Hypothesis

What process might be working to bring iron to the water of the Scotia Sea and the eastern Drake Passage, where the phytoplankton are growing well?

In 2004, Greg Mitchell and an interdisciplinary team of scientists went to the Drake Passage in the Southern Ocean. They spent a month sailing through the Drake Passage from west to east. They studied the shallow areas over the Shackleton Fracture Zone, an underwater mountain ridge. This narrow passage has a gap between the crest of the Shackleton ridge and the continental shelf of the Antarctic Peninsula.

The scientists set up a grid of sample sites for a detailed analysis of the water. As the ship travelled back and forth along this grid, the scientists took samples and studied water chemistry. They measured the amount of phytoplankton and zooplankton in the water. They studied the ocean currents. When they analyzed their samples, the scientists formed an hypothesis to explain the source of iron.

The scientists think that fast-moving currents of deep seawater are forced into the gap formed by the Shackleton Fracture Zone and the Antarctic Peninsula. The rushing currents drag iron sediments off the seafloor. The current carries this iron-rich water eastward and toward the surface, where phytoplankton use it to grow in abundance.

In order to test this hypothesis, the scientific team will return to the area above the Shackleton Fracture Zone. They will use sophisticated instruments to take many measurement and water samples in a new investigation. They hope that their findings will provide answers to questions about other parts of the world’s oceans. This investigation might explain how iron enters the water and enriches it in places far from Earth’s continents.