LB01, Lamon bay LB01, Bifurcation track Figure 1. Station/track map of Lamon Bay 1, May/June 2011 (LB01). Red dots show drifter deployments [13 in total]; red triangles are mooring deployment sites [6 in total, see Table I]. There were 45 CTD stations most with water samples for chemistry. The track extending the coverage to the NEC bifurcation during Tyhpoon Songda [Philippine designated name: Chedeng]  

vertical black bar: core X: XBT V: vertical net tows O: oblique net tows Red triangle: TRBM Vertical red bar: line moorings Figure 2a: Station/track map of Lamon Bay 2, April/May 2012. There were 78 CTD stations (temperature, salinity, oxygen), to 1500 m or to the shallower sea floor; 4 stations descended to 4000 meters to observe the waters within a deep ocean trough within Lamon Bay. Water samples were taken for CTD oxygen standarization and for determination of nutrient, carbon chemistry, ecosystem parameters. Underway data, besides ADCP and Revelle ‘Real-time Underway and Meteorological Data’ (ocean surface temperature and salinity; oxygen; Chlorophyll-A (fluorometer);Transmissivity), included pCO2

Stratification: LB01, LB02, LB02 (NE) S-max NPsubtropical “Port Irene bay” thermocline “Port Irene bay” Pressure db [meters] S-min NPIW Polillo depression Polillo depression Polillo depression O2-min 100-200 m frequent O2-min Figure 3. Potential temperature, salinity and oxygen of the upper kilometer of Lamon Bay as observed in LB01 (black symbols) and LB02 (red, cyan and green symbols). The map in lower left provides positions of the CTD profiles shown in the figure. Tropical water introduced into the Lamon Bay region by the northward flowing limb of the North Equatorial Current (NEC) bifurcation has saltier S-max within the upper thermcline and saltier S-Min at thermocline base than does the subtropical waters of the western North Pacific, identified here as Kuroshio water, which is enriched in North Pacific Intermediate Water (NPIW). The 'Polillo depression' is the ~850 m hole near 14.5°N, 121.75°E, the likely source of the low oxygen layer found over the Lamon Bay southern shelf and adjacent slope. “Port Irene bay” All CTD Lower thermocline O2-min Stratification: LB01, LB02, LB02 (NE)

LB1 LB2 LB1 NEC S-min LB2 NEC S-max Kuroshio S-max LB02 thermohaline pattern (red and cyan) in Lamon Bay reflects dominance of North Equatorial Current (NEC) water; whereas LB01 (black) reflects Kuroshio recirculation gyre regime. The cyan LB02 stations, with Kuroshio T/S, are in the northeastern part of the station array. The LB02 green stations are within the embayment of Port Irene. The LB02 nascent Kuroshio is composed of NEC T/S LB1 LB2 Polillo channel All CTD stations: 1-78 LB1 Figure 4a. Potential temperature vs. salinity scatter observed in LB01 (black symbols) and LB02 (red, cyan and green symbols). The map in lower left provides positions of the CTD stations shown in the figure. The boxes text within the figure provide identify key results in terms of the NEC vs. Kuroshio source of the Lamon Bay stratification. NEC S-min NPIW Kuroshio S-min LB2

LB2 LB1 NEC, S-max Kuroshio NPIW Kuroshio CTD 1-78 Polillo channel Black: LB0-1 Red: LB02 Cyan: LB02 Green: LB02 LB2 LB1 Figure 4b. Potential temperature vs. oxygen (ml/l) scatter observed in LB01 (black symbols) and LB02 (red, cyan and green symbols). The map in upper left provides positions of the CTD stations shown in the figure. Kuroshio s-max higher in oxy than NEC s-max; the Kuroshio oxy-min occurs at colder temperatures than that of the tropical NEC water. NPIW Kuroshio

LB02: dominate NEC signature, except in NE part of stations array Kuroshio Polillo and ‘Port Irene Bay’ All CTD stations: 1-78 NEC Kuroshio Figure 4c Same as Figure 4a, but the LB01 data points removed to show only LB02 T/S scatter. The coastal waters near Pilillo Island and in the embayment at Port Irene display strongly altered profile to a depth of ~350 m, removing the S-max and attenuating the S-min core layer, signifying more than a low salinity surface layer sweeping over the thermocline of the open ocean. LB02: dominate NEC signature, except in NE part of stations array

