For many years, ship captains navigating the waters of Antarctica have seen emerald icebergs. Scientists now say it's because these icebergs are upside down. Icebergs are large blocks of ice that break off frozen snow called ice shelves. Their green look comes from sea water that froze over hundreds of years. This frozen sea water has organic matter that makes it yellow. The fresh water ice above looks blue. When turned upside down, the iceberg looks green because of the mix of yellow and blue. What are icebergs?