Did you know that the ocean plays a fundamental role in the evolution of climate change as part of the planet's climatic system? The ocean has already absorbed over 90% of the excess heat and 30% of the carbon dioxide (CO2) released into the atmosphere by the anthropogenic [1] burning of fossil fuels. [2] The ocean is the second largest carbon reservoir on Earth and holds over 60 times the carbon of the atmosphere. [3]
The present-day ocean carbon cycle involves a complex interplay of physical, chemical, and biological processes. Understanding the processes, interactions and feedbacks governing ocean carbon uptake, cycling and storage is essential for predicting future climate scenarios and developing effective mitigation strategies. [4]
The ocean is a major part of the carbon cycle, exchanging carbon dioxide with the atmosphere and moving carbon through marine life into the deep sea and seafloor sediments. [5] The ocean absorbs carbon dioxide in the atmosphere via
- the physical carbon pump which results from ocean circulation;
- the biological carbon pump which transfers surface carbon towards the seabed via the food web. [6]
How does the biological carbon pump globally work, you ask?
- Phytoplankton (microscopic single-celled algae that drift at the surface of the ocean) in sunlit surface waters absorb dissolved carbon dioxide as they photosynthesize and grow, which lets the surface ocean draw down more CO₂ from the atmosphere.
- Carbon captured by phytoplankton passes up the food web to zooplankton and larger animals, and a portion of it sinks toward the deep sea.
- The fraction of carbon that sinks deep enough can stay sequestered for hundreds to thousands of years, keeping it out of the atmosphere. [7]
So, why did we choose a map on monthly global surface ocean chlorophyll-a concentration this week? Chlorophyll is an indicator for the abundance of photosynthetic plankton. Phytoplankton contain the green pigment chlorophyll, which allows them to use the energy of sunlight to transform CO2 to sugars and oxygen. Because of the distinct green colour of the chlorophyll pigment, optical satellite sensors can be used to visualise the distribution of chlorophyll and thus the phytoplankton in the ocean. Have a look at the Map of the Week to learn more.
Wish to get a better understanding of the biological carbon pump?
Find out about the OceanICU project, a five-year Horizon Europe project that seeks to gain a new understanding of the biological carbon pump.
The project team launched an online Youth Competition on 1 October 2026. The competition invites young people (age 14-30 years old) to discover the work carried out in the project and to explain what they have learned in a creative science outreach material. Selected work will be showcased in a virtual gallery!
Read the Terms of Reference of the OceanICU Youth competition to get all the details and share the information with young people who could be interested in participating in the competition. The deadline for online applications is 17 February 2027 at 18:00 CET.
The data in the map is provided by Copernicus Marine Service.
The European Atlas of the Seas is powered by the European Marine Observation and Data Network (EMODnet). Don’t miss the latest news, register for the monthly EMODnet News Digest.
[1] anthropogenic: resulting from or produced by human activities, https://www.ipcc.ch/report/ar6/wg1/downloads/report/IPCC_AR6_WGI_AnnexVII.pdf
[2] https://woa.un.org/third-world-ocean-assessment/section-1-overall-summary
[4] Integrated Ocean Carbon Research: a vision primed for implementation - UNESCO Digital Library
[5] https://www.whoi.edu/ocean-learning-hub/ocean-topics/how-the-ocean-works/cycles/carbon-cycle/
[6] https://ocean-climate.org/en/awareness/the-ocean-a-carbon-sink/