Mineral-enhanced biological pump—A strategy based on mineral-microbe interactions for increasing carbon sink in water

Abstract

<p indent=0mm>Addressing the threats posed by global climate change by reducing the number of greenhouse gases is currently one of the most important research goals of the scientific community. Ocean iron fertilization (OIF) is a geoengineering strategy aimed at mitigating global warming through human intervention. The OIF concept is based on the idea that artificial adding of iron nutrients into iron-depleted regions of the ocean will lead to a rapid boost of phytoplankton populations and the mass sinking of organic matter that ultimately leads to the sequestration of significant amounts of atmospheric CO₂ in the deep sea and sediments. The OIF experiments have been conducted in past over the time and the space scales of weeks and kilometres in polar, subpolar and tropical areas of the oceans. The results have generated new knowledge and a better understanding of the role of iron in regulating marine ecosystems and have confirmed that the iron supply is one of the key controls on the dynamics of phytoplankton blooms, such as diatom as the base of the marine food chain, which in turn affect the whole biogeochemical cycling of carbon. However, the OIF as an effective carbon control strategy is not adequately supported with concerns about potential significant impacts on marine ecosystems. The iron fertilization also did not significantly strengthen the vertical carbon export to the deep sea and thereby the sequestration of CO₂. The efficacy by which the OIF vertically exports organic carbon associated with diatom blooms to the deep sea remains constrained due to the remineralization and the loss of organic carbon during the sinking process of diatomaceous biogenic silica (BSi). Therefore, to address these limitations, the next generation of the IOF geoengineering experiments should be designed to improve the low efficiency of the vertical export of bloomed phytoplankton, which will reduce the loss of organic carbon during the sinking of biomass. In our recent studies, we observed a noticeable dissolution-inhibition effect of Al-bearing lake diatomaceous BSi, which is caused by the high content of Al incorporation in the structure of the BSi. This finding inspired a new idea about the possibility of incorporating naturally occurring, environmentally safe and Al-rich minerals as an Al source for the geoengineering experiments. We hypothesize that clay minerals, with characteristically high contents of Al and Si, might be good ingredients for mineral fertilization in geoengineering experiments to enhance the efficiency of the vertical carbon export of the biological pump. This new proposed mineral-aided process is termed mineral-enhanced biological pump (MeBP). In this paper, the concept, background and theoretical basis of MeBP for CO₂ sequestration in water bodies as a new and inexpensive geoengineering strategy are explained. The basic idea of the MeBP concept is to use finely grained powders of minerals, such as clay minerals as nutrients for geoengineering or ecological engineering experiment to enhance the efficiency of the complexes of microbial organic matter and minerals and to hinder the loss of particulate organic carbon by adjusting the mineral ratios and regulating the particle properties. If so, the improved carbon sequestration efficiency of the biological pump and the CO₂ sink enhancement in water bodies could be achieved. The MeBP offers several potential advantages such as application simplicity, low-cost, scalability, environmental friendliness, and flexibility, and it could be applied alone or in combination with other carbon sequestration strategies. Also, the approaches for the research and application of MeBP, the environmental and ecological risks of applying MeBP and the possible ways of avoiding these risks are discussed. These discussions aim to stimulate new thinking toward the development of new technologies of increasing carbon sink in water bodies that are sustainable, ecologically acceptable and scalable, and can be translated into real applications and engineering practices.