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Water mass transformation quantifies transport of matter between different density classes of the World Ocean. We present the first observationally based quantification of transformation rates due to air-sea buoyancy fluxes, which considers different parameterizations of shortwave radiation depth penetration, including the influence of albedo and the Chlorophyll a concentration. The results provide a range of solutions that can be used to compare model-based transformation rates against. We compared two air-sea flux products with limited representation of ice dynamics at high latitudes. We find that variations in the air-sea heat fluxes due to Chlorophyll a and its horizontal distribution are as important for water mass transformation rates than differences between the freshwater flux products. An accurate representation of the effects and spatial distribution of Chlorophyll a is required to obtain realistic transformation rates.

Plain Language Summary Air-sea fluxes of heat and freshwater (precipitation, evaporation, warming by the sun, etc.) are difficult to measure accurately. Yet they influence the ocean circulation and, for example, how and how much heat and anthropogenic carbon are absorbed by the ocean. In this study, we measure variations of the effect of air-sea fluxes on ocean dynamics. We found that Chlorophyll a in the ocean (a measure for very small biology), changes both the amount of incoming sunlight (through reflection) and how deep the sunlight can reach. Through this effect, Chlorophyll a may indirectly affect the climate system. Scientist predicting future climates should therefore include this effect carefully in their numerical ocean models.