Ocean Nourishment - Volcanic Ash As A Nutrient Source

Volcanic Ash As A Nutrient Source

Volcanic ash adds nutrients to the surface ocean. This is most apparent in areas that are nutrient limited. Considerable research has been done on the effects of anthropogenic and eolian iron addition to the ocean surface, but some research suggests that nutrient-limited areas benefit most from a combination of nutrients provided by anthropogenic, eolian, and volcanic deposition. Some nutrient-limited oceanic areas are limited in more than one nutrient, so the biological community is more likely to thrive from adding multiple nutrients like P, N, and Fe, than if only Fe were added to the system. Volcanic ash has the potential to add these multiple nutrients to the system, allowing the biota to thrive, but excess metal ions can be harmful to systems limited by nutrients. The positive impacts of volcanic ash deposition are potentially outweighed by their potential to do harm.

There is clear evidence for the presence of as much as 45 percent by weight of ash in some deep marine sediments. In the Pacific Ocean, the largest ocean basin covering half of the Earth's surface area, estimates have shown that (on a millennial-scale) the atmospheric deposition of air-fall volcanic ash has been as high as the deposition of desert dust. This indicates the potential of volcanic ash being a significant source of iron in the surface ocean.

In August 2008 an eruption in the Aleutian Islands, Alaska, deposited ash in the nutrient limited North-East Pacific. There is strong evidence that this ash and iron deposition resulted in one of the largest phytoplankton blooms observed in the subarctic.