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New Discoveries About the Deep Ocean Could Improve Climate Projections

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New discoveries about the deep ocean's temperature variability and circulation system could help improve projections of future climate conditions.

The deep ocean is affected more significantly by surface warming than previously thought, and this understanding allows for more accurate predictions of factors such as sea-level rise and ice-volume changes.

High ocean-surface temperatures have also been found to result in a more vigorous deep-ocean circulation system. This increase results in a faster transport of large quantities of warm water, with possible impacts that include reduction of sea-ice extent and overall warming of the Arctic. See related article "Arctic Could Face Warmer and Ice-Free Conditions," this issue.

Profile of ocean temperature
Above: Profile of ocean temperature along a meridian at approximately 20W (eastern Atlantic Ocean). South Pole at left, North Pole at right. Land areas and seafloor are black; major features, left to right: Antarctica (approx 90-75S), Mid-Atlantic Ridge (approx 40S), continental slope off Africa (approx 15N), Iceland atop Mid-Atlantic Ridge (approx 65N), and eastern edge of Greenland (approx 80N). All temperatures in C; contour interval is 2C. Numbered dots are Deep Sea Drilling Project and Ocean Drilling Program sites from which data were used for mid-Pliocene temperature reconstruction. Black contour lines show modern temperature; colored regions show temperatures during the mid-Pliocene. Differences in temperature can be surmised by comparing color contours to black contour lines. For example, site 959 is slightly cooler than 4C in the modern ocean but was slightly warmer that 4C in the mid-Pliocene. For more information, see article in Climate of the Past. [larger version]

"The deep ocean is relatively unexplored, and we need a true understanding of its many complex processes," said U.S. Geological Survey (USGS) Director Marcia McNutt, speaking from the United Nations Climate Change Conference in Copenhagen last December. "An understanding of climate change and its impacts based on sound, objective data is a keystone to the type of long-term strategies and solutions discussed at the conference."

USGS scientists created the first ever 3D reconstruction of an ocean during a past warm period, focusing on the mid-Pliocene warm period 3.3 to 3 million years ago. This work is discussed in a recently published article, "Pliocene Three-Dimensional Global Ocean Temperature Reconstruction," in the journal Climate of the Past (v. 5, p. 769-783).

"Our findings are significant because they improve our previous understanding that the deep ocean stayed at relatively constant, cold temperatures and that the deep-ocean circulation system would slow down as surface temperatures increased," said USGS scientist Harry Dowsett. "By looking at conditions in the past, we acquire real data that allow us to see the global climate system as it actually functioned."

"The average temperature of the entire ocean during the mid-Pliocene was approximately one degree warmer than current conditions, showing that warming wasn't just at the surface but occurred at all depths," said USGS scientist Marci Robinson. "Temperatures were determined by analyzing marine plankton fossils, which are organisms that inhabited the water's surface, as well as fossils of bottom-dwelling organisms known as ostracodes."

Global average surface temperatures during the mid-Pliocene were about 3°C (5.5°F) warmer than today and within the range projected for the 21st century by the Intergovernmental Panel on Climate Change. Therefore, the mid-Pliocene may be one of the closest analogs in helping to understand Earth's current and future conditions. USGS research on the mid-Pliocene has also produced the most comprehensive global reconstruction of climate conditions for any warm period prior to the last interglacial (approximately 125,000 years ago).

To learn more about USGS research on the mid-Pliocene, listen to a USGS CoreCast interview with Harry Dowsett and Marci Robinson, "Want Clues to Climate Change? Let's Look Back 3 Million Years…" (Episode 115) and read a related Sound Waves article, "Getting Warmer? Prehistoric Climate Can Help Forecast Future Changes" (January/February 2009).

Technical articles on the subject include the recent report in Climate of the Past (v. 5, p. 769-783, http://www.clim-past.net/5/769/2009/cp-5-769-2009.html) and reports in Nature Geoscience (December 6, 2009, http://dx.doi.org/10.1038/ngeo706) and Stratigraphy (v. 6, no. 4, p. 265-275, http://www.micropress.org/stratigraphy/).

The USGS led this research through the Pliocene Research, Interpretation and Synoptic Mapping (PRISM) group. The primary collaborators in PRISM are Columbia University, Brown University, the University of Leeds, the University of Bristol, the British Geological Survey, and the British Antarctic Survey. Learn more about PRISM research at http://geology.er.usgs.gov/eespteam/prism/.

Related Sound Waves Stories
Arctic Could Face Warmer and Ice-Free Conditions
Jan. / Feb. 2010
Getting Warmer? Prehistoric Climate Can Help Forecast Future Changes
Jan. / Feb. 2009

Related Web Sites
Want Clues to Climate Change? Let's Look Back 3 Million Years
Pliocene Research, Interpretation and Synoptic Mapping (PRISM)
Intergovernmental Panel on Climate Change
United Nations Environment Programme (UNEP) and the World Meteorological Organization (WMO)
Pliocene three-dimensional global ocean temperature reconstruction
Climate of the Past
Earth system sensitivity inferred from Pliocene modelling and data
Nature Geoscience
New quantitative evidence of extreme warmth in the Pliocene Arctic

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in this issue:

cover story:
Measuring Tidal Flows in the Cape Cod Canal

Research Peace River Vulnerable to Running Dry

New Discoveries Could Improve Climate Projections

Arctic Could Face Warmer and Ice-Free Conditions

Meetings CCAA Miami Conference on the Caribbean and Central America

Tampa Bay Area Scientific Information Symposium

Antarctic Treaty Summit

SACNAS National Conference

Airborne Lidar Processing System (ALPS) Workshop

Awards Awards for USGS Publication on the Coral Reef of South Molokai, Hawaii

Staff New USGS Director Visits Centers in California

Gaye Farris Retires from the USGS National Wetlands Research Center

Publications Jan. / Feb. 2010 Publications List

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