RAGNARoCC: the story of carbon in the North Atlantic

by Penny Holliday

This cruise is contributing to three related scientific programmes; UK OSNAP which is the focus of this blog, a programme called the Extended Ellett Line that I lead at NOC, and a programme called RAGNARoCC. Today I am explaining what RAGNARoCC is all about so that you can get a sense of what we are doing and why.

Let’s start with the acronym. All good programmes begin with an excellent idea, but they also need a catchy title or better still, a word that is made up (at least vaguely) of the letters of a long title. Our version of the ancient Norse myth stands for “Radiatively Active Gases from the North Atlantic Region and Climate Change” so you can see why it is easier just to say RAGNARoCC. By “radiatively active gases” we mean those that interfere with the natural process of heat coming in from the sun and radiating out through the atmosphere; in other words, greenhouse gases. In a nutshell the programme will address the question of how the North Atlantic ocean absorbs carbon dioxide from the atmosphere and how that changes over time. We are looking at that deceptively simple question from a number of angles by collecting data at sea on research cruises and by examining computer models.

The reason this matters is that only around half of the carbon dioxide that humans are adding to the atmosphere stays there; the remainder is divided approximately equally between being taken up by the ocean and being absorbed by land vegetation. We know from recent research that the North Atlantic ocean is accumulating human carbon emissions faster than anywhere else in the ocean because of the way the ocean currents bring warm surface water here. But we don’t know all the biological and physical ways that accumulation happens, and we don’t know how those ways are adjusting to changes in atmospheric and oceanic concentrations of carbon dioxide. Carbon dioxide is not the only greenhouse gas, and the project is also looking at the exchange between the ocean and the atmosphere of gases called methane and nitrous oxide.

Scientists often talk about “budgets” for heat, energy or carbon. In order to define any budget you need the same kind of information that you use to manage a financial budget; what comes in, what goes out, and any savings or debts you have. To get to grips with the oceanic carbon budget we need to measure the exchange of gases between the air and the ocean, the movement of carbon around the world in ocean currents, and the amount of carbon that is stored in the water. By the end of the RAGNARoCC programme we will have a clearer idea of the carbon budget for the North Atlantic and will be able to point to the parts of the system that are critical in setting the budget. We will be able to describe how the budget has changed over the past 50 years, and will know what measurements we need in the future to keep an eye on how it is responding to climate change.

The measurements we are making on this cruise will be used to work out how much carbon is stored in the deep ocean, and how much is being moved around by the ocean currents. This will be done by combining these measurements with those from a similar cruise in the subtropical North Atlantic. Having said that though, we wont be coming up with single number as being “the answer”. Scientists often talk about defining our “uncertainty” for measurements like these. By this we dont mean that we are not sure about the answer, instead we mean that the answer falls within a range of values, and we know the range, but not the single answer. This happens because it is impossible to measure all of the ocean all the time. By linking up with projects like OSNAP that are measuring changes in ocean currents over several years, we can define that range successfully. RAGNARoCC is a large project with many people involved – it’s very exciting for those of us who have come together for this cruise to be working towards these common goals and to learn more about each other’s research.

Images: I’ve decided to illustrate today’s post with gratuitous images of Greenland and ice again. We did make it back to the Greenland coast one last time, so here are some photos from three days ago (all by Penny Holliday)

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