Posts Tagged ‘Bulls Scarp’

How Far South did Polar Bears (Ursus maritimus) Range During the Ice Age?

February 21, 2015

Almost the entire present day range of the polar bear was uninhabitable for this species during most of the Ice Age.  The ice was too thick then, even for species adapted to arctic conditions.  Polar bear ranges shifted south.  Favorable habitat existed between the mile high Laurentide Ice Sheet and the Atlantic Ocean, and polar bears likely wandered along a strip of the Atlantic Seaboard now submerged by rising sea level.  I hypothesize they occurred as far south as what today is the continental shelf off the coast of South Carolina.

Map of North America during the Last Glacial Maximum.  Polar bears probably ranged on a narrow strip of the Atlantic Seaboard off the coast of what’s now Nova Scotia and Maine to as far south as what today is South Carolina during the height of the Ice Age.  Note the narrow strip of land between the ice sheet and the ocean in the northeast.  Dry land extended well off the modern day shoreline.  During warm climate pulses, icebergs broke off and drifted as far south as off the coast of Pleistocene South Carolina.

The ranges of walruses and 5 species of seals were also shifted south by the massive ice sheet.  All of these marine mammals lived on the narrow strip of land between the ice sheet and the ocean from what today is Nova Scotia south to New Jersey where the ice sheet terminated.  Fossils of 3 species have been found even further south near the South Carolina coast–walrus (Odobenus rosmarus), gray seal (Halichoreus grypus), and bearded seal (Erignathus barbatus).  It should not be surprising, if some day, a fossil hunter finds the remains of Pleistocene age harbor seal (Phoca vitulina) or harp seals (Pagophilus groenlandicus) farther south than their present day ranges.  (Harbor seals were probably more abundant off Pleistocene South Carolina’s coast than walruses, despite the absence of the former in the local fossil record.)  Predators follow prey.  Polar bears feed upon walruses, seals, washed up whale carcasses, sea birds, sea bird eggs, and fish.  All of these resources would have been abundant even further south than Pleistocene South Carolina.  One particular rocky outcropping that would have provided ideal nesting habitat for millions of sea birds existed on the Pleistocene coast of South Carolina.  (See: https://markgelbart.wordpress.com/2014/08/14/bulls-scarp/).  I’m certain this site attracted polar bears.  I think the presence of prey species such as walruses and seals in the fossil record of South Carolina means the presence of polar bears can be inferred.

Video of polar bear slaughtering a walrus.  I doubt ice ever grew this thick in South Carolina, even during the Ice Age.  Walruses were not confined to cold regions prior to the  catastrophic increase in the population of humans.

Predators are less common in the environment than prey animals, and therefore are less likely to be preserved as fossil remains.  Moreover, the southernmost range of the polar bear was restricted to the South Carolina continental shelf, an area now deeply submerged under ocean water.  This explains why polar bear fossil remains have yet to be found in this region.  Polar bear fossil remains dating to the Pleistocene are rare worldwide because much of their habitat during Ice Ages is now submerged.  Some day, a trawler dragging the sea bottom may luckily snag a polar bear specimen well south of the species’ present day range.

Polar bears did occur within historical times at least as far south as Great Breton, Nova Scotia.  In 1534 Jacques Cartier and his French crew of explorers encountered a polar bear on Funk Island, located near the mouth of the St. Lawrence River.  They had embarked on the island to collect now extinct great auks (Pinguinus impenns) and other sea birds for the ship’s larder.  The polar bear was also on the island to feast upon sea birds.  (Bulls scarp, the now submerged rocky outcropping off the coast of South Carolina, would have offered similar habitat.)  The surprised bear jumped back into the ocean.  But the following day, the Frenchmen spotted the bear again.  They manned a longboat, pursued the swimming bear, and dispatched it.  Captain Cartier pronounced the meat as good as that of a “2 year old heifer.”  Fresh meat was a treat after a long sea journey’s fare of heavily salted protein.

Pleistocene polar bears probably didn’t wander far inland.  A report of a polar bear fossil found in Breck Smith Cave, Kentucky about 100 years ago is likely a misidentification, and unfortunately that specimen has been lost.  Polar bears are adapted to hunting seals and scavenging whales, so their range hugged the shoreline where they could find their favorite foods.

