Arctic acidification over the 21st century co-driven by anthropogenic carbon increases & freshening (text & video)

OA Week 2021, Arctic Hub Session

Dr. Jens Terhaar, University of Bern, Switzerland


The Arctic Ocean is particularly vulnerable to ocean acidification due to its naturally low pH and saturation states. Here, we analyse ocean acidification in the Arctic Ocean over the 21st century across models from the latest Coupled Model Intercomparison Project Phase 6 (CMIP6). Compared to the previous model generation (CMIP5), models generally better simulate maximum sea surface densities in the Arctic Ocean and consequently the transport of Cant into the Arctic Ocean interior. Moreover, in CMIP6 the inter-model uncertainty of projected changes over the 21st century in Arctic Ocean saturation states of aragonite (Ωarag) and calcite (Ωcalc) averaged over the upper 1000 m is reduced by 44–64 %. The strong reduction in projection uncertainties of Ωarag and Ωcalc can be attributed to compensation between Cant uptake and total alkalinity reduction in the latest models. Specifically, models with a large increase in Arctic Ocean Cant over the 21st century tend to simulate a relatively weak concurrent freshening and alkalinity reduction, while ESMs with a small increase in Cant simulate a relatively strong freshening and concurrent total alkalinity reduction. Even under the low-emissions Shared Socioeconomic Pathway 1-2.6 (SSP1-2.6), basin-wide averaged Ωarag undersaturation in the upper 1000 m occurs before the end of the century.

Ocean Acidification Week 2021 was sponsored by the following organizations:

(1) GOA-ON, the Global Ocean Acidification Observing Network,

(2) NOAA, the United States National Oceanic & Atmospheric Administration,

(3) IAEA OA-ICC, the International Atomic Energy Agency – Ocean Acidification International Coordination Centre, and

(4) IOC-UNESCO – the Intergovernmental Oceanographic Commission of the United Nations Educational, Scientific and Cultural Organization

For more information, please visit

GOA-ON, YouTube, 24 September 2021. Text and video.

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