Monitoring the ocean to understand how climate will evolve

© Pxhere

Climate change induces major disruptions in the ocean, modifying currents and altering the ocean’s chemistry and biology. The ocean responds to these disturbances and in turn influences the global climate. Scientists are not yet sure whether these modifications of the ocean will slow or increase the rate of climate change.

The ocean reacts to climate change

Taking the ocean’s pulse is essential to understand and predict climate change. The ocean is a major regulator of the global climate system: it absorbs and redistributes heat through its currents, and sequesters an important proportion of anthropogenic CO2 through physical, chemical and biological processes. The problem is that the ocean is warming up, becoming more and more acidic and depleted in oxygen. All these parameters affect its ability to sequester carbon and heat, and therefore slow down global warming.

Scientists are able to predict and model the evolution of the physical and chemical processes in the ocean. For instance, the warmer the water, the less gas it dissolves, including CO2. As a result, a warmer ocean absorbs less carbon dioxide from the atmosphere. The likely consequence is an acceleration of global warming due to decreased efficiency of the oceanic carbon sink.

In contrast, predicting the impact of biological processes (driven by ocean plankton) – also responsible for carbon sequestration and therefore climate regulation – is quite complicated. Scientists do not yet have a clear picture of the way the global composition and activity of plankton will evolve in a changed ocean. Species do not all have the same role. For example, some are more effective than others at sequestering carbon in the deep ocean.
 
3 filtre dolphin
Le “Dauphin” est un filet qui permet de collecter du plancton au cours des navigations – © Caroline Britz / Tara Expeditions Foundation
 

Sampling plankton and understanding its impact on the climate

Because of its microscopic size, we tend to underestimate plankton’s importance. Yet, these small drifting organisms have a crucial role, and their development in the oceans strongly depends on how climate evolves on our planet. The role of the world ocean in regulating climate is tied to the activity and composition of the planktonic community it shelters.

Decrypting the functioning of plankton – a continuous and very complex ecosystem – required an ambitious scientific strategy. The schooner Tara has therefore circumnavigated the world ocean for 4 years to collect a large amount of data. After analysis, they are now providing an accurate picture of the various ocean regions and the organisms inhabiting these ecosystems.

Powerful sequencing methods were used to study this vast and very complex network. Thanks to these techniques, millions of genetic sequences and tens of thousands of new planktonic species have been discovered. The huge plankton network has been brought to light and the interactions within are in the process of being decrypted and understood. Using this database – the most comprehensive ever collected – researchers also seek to understand how plankton will evolve and adapt in a warmer and more acidic ocean, and what climatic impact this will have in the future. Will the amount of atmospheric carbon that plankton sequester and carry to the bottom of the ocean always be as important in the future?

Researchers from the Tara Oceans Consortium have recently developed a tool allowing all scientists, even without computer knowledge, to query the genetic, environmental and taxonomic database. Until then, despite being public and free, these data were still inaccessible to some researchers. Thanks to this new tool, a large number of scientists can now exploit the full potential of the Tara Ocean data via a simple website, and participate in unlocking the mysteries of ocean plankton.

Margaux Gaubert

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