Concentrations of iron however vary throughout the year. Ocean currents are driven by seasonal atmospheric patterns which transport iron from the Kuril-Kamchatka margin into the western Subarctic Pacific. This introduction of iron provides a subsurface supply of micronutrients, which can be used by primary producers during upwelling of deeper waters to the surface. Seafloor depth may also stimulate phytoplankton blooms in HNLC regions as iron diffuses from the seafloor and alleviates iron limitation in shallow waters. Research conducted in the Gulf of Alaska showed that areas with shallow waters, such as the south shelf of Alaska, have more intense phytoplankton blooms than offshore waters. Volcanic ash from the eruption of the Kasatochi volcano in August 2008 provided an example of natural iron fertilization in the Northeast Pacific Ocean. The region was fertilized by raining volcanic dust containing soluble iron. In the days following, phytoplankton blooms were visible from space.