Icebergs are a small but measurable ally in the fight against global warming, according to a new study. The floating mountains of ice—some of which start out Connecticut-sized or larger—scraped up bits of rock when they were parts of glaciers on land. Once they reach the sea and begin melting, they release a bounty of dissolved iron and other nutrients into the nutrient-poor waters around Antarctica. This nourishes phytoplankton, chlorophyll-bearing microorganisms at the base of the ocean’s food chain, which suck up the greenhouse gas carbon dioxide (CO2) as they grow. Satellite data gathered from 2003 through 2013 reveal booming populations of phytoplankton as far as hundreds of kilometers from the bergs, researchers report online today in Nature Geoscience. Those blooms (one example from January 2013 shown, with chlorophyll levels depicted in shades of yellow and red; gray masses are clouds) can last up to a month after an iceberg passes, the team notes. What’s more, currents and winds can sweep nutrients ahead of the slow-moving berg to nourish life there (the yellow swath seen to the northeast of the berg shown at center). Using data from previous field studies, the team estimates that the minerals and other nutrients released by giant Antarctic icebergs (those longer than 18 kilometers) trigger as much as 20% of the CO2 absorption by life in the southern seas. According to previous studies, that amount—between 44 million and 146 million metric tons of CO2—offsets a tiny fraction of the estimated 35.3 billion metric tons of CO2 generated by the burning of fossil fuels and other industrial activity in 2013.