Concurrent Warming and Freshening Led to a Record-High Sea Level in the Labrador Sea

The Labrador Sea plays a pivotal role in the global climate system as a primary source of newly ventilated intermediate-depth water masses and a major carbon sink of the North Atlantic. Since the 1950s, this region has seen significant shifts in heat and freshwater contents, resulting in arguably the largest full-depth deep-ocean temperature and salinity changes ever recorded. However, the contribution of these changes to sea level variability has yet to be thoroughly quantified and investigated. Using satellite altimetry in conjunction with profiling Argo float and ship-based hydrographic measurements, we show that between 2017 and in 2023 the central Labrador Sea experienced an exceptionally fast sea level rise elevating the level to a record high. Six concurrent factors contributed to these rise and, consequently, extreme height – reduced winter surface cooling, increased summer surface warming (i.e., oceanic heat uptake), anomalous freshening, drastically shoaled winter convection, reduced deep-water density, and water-column mass gain. We also claim that the effect of salinity changes on sea level switched from counterbalancing (1948–2015) to reinforcing (2015–onward) the effect of temperature changes in result of Labrador Sea freshening caused by increased Arctic sea ice melt. This mechanism raises possibility of greater environmental impacts of both recent and imminent heat and freshwater regime shifts than predicted.