Final answer:
Cold-core eddies form in high-latitude regions and are significant for marine life productivity, particularly in the Subtropical Convergence of the Southern Ocean. Coral reefs are found in shallow ocean water, where they can receive sunlight necessary for photosynthesis.
Step-by-step explanation:
Cold-core eddies are a type of oceanic feature characterized by swirling masses of water that move against the prevailing current. The correct answer to the question about where cold-core eddies form is (c) In high-latitude regions. These eddies typically form at higher latitudes, away from the equator. Cold-core eddies are associated with cooler, denser water that sinks and spirals in a clockwise direction in the Southern Hemisphere and counter-clockwise in the Northern Hemisphere.
As for marine life productivity, the Subtropical Convergence in the Southern Ocean is an area where the cold, dense waters of the Southern Ocean meet the warmer waters of the Pacific, Atlantic, and Indian Oceans. This convergence creates a zone of upwelling, which brings nutrients from the deep waters to the surface, supporting a high level of productivity for marine organisms like phytoplankton and krill. These conditions are essential for the marine food web and are conducive to vigorous marine life.
Regarding coral reefs, these ecosystems are found in (a) shallow ocean water. Coral reefs require warm, shallow water where sunlight can reach them, as the algae which live in the corals' tissues and provide them with food through photosynthesis need light for energy production.