[A-GE39] [EE] Subsurface Mass Transport and Environmental Assessment

[AGE39-03] Semiannually alternating exchange of intermediate waters east of the Philippines

Fan Wang¹, *Lina Song¹, Yuanlong Li² (1.Institute of Oceanology, Chinese Academy of Sciences, 2.University of Colorado)

Keywords:Strong semiannual variability, Significant correlation between current and salinity, Semiannually reversing water exchange

Intermediate water exchange in the northwest tropical Pacific is explored with the temperature,
salinity, and current measurements of a mooring system deployed at 8°N, 127.05°E during 2010–2014. For the
first time, prominent semiannual variability (SAV; with the maximum power at ~ 187 days) of subthermocline
meridional flow along the Mindanao coast is revealed. A significant correlation between meridional flow and
salinity is found at intermediate depths. This provides direct evidence for the alternating transports of South
Pacific and North Pacific Intermediate Waters by northward and southward undercurrents, respectively.
Further analysis with an eddy-resolving ocean general circulation model demonstrates that the SAV is
generated locally near the western boundary, manifesting as large-scale subthermocline recirculation and
leading to alternating northward and southward flows near the Mindanao coast, which plays an efficient role
in the intermediate water exchange of the northwest tropical Pacific. Mechanisms underlying the observed
SAV are discussed