Carbon export by small particles in the Norwegian Sea

Despite its fundamental role in controlling the Earth's climate, present estimates of global organic carbon export to the deep sea are affected by relatively large uncertainties. These uncertainties are due to lack of observations as well as disagreement among methods and assumptions used to estimate carbon export. Complementary observations are thus needed to reduce these uncertainties. Here we show that optical backscattering measured by Bio-Argo floats can detect a seasonal carbon export flux in the Norwegian Sea. This export was most likely due to small particles (i.e., 0.2-20 m), was comparable to published export values, and contributed to long-term carbon sequestration. Our findings highlight the importance of small particles and of physical mixing in the biological carbon pump and support the use of autonomous platforms as tools to improve our mechanistic understanding of the ocean carbon cycle. Key Points Bio-Argo floats can track small particles in the mesopelagic region Export fluxes from small particles were significant Small particles contributed to long-term carbon sequestration