To cite package seas in publications use:
Toews MW, Whitfield PH, Allen DM (2007). “Seasonal statistics: the 'seas' package for R.” Computers \& Geosciences, 33(7), 1895. doi:10.1016/j.cageo.2006.11.011.
Corresponding BibTeX entry:
@Article{, title = {Seasonal statistics: the 'seas' package for R}, author = {Michael W. Toews and Paul H. Whitfield and Diana M. Allen}, journal = {Computers \& Geosciences}, year = {2007}, volume = {33}, pages = {1895}, number = {7}, doi = {10.1016/j.cageo.2006.11.011}, }