Which two main types of ocean currents are identified?

Master the Navigation, Seamanship, and Shiphandling (NSS) – Officer of the Deck (OOD) Phase 2 Exam with engaging flashcards and multiple choice questions, complete with hints and explanations. Prepare comprehensively for your test!

Currents are classified by how they are generated. The two main types are wind-driven surface currents and thermohaline deep currents. Wind-driven currents arise from wind friction on the sea surface, with the Coriolis effect steering the flow into large gyres that move heat around the globe. Thermohaline circulation is driven by density differences caused by temperature and salinity; cold, salty water sinking in polar regions pulls deep water along, creating a global overturning that connects ocean basins at depth. Together, these two describe the primary mechanisms behind the ocean’s circulation: surface currents controlled by winds, and deep currents controlled by water density. Other groupings like depth (surface vs deep), tidal versus non-tidal, or coastal versus open ocean describe different aspects of currents but don’t represent the fundamental two-mechanism classification.