Editing IPCC:AR6/SROCC/Chapter-5 (section)

===== 5.5.1.2.5 Control of sediment disturbance, enhanced weathering and other geochemical approaches =====

Anthropogenic sediment disturbance, through fishing, dredging and the installation of offshore structures, affects the security of carbon storage in shelf sea sediments (Hale et al., 2017 <sup>[[#fn:r1791|1791]]</sup> ). Management of such activities might therefore increase carbon retention, over relatively large areas of shelf seas (Avelar et al., 2017 <sup>[[#fn:r1792|1792]]</sup> ; Luisetti et al., 2019 <sup>[[#fn:r1793|1793]]</sup> ). However, there is a lack of data and understanding of the complex processes that affect carbon storage in the potentially mobile fraction of marine sediments (van de Velde et al., 2018 <sup>[[#fn:r1794|1794]]</sup> ); exceptions are provided by Hu et al. (2016) <sup>[[#fn:r1795|1795]]</sup> and Diesing et al. (2017) <sup>[[#fn:r1796|1796]]</sup> . Due to these uncertainties, there is currently ''low confidence'' that control of sediment disturbance can be used for climate mitigation.

There is theoretically greater potential for carbon removal by ‘enhanced weathering’ using mineral additions to coastal waters (and the open ocean) (Rau, 2011; Renforth and Henderson, 2017 <sup>[[#fn:r1797|1797]]</sup> ). These approaches are based on increasing the naturally-occurring uptake of CO 2 by carbonates (e.g., calcite and dolomite) or silicate minerals (such as olivine). Such rock-weathering currently sequesters ~0.25 GtC yr –1 , on land and at sea (Taylor et al., 2015) and provides the longterm control of atmospheric CO 2 concentrations. It could be enhanced by adding ground minerals to beaches (Montserrat et al., 2017 <sup>[[#fn:r1801|1801]]</sup> ) or the sea surface. Other geochemical approaches for adding alkalinity that are less directly based on natural processes (Rau et al., 2012 <sup>[[#fn:r1802|1802]]</sup> ; GESAMP, 2019 <sup>[[#fn:r1803|1803]]</sup> ) are not considered here.

Enhanced weathering methods might be used to reduce local impacts, for example, for coral reefs (Albright et al., 2016b <sup>[[#fn:r1798|1798]]</sup> ; Feng et al., 2016 <sup>[[#fn:r1799|1799]]</sup> ), as well as contributing to wider mitigation of climate change. However, their climatic benefits would be difficult to quantify, with other constraints on their development and deployment relating to the governance, cost and uncertain environmental impacts of large-scale application (Gattuso et al., 2018 <sup>[[#fn:r1800|1800]]</sup> ). The combination of these factors results in ''low confidence'' that enhanced weathering can provide a viable and acceptable climate mitigation approach.

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