Melting water from giant icebergs, which contains iron and other nutrients, supports phytoplankton growth that is responsible for as much as 20% of the carbon sequestered to the depths of the Southern Ocean by biological metabolism and growth, reports a study published online this week in Nature Geoscience. These giant icebergs, dozens of which are floating in the Southern Ocean at one time, influence phytoplankton over an area ten times larger than typical icebergs do, even when accounting for the difference in size.
The Southern Ocean plays a significant part in the global carbon cycle, and is responsible for approximately 10% of the ocean’s total carbon sequestration through a mixture of biologically driven and chemical processes, including phytoplankton growth. However, previous studies have suggested that ocean fertilization from icebergs-in the form of iron and other micronutrients from meltwater-makes relatively minor contributions to phytoplankton uptake of CO2, some of which is subsequently sequestered in the deep ocean.
Grant Bigg and colleagues analysed satellite images of ocean colour-an index of phytoplankton productivity at the ocean’s surface-associated with a range of icebergs at least 18 km in length in the open Southern Ocean. They find enhanced phytoplankton productivity extends hundreds of kilometres from giant icebergs, and persists for at least one month after an iceberg passes. The authors suggest their new analysis reveals that giant icebergs may play an outsize role in the Southern Ocean carbon cycle.