Marine life not harmed by ashfall, phytoplankton

The numerous eruptions on Anatahan have recently resulted in many volcanic ash clouds being produced and carried downwind. The transport of these clouds is dependent upon the direction and speed of the prevailing winds. Whenever there is volcanic activity and the winds are coming from the north, people see a hazy sky—remnant of the volcanic ash in the atmosphere.

Given a large enough eruption, people find that small, volcanic ash particles settle upon their vehicles’ windshields and surrounding environment.

While this is common knowledge, a more interesting aspect of the volcanic ash deposition comes from looking at the ocean. Ash outfall events trigger ecological responses in the surrounding ocean. Volcanic ash particles have nutrients and minerals attached to them—iron, silicates, and sulfates, to name a few. Imagine then the vast amounts that fall into the ocean following an eruption.

“Under normal circumstances our offshore waters are nutrient- and mineral-free, leaving clear blue waters. Nutrients and minerals associated with the ash outfall are limiting requirements for the growth of tiny algae called phytoplankton. This means that following an ash outfall event, there are blooms of phytoplankton,” said the Division of Environmental Quality.

On Tuesday, July 12, Tinian DEQ staff responded to a complaint of water pollution near the port area. Water samples were collected and sent to DEQ laboratory for inspection. The DEQ biologist noted an extremely high density of phytoplankton floating on the surface, while ash particles were found sinking to the bottom.

On the same day several phone calls were received describing unusual water quality conditions around Saipan. It appears that the tropical storm passing north of the CNMI pushed the volcanic ash outfall in a southward direction from Anatahan to Saipan and Tinian.

DEQ said the large quantity of phytoplankton found in the Tinian harbor may have resulted from the bilge water associated with the Saipan-Tinian boat ferry.

“It is probable that the ferry collected these water while offshore in route to Tinian, and carried them into the harbor,” the agency said.

Regardless, DEQ said the phytoplankton blooms have not had any negative affect on the marine life. “The only potentially harmful consequence would be if vast amount of these phytoplankton bathe our shores and use up all of the available oxygen in the waters, an event unlikely to occur.”

Interestingly, DEQ said satellite imagery can be used to track these blooms. “We have received a few images showing the phytoplankton blooms in the direction of the prevailing winds.”

If you have further questions or request more information, contact DEQ at 664-8500.