Using multiple geochemical budgets to partition NCP into POC and DOC export

“Carbon export,” refers to the amount of carbon dioxide that is removed from the atmosphere by organisms in the surface ocean and subsequently transported into the deep sea, either through sinking particulate organic carbon (POC; more efficient process) or downward mixing of suspended POC and dissolved organic carbon (DOC and suspended POC; less efficient process), making the ocean a natural sink for atmospheric carbon dioxide and significantly influencing ocean chemistry. The relative proportion of export through each pathway significantly affects the overall efficiency of this process and has implications for the pattern of carbon export globally. Export estimates can now be estimated remotely using autonomous biogeochemical profiling floats, which eliminate the need for persistent ship-based observations throughout the year, which can be costly and perilous for researchers.

In a recent study published in Global Biogeochemical Cycles, my colleagues and I present a new approach utilizing multiple chemical budgets of measurements made by profiling floats over a decade (2009-2017) in the Northeast Pacific and end-member nutrient ratios of the POC and DOC produced to not only estimate carbon export, but also partition this quantity into particulate and dissolved portions across multiple depth horizons. We also use a particle backscatter-based approach to estimate POC attenuation with depth and present a new method to constrain particle export across deeper horizons and estimate in situ export efficiency. Our results are supported by previously published estimates of regional carbon export and suggest that this method has the potential to be applied to other parts of the ocean using new biogeochemical Argo floats equipped oxygen, nitrate and pH sensors.