NaN in tracer.stat --> found the problem!

I used to see NaN in the second time step of tracer.stat. In the first time step you dont see Nan because it is the initial condition.

In the second time step, seawater NO3 was NaN because it was exchanging the NaN value coming from the sea ice NO3, which was due to the lack of epsilon number.

For example, the sink for sea ice NO3 due to ice algal uptake is calculated based on the ratio of NO3 and all other available nitrogen (i.e. NO3 and NH4). When NO3 and NH4 are initially set to 0 in the model (for now), the denominator becomes zero, therefore the sink = NaN, therefore the ice NO3 in the next time step as well as the oceanic NO3 became NaN.

So I fixed this by adding a very small epsilon number to avoid this division by zero.