The salinity of the oceans changes with latitude and with depth. In the tropics, the salinity increases on the surface of the ocean due to rapid evaporation. In the higher latitudes, there is less evaporation and rainfall causes the salinity to be less on the surface than at lower depths. The salinity level (in grams of salt per kilogram of seawater) to depths of 1000 meters at a latitude of 57.5N can be modeled by:

S(d)=31.5+1.1log(d+1)

Where d is the depth in meters. How fast is the salinity in the ocean changing at a depth of 200 meters when at a latitude of 57.5N?