The waters off the California coast are notably cold, a characteristic frequently observed by those who live near or visit the Pacific shoreline. This phenomenon is primarily influenced by a significant ocean current known as the California Current. Understanding the scientific reasons behind this consistent coldness involves examining the current’s properties, the dynamic process of upwelling, and the distant origins of its water.
Understanding the California Current
The California Current is a broad, shallow ocean current flowing southward along the western coast of North America. It extends from British Columbia in Canada down to Baja California in Mexico, reaching several hundred miles offshore into deeper oceanic waters. This current is classified as an eastern boundary current due to the influence of the North American coastline on its path. Its surface velocity is typically less than 10 inches per second (25 cm/sec). The California Current is a cooler surface current compared to others at similar latitudes, contributing to the chilly temperatures along the coast.
The Mechanism of Upwelling
A primary reason for the cold temperatures in the California Current is coastal upwelling, a process driven by prevailing winds. Strong, northwesterly winds blow parallel to the California coastline, pushing surface water away from the shore. This offshore movement of surface water is further enhanced by the Coriolis effect. In the Northern Hemisphere, the Earth’s rotation deflects moving water to the right, causing the displaced surface water to move southwest, away from the coast.
As surface water is pushed away, colder, denser water from deeper ocean layers rises to replace it. This deep water, typically found at depths of 100-125 meters, is much colder, often around 8°C (46.4°F), and rich in nutrients. The continuous influx of this cold, sub-surface water to the surface significantly cools the California Current. This process is most pronounced in spring and summer when northwesterly winds are strongest, and it can occur year-round off the northern and central California coast.
The Influence of Water Origin
The inherent coldness of the California Current is also largely due to the origin of the water it carries. This current is a component of the larger North Pacific Gyre, a vast swirling system of ocean currents in the northern Pacific Ocean. As part of this gyre, the California Current draws water from higher, colder latitudes in the North Pacific. Specifically, it is a southward-flowing continuation of the Aleutian Current and receives water that has circulated through subpolar regions. As this water flows southward along the North American west coast, it combines with the cooling effects of upwelling to maintain the low temperatures of the California Current.