TOP (Present): At present at the equatorial Pacific Gilbert Islands, east-to-west trade winds produce a surface current along the equator. The Equatorial Undercurrent (EUC) flows in the opposite direction at 100 to 200 meters depth. When it hits a barrier (such as an island), the cooler, higher-nutrient water in the EUC flows up toward the surface. The waters near the island exhibit both cooler temperatures (shown as blue) and higher productivity of chlorophyll-containing marine phytoplankton, both of which diminish to the west.
BOTTOM (Future): In the future, global climate models predict a sea surface temperature rise of nearly 3 degrees C (5.4 degrees F) by the end of the century. According to Karnauskas’s and Cohen’s fine-scale model, equatorial trade winds will weaken, causing a weakening of the surface current. In turn, the frictional drag on the EUC will lessen, and the EUC will strengthen, carrying more cool, nutrient-enriched water to the surface around the Gilbert Islands. The result will be enhanced productivity close to the islands, and slower warming during the coming century than neighboring islands not in the EUC’s path. The slower warming may allow corals to adapt and survive, making the Gilberts a refuge for coral reef ecosystems. (Amy Caracappa-Qubeck, Woods Hole Oceanographic Institution)[back]
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