Drawdown of Atmospheric pCO2 Via Variable Particle Flux Stoichiometry in the Ocean Twilight Zone. Issue 22 (19th November 2021)

• Record Type: Journal Article
• Authors: Tanioka, Tatsuro; Matsumoto, Katsumi; Lomas, Michael W.
• Is Part Of: Geophysical research letters. Volume 48:Issue 22(2021)
• Page Start: n/a
• Page End: n/a
• Publication Date: 2021-11-19
• Subjects: carbon cycle -- elemental stoichiometry -- ocean biogeochemistry -- biological pump -- remineralization -- twilight zone; Geophysics -- Periodicals; Planets -- Periodicals; Lunar geology -- Periodicals; 550
• DOI: 10.1029/2021GL094924
• Languages: English
• ISSNs: 0094-8276

Abstract

Abstract: The strength of the biological soft tissue pump in the ocean critically depends on how much organic carbon is produced via photosynthesis and how efficiently the carbon is transferred to the ocean interior. For a given amount of limiting nutrient, phosphate, soft tissue pump would be strengthened if the carbon (C) to phosphorus (P) ratio of sinking organic matter increases as the remineralization length scale of C increases. Here, we present a new data compilation of particle flux stoichiometry and show that C:P of sinking particulate organic matter (POM) in the ocean twilight zone on average is likely to be higher than the C:P ratio of surface suspended POM. We further demonstrate using a physics‐biology coupled global ocean model combined with a theory from first principles that an increase in C:P export flux ratio in the ocean's twilight zone can lead to a considerable drawdown of atmospheric p CO2 . Plain Language Summary: The ocean's twilight zone, located below the ocean's sunlit zone, is a region where many critical biogeochemical processes occur but are not well characterized. Most notably, this is the zone where microbes and animals consume organic matter produced by primary producers in the surface ocean. How efficiently this organic matter is degraded exerts essential controls on atmospheric carbon dioxide levels and energy transfer in the marine food web. Here we show using a new global data compilation that organic carbon and phosphorus particles are degraded at different rates. This leads to a considerable change in carbon to phosphorus ratio at depth. We incorporate this variability into the 3D ocean model to show that such change can substantially increase the ocean's ability to absorb carbon dioxide from the atmosphere. The study ultimately highlights the need to accurately characterize the ocean's role in climate change by studying the particle dynamics in the twilight zone. Key Points: Global particle flux data suggests a systematic increase in carbon (C) to phosphorus (P) flux stoichiometry in the ocean twilight zone Increase in the C:P export flux ratio through the twilight zone can substantially increase atmospheric p CO2 drawdown Further studies are required to elucidate mechanisms leading to spatiotemporal C:P export flux variability in the twilight zone