Sea level rise linked to 20 years of deep ocean warming
SEATTLE, Washington, September 20, 2010 (ENS) – Scientists analyzing 20 years of measurements taken in the deep oceans of the world find a warming trend that is contributing to sea level rise, especially around Antarctica.
“Previous studies have shown that the upper ocean is warming, but our analysis determines how much additional heat the deep ocean is storing from warming observed all the way to the ocean floor,” said Sarah Purkey, an oceanographer at the University of Washington and lead author of the new study. Greenhouse gases in the atmosphere, such as carbon dioxide and methane, cause heating of the Earth. Over the past few decades, at least 80 percent of this heat energy has gone into the ocean, warming it in the process, explain Purkey and her co-author Gregory Johnson, an oceanographer at the Pacific Marine Environmental Laboratory in Seattle, a National Oceanic and Atmospheric Administration research facility. Their study, “Warming of Global Abyssal and Deep Southern Ocean Waters between the 1990s and 2000s: Contributions to Global Heat and Sea Level Rise Budgets,” will be published in an upcoming edition of the Journal of Climate. The study shows that the deep ocean, below about 3,300 feet, is taking up about 16 percent of the heat that the upper ocean is absorbing. “A warming Earth causes sea level rise in two ways,” explained Johnson. “The warming heats the ocean, causing it to expand, and melts continental ice, adding water to the ocean. The expansion and added water both cause the sea to encroach on the land.” Sea level has been rising at around three millimeters (1/8 of a inch) per year on average since 1993, with about half of that caused by ocean thermal expansion and the other half because of additional water added to the ocean, mostly from melting continental ice. Purkey and Johnson note that deep warming of the Southern Ocean accounts for about 1.2 mm (about 1/20th of an inch) per year of the sea level rise around Antarctica in the past few decades. …
