The California Current System (CCS) is a cold water current that flows along the west coast of North America. As the current moves from Canadian waters southwards, surface water is moved away from the coast by offshore winds and the Earth’s rotation, changing the trajectory of water over long distances.
This leaves space for cool, nutrient-rich water from the deep to rise to the surface. The process of replacing warm surface water with cooler, nutrient-rich water is called upwelling. It is a major determinant of biological, geological, and chemical conditions in the CCS. Thriving populations of phytoplankton, microscopic plants that float in the upper levels of the ocean, use energy from the sunlight to make carbon into carbohydrates. They are supported by the high nutrient content of upwelled waters. During times of pronounced upwelling, there is more phytoplankton and overall ecological diversity. This is because phytoplankton are at the base of the food chain and support other larger organisms.
Upwelling in the CCS is also more intense because of mesoscale eddies, which are circular movements of water that are known as the “weather” of the oceans. Eddies generated by the coastline trap cold upwelled water and move it offshore. High nutrient levels carried offshore can support a thriving ecosystem up to 500 kilometers from the coast.
Although upwelled waters contain high nutrient levels, other environmental factors are less favorable for the growth of planktonic organisms. Dissolved oxygen (DO) and saturated carbonate levels are reduced in upwelled waters, such as those common to the CCS. Low levels of oxygen limits photosynthesis of phytoplankton and impacts large-scale ecological activity along the west coast of North America. Low saturated carbonate levels cause degradation of carbonate-based shells, including those produced by pteropods, Dungeness crab larvae, and mollusks. Upwelling also brings high concentrations of dissolved carbon dioxide (CO2) to the surface, resulting in acidic surface waters.
Sources:
Amos, C. M., Castelao, R. M., & Medeiros, P. M. (2019, October 30). Offshore transport of Particulate Organic Carbon in the California current system by Mesoscale Eddies. https://www.nature.com/articles/s41467-019-12783-5.
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