USCG Exam PracticeTides and currents — predictions and corrections
A vessel is making a coastal passage. The navigator determines that surface ocean currents in the area are setting the vessel off track. According to Bowditch, what is the primary driving force behind these surface ocean currents, and how does this differ from tidal currents?
- ✓ Surface ocean currents are driven primarily by wind and form major gyres; tidal currents are driven by the tide and reverse direction with the tideCorrect
- B. Surface ocean currents are driven by the gravitational interaction of the moon and sun; tidal currents are driven by wind and do not reverse
- C. Both surface ocean currents and tidal currents are driven by wind, but tidal currents are modified by the shape of the coastline
- D. Surface ocean currents are driven by density differences due to temperature and salinity; tidal currents are driven by the same gravitational forces that cause tides
Why A is correct
Bowditch Ch. 24 §2401 states that surface ocean currents are driven primarily by wind, with major gyres in each ocean basin, while tidal currents are driven by the tide rather than wind and reverse direction with the tide. Density-driven thermohaline circulation and gravitational forcing are not identified in §2401 as the primary driver of surface ocean currents.
Cited:Bowditch Ch. 24 §2401