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Melting ice sheets in the Southern Ocean – A reason to be positive?

December 22nd 2020

Tagged: Co2, Environment, iron fertilisation, oceans

Generally regarded as the second smallest of the five principal oceans, the Southern Ocean or the Antarctic Ocean is one of the most notoriously challenging oceans to study thanks to treacherous waters, frigid conditions and the complex flow of currents. However, beneath the thousands of miles of ice sheets which canvas this area lies a fascinating discovery and one that could potentially play a role in removing Co2 from the Earth’s atmosphere in the form of biological geo-engineering.

How the Southern Ocean is changing

Sheets of ice cover around 10% of the world’s surface, with most of those being found here in the Southern Ocean. In a recent study research teams from the Potsdam research centre and Florida University discovered elevated quantities of trace elements and micronutrients under these frozen giants, namely iron and cobalt, with some melt waters recording 200 times the anticipated levels of dissolved iron. Although it is clear that these large masses of ice play an important role in the mobilisation of trace elements, the how and in what quantity these elements seep into adjacent ecosystems is unknown. So as further research is conducted, it is important to ask what effects could such a change in chemical balance have on surrounding ecosystems and how might it impact the carbon cycle and Co2 levels?

What is carbon sequestration and iron fertilisation?

Although approximately 70% of the earth’s surface is covered by water and a further 97% of that water is found in our oceans, the full complexity of our oceans are far from understood. Trace elements are found all over the Earth’s surface and as micronutrients in the oceans they are vital in the growth and  existence of countless organisms and the Earth’s carbon cycle. Carbon sequestration is the long-term removal of atmospheric Co2 in order to slow or reverse the process of global warming. One potentially interesting method used to sequester carbon is that of iron fertilisation, a process that has been a divisive and controversial idea for over 20 years.

The basic process involves spiking certain areas of ocean with trace amounts of iron (normally found in limited quantities), which in theory encourages a bloom of phytoplankton growth. These phytoplankton blooms grow through photosynthesis, taking in atmospheric Co2 in the process. Finally as the phytoplankton die and sink to the seabed, the carbon dioxide becomes stored deep in the ocean sediments.

Potentially positive impacts of iron fertilisation

With the water in the Southern Ocean considered to be nutrient rich, but depleted in iron, there is a suggestion that the surrounding ice and melt waters could naturally fertilise the large areas of the Southern Ocean and thus increase the supply of iron for phytoplankton growth.
This could lead to vast amounts of atmospheric Co2 being sequestered into the seabed and potentially help alleviate the process of global warming to an unknown extent. Furthermore, with larger quantities of phytoplankton and other primary producers, one might expect to see an increase in consumers and the ecosystem biomass.

The risks and issues of iron fertilisation

With any changes there are countless unforeseen impacts that can negatively affect the delicate balance of an ecosystem. When manipulating our own environment, we have to take into account the potential consequences and iron fertilisation certainly has the potential to cause more harm than good. History is a powerful reminder of the dangers we face when trying to control Mother Nature. There are multiple examples of minute changes that have led to the collapse of fisheries and extinction of species. Furthermore, seeing that phytoplankton remain at the base of the food chain, a negative impact could cause a dramatic domino effect throughout the whole ecosystem.

In a number of smaller scale iron fertilisation experiments, we have seen not only the rapid bloom of phytoplankton but also the undesired by-product of a bacterial bloom that consumes the decomposing phytoplankton. During this process the bacteria can use up all the oxygen in the given environment, producing carbon dioxide and thus creating large oxygen depleted dead zones, which leads to suffocation of the surrounding marine life.

The final issue regarding these algal blooms is that there are over 5,000 species of phytoplankton. Generating blooms of plankton has been proven to be fairly simple; generating a bloom of the plankton that is going to sink to the ocean floor, taking stored Co2 with it, proves to be far more difficult. Instead it is likely that a form of bioaccumulation will take place as the algae is consumed and passed through the food chain, until eventually the Co2 finds its way back into the atmosphere. The key to successful iron fertilisation requires a specific diatom. These are a unique group of algae composed of silica, which once they meet their demise rapidly sink through the water column.

What can we expect from iron fertilisation in the Southern Ocean?

When studying the melting ice sheets across the globe, it is not always easy to grasp at positives. Although the impacts of such a global phenomena are impossible to predict accurately, the findings from the Southern Ocean melt waters offer a potentially positive effect. Although iron fertilisation could theoretically remove large quantities of Co2 from the atmosphere, there are an enormous amount of unknowns to contend with, as well as many environmentally and ecologically damaging outcomes. With so many unanswered questions surrounding how biogeochemical cycles will change as more ice melts, and what quantity of these trace elements actually reach marine organisms, there is scope for not only further research but also curiosity and possible optimism.


Written by WorkingAbroad blogger, Barnaby Bourton


Photo from Wiki Commons by David Stanley from Nanaimo, Canada

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