Focus on Lamon Bay south of 17.5°N: LB01 Black LB02 Red Figure 4d. Comparison of the S-max and S-min of the two LB cruises. The time period (april/may 2012) of LB02 displays greater presence tropical North Equatorial Current water than the LB01 period (May/June, 2011). LB01 LB02 Message: the time period (april/may 2012) of LB02 displays greater presence tropical North Equatorial Current water than the LB01 period (May/June, 2011), why?

Figure 5 a,b Time series of temperature and salinity and T/S scatter from TRBM3 and the long mooring 2 (see Table I and II). Figure 5c shows the combined T/S scatter of the two moorings [left panel] with the approximate fit overlaid on the LB01 and LB02 T/S [right panel].

Figure 6. Position of the salinity and ship ADCP sections shown in Figure 6.

18.35°N 17.12°N western boundary NEC S-max western boundary North Pacific S-min Kuroshio looking north looking south 17.12°N NEC S-max Figure 7. Salinity distribution for the upper 1000 m along the sections shown in Figure 6. Note: the sections are presented in order of the station number, left to right; the N-S, E-W orientation is noted within the section panel. The right panels show the current speed across the section for the upper ~550 m obtained by the ship mounted 75 kHz ADCP underway system, cm/sec (+60, red to -60, blue cm/sec). The ADCP section is often not for the full lateral length of the salinity section. The km scale is noted at the base of the sections. western boundary western boundary looking north looking north

16.50°N 124.25°E western boundary NEC S-max western boundary North Pacific S-min Kuroshio western boundary looking north looking south 124.25°E Figure 7. Salinity distribution for the upper 1000 m along the sections shown in Figure 6. Note: the sections are presented in order of the station number, left to right; the N-S, E-W orientation is noted within the section panel. The right panels show the current speed across the section for the upper ~550 m obtained by the ship mounted 75 kHz ADCP underway system, cm/sec (+60, red to -60, blue cm/sec). The ADCP section is often not for the full lateral length of the salinity section. The km scale is noted at the base of the sections. NEC S-max S-max & S-min North Pacific Kuroshio Southern boundary Southern boundary looking west looking west

Strong NEC source Lamon Bay cruise 1, 23-55 m current vectors, Lamon Bay cruise 2, 23-55 m current vectors, as of 8 May 2012 Kuroshio recirculation gyre Nascent Kuroshio Nascent Kuroshio SSS color coded Kuroshio recirculation gyre anticyclonic dipole anticyclone dipole Lamon bifurcation Lamon bifurcation cyclonic dipole cyclonic dipole Figure 8. Sea surface salinity (SSS) color-coded current vectors within Lamon Bay for LB01 (right panel) and LB02 (left panel). Weak NEC signal Kuroshio feeder current Polillo current Strong NEC source Polillo current SSS color coded Solid arrows denote stronger flow, with clear T/S source water signal. LB02 Kuroshio recirculation gyre retreats northward to be replaced by NEC waters; LB01 shows southward penetration of the Kuroshio recirculation gyre, with reduced NEC water [vectors not to same scale]

Figure 9. Comparison of the northward flow across 18 Figure 9. Comparison of the northward flow across 18.35°N of LB01 and LB02. The maximum speed of the nascent Kuroshio in LB02 was twice that of LB01 and the transport 50% greater. The geostrophic speed relative to 1000 db of the Kuroshio axis in LB02 as determined by the CTD data is 1.35 m/sec.

LB02 Transports [~±15%?], upper 300 m +15.3 Sv +10 Sv, LB01 D+2.6 Sv -5.5 Sv +12.4 Sv +11 Sv, LB01 D-2.2 Sv -10.2 Sv Figure 10. Transport across select zonal and meridional sections of Lamon bay LB02 Transports [~±15%?], upper 300 m

During R/V Revelle transit, Freemantle to Legaspi. Bifurcation ~13° - 14° N North Equatorial Current Bifurcation 10° - 11° N North Equatorial Current [weaker] Mindanao Current [stronger] Mindanao Current NEC bifurcation, late May 2011, during R/V Revelle transit to south to avoid tyhpoon Songda Figure 11. North Equatorial Current Bifurcation observed during LB01 and LB02. NEC bifurcation, April 2012, During R/V Revelle transit, Freemantle to Legaspi.

