Oceanography — NDA Geography

Oceanography is a compact but high-yield NDA Geography chapter — 20 PYQs across 2017–2026, and it splits cleanly into a SPATIAL half (what the sea floor looks like and how the water moves) and a RECALL half (which named current is warm or cold, and which ocean a feature sits in). The marks come in two flavours. Some questions ask you to TRACE A MECHANISM — why two tides arrive 12 h 26 min apart, why the Sun-Earth-Moon line makes a spring tide, why a current runs warm or cold. Others ask you to RECALL A LIST — name the cold currents, name the Pacific currents, name the sea-floor zones. The chapter teaches in one logical arc, from the solid floor up to the living reef: (1) Ocean waves and sea-floor topography — the shape of the basin (shelf, slope, abyssal plain, trench, mid-ocean ridge) and what a wave actually is; (2) Tides and ocean movements — the Moon-and-Sun mechanism that lifts the sea twice a day, and spring vs neap tides; (3) Ocean currents — why surface water flows in great loops, and the warm/cold named-current lists the NDA tests relentlessly; (4) Marine ecosystems — coral reefs, reef bleaching, and the ocean's named features. 11 concepts, every PYQ tagged. The current lists carry the bulk of the questions; the tide and sea-floor mechanisms carry the HARD ones.