This UK-US programme aims to aid long-term climate prediction by improving understanding of the Subpolar North Atlantic. It will extend an international observation project in the area by a decade and use ocean-climate models to increase understanding of subpolar variability and its impacts.
The Atlantic Meridional Overturning Circulation (AMOC) is a key component of the global climate system, and dominates northward ocean heat transport over most of the Atlantic. The Subpolar North Atlantic is the region where the AMOC is actively shaped through a combination of surface fluxes of heat, freshwater and momentum.
There is increasing evidence that Subpolar North Atlantic knowledge is important for decadal climate prediction. Through a collaboration with the National Science Foundation, this programme will extend the observations of the Overturning in the Subpolar North Atlantic Program (OSNAP) to a decade and support using the observations effectively in science and policy predictions.
The AMOC is usually defined as the zonally-integrated meridional flow, as a function of latitude and depth and is characterised by a northwards flow of warm, salty, upper ocean waters and a return southwards flow of cool, fresher, deep waters. However, this characterisation is over simplistic in the Subpolar North Atlantic where the circulation is three-dimensional and interacts in a complex way with the bathymetry.
The Subpolar North Atlantic contains three major current systems: the North Atlantic Current, the Deep Western Boundary Current, and the Western Boundary Current system. In 2014 the OSNAP international partners deployed the OSNAP array (a trans-basin observing system) to measure the AMOC in the Subpolar North Atlantic.
Subpolar North Atlantic variability timescales span from sub-seasonal to a decade, and it can take up to a decade for the Subpolar North Atlantic to impact the overturning at lower latitudes. As there is increasing evidence that Subpolar North Atlantic knowledge is important for decadal climate prediction, Subpolar North Atlantic observations over a similar timescale are therefore critical if such decadal climate prediction is to prove a useful tool for science and policy decisions.
It is also critical to assess the performance of the climate models’ representation of the Subpolar North Atlantic in terms of fidelity. The major changes occurring in the Subpolar North Atlantic at the moment provide an ideal opportunity to understand the cause and impact of a major signal in the observations and to study the relationship between the AMOC and local and remote processes.
This programme will extend the OSNAP observational period to a decade. Through collaboration with the US and by using the OSNAP observations, it will address two challenges:
- combine observations and ocean-climate models to deliver a step change in quantitative understanding of processes that matter for subpolar variability
- determine the impacts of subpolar variability on the ocean-atmosphere-ice system.