Ocean biological carbon pump

The ocean biological carbon pump (BCP) is the suite of biological and physical processes that transfer organic carbon produced in the surface of the ocean by photosynthetic organisms to the ocean interior. With this mechanism, the ocean removes carbon dioxide (CO2) from the atmosphere and sequesters it in the deep ocean for long time scales, becoming a key component of the global carbon cycle. The BCP strongly influences climate, but also the cycling of chemical species in the ocean and marine food-webs. Despite its global importance, the BCP is poorly constrained because it involves complex processes, it is temporally and spatially dynamic, and it is challenging to measure. Here is where radionuclides come into play. Radionuclides can be used as powerful indirect methods (e.g., 234Th/238U, 210Po/210Pb) to study the BCP, particularly to quantify the largest export pathway by which organic carbon can reach the deep ocean: the gravitational sinking of particles or “marine snow”. In the recent years, significant advances in the understanding of the BCP have been made and radionuclides have been instrumental to this progress, but important knowledge gaps remain

Specific focus areas are:

· Improving the determination of natural radionuclides in seawater and their application as tracers of ocean particle fluxes.

· Quantifying the magnitude of BCP-driven fluxes, including particulate organic carbon (POC) and other bioelements (e.g., particulate nitrogen, inorganic carbon, biogenic silica) from the ocean surface to depth using radionuclides in combination with other approaches (e.g., sediment traps, marine snow catchers).

· Determining the efficiency by which POC is transferred to the ocean interior across a wide range of oceanic regions.

· Constraining the spatiotemporal variability and the controls of the BCP to better understand how the BCP will respond to climate change.

· Exploring the application of radionuclides as tracers of particle deposition and resuspension processes in coastal systems.