Burial-nutrient feedbacks amplify the sensitivity of atmospheric carbon dioxide to changes in organic matter remineralisation

Abstract

Abstract. Changes in the marine remineralisation of particulate organic matter (POM) and calcium carbonate potentially provide a positive feedback with atmospheric CO 2 and climate change. The responses to changes in remineralisation length scales are systematically mapped with the Bern3D ocean-sediment model for atmospheric CO 2 and tracer fields for which observations and palaeoproxies exist. Results show that the "sediment burial-nutrient feedback" amplifies the response in atmospheric CO 2 by a factor of four to seven. A transient imbalance between the weathering flux and the burial of organic matter and calcium carbonate lead to sustained changes in the ocean's phosphate and alkalinity inventory and in turn in surface nutrient availability, marine productivity, and atmospheric CO 2 . It takes decades to centuries to reorganise tracers and fluxes within the ocean, many millennia to approach equilibrium for burial fluxes, while δ 13 C signatures are still changing 200 000 years after the perturbation. At 1.7 ppm m −1 , atmospheric CO 2 sensitivity is about fifty times larger for a unit change in the remineralisation depth of POM than of calcium carbonate. The results highlight the role of organic matter burial in atmospheric CO 2 and the substantial impacts of seemingly small changes in POM remineralisation.

Effects of eustatic sea-level change, ocean dynamics, and nutrient utilization on atmospheric <i>p</i>CO<sub>2</sub> and seawater composition over the last 130 000 years: a model study

“…It is not our intention to promote box modelling per se as the method of choice. Rather, we hope that the concepts and ideas advanced in our paper may stimulate the community and help to further enhance cutting-edge Earth system models with explicit ocean dynamics (Tschumi et al, 2011;Menviel et al, 2012;Brovkin et al, 2012;Roth et al, 2014;Lambert et al, 2015).…”

A probabilistic assessment of calcium carbonate export and dissolution in the modern ocean

“…Here an ocean version with a horizontal resolution of 41 by 40 grid cells and 32 logarithmically scaled vertical layers is used (see also Roth et al, 2014). The horizontal resolution is the same for the components atmosphere, ocean, sea ice, and sediments of the Bern3D model.…”

The devil's in the disequilibrium: sensitivity of ocean carbon storage to climate state and iron fertilization in a general circulation model

“…Thus, the changes in DIC sat 30 reflect only changes in temperature, salinity, alkalinity and ocean circulation, and not changes in pCO 2 . Nor do they explicitly consider changes in the total carbon or alkalinity inventories, although these may have changed significantly due to changes in outgassing and/or burial (Roth et al, 2014;Tschumi et al, 2011). As such, the experiments here should be seen as idealized climate-driven changes, and should be further tested with more comprehensive models including interactive CO 2 .…”