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13 July 2017

Oceanic Carbon Capture Processes Disrupted by Rising Temperatures

As a species we are doing some pretty serious harm to our planet, via countless methods if truth be told. One such method is the vast quantities of carbon dioxide we pump into the atmosphere on a constant basis, which contributes massively to global warming and by extension has an effect on just about every natural process on Earth. Our little blue planet is not helpless however, making use of ‘carbon sinks’ such as forests and oceans to draw some of that excess CO2 out of the air and thereby offset the damage we continue to inflict. Unfortunately, a new study has found that oceanic heat sinks are no longer as efficient as they once were as a direct result of rising global temperatures, which could spell trouble if we fail to act.

Img: MIT News Office
To understand the issue we must first understand how these oceanic carbon sinks work, which is in fact fairly simple as it basically boils down to photosynthesis. Plankton present in surface waters, more specifically phytoplankton, rely upon the process of photosynthesis for their survival, drawing carbon from the water throughout their lives and then upon death sinking to the depths, taking that carbon along with them at a rate of approximately 6 billion tonnes per year.

However the new study, conducted by MIT and published in the journal Limnology and Oceanography, found that warming waters are slowing down this process due to the way in which different organisms flourish at different temperatures. Those creatures which rely upon photosynthesis, such as the aforementioned phytoplankton, fare better in cooler waters, whereas ‘respirers’ are more active as temperatures rise. This disrupts the delicate symbiotic relationship of ocean-dwelling species and leads to less carbon being absorbed as a result.

The get to grips with the true extent to which rising temperatures are affecting the ocean’s ability to function as a carbon sink, the research team developed a model designed to measure the “export efficiency” of the oceans – the rate at which carbon is absorbed and taken to the depths – in relation to different temperatures. The model centred on the interplay between photosynthesizers and respirers.

“We had a simple way to describe how we think temperature influences export efficiency, based on this fundamental metabolic theory,” says B.B. Cael, first author of the study. “Now, can we use that to see how export efficiency has changed over the time period where we have good temperature records? That's how we can estimate whether export efficiency is changing as a result of climate change.”

Over the course of the study the researchers compiled temperature data from three different sources, providing measurements for each month between 1982 and 2014 from various locations across the world. This data was then fed into the export efficiency model to estimate the average rate of carbon absorption each month and then track how this rate changes over time in relation to surface temperatures. Export efficiency over those years was found to have decreased by 1-2% as temperatures rose accordingly. That may sound like a small percentage, but it equates to roughly 100 million tonnes of plankton remaining near the surface each year. The implications of this in terms of climate change could well be quite severe.

“We figured the amount of carbon that is not sinking out as a result of global temperature change is similar to the total amount of carbon emissions that the United Kingdom pumps into the atmosphere each year,” says Cael. “If carbon is just standing in the surface ocean, it's easier for it to end up back in the atmosphere.”

Sam Bonson

Sam is an aspiring novelist with a passion for fantasy and crime thrillers. He is currently working as a content writer, journalist & editor in an attempt to expand his horizons.