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Assessing the "ballast" hypothesis for carbon transport in the ocean : global sediment trap data analysis and simulation in an Earth System Model Izumi, Ryusuke


Sediment trap particle flux data analysis and development of a model representation of mineral “ballast” mechanism for carbon transport in the ocean is presented in this study. The validity of several classical POC remineralization models as well as recently hypothesized “ballast” mechanism based POC remineralization models were tested by analyzing data from selected 79 sediment traps at >1500 m from around the world. POC flux modelled with different variations of model representations at each sediment trap site was statistically compared with corresponding measured POC flux in order to evaluate the overall predictability of each model at the global scale. A CaCO₃ single-mineral-ballast model could explain up to —79% of the global F variability at depth >1500 m and suggests that CaCO₃ may potentially be the mineral type that has dominant control on the vertical transport of Fc,c from sea surface to depth in the open ocean. In addition, ai assessment of the impact of reduced CaCO₃ production (as a result of ocean surface acidification) on the marine carbon cycle and implications for future atmospheric CO₂ concentration under the assumption of mineral ballasting of POC is presented. A CaCO₃ single-mineral-ballast model derived from the data analysis is incorporated into GENIE-i, a computationally efficient carbon-climate Earth System Model of intermediate complexity. Simulation results from a “business as usual” future carbon emissions scenario in GENIE-i suggest that, by year 2300, calcification response of marine calcifying organisms to increased atmospheric CO₂ concentrations in a CaCO₃-ballasting ocean is —63% weaker compared to that in a non-ballasting ocean. With the “ballast” effect in operation, the net effect of climate feedback and calcification feedback is a global decrease in POC export production, except for in some high latitude regions where enhanced POC production due to decreased sea-ice coverage overrides. If the “ballast” hypothesis is true, a CaCO₃-ballasting mechanism could completely counter the reduction in atmospheric CO₂ concentration by calcification feedback alone in an ocean where no ballasting mechanism is present.

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