How does a narrow gulf mouth reduce water exchange with the ocean?

A narrow mouth reduces water exchange between a gulf and the ocean by increasing the degree of isolation of the gulf's waters. This isolation is determined by the ratio of the width of the mouth to the total surface area of the gulf, or by the ratio of the mouth's cross-sectional area to the total water volume.1

When a gulf has a narrow mouth, it restricts the movement of water, which can lead to independent circulation patterns driven by local winds and river runoff rather than oceanic currents. This limited exchange often results in distinct water properties compared to the adjacent ocean, such as variations in salinity or, in some cases, stagnation and oxygen deficiency. Additionally, a narrow mouth prevents open-ocean waves from penetrating the gulf, or significantly reduces their energy if they do enter.1