Just contemplate the diversity of bears that existed in southeastern North America during the Pleistocene.  15,000 years ago, a paleoindian journeying from west Texas or Kentucky to the Atlantic Coast could have possibly encountered grizzly (Ursus arctos), black (Ursus americanus), spectacled (Tremarctos floridanus), giant short-faced (Arctodus simus) and polar bears. I’m 52 years old and have never seen a live wild bear of any kind in person.  The loss of wild lands that support this diversity of bears saddens me.

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Bulls Scarp

August 14, 2014

Bulls Scarp is an uneven rocky cliff located approximately 66 miles to the east of the South Carolina coast.  This sloping underwater feature is on the edge of the continental shelf, and it covers about 20 square miles.  Today, Bulls Scarp varies in depth from 42 yards to 220 yards beneath the surface of the sea, depending upon the height of its rocky outcroppings.  But during the last Ice Age between ~24,000 BP-~16,000 BP, it was above sea level because the Laurentide Glacier had advanced over all of eastern Canada, locking up a great quantity of earth’s atmospheric moisture.

Sonar image of Bulls Scarp, about 66 miles east of the South Carolina coast.  This image was taken by researchers from the College of Charleston.  20,000 years ago, this was a rocky location right at sea level and it probably hosted breeding colonies of walruses, seals, and sea birds.  Note how it stuck out into the ocean like a kind of natural pier.

Bulls Scarp fascinates me because it represented an environment that no longer exists anywhere in southeastern North America.  The closest above sea level cliffs today are in Maine.  Scientists from the College of Charleston believe Bulls Scarp would have provided favorable habitat for marine mammals such as seals and walruses.  Fossils of both have been found near Charleston.  (See: https://markgelbart.wordpress.com/2011/01/28/seals-and-walruses-off-southeastern-north-americas-pleistocene-coast/).  Puffins and other sea birds nested here as well, and oyster reefs attached to rocks would have been abundant.  Researchers think these resources may have attracted paleo-indians.  Bulls Scarp also offered rock shelters, stone for tool-making, and freshwater springs.  Herds of mammoths, bison, horses, and llamas likely wandered all the way to the coast, and Indians following this game may have discovered these seaside cliffs.  Most of the continental shelf that was above sea level during the last Ice Age has been eroded by currents and wave action, destroying potential archaeological sites, but Bulls Scarp may have lag deposits containing fossils and human artifacts because the rocky outcroppings served as an impediment that trapped sediment. Scientists have identified it as a likely site where Clovis artifacts may be found.

Walruses on rocky shore with mist, Arctic  Jupiterimages

Walruses on a rocky shore off the coast of Alaska.  Strange as it may seem, an area off the coast of what today is South Carolina likely had a scene just like this 20,000 years ago.

A great variety of environments existed on the exposed continental shelf between Bulls Scarp and what today is the modern shoreline.  The climate was on average cooler and drier, though not especially cold during winter, thanks to the nearby Gulf Stream.  Lightning-induced wildfires were infrequent while draughts were common.  These climatic conditions favored prairies and scrub oak thickets.  Pine savannahs and river bottomland forests were less common than they are today.  “Sand dune fields” and Carolina bays formed on the northeast side of the braided rivers flowing on the shelf.  Rivers didn’t meander during this time period, but instead were shallow and clogged with sandbars.  Grassy marshes occurred near springs, and cypress swamps were relict habitats on low poorly drained sites.

When the Ice Age ended,  the Laurentide Glacier melted rapidly, and sea levels rose at an astonishing rate—40 yards per year.  Ocean front condos would have been a really bad investment then.  Cypress tree stumps found 19 yards below modern sea level date to 11,500 BP.  The Atlantic Ocean inundated cypress swamps and all the other types of environments mentioned above within a few thousand years.  Modern sea level was reached about 6,000 years ago. 

We can study the ocean floor off the South Atlantic Bight and imagine what it used to be like, but for me it’s not nearly as satisfying as it would be to have actually seen it.  The paleo-indians didn’t enjoy our modern technological wonders, but they did get to see interesting pristine landscapes.

Reference:

Lepper, Brad

“Paleolandscapes of the South Atlantic Bight”

Mammoth Trumpet 29 (3) July 2014