The STF features prominently in this leg, but where exactly it is located is open to debate. A starting point could be the STF surface characteristics found at 120°E (Leg 1):

temperature: 12¡ - 13¡C, salinity: 34.9 - 35.2, density: 26.50 - 26.55

Another often used identification is the position where the 12°C isotherm crosses the 200 m depth level.

The SST criterion (12° - 13°C) and the density criterion (26.50 - 26.55) place the STF at km 30. But at that location the 12°C isotherm moves down to only just above the 200 m depth level and does not sink distinctly deeper until the transect reaches km 230. This is the location of a second surface front where the SST changes from 12.5°C to > 14°C.

The salinity changes from 34.8 to 35.1 at the first front (km 30) and from 35.1 to 35.4 at the second front (km 230). The salinity criterion (34.9 - 35.2) sits somewhere inbetween and suggests that both fronts together make up the STF.

It appears that the STF is split into two fronts. The major front is associated with the 12°C isotherm, the 34.9 isohaline and the 26.5 isopycnal. The density gradient is determined by the temperature.

The second surface front is located where the 12°C isotherm dives below 200 m depth. Although the SST and SSS gradients are as large as in the major surface front, this front is largely density compensated.