The response to pulse-like perturbations in atmospheric carbon and carbon isotopes

Abstract

Abstract. Measurements of carbon isotope variations in climate archives and isotope-enabled climate modelling foster the understanding of the carbon cycle. Perturbations in atmospheric CO2, and in its isotopic ratios (δ13C, ∆14C) are removed on different time scales and by partly different processes. We investigate these differences on timescales of up to 100,000 years in idealized pulse release experiments with the Bern3D-LPX Earth system model of intermediate complexity and by analytical solutions from a box model. Isotopic perturbations are initially removed much faster from the atmosphere than perturbations in CO2 as explained by aquatic carbonate chemistry. On longer time scales, the CO2 perturbation is removed by carbonate compensation and silicate rock weathering. In contrast, the δ13C perturbation is removed by the relentless flux of organic and calcium carbonate particles buried in sediments. The associated removal rate is significantly modified by spatial δ13C gradients within the ocean influencing the isotopic perturbation of the burial flux. Space-time variations in ocean δ13C perturbations are captured by three Principal Components and Empirical Orthogonal Functions. Analytical impulse response functions for atmospheric CO2 and δ13CO2 are provided. Our results show that changes in terrestrial carbon storage are unlikely the sole cause for the abrupt, centennial CO2 and δ13C variations recorded in ice during Heinrich Stadials HS1 and HS4 of the last glacial period. Ocean processes likely played a significant role. The δ113 offset between the penultimate and last glacial maximum reconstructed for the ocean and atmosphere is most likely caused by imbalances between weathering, volcanism and burial fluxes.

Carbon Cycle Responses to Changes in Weathering and the Long‐Term Fate of Stable Carbon Isotopes

“…Data used for the figures and necessary for construction of the emulator are available at Jeltsch‐Thömmes and Joos (2023).…”

Lower oceanic 𝛿<sup>13</sup>C during the Last Interglacial compared to the Holocene

“…It has been estimated that the amount of carbon both entering and exiting the lithosphere due to weathering and burial of organic carbon fluxes could be from 0.274 to 0.344 Gt C yr −1 (Schneider et al, 2013), though these vary through time (Hoogakker et al, 2006). Over timescales greater than 10 ka, the influence of weathering and burial of carbon might therefore dominate the δ 13 C signal (Jeltsch-Thömmes et al, 2019;Jeltsch-Thömmes and Joos, 2020).…”

The seasonal cycle of δ13C of atmospheric carbon dioxide: Influences of land and ocean carbon fluxes and drivers.

“…In addition, the release of isotopically depleted (or light) CO 2 to the atmosphere due to land use change further lowers δ 13 C a . The isotopic perturbation in the atmosphere is moderated by the plemented as a tracer and features kinetic fractionation in air-sea gas exchange and the production of organic material and CaCO 3 Menviel et al, , 2015Jeltsch-Thömmes & Joos, 2020). We use the default model configuration of Bern3D with the addition of monthly output of air-sea CO 2 and 13 CO 2 fluxes.…”