Presentation_1_Dissolved Inorganic Carbon Pump in Methane-Charged Shallow Marine Sediments: State of the Art and New Model Perspectives.pdf

• Main Authors: Sajjad A. Akam, Richard B. Coffin, Hussain A. N. Abdulla, Timothy W. Lyons
• Format: Conference Object
• Language: unknown
• Published: 2020
• Subjects: Oceanography; Marine Biology; Marine Geoscience; Biological Oceanography; Chemical Oceanography; Physical Oceanography; Marine Engineering; marine carbon cycle; marine methane fluxes; sulfate methane transition zone; anaerobic methane oxidation; methane derived authigenic carbonates; dissolved inorganic carbon; sediment carbon budget; ocean acidification; Ocean acidification
• Online Access: https://doi.org/10.3389/fmars.2020.00206.s002; https://figshare.com/articles/Presentation_1_Dissolved_Inorganic_Carbon_Pump_in_Methane-Charged_Shallow_Marine_Sediments_State_of_the_Art_and_New_Model_Perspectives_pdf/12128424

Methane transport from subsurface reservoirs to shallow marine sediment is characterized by unique biogeochemical interactions significant for ocean chemistry. Sulfate-Methane Transition Zone (SMTZ) is an important diagenetic front in the sediment column that quantitatively consumes the diffusive methane fluxes from deep methanogenic sources toward shallow marine sediments via sulfate-driven anaerobic oxidation of methane (AOM). Recent global compilation from diffusion-controlled marine settings suggests methane from below and sulfate from above fluxing into the SMTZ at an estimated rate of 3.8 and 5.3 Tmol year –1 , respectively, and wider estimate for methane flux ranges from 1 to 19 Tmol year –1 . AOM converts the methane carbon to dissolved inorganic carbon (DIC) at the SMTZ. Organoclastic sulfate reduction (OSR) and deep-DIC fluxes from methanogenic zones contribute additional DIC to the shallow sediments. Here, we provide a quantification of 8.7 Tmol year –1 DIC entering the methane-charged shallow sediments due to AOM, OSR, and the deep-DIC flux (range 6.4–10.2 Tmol year –1 ). Of this total DIC pool, an estimated 6.5 Tmol year –1 flows toward the water column (range: 3.2–9.2 Tmol year –1 ), and 1.7 Tmol year –1 enters the authigenic carbonate phases (range: 0.6–3.6 Tmol year –1 ). This summary highlights that carbonate authigenesis in settings dominated by diffusive methane fluxes is a significant component of marine carbon burial, comparable to ∼15% of carbonate accumulation on continental shelves and in the abyssal ocean, respectively. Further, the DIC outflux through the SMTZ is comparable to ∼20% of global riverine DIC flux to oceans. This DIC outflux will contribute alkalinity or CO 2 in different proportions to the water column, depending on the rates of authigenic carbonate precipitation and sulfide oxidation and will significantly impact ocean chemistry and potentially atmospheric CO 2 . Settings with substantial carbonate precipitation and sulfide oxidation at present are contributing CO 2 and ...