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

==== 5.4.4.1 Physical Drivers of Future Ocean Carbon Uptake and Storage ====

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The principal contribution to increasing global ocean carbon is the air–sea flux of CO <sub>2</sub> , which changes the dissolved inorganic carbon (DIC) inventory ( [[#5.4.2|Section 5.4.2]] ; [[#Arora--2020|Arora et al., 2020]] ). The processes that influence the variability and trends of the ocean carbon–heat nexus are assessed in Cross-Chapter Box 5.3. Climate has three important impacts on the ocean uptake of anthropogenic CO <sub>2</sub> : (i) ocean warming reduces the solubility of CO <sub>2</sub> , which increases ''p'' CO <sub>2</sub> and increases the stratification of the mixed layer, both acting as positive feedbacks weakening the ocean sink ( [[IPCC:Wg1:Chapter:Chapter-9#9.2.1|Section 9.2.1]] and Cross-Chapter Box 5.3; [[#Arora--2020|Arora et al., 2020]] ); (ii) changing the temporal and spatial characteristics of wind stress and storms alters mixing – entrainment in, and across the bottom of, the mixed layer ( [[#Bronselaer--2018|Bronselaer et al., 2018]] ); and (iii) warming and wind stress influence the large-scale meridional overturning circulation (MOC) circulation, which modifies the rate of ventilation, storage or outgassing of ocean carbon in the ocean interior ( [[#5.2.3.1|Section 5.2.3.1]] ; [[#Gruber--2019b|Gruber et al., 2019b]] ; [[#Arora--2020|Arora et al., 2020]] ). The land-to-ocean riverine flux and the carbon burial in ocean sediments play a minor role ( ''low confidence'' ) ( [[#Arora--2020|Arora et al., 2020]] ). Based on ''high agreement'' of projections by coupled climate models, there is ''high confidence'' that the resultant climate–carbon cycle feedbacks are positive, but the extent of the ocean sink weakening is scenario dependent ( [[#Arora--2020|Arora et al., 2020]] ).

Regionally, the Southern Ocean is a major sink of anthropogenic CO <sub>2</sub> (Figure 5.8a), although challenges in modelling its circulation and Antarctic sea ice transport (Sections 3.4.1.2, 9.2.3.2 and 9.3.2) generate uncertainty in the response of its sink to future carbon–climate feedbacks. Increased freshwater input may cause a slowdown of the lower overturning circulation, leading to increased Southern Ocean biological carbon storage ( [[#Ito--2015|Ito et al., 2015]] ); alternatively, increased winds may intensify the overturning circulation, reducing the net CO <sub>2</sub> sink in the Southern Ocean ( [[#Bronselaer--2018|Bronselaer et al., 2018]] ; [[#Saunders--2018|Saunders et al., 2018]] ). On centennial time scales, there is thus ''low confidence'' in the overall effect of intensifying winds in the Southern Ocean on CO <sub>2</sub> uptake.

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