Sarah Purkey is a Ph.D. student in the University of Washington's School of Oceanography. Gregory Johnson is an oceanographer with the National Oceanic and Atmospheric Administration (NOAA) Pacific Marine Environmental Laboratory. They contributed this article to LiveScience's Expert Voices: Op-Ed & Insights.
The oceans are the flywheel of the climate system. As atmospheric concentrations of greenhouse gases increase, the Earth system is warming, and over 90 percent of that increase in heat goes into the ocean. Knowing how much heat the ocean absorbs is vital to understanding sea level rise (the oceans expand as they warm), and predicting how much, and how fast, the atmosphere will warm.
Most estimates of ocean warming have been limited to the upper 700 meters of water, owing to the limited availability of ocean-temperature data below that depth. Since about the turn of the millennium, the Argo array, an international system of robotic profiling floats, has massively increased ocean sampling to 2,000 meters, and allowed scientists to show conclusively that ocean warming extends below 700 meters.
However, the ocean is also warming near the bottom, in the coldest waters of the abyssal zones. Oceanographers measure the abyssal ocean to depths of 6,000 meters by lowering accurate recording thermometers and other instruments to the ocean floor on long cables from research vessels. During the 1980s and 1990s, an international program called the World Ocean Circulation Experiment collected thousands of such profiles around the globe.
During the 2000s, we and our fellow oceanographers returned and re-measured ocean properties at many of those sites. We detected a consistent warming signal in the abyssal ocean around the globe. The strongest warming is occurring in the Southern Ocean, around Antarctica, at a rate of approximately 0.03 degrees Celsius per decade. [Warming in Deep Southern Ocean Linked to Sea-Level Rise]
More here: http://www.livescience.com/28248-deep-ocean-warming.html
