Revealing the ancient sea levels recorded in reefs

Buildings near Crane Beach are perched on a coral terrace, an ancient reef from which past sea levels can be determined using age and elevation. Credit: ©Terri Cook and Lon Abbott Buildings near Crane Beach are perched on a coral terrace, an ancient reef from which past sea levels can be determined using age and elevation. Credit: ©Terri Cook and Lon Abbott

Deriving the ancient sea levels in Barbados is easier than in other places, but still involves several steps.

First, researchers collect samples of the coral Acropora palmata, which only lives in the top five meters of the ocean, thus providing the tightest constraint on the elevation of sea level during its growth. Second, researchers date the coral via the uranium-thorium radiometric technique and measure its oxygen isotopic values so they can tie the data directly to the marine record of past global temperatures. Third, they survey the current elevation of each reef terrace.

Finally, they subtract from the current elevation the amount of uplift the terrace has undergone since its formation, using the steady uplift rate that has been calculated for that portion of the island. The result is a dataset providing the height of sea level at a series of well-constrained times in the past, which is directly tied to the global paleoclimate record.

Terri Cook and Lon Abbott

Terri Cook (www.down2earthscience.com) is a science and travel writer based in Colorado and an EARTH roving correspondent. Lon Abbott is a geology professor at the University of Colorado at Boulder.

Wednesday, December 7, 2011 - 06:00