Temperature is one of the most fundamental descriptors of the physical state of the ocean
Beyond simply knowing that the oceans are warming, the results will help us answer a few climate questions," Roemmich was quoted as saying by LiveScience.
Scientists among the 200-member crew on board had taken 300 ocean-temperature profiles, or measurements at several depths in each spot, with pressure-protected thermometers and compared temperatures
It showed a 1.1-degree Fahrenheit (0.59-degree Celsius) rise in temperatures at the ocean's surface over the last 135 years, a result corroborated by a large body of sea-surface temperature data that goes back more than 100 years.
"That is a substantial amount of warming. Ocean warming has been previously linked to glacial melting and mass coral bleaching," Roemmich said.
Scientists have previously determined that nearly 90 per cent of the excess heat added to Earth's climate system since the 1960s has been stored in the oceans.
One issue with the Challenger data, Roemmich said, is that the scientists onboard didn't directly measure the depth of their thermometers; but measured only the length of the line extending the instruments into the water. Because of ocean currents, it's nearly impossible to get a line to be completely vertical in the water, resulting in an actual depth that is a little less than the full length of the line, he said.
"What you are then going to see is a temperature that is a little warmer than it would have been if the line has been perfectly vertical," he said, referring to the fact that temperatures are typically warmer at shallower depths