Is it possible to put a value on how useful our seas are in the mitigation of climate change?

Oceans

Our oceans aren’t just pretty to look at, they are doing a vital job storing away millions of tonnes in carbon emissions and mitigating climate change.

That’s the headline from a new report published by the Global Ocean Commission, co-authored by Alex Rogers of Oxford University’s Department of Zoology and Somerville College. I asked Alex how the report’s authors assessed the many ways we benefit from ocean ecosystems – benefits known collectively as ‘ecosystem services’ – and what more we can do to preserve them…

How do the oceans help to store our carbon emissions?

The oceans have taken up about 25-30% of all human carbon emissions and about 50% of those from the burning of fossil fuels. There are several routes by which this carbon enters the ocean. The primary one is the ‘solubility’ carbon pump by which CO2 dissolves into the ocean and is transported via ocean circulation into the deep sea. There is also the biological carbon pump whereby phytoplankton, microscopic organisms that use photosynthesis to fix carbon and convert it to tissue, take up CO2. 

These microscopic organisms form the basis of the food chains of most of the ocean. As they die and sink into the deep sea or are eaten and their carbon is transported into deep water through the movement of animals or the sinking of their faecal material the carbon is transported downwards. 

A small proportion of the surface derived carbon is stored in the deep sea. In our report we only looked at the biological carbon pump to look at how much CO2 is potentially sequestered through the actions of living organisms. This only represents a fraction of the CO2 sequestered in the oceans (total amount is estimated to be ~2.5 billion tonnes of carbon).

What impact could mining and other high seas industry have on their ability to store carbon?

One of the fascinating things we found in our research was the evidence for the intimate connection of the activities of living organisms to nutrient cycling in the oceans. Fish, whales, gelatinous zooplankton all carry out a multitude of functions in ecosystems from feeding on other organisms and controlling their abundance to influencing the concentration of nutrients, such as iron, in surface waters and even stirring the oceans through their vertical and horizontal movements. When parts of the ecosystem are damaged by, for example, overfishing, then some of these functions are degraded with knock on effects to the rest of the ecosystem.

Why is it so hard to put a value on high-seas ecosystem services?

We identified about 15 types of ecosystem service provided by the high seas but could only put a monetary value on a few of them. These services, which benefit humankind, range from the provision of food (i.e. fish) to the regulation of atmospheric gases (such as CO2). 

Many of them cannot be quantified at present. This is for a variety of reasons but the main one was simply insufficient scientific knowledge of how the ocean works and the complex relationships between its biological and physical (or biochemical) components. Another reason was that even where values could be identified we could not ascertain what share of a particular service was attributable to the high seas. 

An example of this is fishing (or mining!) of precious corals, where a significant component of global catch comes from the high seas but because of poor documentation of catches we do not know how much. In other cases the high seas contribute to ecosystem services that are in fact derived in coastal waters, examples including many fish species which might feed for part of the time in the high seas but which are caught in coastal waters.

How will these findings feed into your future research?

The study has made us much more aware of the enormous knowledge gaps in terms of how the ocean works. For example, although our examination of carbon sequestration could estimate the rate of sinking of phytoplankton into the deep ocean there was little knowledge of active transport of carbon into the deep sea. This is where large numbers of organisms feed in surface waters, especially at night, and then dive into the deeps by day to avoid predators. These animals transport carbon into the deep sea but we do not even know how many there are, even, in some cases to orders of magnitude. Our research on deep-sea ecosystems will focus more on these questions in the future.

What could governments do to save high-seas ecosystems?

Clearly there are problems with the management of human activities on the high seas. Overfishing and illegal fishing are two serious issues in a world of increasing human population and a resultant increasing need for fish protein. 

At present governance of the high seas is very fragmented. Management of different industrial sectors is undertaken by different bodies, some of which are ineffective and do little more than divide up the proceeds from extracting ocean resources. These organisations often operate in isolation of international agreements on the protection and sustainable use of the environment. 

Clearly a more joined up approach to ocean governance is required with increased transparency of decision making and assessment of institutional effectiveness. Where these organisations are failing, this must be identified and corrected. Policing the oceans must also be improved and we now have the technology to monitor much more closely what various parties are doing on the oceans. Some of these measures can be incredibly simple and cost effective. For example, insisting that all fishing vessels on the high seas, like other shipping, must carry an internationally registered identification number would help us identify those not following regulations.

This article first appeared on the Oxford Science Blog and is republished with kind permission. Image by Kevin N. Murphy under Creative Commons license.