TOP: WHOI climate scientist Kristopher Karnauskas examined this global satellite map of chlorophyll in surface waters, indicating the growth of phytoplankton. Higher chlorophyll is shown in aqua, green, yellow, and red; lower in blue and purple. To the left of South America, a line of chlorophyll extends westward toward the left side of the map.
MIDDLE: When Karnauskas moved the map to look at the whole Pacific basin and focus on the equator (black line), he saw higher chlorophyll values (top map) toward the west at the Gilbert Islands. At the right are the Galapagos Islands, west of South America, where the Equatorial Undercurrent (EUC) carries nutrients and cooler water toward the surface around the islands. As a result, the islands have higher chlorophyll levels (red) than surrounding areas.
BOTTOM LEFT: The ECU also hits the Gilbert Islands, which have localized regions of higher chlorophyll. In a close-up map of sea surface temperatures (SST) near the Gilberts (part of the nation of Kiribati), dark blue on the islands’ west sides indicates cool water upwelling from the Equatorial Undercurrent.
BOTTOM RIGHT: The Gilbert Islands lie in a line across the equator, and the Equatorial Undercurrent spans the area from about 2 degrees (138 miles) north to 2 degrees south of the equator. Chlorophyll values, shown in shades of green, decline from east to west but increase again around the islands (Images courtesy of NASA)