Abstract
Abstract. The subpolar North Atlantic (SPNA) is a region with prominent decadal variability that has experienced remarkable warming and cooling trends in the last few decades. These observed trends have been preceded by slow-paced increases and decreases in the Labrador Sea density (LSD), which are thought to be a precursor of large-scale ocean circulation changes. This article analyses the interrelationships between the LSD and the wider North Atlantic across an ensemble of coupled climate model simulations. In particular, it analyses the link between subsurface density and the deep boundary density, the Atlantic Meridional Overturning Circulation (AMOC), the subpolar gyre (SPG) circulation, and the upper-ocean temperature in the eastern SPNA. All simulations exhibit considerable multidecadal variability in the LSD and the ocean circulation indices, which are found to be interrelated. LSD is strongly linked to the strength of the subpolar AMOC and gyre circulation, and it is also linked to the subtropical AMOC, although the strength of this relationship is model-dependent and affected by the inclusion of the Ekman component. The connectivity of LSD with the subtropics is found to be sensitive to different model features, including the mean density stratification in the Labrador Sea, the strength and depth of the AMOC, and the depth at which the LSD propagates southward along the western boundary. Several of these quantities can also be computed from observations, and comparison with these observation-based quantities suggests that models representing a weaker link to the subtropical AMOC might be more realistic.
Highlights
The North Atlantic Ocean is a key component in Earth’s climate through, for example, its role in redistributing heat and in taking up excess heat and carbon from the atmosphere
We focus on the question of how robust the relationship is between subsurface Labrador Sea density anomalies and the basin-wide Atlantic Ocean circulation on decadal timescales
Because our goal is to provide further insight into the suggested relationships established from observed trends in the North Atlantic (e.g. Robson et al, 2016), all statistical analyses in this study exploring the relationships between variables and associated lags are based on 10-year running trends
Summary
The North Atlantic Ocean is a key component in Earth’s climate through, for example, its role in redistributing heat and in taking up excess heat and carbon from the atmosphere. The North Atlantic is expected to change significantly in the future due to the effects of climate change and produce substantial climate impacts on the surrounding regions (Sutton and Hodson, 2005; Woollings et al, 2012). On decadal timescales, it is the interaction between natural variability and externally forced changes that will shape how the Atlantic region’s climate will evolve. In order to improve predictions of the North Atlantic, it is imperative that we improve our understanding of the processes that control decadal-timescale changes in this region
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