I have a time series of monthly chlorophyll-a observations that spans from 1997 to present day. I have computed the p-value of the time series without removing the seasonality, and it doesn't quite show much of a trend. So, my question is, is the seasonality of the data affecting my computation, and if so, should I remove it? And, any recommendation on which methods that I should use to deseasonalise the time series.
I apologise if my question makes no sense. Thank you in advance.