Trends and Projections in Climate-Related Stressors Impacting Arctic Marine Ecosystems—A CMIP6 Model Analysis

Abstract

Eleven Earth System Models (ESMs) contributing to the Coupled Model Intercomparison Project (CMIP6) were evaluated with respect to climate-related stressors impacting Arctic marine ecosystems (temperature, sea ice concentration, oxygen, ocean acidification). Stressors show regional differences and varying differences over time and space among models. Trends calculated over three consecutive 40-year time periods are highest for 2061–2100 for temperature and O₂. Differences between scenarios SSP2-4.5 and SSP5-8.5 vary among models and regions, mainly driven by sea-ice retreat and dilution effects. Differences in biogeochemical parameterizations contribute to acidification differences. Projections indicate consistent ocean acidification until 2040 and faster progression for the high-end emission scenario thereafter. For SSP5-8.5 all Arctic regions show aragonite undersaturation by 2080, and calcite undersaturation for all but two regions by 2100 for all models. Most regions can avoid calcite undersaturation in a medium emission scenario (SSP2-4.5). All variables show increases in seasonal amplitude, most prominently for temperature and oxygen. Calcium carbonate saturation state $\left(\Omega \right)$ shows little change to the seasonal range but temporal shifts in extrema. Seasonal changes in $\Omega$ may be underestimated due to lacking carbon cycle processes within sea ice in CMIP6 models. The analysis emphasizes regionally varying threats from multiple stressors on Arctic marine ecosystems and highlights the propagation of uncertainties from physical to biogeochemical variables. Large model differences in seasonal cycles emphasize the need for improved model constraints regarding the representation of sea-ice decline, river inflow and Atlantic and Pacific water circulation to enhance the applicability of CMIP models in multi-stressor impacts assessments.