This biological influence on future ocean storage of carbon (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 (WCRP), which coordinates climate research internationally and is sponsored by United Nations (UN) organisations, has expressed its greatest priorities as 3 questions.
This programme will address 2 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 3 interlinked programme challenges, which will address three aspects of biological influence:
Challenge 1: how does marine life affect the potential for seawater to absorb carbon dioxide, and how will this change?
The ability of the ocean to absorb carbon dioxide is influenced by its alkalinity. Reducing alkalinity pushes more of the dissolved carbon in seawater into the form of carbon dioxide. This reduces the capacity of the ocean to take up further carbon dioxide 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 carbon dioxide. However, estimates of global ocean calcium carbonate production, vertical transport and dissolution vary by up to a factor of 5.
This uncertainty is important because failure to reproduce alkalinity accurately in a climate model significantly impacts future projections of ocean carbon dioxide 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 2: how will the rate at which marine life converts dissolved carbon dioxide into organic carbon change?
Primary production by marine phytoplankton converts a similar amount of carbon dioxide into organic material each year as do all land plants combined.
Climate models cannot constrain this crucial global flux to within a factor of 3 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 3: 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 carbon dioxide 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 the 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 affected by climate change 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 carbon dioxide?
- what are the relative magnitudes of the carbon dioxide 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?