Divergence in Climate Model Projections of Future Arctic Atlantification

Abstract

The Arctic Ocean is strongly stratified by salinity in the uppermost layers. This stratification is a key attribute of the region as it acts as an effective barrier for the vertical exchanges of Atlantic Water heat, nutrients, and CO2 between intermediate depths and the surface of the Eurasian and Amerasian basins (EB and AB). Observations show that from 1970 to 2017, the stratification in the AB has strengthened, whereas, in parts of the EB, the stratification has weakened. The strengthening in the AB is linked to freshening and deepening of the halocline. In the EB, the weakened stratification is associated with salinification and shoaling of the halocline (Atlantification). Simulations from a suite of CMIP6 models project that, under a strong greenhouse-gas forcing scenario (ssp585), the overall surface freshening and warming continue in both basins, but there is a divergence in hydrographic trends in certain regions. Within the AB, there is agreement among the models that the upper layers will become more stratified. However, within the EB, models diverge regarding future stratification. This is due to different balances between trends at the surface and trends at depth, related to Fram Strait fluxes. The divergence affects projections of the future state of Arctic sea ice, as models with the strongest Atlantification project the strongest decline in sea ice volume in the EB. From these simulations, one could conclude that Atlantificaton will not spread eastward into the AB; however, models must be improved to simulate changes in a more intricately stratified EB correctly.

Future Arctic Climate Change in CMIP6 Strikingly Intensified by NEMO‐Family Climate Models

“…Climate models are key tools for understanding future climate changes (Jahn, 2018; Landrum & Holland, 2020; Screen et al., 2018), although they are often subject to large uncertainties in the Arctic, such as for the simulated Arctic warming (Latonin et al., 2021; Pithan & Mauritsen, 2014; Smith et al., 2019), sea ice decline (Docquier et al., 2019; Li et al., 2017; Notz & Community, 2020), and Arctic Ocean hydrography and stratification (Heuzé et al., 2023; Khosravi et al., 2022; Muilwijk et al., 2022; Shu et al., 2019). Future changes in the Arctic climate will have significant impacts on human life and marine ecosystems (Chambault et al., 2022; Ingvaldsen et al., 2021).…”

Expanding Influence of Atlantic and Pacific Ocean Heat Transport on Winter Sea‐Ice Variability in a Warming Arctic

“…(2022), and Muilwijk et al. (2023). The connection between the Fram Strait heat transport and winter sea‐ice variability is limited in all models.…”

Anthropogenic Carbon in the Arctic Ocean: Perspectives From Different Transient Tracers

“…Nevertheless, because our estimates agree to previous results for the sampled area and along the first 1,500 m, we can confirm that in 2015 the AO represented ∼2% of the global oceans' C ant inventory. As the rate of “Atlantification” of the Eurasian Basin is expected to increase in the future (Muilwijk et al., 2023), and since the Atlantic‐origin waters are the main source of C ant to this region, the magnitude and distribution of such inventory is also likely to change. Therefore, this work highlights the potential of Atlantic‐derived tracers such as 129 I and 236 U (among others released from nuclear reprocessing plants), to target future changes in C ant in the Arctic Ocean.…”