On the one hand, an intense oceanographic campaign launched a month ago, which expressly focuses on the link between the transport of carbon from the surface to the deep ocean. On the other, an observation site in the middle of the North-East Atlantic which, for nearly 40 years, has been collecting data on carbon fluxes at depth. An explosive scientific cocktail and a winning collaboration to better understand how the ocean stores carbon.
By Laurie Henry
The issue of climate change and the role of the oceans in the carbon cycle has become central to contemporary scientific research. The oceans play a crucial role in absorbing a significant amount of atmospheric carbon dioxide (CO2) (2.5 gigatonnes per year), and burying it towards the greatest ocean depths for thousands of years.
While this natural phenomenon has the positive effect of partially mitigating the effects of climate change, the full mechanisms of atmospheric CO2 absorption by the oceans are not yet fully understood, and questions remain about the future effectiveness of this pump. ocean of carbon on an increasingly hot planet.
PAP-SO, a key observatory for monitoring long-term ocean changes
Covering an area equivalent to roughly half the landmass of Europe, the Porcupine Abyssal Plain (PAP) is located in international waters close to the Irish continental margin. Its seabed is muddy and dotted with abyssal hills, and its depth varies from 4,000 to 4,850 meters.
Since 1985, the English oceanographic center of the National Oceanography Center (NOC) has maintained the PAP-Sustained Observatory (PAP-SO), a fixed scientific observatory located at a depth of 4,850 meters in this region of the North-East Atlantic.
An English institution for marine science research and technology based in Southampton and Liverpool, a partner of French Ifremer and the German GEOMAR institute, the NOC is also a member of the European Global Ocean Observing System (EuroGOOS) .
Position of the PAP observation site in the North-East Atlantic, operated by the NOC since 1985. © NOC
On this PAP-SO site in particular, the work of the NOC and its partners focuses mainly on carbon transport. The PAP-SO region, with over 30 years of serial data, is one of the most sampled regions in the world in terms of deep carbon flux. The PAP Observatory is one of a small number of ocean sites that have successfully obtained time series of data at full ocean depth over several decades, providing key information for the assessment of long-term change in the ocean and its ecosystems.
An APERO expedition in search of understanding carbon storage in the ocean
It was launched on June 2, taking the direction of the PAP, and will end on July 17. Featuring simultaneously, and for 40 days, the two most important French oceanographic vessels (the Thalassa and the Pourquoi pas?), the APERO mission (Assessing marine biogenic matter Production, Export and Remineralization: from the surface to the dark Ocean) is co-directed by CNRSresearchers. It aims to deepen the understanding of carbon storage in the ocean and more specifically of the functioning of this “biological carbon pump”.
The oceanographic vessels of the APERO campaign; the Thalassa (left) and the Why not? © Michel Gouillou; Nicolas Fromont / Ifremer
The innovation of this large-scale APERO campaign lies in its interdisciplinary approach, mobilizing more than 120 scientists from various international institutions, and in its use of advanced oceanographic techniques and instruments to collect precise data on the production, export and remineralization of marine biogenic material.
Identification of possible viruses present in the water samples taken © Simon Rondeau
A key element of the research carried out during the APERO campaign at the PAP site is the use of “sediment traps”. These cone-shaped instruments, placed 3,000 meters deep in the ocean, collect carbon molecules from the surface to the bottom of the water column.
These measurements contribute to a better understanding of the “biological pump” process that allows the storage of carbon in the ocean and its burial for several thousand years in the great ocean depths thanks to phytoplankton. Indeed, when this phytoplankton, which absorbs atmospheric carbon dioxide at the surface by photosynthesis, dies or is consumed by other marine organisms, the carbon it has absorbed is transformed into particles which sink towards the depths of the ocean. , helping to store carbon away from the atmosphere.
The goal of the scientists is to succeed in designing a numerical model, integrating the data collected in situ, which will be able to predict the area on the surface of the ocean from which these carbon particles come. In other words, the goal is to better understand how, and where, carbon is absorbed on the surface of the ocean, and especially where it ends up being stored in the depths of the ocean. This work should help to better understand the crucial role that the ocean plays in limiting the amount of carbon in the atmosphere, to better predict how climate change could affect this important function of the ocean.
On board the Thalassa, launching of the Multinet BIONESS net, which has 9 nets, open to 9 different depths and intended to sample different sizes of organisms with very high precision. © Simon Rondeau
A robust collaboration between APERO and PAP, an example of a fruitful synergy between research programs
The results of this APERO mission should therefore provide valuable information. By identifying the consequences of excess absorption of CO2 by the oceans, due to climate change, it will be possible to specify the phenomena linked to it, in particular that of ocean acidification and the drop in ocean pH that could affect marine life.
A solid collaboration between APERO and the JC247 long-term observation mission of biogeochemistry and ecological variables has been set up. This will be NOC-led research, focused on long-term ocean observation. During the JC247 cruise, a BGC ARGO float was deployed to sample the area one month before the start of the APERO expeditions. The data collected by this float will be extremely valuable for the strategy of the next oceanographic campaigns.
On board the Thalassa, launching an Argo biogeochemical float © Simon Rondeau
The APERO expedition and the PAP-SO observatory represent two major initiatives that contribute to our understanding of the role of the ocean in the carbon cycle. The robust collaboration between scientists from the PAP and APERO programs provides a wonderful opportunity for researchers to work in the field and better understand the instruments and data used for their research.
This collaboration illustrates the importance of collective effort and the necessary synergy between different disciplines and projects to address the complex challenges posed by climate change.
Link to the PAP-SO site by the NOC : https://projects.noc.ac.uk/pap/
Links to the APERO mission website : https://www.aperocruise.fr
Read the logbook of the APERO-2023 campaign : https://www.aperocruise.fr/jdb/