Marine and Maritime Environments
Core concepts
Candidates must distinguish salinity, temperature, density and stratification in coastal versus open-ocean water, and explain how these drive layering and mixing. Know the tidal system: spring and neap tides, tidal range, tidal streams, and the rule of twelfths. Understand waves (fetch, duration, wind speed, swell versus sea), currents (boundary currents, longshore drift, rip currents) and coastal processes (erosion, deposition, sediment transport). Recognise marine zones - intertidal, neritic, pelagic, benthic, abyssal - and the physical factors (light, pressure, oxygen, nutrients) that define them. Also cover seabed features (continental shelf, slope, abyssal plain, trenches) and ocean–atmosphere interactions such as El Niño and upwelling.
Traps in questions
- Confusing tidal range with tidal stream speed: range is vertical, stream is horizontal.
- Assuming spring tides occur in spring season; they occur at new and full moon.
- Mixing sea (wind-generated, local) with swell (distant, organised).
- Forgetting that density increases with salinity and decreases with temperature.
- Misreading longshore drift direction, which follows the dominant wave approach, not the wind.
Rule of thumb: the rule of twelfths
Tidal height change is not linear. In a 6-hour flood, roughly 1/12 rises in hour 1, 2/12 in hour 2, 3/12 in hour 3, 3/12 in hour 4, 2/12 in hour 5, and 1/12 in hour 6.
Worked example: Range 3.0 m, low water 1.2 m at 09:00. Height at 12:00 (3 hours after LW) = 1.2 + (1+2+3)/12 × 3.0 = 1.2 + 1.5 = 2.7 m.
Always state units, reference datum (usually chart datum) and time zone when answering.