Estimated decadal changes in the North Atlantic meridional overturning circulation and heat flux 1993-2004

Results from a global 1 model constrained by least squares to a multiplicity of datasets over the interval 1992-2004 are used to describe apparent changes in the North Atlantic Ocean meridional overturning circulation and associated heat fluxes at 26 degrees N. The least squares fit is both stable and adequately close to the data to make the analysis worthwhile. Changes over the 12 yr are spatially and temporally complex. A weak statistically significant trend is found in net North Atlantic volume flux above about 1200 m, which drops slightly (-0.19 +/- 0.05 Sv yr(-1); 1 Sv equivalent to 10(6) m(3) s(-1)) but with a corresponding strengthening of the outflow of North Atlantic Deep Water and inflow of abyssal waters. The slight associated trend in meridional heat flux is very small and not statistically significant. The month-to-month variability implies that single-section determinations of heat and volume flux are subject to serious aliasing errors.