Fates of the Beaufort Gyre: Location, Extent and Strength

The Beaufort Gyre is a major reservoir of freshwater in the Arctic Ocean and plays an important role in shaping the sea ice distribution. The variations in Beaufort Gyre strength, and its capacity to accumulate or release freshwater, are primarily determined by the stationary Beaufort High pressure system. Multiple studies have suggested a potential future weakening of the Beaufort High, thus driving a projected weakening of the Beaufort Gyre. Yet, in contrast, the ongoing reduction and thinning of the Arctic sea ice has been shown to strengthen the Gyre in recent years – a trend likely to continue into the future. We investigate these potentially competing effects of projected sea ice decline and changing atmospheric patterns on the Beaufort Gyre location, extent, and strength. To this end, we employ a novel storyline approach to identify plausible fates of the Beaufort Gyre in a warming climate, generated from the suite of available CMIP6 models. The different storylines are determined based on the strong or weak modelled response to these two local drivers - Arctic sea ice decline and Beaufort High pressure system weakening - on changes in Beaufort Gyre strength. While the CMIP6 multi-model mean response in the location, extent and strength of the Beaufort Gyre does not exhibit any distinct future changes under emission scenario SSP585, the storylines however reveal contrasting futures. For example, in a future with strong sea ice decline but only a weak decrease of Beaufort High pressure, the storyline indicates a spin-up of the Beaufort Gyre alongside a strong Arctic-wide surface salinity reduction. In contrast, a future with weak sea ice decline but a strong Beaufort High pressure decrease is characterised by a slow-down of the Beaufort Gyre and more regionally confined surface salinity changes. The storyline approach thus highlights that we urgently need to better constrain our model projections in order to reliably predict changes in upper Arctic ocean circulation and freshwater distribution, which play a crucial role for the future Arctic climate and response of both marine and terrestrial ecosystems.