A scientific expedition to discover the memory of the ocean – 17/08/2023 – Ciência Fundamental

In geosciences, as well as in history, knowing the past is fundamental to understanding the present and projecting the future. As much as it is not possible to go back in time physically, there are places that can give us valuable information about the trajectory of the planet and, in some way, open a door for us to know that hitherto unattainable moment. One such place is the ocean.

The geological archives they keep function as the Earth’s memory. They are the diary in which our planet leaves notes, memories in the form of rocks and sediments that allow us to recover different types of information. In addition to the fauna and flora, it is possible to trigger memories about variations in the composition and temperature of both the atmosphere and the ocean, and also to assess changes in rainfall patterns and biodiversity patterns over the years. In climatology, studying the past is fundamental to understanding the patterns of climate functioning and creating projection scenarios for the future.

The bottom of the ocean is a precious record, but difficult to access to study the climate of the past (we know better the surface of the Moon). At great depths (more than a thousand meters) there is normally no erosion, and for this reason over time materials accumulate with information from their time, accessible through a tube — which scientists call testimonies —cut into the bottom of the ocean.

In order to obtain marine cores, since the 1960s, a joint and international effort comparable to the construction of the space station has been carried out. It was in this scientific cooperation environment that the Amaryllis-Amagas project cruise took place — aboard the Marion Dufresnethe largest scientific ship in France and one of the largest in the world —, the result of the union of institutions and scientists from Brazil and France, in which I participated.

Over 21 days, led by a Brazilian coordinator, Cristiano Mazur Chiessi, and a French coordinator, Aline Govin, we sailed along the coast of French Guiana and northeastern Brazil, in places under the influence of the Amazon and Parnaíba rivers. The sediments deposited there make it possible to retrieve information about both the ocean and the continent. We collected testimonies that, together, reach almost half a kilometer in length.

“This material will make it possible to reconstruct variations in the ocean, climate and vegetation in this very important region”, Chiessi, from the University of São Paulo, told me. And he added that the Amazon and the ocean are crucial for global climate regulation (think that, even if you are in the interior of Brazil, most of the rainwater that falls on your house is water that has evaporated from the surface of the ocean) . Knowing their functioning patterns is crucial to understanding the future effects of climate changes that are already underway.

In the Atlantic Ocean, there is a set of currents — one of the most expressive water mass circulations in the world — that transport heat from the tropical region to that close to the North Pole. As winds blowing from west to east carry part of the heat from the surface of the water to the European continent, winter in Europe is less severe than in Canada. But, in South America, it is the rainfall that decides the temperature of the ocean surface, since it is controlled by the intensity of this circulation of water in the Atlantic.

Collecting the material is only the first part of the job. Chiessi says that the testimonies collected in this French-Brazilian mission will be used for the next ten years to produce cutting-edge science. Some analyzes were made while still on the ship. The team had around 50 researchers, including professors, postdoctoral students, doctoral, master’s and even undergraduate students, who worked 24 hours a day, in four-hour shifts.

In addition to the traditional methods, this shipment had something new: a new method and equipment developed entirely in Brazil. This innovation, created by the research group of which I am a member, allows access to information on changes in rainfall patterns based on the analysis of sediments that are brought by rivers that flow into the sea. Our method allows us to evaluate changes in the characteristics of the grains that make up the sand and, with the variations that we observe in these grains, we are able to infer changes in the patterns of rainfall distribution over the entire hydrographic basin. This method is based on luminescence, which is the ability of some materials to emit light when stimulated — and our equipment is able to scan this property along the core.

The equipment, still under development, was tested for the first time during the scientific cruise and received adjustments while still on board, with the tools and resources we had available. I had to solve problems that were outside my area of ​​expertise, such as programming. For that, I had the help of the command base on land, which sent me updates through a very limited internet. I felt like an astronaut.

Each new tool like this allows scientists to understand the climate’s past a little better. With each new discovery, the global climate puzzle becomes more complete.

The Amaryllis-Amagas expedition is a milestone for national science. Brazil is emerging as an important player in the study of climatology in the past, and this cruise led by a Brazilian scientist and a French scientist is the demonstration that our science walks at the same pace as international science.

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Vinícius Ribau Mendes is a geologist and professor at the Institute of the Sea at the Federal University of São Paulo (Unifesp).

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