By Dr. Sebastian Lüning and Prof. Fritz Vahrenholt
German text translated by P. Gosselin)
We would like to take a look at the oceanic warming of the Atlantic. From the latest Climate4You Newsletter (pdf her) We look at the heat content curve of the last 60 years for the upper most 100 meters of the Atlantic:
Fig. 1: Atlantic heat content curve for the past 60 years (upper 100 meters of the Atlantic water mass). Chart: Climate4You.
Clear to see: Over the past 13 years the Atlantic has not warmed further. The chart shows a large plateau. There was a plateau 1955-1985, followed by a rise, then another plateau starting in 2004.
The current missing warming of the upper layer of the Atlantic was also the subject of publication by Somavilla et al, which appeared in March 2016 in the Geophysical Research Letters. It claims that the heat simply moved from the upper levels to the lower layers of the Atlantic:
Mid-2000s North Atlantic shift: Heat budget and circulation changes
Prior to the 2000s, the North Atlantic was the basin showing the greatest warming. However, since the mid-2000s during the so-called global warming hiatus, large amounts of heat were transferred in this basin from upper to deeper levels while the dominance in terms of atmospheric heat capture moved into the Indo-Pacific. Here we show that a large transformation of modal waters in the eastern North Atlantic (ENA) played a crucial role in such contrasting behavior. First, strong winter mixing in 2005 transformed ENA modal waters into a much saltier, warmer, and denser variety, transferring upper ocean heat and salt gained slowly over time to deeper layers. The new denser waters also altered the zonal dynamic height gradient reversing the southward regional flow and enhancing the access of saltier southern waters to higher latitudes. Then, the excess salinity in northern regions favored additional heat injection through deep convection events in later years.”
And if you take a look at the temperature anomaly chart in the paper’s supplement (Fig. S1), you can see how heterogeneous this trend really is. We’ll have to keep an eye on it.
Heat distribution had been already the topic in a paper by Desbruyères et al 2014 in the Geophysical Research Letters:
Full-depth temperature trends in the northeastern Atlantic through the early 21st century
The vertical structure of temperature trends in the northeastern Atlantic (NEA) is investigated using a blend of Argo and hydrography data. The representativeness of sparse hydrography sampling in the basin mean is assessed using a numerical model. Between 2003 and 2013, the NEA underwent a strong surface cooling (0–450 m) and a significant warming at intermediate and deep levels (1000 m to 3000 m) that followed a strong cooling trend observed between 1988 and 2003. During 2003–2013, gyre-specific changes are found in the upper 1000 m (warming and cooling of the subtropical and subpolar gyres, respectively), while the intermediate and deep warming primarily occurred in the subpolar gyre, with important contributions from isopycnal heave and water mass property changes. The full-depth temperature change requires a local downward heat flux of 0.53 ± 0.06 W m−2 through the sea surface, and its vertical distribution highlights the likely important role of the NEA in the recent global warming hiatus.”
We wish to take another look at the mentioned North Atlantic cooling in an up-to-date chart from Climate4You:
Fig. 2: North Atlantic heat content curve for the past 60 years (upper 700 of the North Atlantic water mass). Chart: Climate4You.