Deep Atlantic Ocean Warming: Its Evolution Structure and Dynamics
Prof. Zhaohua Wu
Florida State University, USA
Increased heat storage in deep oceans has been proposed to account for the slowdown of global surface warming since the end of twentieth century. How the imbalanced heat at the surface has been redistributed to deep oceans remains to be elucidated. Here, the evolution of deep Atlantic Ocean heat storage since 1950 on multidecadal or longer timescales is revealed. The anomalous heat in the deep Labrador Sea was transported southward by the shallower core of the deep western boundary current (DWBC). Upon reaching the Equator around 1980, this heat transport route bifurcated into two, with one continuing southward along the DWBC and the other extending eastward along a narrow strip (about four-degree width) centered at the Equator. In 1990s and 2000s, meridional diffusion helped to spread warming in the tropics, making eastward equatorial warming extension have a narrow head and wider tail. The deep Atlantic Ocean warming since 1950 had overlapping variability of approximately sixty years.
The results suggest that the current basin-wide Atlantic Ocean warming at depths of 1000-2000 m can be traced back to the subsurface warming in the Labrador Sea in 1950s. An inference from these results is that the increased heat storage in the twenty-first century in deep Atlantic Ocean is unlikely to partly account for the atmospheric radiative imbalance during the last two decades and to serve as an explanation for the current warming hiatus.