Austral winter Austral summer Trade winds NW monsoon NGCC  NGCC  Cold water from Solomon Sea Coastal upwelling Current convergence near Sepik River

Interannual variations El Niño La Niña SST and Ua chl and Ua SOI, x, SLA SST, chl Ua 099 023 201 251 Ua 125 049 A (160°E, 0°) El Niño La Niña SST  and chl  SST  and chl  Same chlorophyll pattern than in summer Less efficient processes Upwelling Same SST pattern than in winter Penetration of cold and low chlorophyll water from the Solomon Sea El Niño more westerlies prior to EN elevated SLA  shallow nutricline/thermocline NGCC  in the east (WBC influence) equatorial influence in the west

El Niño upwelling vs. seasonal upwelling Assuming that vertical advection is the main driver of SST variations τ ∥ = along shore wind L = width of the horizontal Ekman layer = 12 km AH = 10-100 m2 s-1  L = 4-12 km wupw T stratification 𝜕𝑇 𝜕𝑡 = 𝜏 ∥ 𝜌𝑓𝐿 ∙ 𝜕𝑇 𝜕𝑧 𝐿=𝜋 2 𝐴 𝐻 𝑓 El Niño Feb. // (N m-2) 0.01 0.04 wupw (m d-1) 5.7 22.7 T / z (°C m-1) 2.55 10-2 1.35 10-2 NO3 / z (mol L-1 m-1) 0.052 0.035 T / t (°C d-1) 0.14 0.31 NO3 / t (mol L-1 d-1) 0.29 0.79 ( 2) ( 2.7) Upwelling inhibition by onshore geostrophic flow Influence of Ekman pumping

current anomaly west of Sepik current anomaly east of Sepik Summary   wind direction current anomaly west of Sepik current anomaly east of Sepik SST anomaly chlorophyll anomaly processes WWE  < 0 > 0 UPW austral summer austral winter  CCT El Niño ≈ 0 UPW & CCT La Niña main observations and processes at work at different time scales UPW = upwelling CCT = coastal cold tongue