Oceans & Currents — Set 1

Correct Answer: C. Sargasso Sea

• **Sargasso Sea** = the only sea on Earth located entirely within the Atlantic Ocean with no land boundaries, defined instead by surrounding ocean currents. • **Gulf Stream** — one of four ocean currents (Gulf Stream, North Atlantic Drift, Canary Current, North Atlantic Equatorial Current) that form the Sargasso Sea's boundaries. • 💡 Wrong-option analysis: Caspian Sea: landlocked by land on all sides, not by ocean currents; Red Sea: bounded by Arabian Peninsula and Africa; Black Sea: enclosed by Eastern Europe and Turkey.

Correct Answer: B. Isohalines

• **Isohalines** = lines on a map connecting all points in the ocean that have equal salinity (dissolved salt content). • **35 ppt (parts per thousand)** — average ocean salinity; isohalines show deviations from this baseline, with higher values near evaporation zones. • 💡 Wrong-option analysis: Isobars: connect points of equal atmospheric pressure; Isobaths: connect points of equal water depth; Isotherms: connect points of equal temperature.

Correct Answer: D. Agulhas Current

• **Agulhas Current** = a warm ocean current flowing south along the east coast of Africa in the Indian Ocean, significantly influencing Southern Africa's climate. • **Indian Ocean location** — Agulhas runs along Africa's east coast; it plays a key role in the climate and marine ecosystems of the Western Indian Ocean. • 💡 Wrong-option analysis: Falkland Current: cold current in South Atlantic; Canary Current: cold current in North Atlantic; Benguela Current: cold current along Africa's west coast in South Atlantic.

Correct Answer: C. Continental Shelf

• **Continental Shelf** = the shallowest part of the ocean floor extending gently from the coast toward the ocean basin, rich in oil, gas, and fishery resources. • **~200 meters** — the average depth of the continental shelf; it ends at the shelf break where the steeper continental slope begins. • 💡 Wrong-option analysis: Abyssal Plain: deepest flat area, 3000-6000 m deep; Continental Rise: gradual slope at base of continental slope; Continental Slope: steep gradient connecting shelf to deep ocean floor.

Correct Answer: D. S

• **Mid-Atlantic Ridge (S-shape)** = a divergent tectonic plate boundary along the Atlantic Ocean floor that follows the S-shape of the Atlantic Ocean, forming new ocean floor. • **Volcanic activity** — new ocean crust is continuously created at the Mid-Atlantic Ridge as magma rises through the diverging plates. • 💡 Wrong-option analysis: L: no major oceanic ridge follows this shape; U: describes some trench shapes; C: describes some bay or gulf shapes, not this ridge.

Correct Answer: D. Peru

• **Humboldt Current (Peru Current)** = a cold, low-salinity ocean current flowing north along the west coast of Peru and Chile, supporting one of the world's richest fisheries. • **Named after Alexander von Humboldt** — the Prussian naturalist who scientifically documented this current; it brings nutrient-rich cold water to the surface via upwelling. • 💡 Wrong-option analysis: Australia: East Australian Current flows along its coast; Brazil: Brazil Current flows along its coast; Japan: Kuroshio (warm) and Oyashio (cold) flow near Japan.

Correct Answer: C. Gulf Stream and Labrador

• **Gulf Stream (warm) + Labrador Current (cold)** = convergence off Newfoundland creates the Grand Banks, one of the world's most productive fishing grounds. • **Plankton bloom** — the mixing of warm and cold waters triggers massive plankton growth, forming the base of the rich fishery food chain at the Grand Banks. • 💡 Wrong-option analysis: Brazil and Falkland: meet near Rio de la Plata in South Atlantic; Kuroshio and Oyashio: meet near Japan, creating similar productive fishing grounds; Agulhas and Benguela: meet near Cape of Good Hope, South Africa.

Correct Answer: A. Pacific Ocean

• **Pacific Ocean** = the deepest ocean on Earth, containing the Mariana Trench with Challenger Deep (~11,000 m), and having the highest average depth. • **Mariana Trench** — at ~11,000 m depth, the Mariana Trench is deeper than Mount Everest is tall (8,849 m), located in the western Pacific. • 💡 Wrong-option analysis: Arctic Ocean: shallowest ocean, average depth ~1,000 m; Indian Ocean: third largest, average depth ~3,890 m; Atlantic Ocean: second largest, average depth ~3,332 m.

Correct Answer: C. Thermocline

• **Thermocline** = the ocean layer (typically 200-1000 m deep) where water temperature drops rapidly with increasing depth, separating warm surface water from cold deep water. • **200-1000 m** — the typical depth range of the permanent thermocline, acting as a barrier to vertical water mixing. • 💡 Wrong-option analysis: Pycnocline: zone of rapid density change with depth; Photic zone: sunlit upper layer where photosynthesis occurs (0-200 m); Halocline: zone of rapid salinity change with depth.

Correct Answer: C. Atlantic Ocean

• **Canary Current (North Atlantic)** = a cold ocean current flowing south along the west coast of North Africa, forming the eastern limb of the North Atlantic Gyre. • **North Atlantic Gyre** — a system of rotating currents; the Canary Current forms the eastern boundary flowing toward the equator. • 💡 Wrong-option analysis: Arctic Ocean: Canary Current is in subtropical Atlantic, not Arctic; Indian Ocean: no Canary Current here; Pacific Ocean: California Current is the equivalent cold eastern boundary current in the Pacific.