Stronger Kuroshio, enriched in April 2012 La Niña Stronger Kuroshio, enriched in Equatorial water May 2011 Neutral Weaker Kuroshio Kuroshio Kuroshio Weak or ~0 Luzon Strait throughflow Luzon Strait throughflow Weak South China Sea throughflow South China Sea throughflow bifurcation North Equatorial Current North Equatorial Current bifurcation Figure 12. The schematic shown above is based on the CTD (T/S stratification) and ship-based ADCP currents of the upper ~600 m obtained by the Lamon Bay research cruises of May/June 2011 and April/May 2012, which covered the area south of ~19°N west of ~126°E and the NEC bifurcation region [typhoon detour in 2011 and transit from Fremantle in 2012]. The nino4 in May 2011 was near zero, but we take it as representative of an El Niño condition relative to the La Niña condition of April 2012. Maximum La Niña phase occurred in December 2011. The South China Sea throughflow connection is from Gordon et al, 2012, GRL; Luzon Strait throughflow and ENSO from Hurlburt, et al., 2011, Oceanography. The relationship of the NEC bifurcation to ENSO is from Qiu and Chen 2010, JPO. The connection of the Mindanao to the ITF leakage is spectulation. Models suggest that the Agulhas retroflection leaks less water into the South Atlantic when the Agulhas transport is large. 4 may 2012 message from Bo Qiu: My understanding with the MC/ENSO connection is that MC increases in transport during ENSO. This is supported by modeling study, available sea level difference data between Davao and Malakal (see Fig.14b in http://www.soest.hawaii.edu/oceanography/bo/QL96.pdf), and the appearence of a positive wind stress curl in the low-latitude Philippine Sea during El Nino (slide 4 in my preceding e-mail ppt to you). As you mentioned, an increased MC during El Nino does NOT imply a larger ITF through Celebes Sea. In fact, during El Nino, more MC water is retroflected into the NECC and, as the northerly NEC bifurcation implies, the entire wind-driven North Pacific tropical gyre (NEC-MC-NECC) shifts northward. Mindanao Mindanao Stronger Makassar ITF Weaker Makassar ITF For supporting information see ppt slide ‘Notes page’; see next slide for relation to Aviso

Possible Implications of an ENSO [bifurcation] dependent Kuroshio source: § During La Niña there is increased injection of  NEC tropical Pacific water into the subtropical North Pacific; during El Niño the subtropical North Pacific is more 'isolated' from the NEC.   § The NEC enhanced Kuroshio transport during La Niña, leads to greater northward heat flux into the North Pacific; reduces western pacific warm pool volume. § The NEC injection into the subtropical regime, on climatic average (the integrated La Niña/El Niño phases), balances the loss of North Pacific water through the Bering Straits (~1 Sv) and through Luzon Strait (~3 Sv) into the South China Sea (that most likely advects into the Indian Ocean as part of the Indonesia Throughflow). During El Niño the Kuroshio recirculation gyre reaches into Lamon Bay, to can feed the westward ‘leakage’ into the South China Sea,  (Luzon Strait westward transport is increased during El Niño, HYCOM, Hurbert et al 2011). In this way the Kuroshio recirculation gyre exports the accumulated NEC injected during the previous La Niña phases. § More...  effect on ecosystems, linkage with PDO, impact on ITF, WPWP ... ITF comment: During El Niño the SCS throughflow via Sibutu Passage blocks Mindanao surface layer leakage to Makassar Strait, which lowers the Makassar net transport, counteracting thegreater Mindanao transport associated with the northern bifurcation position.

Kuroshio Dt = 4°C @ 200 m; 18°C isotherm Dz = @ 70 m Deeper isotherms Figure 13 b Kuroshio Shallower isotherms