Day 12 The importance of iron in our oceans: Chantelle Cook

Now to the bow! Morgane, a scientist from University of Tasmania, walks us to her lab through the area on the ship where the anchors and mooring lines are housed. The ocean is visible through the many open ports, and she explains that on voyages through the Tasman Sea it is often impossible to get to her lab, as the ocean roars through the area. She is also not able to come to the lab unaccompanied at night or in bad weather to ensure her safety.

Morgane is working on a project called Natural iron fertilisation of oceans around Australia: linking terrestrial dust and bushfires to marine biogeochemistry. What exactly does that mean, I hear you ask?

Iron is a key micronutrient for marine phytoplankton, and as we learnt from my previous blog, phytoplankton is essential for the growth of marine ecosystems. However, iron is not naturally found in oceans and must come from other sources, including the land and the atmosphere.

So, why don’t we just give the ocean a nice dose of iron and dump a heap of it the ocean? It’s not that easy, which is why this research is so important! In the past, dumping of iron rich soil into the ocean has been trialled. However, soil is not soluble, whereas carbon dioxide, found in terrestrial dust such as bushfires, volcanoes and even pollution from industry, provides iron rich particles that are far more soluble and absorbed into ocean more readily.

Like many of the labs on board, there is strict quality control in Morgane’s tiny little lab, tucked away in the ship’s bow. The walls are covered in padding and plastic so that no iron from the ship’s iron walls can contaminate the samples; all tables, tubing and cables are plastic; and it is temperature controlled.

Morgane shows us the air sampling unit that catches the samples from the aft mast, directly above it. Permanent connections and pumps lead from there to the air sampling station, where the air is filtered onto a cellulose filter to catch trace elements of iron.

The air sampling runs fairly continuously, as 20 metres cubed is the minimum sample to get enough particles. There are times when the sampling will get switched off, sometimes manually, but mostly automatically by the ship’s sensors. For example, the pump will switch the unit off if it is running below five knots, as it would then be collecting exhaust emissions that would compromise the sample. It also switches off over 80 knots, as the speed of the sample cannot be controlled. Direction of the wind can also contaminate, mostly from exhaust fumes. If the wind is blowing the wrong way, it will automatically shut off.  

The sampling unit has a carbon sensor connected to measure the level of carbon dioxide in the air. However, on this trip we have had so much humidity that it seeped into the lines and had to disconnected!

Once Morgane gets her samples back to the lab, she applies a leeching solution to the filters to measure the iron trace elements. Once she knows the volume of iron, she then meticulously studies where the air has come from by performing back trajectory analysis based on meteorology reports. She looks at where the wind has come from over the 10 days prior to the sample being taken and then looks at weather patterns or environment factors in those areas that may have attributed to the high or low iron levels in that area.

This is cutting edge research, a relatively new area of study for scientists. There has been a lot of research done on oceanography but little on how the atmosphere relates to and affects life in the ocean. It is very hard to observe air particles and there is still a lot to be hypothesised and proven in this field. While we do know that iron acts as a ‘fertiliser’ for the phytoplankton and that terrestrial dust is the best way for the ocean to absorb the iron, we know there is also another variable missing. From information gathered from dust storms around the world, we know that when dust storms go over oceans, sometimes there is a plankton bloom and at other times there is not. So what other biological factors are needed to make this bloom happen? Hopefully, Morgane’s further research in this area will help us to find the answer to these questions and find a bridge between the land and the ocean.