Global patterns of biological carbon pump particle transfer efficiency by particle size

The transfer efficiency (TE)—the fraction of carbon exported out of the surface ocean that makes it to a specified depth horizon—of the ocean biological carbon pump is an important metric for quantifying the global carbon cycle. There is, however, large uncertainty in the magnitude, variability, and spatial patterns of TE, ultimately making modeling the biological carbon pump highly uncertain. Some studies have found high TE at high latitudes and low TE at low latitudes, suggesting temperature-dependent mineralization rates control these patterns, while others have found the opposite relationship, suggesting ecosystem structure and its impacts on particle types is the dominant control. In this study, we leverage the particulate backscatter data from the global Biogeochemical Argo float array to investigate the magnitude, variability, and latitudinal patterns of the particle transfer efficiency, TE p , for both small and large particles, applying a consistent, global analysis. We define the particle transfer efficiency to clearly distinguish from the transfer efficiency, TE, which is derived from POC flux measurements directly. Data is segmented by dynamic oceanographic biomes, and the accompanying biogeochemical measurements are utilized to evaluate controls of these patterns. Here, we quantify how large particles have a higher TE p than small particles and that TE p tends to be lowest during periods of high productivity. Furthermore, we find that large particle TE p most strongly correlates with temperature (+) and nitrate (-), and small particle TE p is most strongly correlates with oxygen saturation (-) and apparent oxygen utilization (+).