The disturbance that islands cause in the flow of water currents in the ocean creates turbulence that mixes surface waters with deeper ocean layers. This mixing increases the amount of nutrients available in the warm surface waters where microscopic ocean plant life grows. Iron-rich sediments running off the islands also enhance plant productivity, particularly when the islands are steep and do not have shallow lagoons where the sediment can settle.
This colorful image shows the concentration of chlorophyll in the waters around the Marquises Islands (or “Marquesas,” as they are commonly known in English) in French Polynesia, a collection of islands in the western Pacific Ocean about ten degrees south of the equator. Surface waters with less chlorophyll are colored in blue, while progressively higher amounts of plant chlorophyll are yellow. Clouds are white, and the islands are dark gray.
The largest of the three islands arranged in a triangle in image center is Nuku Hiva. To its east is Ua Huka, while to the south is Ua Pou. The highest chlorophyll levels in the region are south of this triangle of islands, while another strong plume is visible stretching northward from Hiva Oa, farther east. Although these islands appear as just a speck on a map of the entire Pacific Ocean, they have a large influence on plant, and, in turn, animal life in the region.
NASA image by Norman Kuring, MODIS Ocean Color Team
Located in the southern Indian Ocean roughly midway between Africa, Australia, and Antarctica, the Kerguelen Islands experience a fierce climate, with incessant, howling winds and rain or snow nearly every day. At a latitude of about 49 degrees South, the islands lie in the path of the “Furious Fifties,” a belt of westerly winds that whip around the Southern Hemisphere, mostly unimpeded by land.