The BIO-Carbon programme will provide new insights into the role of marine life in ocean carbon storage and robust predictions of future ocean carbon storage in a changing climate. The programme aims to highlight the importance of international waters in carbon policy and will focus on processes that are globally relevant.
The ocean stores huge amounts of carbon dioxide (CO2) that would otherwise be in the atmosphere.
Marine organisms play a critical role in this process, but emerging evidence indicates that climate models are not fully accounting for their impact.
This undermines carbon policies, such as national net zero targets.
This BIO-Carbon research programme is carefully designed to produce new understanding of biological processes. It will provide robust predictions of future ocean carbon storage in a changing climate.
The World Climate Research Programme, which coordinates climate research internationally and is sponsored by UN organisations, has expressed its greatest priorities as three questions.
This programme will address two of those questions:
- what biological and abiological processes drive and control ocean carbon storage
- can and will climate-carbon feedbacks amplify climate changes over the 21st century?
There are three interlinked programme challenges, which will address three aspects of biological influence.
Challenge one: how does marine life affect the potential for seawater to absorb CO2 and how will this change?
The ability of the ocean to absorb CO2 is influenced by its alkalinity. Reducing alkalinity pushes more of the dissolved carbon in seawater into the form of CO2.
This reduces the capacity of the ocean to take up further CO2 from the atmosphere.
Seawater alkalinity is influenced by a range of natural processes. The most important of these is the biological production of calcium carbonate (for example, by molluscs and fish), which removes alkalinity from seawater.
As the calcium carbonate sinks, it dissolves and the alkalinity is returned to the seawater.
Maintaining the vertical distribution of alkalinity fundamentally sets the capacity of our oceans to take up CO2. However, estimates of global ocean calcium carbonate production, vertical transport and dissolution vary by up to a factor of five.
This uncertainty is important because failure to reproduce alkalinity accurately in a climate model significantly impacts future projections of ocean CO2 uptake and storage.
Examples of significant knowledge gaps relating to key processes include:
- what organisms are producing highly soluble carbonates in the surface ocean and where
- which forms of calcium carbonate are dissolving where in the ocean
- what are the factors involved in the dissolution of different forms of carbonate, and what is their sensitivity to the anticipated impacts of climate change?
Challenge two: how will the rate at which marine life converts dissolved CO2 into organic carbon change?
Primary production by marine phytoplankton converts a similar amount of CO2 into organic material each year as do all land plants combined.
Climate models cannot constrain this crucial global flux to within a factor of three for the contemporary climate, which points to major gaps in understanding.
Furthermore, uncertainty about our estimates for how oceanic primary production will change under climate warming has increased, rather than lessened, this decade. Whether global primary production will increase or decrease is unknown.
Primary production is strongly influenced by ocean warming and the availability of light and nutrients. However, the contributions of changes in these drivers to trends across climate models are poorly constrained.
The importance of organism interactions and metabolism, and their associated demands for carbon and other resources, is neglected by climate models. This is despite emerging observational indications of their significance.
Examples of knowledge gaps relating to key processes, operating across different scales, include:
- what controls the efficiency of primary production
- what are the contributions of nutrient recycling and the consumption of phytoplankton by zooplankton to this efficiency
- how do these processes vary across different ocean environments, and how might future change, such as warming and acidification, affect them?
Challenge three: how will climate change-induced shifts in respiration by the marine ecosystem affect the future ocean storage of carbon?
Organic carbon produced in the upper ocean cannot be returned to the atmosphere until it is converted back into CO2 by the respiration of marine organisms.
Deeper ocean respiration supports longer carbon storage as it takes longer to return to the ocean surface and make contact with the atmosphere.
We still have poor understanding of how respiration varies with depth, location or season. We know it reflects the diversity of the organisms, from bacteria attached to sinking dead material to fish migrating daily between the surface and ocean interior.
We also know that these organisms are responding to anthropogenic changes, such as changes in temperature which affect the metabolism of organisms.
In addition, existing models only reproduce a limited selection of relevant processes, with no consistency in that selection across models.
Examples of significant knowledge gaps relating to key processes include:
- what is the relative influence of size, shape and composition of non-living organic material in determining the rate at which it is converted back to CO2
- what are the relative magnitudes of the CO2 generated by bacterial degradation of non-living organic matter and that respired directly by other organisms
- how might ongoing changes in the environment (for example, to oxygen or temperature) affect respiration?