We investigated WOA18 to reveal if there was a notable bias in the months nutriclines were sampled. First, we indexed each nutricline depth based on the latitude, longitude, and month of the respective cast. We then replaced each observed nutricline depth with its respective monthly value in WOA18. Next, we proceeded to find the annually-averaged nutricline depth for each geographic coordinate of each year. Then, we determined the trends of nutricline depths with time. If there were considerable seasonal biases in cruise casts, then the global medians of these trends would deviate from zero.