Ocean currents and climate
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When currents from low-latitude regions move into higher latitudes, they transfer heat from warmer to cooler areas on Earth. Warm ocean currents are felt mostly in the middle latitudes in winter. In contrast, the influence of cold currents is most felt in the tropics or during summer months in the middle latitudes. As cold water currents travel toward the equator, they help moderate the warm temperatures of adjacent land areas. Ocean currents also play a major role in maintaining Earth's heat balance by transferring heat from the tropics, where there is an excess of heat, to the polar regions, where less heat exists.
Upwelling
Upwelling is the rising of cold water from deeper layers to replace warmer surface water. Coastal upwelling occurs in these areas when winds blow toward the equator and parallel to the coast. Coastal winds combined with the Coriolis effect cause surface water to move away from shore. As the surface layer moves away from the coast, it is replaced by water that "upwells" from below the surface. Upwelling brings greater concentrations of dissolved nutrients, such as nitrates and phosphates, to the ocean surface.