Scientists assess impact of Icelandic volcanic ash on ocean biology

The team is led by Professor Eric Achterberg from the University of Southampton's School of Ocean and Earth Science (SOES) who is based at the National Oceanography Centre in Southampton. They are aboard the RRS Discovery in the region of the North Atlantic Ocean affected by ash from the eruption of Eyjafjallajökull.

This is the second cruise this year to the study region. The first cruise took place over a period of 14 days in April-May 2010, with the aim of determining biological and chemical conditions in the ocean before the large annual spring phytoplankton bloom starts. On this first cruise the team took the opportunity to observe large Icelandic volcanic ash inputs to the ocean from Eyjafjallajökull, which was erupting at the time. The team's return to the Irminger and Iceland Basin region this summer will allow them to assess how phytoplankton blooms have developed. They will also investigate whether phytoplankton in the region are growth limited because of a lack of iron, or whether the volcanic ash inputs have supplied sufficient iron to sustain the spring blooms longer than usual.

The team will sample for atmospheric dust and nutrients in the seawater, and measure the activity of phytoplankton, microscopic plants that form the base of the marine food web and take carbon dioxide from the atmosphere. There is an expedition blog which can be viewed at: http://www.classroomatsea.net/D354/

In many regions of the ocean, the productivity of phytoplankton is limited by the availability of iron, which is essential for their growth. On a previous cruise in 2007, scientists from NOCS demonstrated that the high-latitude North Atlantic Ocean -- just south of Iceland and east of Greenland -- might be one such region. Consequently biological productivity, and ultimately the carbon cycle, may be sensitive to any changes in iron inputs there.

The sub-polar Atlantic Ocean is a globally important ocean region, as it is a sink for atmospheric CO2, and an area where deep-water formation takes place. Potential iron limitation of CO2 fixation by phytoplankton in this region would represent an inefficiency in atmospheric CO2 uptake by the ocean.

Volcanic ash is thought to be capable of providing a significant source of iron for phytoplankton, so the recent eruption of Eyjafjallajökull presented an unexpected opportunity to study a 'natural experiment' where the system has potentially been alleviated from the normal potential iron-limited condition.

Dr Mark Moore from SOES, who led the first cruise, says: "it will be really interesting to return to the region where we observed significant ash inputs earlier in the year. We are very fortunate to be able to go back and see whether there is an effect on ocean productivity."

Professor Eric Achterberg, also from SOES and leading the second cruise, says: "We will be doing further biological experiments at sea in the Iceland and Irminger Basins during this five-week cruise. In particular we will add volcanic ash collected on the first cruise to seawater samples (and also add iron separately) to study the response of phytoplankton. This work is built into our original programme and provides a unique opportunity to determine the biological effects of volcanic ash inputs to the ocean."

The team, which also includes scientists from the Universities of Portsmouth, Cape Town, East Anglia and Seville, set sail from Avonmouth on July 4 and is scheduled to return to the UK on August 11.