How are gulfs classified by their geologic setting and water depth?

Gulfs are classified based on their geologic structure, developmental history, and depth, which together determine their morphological characteristics. A common classification scheme divides them into several groups:1

• Group A1: These are situated in open concavities of the continental coast. They typically feature depths on the order of kilometers at their mouths, with pronounced continental shelves and slopes.1
• Group A2: These are large areas significantly isolated from the open ocean, often connected by narrow, shallow straits. Examples include the Gulf of Mexico and Baffin Bay.1
• Group A3: These ocean gulfs, such as the Gulf of California, are shaped by young faults and fractures. Their depths generally exceed 1 kilometer, and they typically result from a single episode of deformation.1
• Group B: Located on the continental shelf, these gulfs—such as the Bay of Fundy—are generally up to 200 meters deep. Their final shapes were often determined during the Pleistocene Epoch.1
• Groups C and D: These categories include gulfs of intercontinental, marginal, and shelf seas. Group D, in particular, consists of shallow shelf seas where limited water exchange often leads to sediment accumulation.1