RISING TEMPERATURES IN THE SUBTROPICAL NORTH-ATLANTIC OCEAN OVER THE PAST 35 YEARS

As an oceanographic contribution to the quincentennial celebrations of Columbus's voyage of discovery in 1492, a collaborative expedition wa s carried out in July-August 1992 to make a transatlantic, deep-ocean hydrographic section along Columbus's route at 24 degrees N. The 24 de grees N section is of interest for studies of climate change because i t has been surveyed twice before, during the International Geophysical Year of 1957(1) and during 1981(2) and hence represents one of the be st known of all oceanographic sections. Here we use the temperatures f rom all three surveys to show that the waters between 800 and 2,500 m depth have consistently warmed over the past 35 years and that the war ming since 1957 is remarkably uniform across the east-west extent of t he North Atlantic. The maximum warming, found at 1,100 m depth, is occ urring at a rate of 1 degrees C per century. This trend is broadly con sistent with model predictions of climate change due to increases in a tmospheric CO2 concentration(3,4), but the observed warming occurs in the interior ocean, in contrast to the surface-warming predicted by th e models. The observed patterns of decadal-scale changes in ocean temp erature are thus powerful signatures that can help us to understand th e nature and causes of climate change.