Winter (February 15) T along 65W to a depth of 500m. The thick line is the mixed layer base. These cross-sections illustrate the subtropical mode water (STMW). Reasons why the STMW is too cold when isopycnic coordinates are used need to be determined. Note that the winter mixed layer is deeper in the STMW formation region for the HYCOM MICOM-mode simulation, and the mixed layer water is colder. performance of the MICOM K-T mixed layer model is probably largely responsible for the cold STMW.