Modeling the evolution of pulse-like perturbations in atmospheric carbon and carbon isotopes: the role of weathering–sedimentation imbalances

Jeltsch-Thömmes, Aurich; Joos, Fortunat (2020). Modeling the evolution of pulse-like perturbations in atmospheric carbon and carbon isotopes: the role of weathering–sedimentation imbalances. Climate of the past, 16(2), pp. 423-451. Copernicus Publications 10.5194/cp-16-423-2020

Preview

Text jeltsch20cp_cp-16-423-2020.pdf - Published Version Available under License Creative Commons: Attribution (CC-BY). Download (5MB) | Preview

Measurements of carbon isotope variations in climate archives and isotope-enabled climate modeling advancethe understanding of the carbon cycle. Perturbations in atmospheric CO₂ and in its isotopic ratios (δ¹³C,Δ¹⁴C) are re-moved by different processes acting on different timescales. We investigate these differences on timescales of up to100 000 years in pulse-release experiments with the Bern 3D-LPX Earth system model of intermediate complexity and byanalytical solutions from a box model. On timescales fromyears to many centuries, the atmospheric perturbations in CO₂ and δ¹³CO₂ are reduced by air–sea gas exchange, phys-ical transport from the surface to the deep ocean, and by the land biosphere. Isotopic perturbations are initially removed much faster from the atmosphere than perturbations in CO₂ as explained by aquatic carbonate chemistry. On multimillennial 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 principal components and empirical orthogonal functions. Analytical impulse response functions for atmospheric CO₂ and δ¹³CO₂ are provided. Results suggest that changes in terrestrial carbon storage were not the sole cause for the abrupt, centennial-scale CO₂ and δ¹³CO₂ variations recorded in ice during Heinrich stadials HS1 and HS4, though model and data uncertain-ties prevent a firm conclusion. The δ¹³C offset between the Penultimate Glacial Maximum and Last Glacial Maximum reconstructed for the ocean and atmosphere is most likely caused by imbalances between weathering, volcanism, and burial fluxes. Our study highlights the importance of isotopic fluxes connected to weathering–sedimentation imbalances, which so far have been often neglected on glacial–interglacial time scales.

Interest & Impact

Downloads

110 since deposited on 30 Mar 2020
10 in the past 12 months

Citations

5 Citations in Web of Science ®
6 Citations in Scopus

Search

in Google Scholar™

Services

Actions (login required)

Edit item

Actions (login required)

Edit item