| Historical hydrographic sections are used to investigate the seasonal and low frequency variability in the meridional heat flux at 36{dollar}spcirc{dollar}N in the North Atlantic. Eleven transatlantic sections were selected from the World Ocean Atlas 1994. A second set of data set consists of sections from four sectors along 36{dollar}spcirc{dollar}N which combined cover the entire basin. These sectors are: the Slope Water, the Gulf Stream, the Sargasso Sea and the Mid-ocean. The Gulf Stream is the most sampled sector with 140 sections. The horizontal interpolation of the Gulf Stream sections required a parametric model which takes into account the persistent shape of its temperature field. The model is based on least-squares fitting a hyperbolic tangent to the sections and effectively reduces the dependence of the heat flux estimates on the horizontal resolution. The annual mean heat flux of the sector, after the model was used, increased by 0.3 pW. The total upper layer volume transport, above 2000 dbar, comes from the contribution of the baroclinic geostrophic transport from the four sectors plus the wind forced Ekman transport. The total upper layer transport across 36{dollar}spcirc{dollar}N is 16 Sv to the north, with a peak to peak range of 5 ({dollar}pm{dollar}3) Sv and with a maximum in the late summer. The zero net mass flux across the transect can be accomplished by assuming that in the deep layer, below 2000 dbar, an equivalent amount of water to the estimated for the upper layer flows in the southward direction preferably following the pathways of the Deep Western Boundary Current. The temperature flux of the deep layer, which includes the barotropic component of the heat flux, has an annual mean of {dollar}-{dollar}0.14 pW and a peak to peak range of 0.04 ({dollar}pm{dollar}0.02) pW. The total oceanic heat flux is estimated adding the temperature fluxes from the upper and deep layer. The annual mean of the meridional heat flux is 1.1 pW and the annual cycle has a range of 0.5 ({dollar}pm{dollar}0.1) pW. The heat flux residual of the North Atlantic does not show significant low frequency variability. The observed interpentadal changes are smaller than the errorbars associated with the heat flux estimates. |
