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Q: ancient shorelines ( Answered 5 out of 5 stars,   0 Comments )
Subject: ancient shorelines
Category: Science > Earth Sciences
Asked by: zberryfunk-ga
List Price: $20.00
Posted: 06 May 2003 21:54 PDT
Expires: 05 Jun 2003 21:54 PDT
Question ID: 200462
Assuming global warming has raised the ocean level about 1 foot every
100 years, what would the Caribbean shorelines have looked like 2000
years ago? Would it have been possible to have a land bridge from the
Yucatan Penninsula to Cuba to Florida?
Subject: Re: ancient shorelines
Answered By: hlabadie-ga on 07 May 2003 09:40 PDT
Rated:5 out of 5 stars
Sea levels of minus 20 feet (20 centuries X 1 ft./Century) would have
produced a negligible difference compared to present coastlines with
respect to movement in the Caribbean Basin. In the Real World,
coastlines have been relatively stable in the present configurations
during that period. Sea level changes would need to be in the range of
minus 20-60 Meters (in other words, at least three times the assumed
change) to make any significant alterations in coastlines sufficient
to facilitate land travel between continental NA and Cuba. During and
immediately following the last Ice Age (12-8 thousand years ago) was
the most recent time for such lowered sea levels. (That should not be
read to mean that a difference in 20 ft. would not have had cultural
impact on the coastal inhabitants. Some coastal archaeological sites
have been submerged by the smaller rise during the last 2500 years.)

Caribbean Prehistory, SEAC
Prehistory of the Caribbean Culture Area

"Although the Lesser and Greater Antilles were home to various types
of extinct Pleistocene megafauna, such as the giant ground sloth
(Megaelocsus), no actual cultural artifacts have been identified for
this time period (ca. 10,000 - 6,000 B.C.) for the Caribbean Islands.
Some authors have treated the occurrence of Pleistocene megafauna and
an acknowledged lower sea level of nearly 20-meters that could
facilitate travel between the northern coast of South American and the
Antilles during the Paleoindian period as positive conditions for
Paleoindian occupation (Veloz Maggiolo and Ortega 1976)."

You will note in the following the graphed curves for sea level, as
well as the photographs of coastline features with Pleistocene
coastlines superimposed.

Middle Holocene Sea-Level and Evolution of The Gulf of Mexico Coast
Michael D. Blum, Amy E. Carter, Tracy Zayac, and Ron Goble

"During the OIS 4-2 glacial period (ca. 70-15 ka.), large coastal
plain rivers cut distinct valleys across OIS 5 Beaumont
alluvial-deltaic plains and the Ingleside shoreline, and extended
their courses to mid-shelf or farther basin-ward positions (BLUM et
al., 1995; BLUM and STRAFFIN, 2001; ANDERSON et al., 1996).
Development of the present shoreline is directly coupled to the
sea-level rise that accompanied deglaciation. A number of late
Pleistocene to Holocene sea-level curves have been published for the
western Gulf of Mexico (CURRAY, 1960; S H E PARD, 1963; COLEMAN and
SMITH, 1964; NELSON and BRAY, 1970; FRAZIER, 1974; THOMAS, 1990), with
each showing continual submergence until ca. 4-3 ka or later (Figure
2A). Most sea-level curves from the eastern Gulf of Mexico and the
Atlantic coast of Florida also interpret continual submergence until
ca. 3-2 ka or later (e.g. SCHOLL et al., 1969; PARKINSON, 1989;
TOSCANO and LUNDBERG, 1998; GOODBRED et al., 1998). ANDERSON and
THOMAS (1991) note that most curves, FRAZIER’s (1974) in particular,
show discontinuous rates of rise similar to the "eustatic" curve
published by FAIRBANKS (1989) using data from Barbados."
"and present bay outlines were not reached until ca. 4000 yrs BP. Work
by PAINE (1991) in Copano Bay, as well as ANDERSON and THOMAS (1991),
ANDERSON et al. (1991; 1992), SIRINGIN and ANDERSON (1993), and
RODRIGUEZ (1999) in Galveston Bay refined this general model. Most
recently, RODRIGUEZ (1999) argued that seismically-identified
"flooding surfaces" at –14 and –10 m demarcate rapid landward
translation of environments and modification of bay morphologies due
to episodic sea-level rise. RODRIGUEZ (1999) further suggested the
last event of this kind occurred ca. 4 ka, and that modern sea-level
positions were not reached until ca. 3 ka."
"BLUM et al.’s (2001) interpretation of sea level history along the
northwestern Gulf of Mexico shoreline in Texas implies that sea level
reached present positions some 3-5 kyr before traditional
interpretations would suggest, and raises a number of questions
regarding coastal evolution."


Chapter 8. NORTH PENINSULAR GULF COAST, 2500 B.P.-A.D. 1600

T10. Holocene Climate Change: Seasonal Variability to Centennial



Clarification of Answer by hlabadie-ga on 07 May 2003 15:06 PDT
Thanks for the rating.

Just to clarify, even at maximum glaciation during the last Ice Age,
the Florida Strait and The Yucatan Strait would not have been dry:
they are too deep. The periphery of the Gulf would have been open to
travel, and the distances over water would have been reduced, but
there could have been no continuous land passage across the Gulf.

Gulfbase: General Facts About the Gulf of Mexico

NOAA : Gulf of Mexico Expedition

"The Gulf is rather isolated, and we know that it is 3600m deep. The
Yucatan Strait is about 2000m deep, but the Florida Strait is only
about 800m deep. This means that the deep water in the Gulf flows in
from the Caribbean, not directly from the Atlantic. In effect, the
islands of the eastern Caribbean form a very leaky wall with many
shallow gaps, but only a few deep gaps. Just as this wall limits deep
water flow, it might partially isolate animal populations in the deep
Gulf from the populations in the larger deep Atlantic."

zberryfunk-ga rated this answer:5 out of 5 stars
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