Prof. Dr. Rob Middag

Chemical oceanographer Rob Middag has specialised in the chemistry of the oceans. ‘I mainly examine the role of metals in marine ecosystems. Metals like copper, zinc, nickel and manganese might elicit negative associations, but ultimately they are just as vital for life, for example, iron that enables the transport of oxygen in our blood. However, the concentrations in the oceans are very low. For healthy marine life, the amount of iron in a single paperclip dissolved in fifteen Olympic swimming pools of seawater is sufficient.

One of the challenges of my discipline is that it has only been possible to accurately measure such minuscule quantities of metals since the 1980s, so quite recently. Researching metals in seawater means: working with titanium instruments on plastic cables and wearing protective suits and hair nets in the lab because a single drop of sweat or a flake of skin can ruin the measurement.’

Iron fertilisation

‘We now know that in almost half of the world’s oceans, iron is limiting the growth of algae, which form the basis of the marine food web. This means that more algal growth will occur when more iron is added and that those algae will therefore take up more CO₂. But that does not mean that the climate issue can be solved by chopping up a rusting tanker and using it to fertilise the oceans. That is because those algae will largely remain in the food chain and will therefore not remove CO₂ from the cycle for the long term.’

‘Similar mechanisms occur for the other essential metals, although nickel and zinc, for example, are not directly limiting. However, they could cause a shift in the species composition of algae if their concentration in the seawater changed.’

Metal tool

‘Nevertheless, I do not exclude the possibility that a certain point, we will investigate metals in seawater if we want to tinker on the climate effect. That is because the ocean is by far the biggest reservoir of CO₂. But understanding metal metabolism is also vital if we want to responsibly stimulate the fishing sector or ocean aquaculture. Just like a dairy farmer needs to know how to fertilise their grass, a salmon fish farmer in Canada or a seaweed farmer in the North Sea needs to understand how iron ultimately influences the growth of salmon or seaweed.’