When Seawater Freezes

At typical ocean salinity of about 35 PSU, seawater begins to freeze at roughly −1.8 °C, so the rounded value of −2 °C is sound. The exact temperature depends on salinity and pressure; less saline water freezes closer to 0 °C. As sea ice forms, most salt is expelled into the surrounding water, although young ice can retain brine. [1–3]