Carolina bay

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The Carolina bays are oval-shaped depressions found along the Atlantic coast within coastal Delaware, Maryland, New Jersey, North Carolina, South Carolina, Virginia, Georgia, and northcentral Florida. They are also found within the northern Gulf of Mexico coastal plain within southeast Mississippi and Alabama where they are called "Grady Ponds". They vary in size from one to several thousand acres. About 500,000 of them are present, often in groups which vary in alignment around a northeast-southeast trend. The bays have many different vegetative structures, based on the depression depth, size, hydrology, and subsurface. Many are marshy; a few of the larger ones are (or were before drainage) lakes. Some bays are predominantly open water with large scattered pond cypress, while others are composed of thick, shrubby areas (pocosins), with vegetation growing on floating peat mats. Generally the southeastern end has a higher rim composed of white sand. They are named for the Bay trees that are frequently found in them, not because of the frequent ponding of water.

USGS aerial photo of Carolina bays; north is at top.

Contents

1 Biodiversity
2 Theories of Origin

2.1 Cometary Theory

3 External links

Biodiversity

The bays are especially rich in biodiversity, including some rare and/or endangered species. Species that thrive in the bays' habitat include birds, such as wood storks, herons, egrets, and other migratory waterfowl, mammals such as deer, black bears, raccoons, skunks, and opossums. Other residents include dragonflies, green anoles and green tree frogs. The bays contain trees such as black gum, bald cypress, pond cypress, sweet bay, loblolly bay, red bay, sweet gum, maple, magnolia, pond pine, and shrubs such as fetterbush, clethra, sumac, button bush, zenobia, and gallberry. Plants common in Carolina bays are water lilies, sedges and various grasses. Several carnivorous plants inhabit Carolina bays, including bladderwort, butterwort, pitcher plant, and sundew.

Some of the bays have been greatly modified within human history, under pressure from farming, highway building, housing developments and golf courses. Carvers Bay, a large one in Georgetown County was used as a bombing practice range during World War II. It has been drained and is mostly used for tree farming today. Others are used for vegetable or field crops with drainage.

In South Carolina, Woods Bay, on the Sumter-Clarendon County line near Turbeville has been designated a state park to preserve as much as possible in its natural state. Also in Clarenden County (near Manning) another bay, Bennett's Bay is a Heritage Preserve.

Theories of Origin

Various theories have been proposed to account for them, including action of sea currents when the area was under the ocean or the upwelling of ground water at a later time. The most acceptable theory within the earth sciences academic community is that a combination of processes including climate change, wind erosion, and changes in the water table are responsible for the shapes and orientations of these ancient landforms. Proposals that they are impact craters created by a meteor shower are criticized by scientists because of the lack of extraterrestrial material, absence of shocked quartz and "bedrock" deformation associated with larger bays, and extremely low ratio of depth to diameter of the larger bays.

Although the origin of the Carolina Bays has been a topic of considerable controversy, ongoing research by Andrew H. Ivester (University of West Georgia), Mark J. Brooks (University of South Carolina), Barbara E. Taylor (University of Georgia), and their colleagues using Optically Stimulated Luminescence (OSL) Dating, ground penetrating radar, sediment cores, and other techniques has had better success with the question of their approximate age. As a result of studies of Carolina Bays in South Carolina involving detailed analysis of their stratigraphy and OSL dating of their rim deposits, they concluded that Carolina Bays are between 70,000 to 100,000 years old. For example, according to OSL dates the age of Flamingo Bay in South Carolina is about 108,700±10,900 BP and the age of adjacent Bay-40 is about 77,900±7,600 BP. Further south, another Carolina Bay, Big Bay, was found to be over 74,000 years old. Thus, as collaborated by the presence of alternating layers of sediments containing glacial and interstadial pollen found filling individual Carolina Bays, Carolina Bays are ancient landforms whose origin predate the end of the last glacial epoch by several tens of thousands of years to possibly over a 100,000 years. Furthermore, the OSL dates indicate that the formation of the Carolina Bays was not an instantaneous event, but rather individual bays were formed at different times over a period of about 30,000 years. Any hypothesis of their formation will need to consider not only their age but also explain why Carolina Bays formed over a period of tens of thousands of years.

Andrew H. Ivester and his colleagues also concluded from their research that the original morphology, orientation and shape, of the Carolina Bays has been completely destroyed by tens of thousands of years of modfication by wind during dry periods and lake waves and currents during wet periods. As a result, it is likely impossible to use the modern orientation and shape of these bays as criteria for understanding the origin of these landforms.

Carolina Bays: An Annotated Bibliography by Thomas E. Ross and published by Carolinas Press ISBN 1-891-02608-09 includes summaries of every academic article published about Carolina bays up to the year 2,000.

Cometary Theory

One theory still extant in some circles is the suggestion of cometary impact[link]. Typically, this is an easy conclusion to jump to when analysing the orientation of the bays, a substantial number of which are aligned in a parallel fashion and frequently overlap, a fact which remains largely unexplained by the recent research of Ivester and others.

External links

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