This kind of trade barrier would be considered a natural barrier. The restriction on shipping cargo during certain months is a result of natural factors, specifically the climate and weather conditions.
The trade barrier described, which is caused by the climate conditions on the St. Lawrence Seaway, would be considered a natural trade barrier. Natural trade barriers are factors beyond human control that hinder or limit the movement of goods and services between countries or regions. In this case, the harsh weather conditions during November to April make shipping cargo on the St. Lawrence Seaway impossible, thus creating a natural trade barrier.
The trade barrier in this case is considered to be natural.
