Climate change decouples oceanic primary and export productivity and organic carbon burial

Abstract

Understanding responses of oceanic primary productivity, carbon export, and burial to climate change is essential for model-based projection of biological feedbacks in a high-CO2 world. Here we compare estimates of productivity based on the composition of fossil diatom floras with organic carbon burial off Oregon in the Northeast Pacific across a large climatic transition at the last glacial termination. Although estimated primary productivity was highest during the Last Glacial Maximum, carbon burial was lowest, reflecting reduced preservation linked to low sedimentation rates. A diatom size index further points to a glacial decrease (and deglacial increase) in the fraction of fixed carbon that was exported, inferred to reflect expansion, and contraction, of subpolar ecosystems that today favor smaller plankton. Thus, in contrast to models that link remineralization of carbon to temperature, in the Northeast Pacific, we find dominant ecosystem and sea floor control such that intervals of warming climate had more efficient carbon export and higher carbon burial despite falling primary productivity.

Climate engineering by mimicking natural dust climate control: the iron salt aerosol method

“…Table 2 gives an overview of some trends in C burial depending on the climate condition change between main glacial and interglacial. Lopes et al (2015) found just the opposite in ocean sediment layers produced during the warm interstadial compared to the cold main glacial, i.e., a high burial rate of organic C in the ocean bottom sediment. But in spite of the high organic C burial rate, the interstadial CO 2 levels were kept higher than those of the main glacial.…”

“…The ratio of organic C burial to carbonate C burial is much smaller than 1. The results of Lopes et al (2015) from northeast Pacific sediments demonstrate that, although primary productivity was estimated to be highest during the Last Glacial Maximum, organic C burial was lowest. This coincides with our proposed optimum mixed O 2 -rich milieu throughout the whole water column.…”

“…But in spite of the high organic C burial rate, the interstadial CO 2 levels were kept higher than those of the main glacial. Even in this regard, the Lopes et al (2015) Figure 6. This figure presents the essential differences between an unstratified well-mixed ocean basin under a cold and dusty atmosphere during the cold main glacial, with low atmospheric GHG concentrations (a) and a stratified ocean basin with a meltwater layer on top of a saline ocean water layer during a warm interglacial, with a hot and dust-free greenhouse atmosphere (b).…”

“…During cold climate epochs, with unstratified water columns and undisturbed THC, the CO 2 conversion to ocean crust carbonate is activated, as is the CO 2 conversion to the organic fraction of ocean sediments. Just the opposite has been found to be true for the burial of organic C in ocean basin bottom sediments: according to Lopes et al (2015) the overwhelming organic debris fraction produced during the main glacial episodes from the phytoplankton habitat at the surface is oxidized and remineralized in the well-mixed ocean basin (Lopes et al, 2015). As the CO 2 level in the atmosphere is at its lowest during the main glacials, the remaining C sinks of the oceans seem to be of much greater efficiency than the iron-induced production of organic C by assimilation: the most prominent C sink is the authigenic carbonate C burial in the alkaline ocean crust.…”

“…According to this, Fe transport from basin bottom sources and dust sources to the phytoplankton was at its maximum and produced a maximum primary productivity at the ocean surface, but carbon burial became lowest during that time (Lopes et al, 2015) although GHGs were at their lowest levels during the glacial maximum. The cause of this seeming contradiction are the changing burial ratios of organic C / carbonate C at the basin bottom(s).…”