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Tropical winds support the world's most productive ocean systems

The tropical Pacific Ocean is home to most of the islands on Earth, including reef islands and atoll reefs. A new study led by Flinders University in Australia has found that Southeast Asian regions of the Pacific produce more fish than all the world’s largest coastal upwelling areas combined, despite many scientists previously believing that tropical oceans are low in both nutrients and phytoplankton productivity.

According to the experts, transient short-lived wind events trigger the formation of massive phytoplankton blooms – which occupy the base of many marine food webs – close to tropical reef islands, such as the disputed Spratly Island in the South Island Sea, as well as a variety of other islands in the Pacific Ocean.

“The key here is that the tropical Pacific contains thousands of such islands, which implies that tropical wind events can create a large network of marine ecosystems existing year-round and spanning thousands of kilometers, possibly forming one of the largest upwelling biomes on Earth,” said study lead author Jochen Kaempf, an associate professor of Coastal Oceanography at Flinders.

Upwelling is a physical process which enriches oceans’ surface waters with dissolved nutrients, thus fueling the production of phytoplankton. The scientists discovered that coastal winds are the main drivers of the most productive upwelling systems on our planet, including those forming on the coasts of California and Peru-Chile, which are major global fish producers.

“We believe that this (Asia-Pacific) upwelling biome provides critical feeding habitats for migratory marine species such as sea turtles, tuna, and whales,” Kaempf explained. “For instance, pygmy blue whales migrate from their feeding habitat in upwelling regions of southern Australia to their breeding grounds in Indonesian waters, where they seem to gather near Christmas Island and volcanic arc islands of the Banda Sea. Our findings suggest that this behavior is primarily feeding-related.”  

These findings opens new paths for examining the phytoplankton bloom mechanisms in tropical oceans, especially in the light of new worrisome phenomena caused by climate change, such as sea-level rise, enhanced wave erosion, and shifts in tropical rainfall and winds patterns.

The study is published in the Journal of Oceanography.

By Andrei Ionescu, Staff Writer

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