Correct Option
The correct option is Upwelling of cold water due to winds.
Explanation
The distribution of ocean temperature is studied horizontally (latitudinal and longitudinal) and vertically (depth). While latitudinal variation is primarily governed by the amount of solar insolation received, longitudinal (East-West) variation is influenced by dynamic factors such as ocean currents, upwelling, and the distribution of land and sea.
Detailed Analysis:
- Latitude is Incorrect: Latitude is the dominant factor for latitudinal variation. The temperature of surface water decreases from the equator toward the poles due to the decreasing angle of the sun's rays. This explains North-South gradients, not longitudinal ones.
- Upwelling of cold water due to winds is Correct: Longitudinal variation in temperature is largely caused by the upwelling of cold water and the influence of ocean currents. Trade winds often drive warm surface water away from the western coasts of continents (eastern boundaries of oceans), allowing cold deep water to rise to the surface. Consequently, at the same latitude, the eastern part of an ocean (e.g., the Peru Current region) is significantly colder than the western part (e.g., the Western Pacific warm pool).
- Depth of the ocean is Incorrect: The depth of the ocean determines the vertical distribution of temperature. Temperature decreases with depth, characterized by the thermocline layer, but this does not explain surface temperature differences across longitudes.
- Salinity gradients is Incorrect: Salinity gradients influence the density and freezing point of water but are not the primary factor responsible for the large-scale longitudinal variation in surface temperature compared to the mechanical movement of water masses (currents and upwelling).
Key Takeaway:
Latitude determines the general decrease in temperature from equator to poles, while ocean currents and upwelling are responsible for temperature anomalies and variations across longitudes.