Atlantic time-mean heat transport is northward at all latitudes and
exhibits strong multidecadal variability between about 30N and 55N.
Atlantic heat transport variability influences many aspects of the
climate system, including regional surface temperatures, subpolar heat
content, Arctic sea-ice concentration and tropical precipitation
patterns. Atlantic heat transport and heat transport variability are
commonly partitioned into two components: the heat transport by the AMOC
and the heat transport by the gyres. In this paper we compare three
different methods for performing this partition, and we apply these
methods to the CESM1 Large Ensemble at 34N, 26N and 5S. We discuss the
strengths and weaknesses of each method. One of these methods is a new
physically-motivated method based on the pathway of the
northward-flowing part of AMOC. This paper presents a preliminary
version of our method. This preliminary version works only when the AMOC
follows the western boundary of the basin. In this context, the new
method provides a sensible estimate of heat transport by the overturning
and by the gyre, and it is easier to interpret than other methods.
According to our new diagnostic, at 34N and at 26N AMOC explains 120%
of the multidecadal variability (20% is compensated by the gyre), and
at 5S AMOC explains 90% of multidecadal variability.