Major dust storms in the south of Alaska were first recorded in 1911, but only during the last decade did scientists begin to notice that they play a role in the bloom of phytoplankton.
In 2011, Santiago Gasso of NASA’s Goddard Space Flight Center, John Cruz of the US Geological Survey and other scientists published the first study on the role of dust storms in the supply of nutrients, especially iron, to the Gulf of Alaska. Since then, each subsequent dust storm has revealed new details of the complex relationship between dust and phytoplankton.
On Saturday, November 11, the MODIS spectroradiometer on NASA’s Aqua satellite received this coastline image along the Gulf of Alaska. The thick dust trails extending south of the river valleys are a predominantly fine-grained loess formed as a result of the crushing of rocks by glacial ice. Dust storms in the south of Alaska usually occur at the end of autumn, when the level of the rivers is relatively low, snow has not yet fallen out, and layers of forest rich silt are exposed to wind.
Since light is also crucial for the development of phytoplankton, Gasso and his colleagues suggest that the effect of dust entering the ocean can be delayed until next spring. To better understand these relationships, scientists are trying to determine how much iron is supplied by dust storms compared to the rise of nutrient-rich water from the depths or by the mixing of iron-rich sediments from rivers by surface circular currents. However, the latter phenomena tend to be coastal, while wind dust can cross hundreds of miles across the open ocean, reaching areas where iron stores are depleted.
“It is convenient that we have an accessible phenomenon that allows us to study the factors controlling the development of marine phytoplankton,” Gasso said, noting that most of the research on this topic was conducted in the Southern Ocean around the Antarctic.
The study of modern dust storms can also help in the interpretation of ice samples that record past environmental conditions and climate changes. Many samples testify both to an increased deposition of dust, and to a decrease in the concentration of carbon dioxide in the air during glacial periods. It is not yet clear why an increased concentration of dust and low levels of carbon dioxide in the atmosphere go hand in hand, but some scientists believe that phytoplankton, fueled by dust that can absorb large amounts of carbon dioxide, could play a key role.