Global database of ratios of particulate organic carbon to thorium-234 in the ocean: improving estimates of the biological carbon pump

International audienceThe ocean's biological carbon pump (BCP) plays a major role in the global carbon cycle. A fraction of the photosynthetically fixed organic carbon produced in surface waters is exported below the sunlit layer as settling particles (e.g., marine snow). Since the seminal works on the BCP, global estimates of the global strength of the BCP have improved but large uncertainties remain (from 5 to 20 Gt C yr −1 exported below the euphotic zone or mixed-layer depth). The 234 Th technique is widely used to measure the downward export of particulate organic carbon (POC). This technique has the advantage of allowing a downward flux to be determined by integrating the deficit of 234 Th in the upper water column and coupling it to the POC/ 234 Th ratio in sinking particles. However, the factors controlling the regional, temporal, and depth variations of POC/ 234 Th ratios are poorly understood. We present a database of 9318 measurements of the POC/ 234 Th ratio in the ocean, from the surface down to > 5500 m, sampled on three size fractions (∼> 0.7 µm, ∼ 1-50 µm, ∼> 50 µm), collected with in situ pumps and bottles, and also from bulk particles collected with sediment traps. The dataset is archived in the data repository PANGAEA ® under https://doi.org/10