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Posted March 30, 2000

Beach Cores Yield Clues to Famous Acadia Landmark

A quiet backwater lagoon was once located where Sand Beach and the crash of ocean waves now attract tourists at Acadia National Park, according to evidence from beach cores collected by a University of Maine graduate student. Over the last few thousand years, the beach has been migrating landward as sea levels have slowly risen, according to work by Alison Brandes, a native of Ridgewood, New Jersey and a master's degree candidate in the UMaine Dept. of Geological Sciences.

Brandes worked with park staff and Joseph Kelley and Daniel Belknap, professors in the department, to collect sand cores as deep as ten feet below the surface of the beach. In addition to studying geologic history, Brandes found that the concentration of shell fragments across the surface of the beach varies dramatically from about 70% within the tidal zone to about 30% by the dunes behind the beach.

Brandes presented a paper on her findings March 13 at the Northeast regional meeting of the Geological Society of America in New Jersey.

Research in 1992 by Walter Barnhardt, then a UMaine graduate student, revealed the high concentration of shell, or carbonate material, at Sand Beach. His and other studies raised questions concerning the abundance of these shell beaches in cool-water settings.

“My goal,” says Brandes, “was to continue that work, to understand the history of Sand Beach, why it is located there and how stable it is. Normally, carbonate tends to dissolve in conditions of cold temperatures, high acidity (such as acid rain) and low salinity.”

In March, 1999, Brandes used a vibracorer, a machine that pushes a hollow pipe into the ground, to extract four cores from the high dunes behind the beach. She also measured the beach profile at low tide once every two weeks, collected samples of surface sand and used a ground penetrating radar to look for the boundaries between underground layers of sand, gravel and clay.

“I found a sequence of glacial material at the bottom followed by intertidal material from flats and dune material on top. The glacial material is about two meters below the surface at the back of the dune. It had been assumed to be there, but this is the first time that anyone has taken cores to document the underlying stratigraphy.”

In analyzing surface samples, Brandes also found a sharp drop in the concentration of carbonate in sand between the low and high tide lines. “I think that what's going on is that shells are picked up by the wind. They're more aerodynamic than the land-derived material, more like little airplane wings, and they get blown toward the dunes,” she says.

Since wind tends not to pick up wet material, high carbonate concentrations remain in the wet sand within the tidal zone, while shell material is removed from the dry part of the beach. Thus the carbonate concentration in that area is lower.

So-called carbonate beaches are relatively rare in temperate climates, says Brandes. At least two others have been identified in Maine, one on Little Cranberry Island and the other at Georgetown.

Brandes is also pursuing a teaching certificate and hopes to teach earth science at the high school level.

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