Abstract
To predict the impacts of climate change it is essential to understand how anthropogenic change alters the balance between atmosphere, ocean, and terrestrial reservoirs of carbon. It has been estimated that natural atmospheric concentrations of CO2 are almost 200 ppm lower than they would be without the transport of organic material produced in the surface ocean to depth, an ecosystem service driven by mechanisms collectively referred to as the biological carbon pump. Here we quantify potential reductions in carbon sequestration fluxes in the North Atlantic Ocean through the biological carbon pump over the twenty-first century, using two independent biogeochemical models, driven by low and high IPCC AR5 carbon emission scenarios. The carbon flux at 1000 m (the depth at which it is assumed that carbon is sequestered) in the North Atlantic was estimated to decline between 27 and 43% by the end of the century, depending on the biogeochemical model and the emission scenario considered. In monetary terms, the value of this loss in carbon sequestration service in the North Atlantic was estimated to range between US$170–US$3000 billion in abatement (mitigation) costs and US$23–US$401 billion in social (adaptation) costs, over the twenty-first century. Our results challenge the frequent assumption that coastal habitats store more significant amounts of carbon and are under greater threat. We highlight the largely unrecognized economic importance of the natural, blue carbon sequestration service provided by the open ocean, which is predicted to undergo significant anthropogenic-driven change.
Highlights
Anthropogenic emissions of CO2, through fossil-fuel combustion and land-use changes, have driven increases in its atmospheric concentration from pre-industrial conditions (Hartmann et al, 2013)
At 500 m deep the decline is consistent until ∼2040, at which point the decline is larger for emissions scenario RCP8.5 and larger for MEDUSA than ERSEM (Figure 1)
Over the baseline period (1990–2009), the North Atlantic operated as a significant sink of organic carbon to the deep ocean (Figures 2A,B), but the declines in carbon export by the end of the century (Figure 1) are not geographically consistent
Summary
Anthropogenic emissions of CO2, through fossil-fuel combustion and land-use changes, have driven increases in its atmospheric concentration from pre-industrial conditions (Hartmann et al, 2013). To date, ∼25% of anthropogenic CO2 emissions have entered the ocean (Khatiwala et al, 2013), driven primarily by physicochemical processes, contributing to the reservoir of dissolved inorganic carbon (DIC). Through a suite of biogeochemical processes collectively known as the biological carbon pump (BCP; Broecker, 1982; Volk and Hoffert, 1985), a fraction of the organic carbon produced in sunlit surface waters is transported to the deep ocean via gravitational sinking and vertical migration. About 1% of primary production is thought to sink into the deep ocean interior or into seafloor sediments (Sanders et al, 2014), where it may be sequestered for hundreds to thousands of years
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