Upwelling describes an oceanic phenomenon where cold, dense, and nutrient-rich water moves from the deep ocean towards the surface. This process replaces warmer, nutrient-depleted surface water. Upwelling creates areas of immense biological productivity in the ocean. These productive regions attract and sustain large numbers of fish.
The Upwelling Process
The physical mechanisms driving upwelling involve an interaction of wind and Earth’s rotation. Winds blowing across the ocean surface create friction, pushing surface water in a particular direction. This movement is not directly in line with the wind’s direction due to the Coriolis effect. The Coriolis effect deflects moving water to the right in the Northern Hemisphere and to the left in the Southern Hemisphere.
This deflection leads to a net movement of surface water, known as Ekman transport, perpendicular to the wind direction. When this Ekman transport pushes surface water away from a coastline, deeper water rises to fill the void. This upward movement brings water from depths to the surface. Coastal upwelling is a well-known type that supports some of the world’s most productive fisheries.
Nutrient Enrichment and Primary Production
Upwelling brings deep waters to the surface that are rich in dissolved inorganic nutrients. These nutrients accumulate in the deep ocean from the decomposition of organic matter that sinks from surface waters. Surface waters lack these essential compounds because they are consumed by marine organisms or remain unavailable in deeper layers.
Once these nutrient-laden waters reach the sunlit upper layers of the ocean, conditions become ideal for growth. The influx of nutrients, combined with ample sunlight, fuels large blooms of phytoplankton. Phytoplankton are microscopic marine algae, acting as the primary producers at the base of marine food webs. Their growth transforms inorganic nutrients into organic matter through photosynthesis, becoming the initial energy source for the entire ecosystem. Upwelling regions exhibit high levels of primary production compared to other ocean areas, contributing significantly to global marine productivity.
Building the Marine Food Web
The abundant phytoplankton blooms in upwelling zones form the foundation for a marine food web. These microscopic plants become a food source for zooplankton, which are tiny marine animals. Zooplankton graze on the phytoplankton populations, converting the primary production into a form accessible to larger organisms.
This biomass of zooplankton attracts small pelagic fish, which feed directly on them. These small fish form large schools, creating aggregations of prey. The presence of these smaller fish draws in larger predatory fish. These larger predators are attracted to upwelling areas due to the concentrated food supply, supporting diverse marine life.
Ecological Significance of Upwelling Zones
Upwelling zones support a large share of global marine biodiversity. These areas sustain diverse ecosystems, from microscopic organisms to marine mammals and seabirds.
Their enhanced productivity has a significant impact on global fisheries. Coastal upwelling regions, despite accounting for only about one percent of the ocean surface, contribute roughly 50 percent of the world’s fisheries landings. This contribution underscores their importance for food security and the livelihoods of coastal communities. Understanding and protecting these dynamic regions is important for maintaining ocean health and sustainable marine resources.