A robust relationship between multidecadal global warming rate variations and the Atlantic Multidecadal Variability

Li, Zhiyu; Zhang, Wenjun; Jin, Fei-Fei; Stuecker, Malte F.; Sun, Cheng; Levine, Aaron F.; Xu, Haiming; Liu, Chao

doi:10.1007/s00382-020-05362-8

An industrial-era drop in Greenland ice core methanesulfonic acid (MSA) is thought to herald a collapse in North Atlantic marine phytoplankton stocks related to a weakening of the Atlantic Meridional Overturning Circulation. In contrast, stable levels of marine biogenic sulfur production contradict this interpretation and point to changes in atmospheric oxidation as a potential cause of the MSA decline. However, the impact of oxidation on MSA production has not been quantified, nor has this hypothesis been rigorously tested. Here we present a multi-century MSA record from the Denali, Alaska, ice core, which shows an MSA decline similar in magnitude but delayed by 93 years relative to the Greenland record. Box model results using updated chemical pathways indicate that oxidation by industrial nitrate radicals has suppressed atmospheric MSA production, explaining most of Denali’s and Greenland’s MSA declines without requiring a change in phytoplankton production. The delayed timing of the North Pacific MSA decline, relative to the North Atlantic, reflects the distinct history of industrialization in upwind regions and is consistent with the Denali and Greenland ice core nitrate records. These results demonstrate that multi-decadal trends in industrial-era Arctic ice core MSA reflect rising anthropogenic pollution rather than declining marine primary production.

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