The ocean is the second lung on the planet, behind forests. It absorbs more than a quarter of the carbon dioxide (CO2) from the combustion of fossil fuels and almost all the heat from the atmosphere. It thus regulates the climate. But by playing this role, the ocean degrades and loses its ability to regulate. To understand this regulatory role of the ocean and to best anticipate future changes, Ifremer is studying the changes that are made to the currents and acidity of marine waters. The institute also analyzes the consequences on ecosystems and living organisms.
The ocean at the heart of climate regulation
Ocean circulation contributes to the storage of CO2
Ocean circulation refers to the large-scale movement of seawater in the oceans. The large bodies of water in the ocean, in motion, cool and warm during their journey around the globe: they act as an air conditioner for the planet. This circulation is a key element of the Earth’s climate system and has a profound impact on weather conditions or on the distribution of nutrients.
Ocean circulation also plays a role in the storage of CO2 captured and dissolved in the ocean. The carbon « oceanic pump » involves processes that transport dissolved carbon from the surface of the ocean to the deep layers, thus sequestering it for long periods (from a few years to several hundred years).
Ifremer contributes to the global observation of ocean circulation, necessary to understand and predict the climate. Before 1950, the characteristics of the ocean below its surface were virtually unknown. Ocean observation was initially based on oceanographic campaigns. Data from sea campaigns, such as the OVIDE campaigns launched since 2002, allow Ifremer scientists to study ocean currents and their variability, quantify and inform about ocean warming, sea level rise, deoxygenation and the increase in CO2 and other carbon compounds that create ocean acidification. These estimates allow Ifremer researchers to better understand and differentiate more finely the changes related to climate change from those due to natural variability.
During the last two decades, satellite observation systems (ocean surface) and autonomous instrumentation at sea, such as anchorages (fixed and permanent instruments), gliders (underwater gliders) or autonomous Argo floats (float-profiler measuring the ocean at depth), have developed very rapidly. The ocean is now monitored more systematically and globally in real time, all year round and regardless of weather conditions.
Closely linked to changes in ocean circulation, ocean warming would also reduce the solubility of CO2 and oxygen in water, by further reducing the ability of the oceans to absorb CO2 contained in the atmosphere.
The role of marine organisms in climate regulation
In addition to the sequestration of carbon by ocean circulation, the biological carbon pump participates in the carbon cycle. The CO2dissolved in seawater is transformed into organic matter by the photosynthetic organisms of plankton (microalgae, bacteria…), by organisms that integrate it into their shell or shell (shellshells, crustaceans) or, in the great depths, by organisms practicing chemosynthesis. Ifremer has been studying these processes for several decades using ocean campaigns and laboratory experiments. The organizations of the deep funds are still little known, so Ifremer has been studying them particularly since their discovery in the 1970s. Part of the organic matter created by these organisms is consumed by animals. When organisms that have captured or consumed carbon die, bacteria will participate in their decomposition, enhance this carbon in energy or re-relaunch it by breathing. The remaining particles, also loaded with carbon, are deposited in the sediment or flow into the deep ocean, and can remain stored for a long time in these compartments.
How does climate change impact the ocean and marine organisms?
Climate change induces a global trend towards warming and rising marine waters, their acidification and the increase in extreme events (heat waves, lack of oxygen, efflorescence of harmful phytoplankton…). These climatic hazards impact the coastline and marine biodiversity.
The effects of climate change on the coast
The rise in sea levels under the effect of climate change had so far a gradual evolution: the coasts adapted, currents and waves brought sediment that filled the parts displaced by the storms. However, in the next 50 years, the expected scenarios are a more marked rise in sea level and an increase in the intensity of storms and rainfall. The coasts would thus be subjected to greater erosion and the estuaries to an increase in the flow of the river. To anticipate these consequences, Ifremer develops numerical models that combine the effects of tides, wind, waves, river flow, etc.
Climate change impacts marine biodiversity
In the long term, water warming and acidification caused by climate change disrupts marine biodiversity at different levels, whether it’s shell formation or fish growth. Ifremer scientists are also studying how certain species, such as corals or oysters, adapt to future climate change.
Fish, for example, are particularly sensitive to changes in the environment. Recent studies by Ifremer have shown, especially in sea bass, a change in the laying period, growth, behavior or quality of eggs, as a result of temperature change and acidification.
The underwater mountains are also home to key ecosystems in the deep ocean, vulnerable to the impacts of human activities and climate change. Ifremer seeks to fill the lack of knowledge about the benthic species present in these deep seas.
Climate change and human activity cause the degradation of certain marine environments, especially coastal areas. Ifremer conducts research on the restoration and rehabilitation of these environments.
Learn from old climates to better anticipate future climates
Ifremer participates in exploration campaigns to better understand geological history through sediments and the global context of climate change.
Sediments, archives of current and ancient climates
Sediments are used as archives to know past events in order to understand and anticipate what may happen in the future. When sediments accumulate, and are preserved over time, this is the time that we can go back!
Ifremer teams can therefore go back far into the past, throughout the Quaternary era (which corresponds to the last 2.6 million years to the present day). Scientists analyze the sediments transported by rivers at that time along a land-sea continuum, until they accumulate at the bottom of bays, on continental shelf and in deep basins.
Thus, the millions of cubic meters of sediment deposited off major rivers (Atlantic facade, Mediterranean, etc.), constitute valuable archives of the history of glaciations and their impacts on sedimentary transport during the last glacial-interglacial cycles. Closer to us, studies on coastal sediments also provide information on rapid climate change in the Holocene (last 12 thousand years) and on the impact of humans on watersheds since the Bronze Age (2700 years BC).
All these sediments contain fossil carbon and anthropogenic carbon (pollutants). The geochemical study of sediments provides a better understanding of the links between continent erosion and climate during the history of the Earth. Other studies conducted at Ifremer on the deep sediments of the Atlantic provide information on the climate and ancient currents of these regions. It is then a matter of establishing a clear link between ocean circulation and climate change over the last thousands to hundreds of years and providing the essential data to improve the ability of numerical models to predict the future evolution of ocean circulation. This work therefore contributes to a better understanding of the climate processes involved and to a better anticipation of future climate change.
Carbonated platforms, witnesses of sea level
With climate change, sea levels are rising. However, we have only had records of this level for 150 years. IPCC predictions show large fluctuations (from 0.28 m to 1.02 m) on the predicted average sea level rise, depending on the likely scenarios. This is where the study of current and past carbonate platforms and the exact mechanisms that lead to the appearance and disappearance of coral reefs comes in.Coral reefs or formations created by calcareous algae, carbonate platforms are composed of calcareous sediments accumulated by marine organisms. They are true archives of climate and ecosystem changes.
Ifremer analyzes these limestone sediments from drilling, surveys, observations, studies of existing data and documents… Scientists can thus go back up to 20,000 years!
Ifremer studies the sediments that make up carbonate platforms to:
- situate the history of a structure by dating the sediment layers,
- study the organisms present in sediments, witnesses of climate and environmental changes (changes in surface water temperature, change in the dynamics of ocean currents, etc.),
- understand the climate system as a whole thanks to corals, these organisms have the potential to be able to record with their skeleton all the small changes in their environment.
source : ifreme
