Rising temperatures in the subtropical North Atlantic Ocean over the past 35 years

Abstract

As an oceanographic contribution to the quincentennial celebra-tions of Columbus's voyage of discovery in 1492, a collaborative expedition was carried out in July-August 1992 to make a transat-lantic, deep-ocean hydrographic section along Columbus's route at 24^o N. The 24^o N section is of interest for studies of climate change because it has been surveyed twice before, during the Inter-national Geophysical Year of 1957¹ and during 1981², and hence represents one of the best known of all oceanographic sections. Here we use the temperatures from all three surveys to show that the waters between 800 and 2,500m depth have consistently warmed over the past 35 years and that the warming since 1957 is remarkably uniform across the east-west extent of the North Atlantic. The maximum warming, found at 1,100m depth, is occurring at a rate of 1^oC per century. This trend is broadly consistent with model predictions of climate change due to increases in atmospheric CO₂ concentration^3,4, but the observed warming occurs in the interior ocean, in contrast to the surface-warming predicted by the models. The observed patterns of decadal-scale changes in ocean temperature are thus powerful sig-natures that can help us to understand the nature and causes of climate change.