Irminger Sea Is the Center of Action for Subpolar AMOC Variability

Abstract

The climate-regulating meridional overturning circulation in the Atlantic Ocean is largely hidden from us (Lozier, 2012) and although continuous monitoring of its strength only commenced in 2004 and 2014 in the subtropical (Frajka-Williams, 2015) and subpolar (Lozier et al., 2017) North Atlantic, respectively, this rich system of ocean currents conveying heat and freshwater to higher latitudes is claimed, largely based on sea-surface temperature proxies, to have slowed down during the twentieth century (e.g., Caesar et al., 2018). Some studies have, however, pointed out that serious care should be taken when interpreting and attributing North Atlantic sea-surface temperature change to Atlantic Meridional Overturning Circulation (AMOC) slowdown since atmospheric effects play a large role in establishing these trends and, as such, these proxies are poor predictors of

Ventilation of the deep Gulf of Mexico and potential insights to the Atlantic Meridional Overturning Circulation

“…The same study also indicated that different components of the lower limb of AMOC respond differently over time with temperature increases being greater and starting sooner in UNADW, while the deeper components of AMOC (Iceland-Scotland Ridge Overflow and Denmark Strait Overflow) show a weaker and later temperature increase ( 60 ). A weakening of the UNADW formation in the Irminger-Labrador Sea region, at least over the past 70 years, was recently demonstrated on the basis of density observations and an ocean reanalysis ( 61 ). It is conceivable that here presented changes in GoMDW are likely caused by a weakening of UNADW formation allowing more older and warmer intermediate water from the South Atlantic to enter through Windward Passage along with UNADW.…”

“…Many of the decadal variability studies of NA convection and AMOC have been linked to the NAO index ( 22 , 24 , 61 ). The observational record starts after the second world war in the late 1940s and is characterized by particularly negative NAO index values into the 1960s.…”

“…The explanation for these changes seen in GoMDW are likely rooted in the NA and climate change. Although a decrease in ∆ 14 C is also evident in the preindustrial atmosphere (35), it is unlikely that a 5‰ decrease in atmospheric and surface water ∆ Many of the decadal variability studies of NA convection and AMOC have been linked to the NAO index (22,24,61). The observational record starts after the second world war in the late 1940s and is characterized by particularly negative NAO index values into the 1960s.…”

What Can Hydrography Between the New England Slope, Bermuda and Africa Tell us About the Strength of the AMOC Over the Last 90 years?

“…The marginal decrease in AMOC strength reported here is probably associated with changes in the subpolar North Atlantic, since the outflow from the Nordic Seas shows no trend over the last 70 years (Rossby et al., 2020). On the other hand, a recent study (Chafik et al., 2022) suggests a possible 2.2 Sv weakening of the subpolar AMOC over the last 70 years, but its significance remains unclear due to large interannual variations (variations that are not observed in the Nordic Seas overflow due to the large reservoir of the Nordic Seas acting as a low‐pass filter). Thus, AMOC variability over the last 70–100 years appears to be tied to variations in the production of North Atlantic intermediate depth water.…”

The Irminger Gyre as a key driver of the subpolar North Atlantic overturning on monthly timescales

“…Direct observations have determined that monthly to interannual AMOC variability across OSNAP East is not constrained to a single region but is spread across the western boundary current (i.e., East Greenland Current), as well as the Irminger and Iceland basin (Li et al, 2021). However, satellite and model [hindcast] simulations have shown that the Irminger Sea is a key region for AMOC variability on interannual to decadal time scales (Megann et al, 2021;Cha k et al, 2022).…”