Current Oceanic CO2 Uptake: The Priming Effect of the Marine Carbon Pumps

The impact of marine biological carbon pumps (BCPs) on atmospheric pCO2 (pCO2atm) is considered to be very important in the context of long-term climate swings (e.g. glacial-interglacial). However, under the current climate change transient their impact is considered low and difficult to detect, being masked by the massive invasion of anthropogenic CO2 (Canth) into the ocean. Here we show and quantify how BCPs prime the ocean for a significantly elevated Canth uptake, compared to a hypothetically abiotic ocean, through their control on the preindustrial CO2-buffer capacity. Using an Earth System model of intermediate complexity, run in model variants where individual marine carbon pumps have been turned off, we find strong and opposing effects from the soft-tissue (+194 Pg) and the CaCO3 counter pumps (-61 Pg) on Canth uptake between years 1765 and 2100 for a high emission scenario. This “priming effect” from both pumps combined is +130 Pg C, i.e. a 24% share of the net CO2 uptake (541 Pg C), which is larger than the priming effect of the solubility pump (+93 Pg C). We further quantify the impact of marine carbon pumps on marine carbon-climate feedbacks. In total, marine carbon-climate feedbacks reduce the marine carbon sink, compared with the gross Canth uptake of an ocean without climate change. Biological carbon pumps (soft tissue + CaCO3 counter pump), however, dampen the magnitude of carbon-climate feedbacks by 30 Pg C over the simulation period, while the solubility pump enhances it by about 20 Pg C. Overall, an ocean without marine carbon pumps would take up considerably less anthropogenic CO2 (- 222 Pg C) until year 2100 under a high emission scenario. On top of this, such an ocean would show stronger carbon-climate feedback, i.e. being more sensitive to climate change, it would respond with stronger CO2-release to warming and circulation changes.