Reconstruction of the Florida Coast
During the Late Wisconsin Glaciation

Created by
Patrick Laird

This web page was created to fulfill, in part, the requirements of ES 767 Quaternary Geology at
Emporia State University.


Table of Contents
Introduction Location:  Florida Data & Ice Volume Conversion
GIS Modeling Conclusion References

Introduction

The Wisconsin Glaciation is the last major glaciation to occur during the Holocene.  The advancement of ice during the late Wisconsin started roughly between 25,000 and 27,000 mya (million years ago).  The maximum extent of glaciation is thought to have occurred around 18,000 mya, while the emergence from the Wisconsin Glaciation occurs around 10,000 mya (Carroll, 2002).  During the maximum extent of glaciation, sea level dropped to the point that is well below today's sea level.  Using Arc View 8.3 and Arc/Info along with values obtained from a variety of sources, the Florida coast line can be reconstructed.

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Why Florida

The Florida coast line (figure 1) was chosen because of its tectonic stability (Muhs et al., 2003).  According to Muhs et al. (), sea level lowering along the coasts of the United States due to glacial periods has been studied less than sea level rise of inter-glaciations.  Two common ways to to help determine sea level lowering are by reconstructing the glaciers to determine the volume of ice locked up in glaciers and by studying submerged reefs, particularly the Acropora palmata.
 
 
Figure 1.  The Florida coast line and study area are marked by the blue box.

Acropora palmata is more accurate in both dating methods and as a sea level indicator than records from shell beds or peat/marine sediments (Muhs et al., 2003 ).  Estimating sea levels using the Acropora palmata reef is beneficial because of five components (Muhs et al., 2003):

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Data and Ice Volume Conversion

Sea floor and topography elevation data to be used in Arc/View and Arc/Info was obtained in ascii raster format from the National Geophysical Data Center's (NGCD) U.S. Coastal Relief Model.  Grid cell size for both sea floor and Florida elevation are three seconds.  Ice volumes of individual ice sheets were obtained from Hughes' The Last Great Ice Sheet and are located in table 1.  Ice volumes from Hughes are based on the reconstruction of ice sheets during the minimum and maximum extent.  These values only indicate the ice sheets values at these times.  Total values taken from Hughes do not take into account for sea floor isostasy.  It is unlikely that all of the ice sheets reached maximum extent at the same time.  However, the total value for maximum reconstruction gives an indication that sea level could not have dropped past this value.  The sea level during the Wisconsin Glaciation is still being debated, although most sources agree that it is somewhere around 120 meters below current sea level (Schweitzer & Thompson, 1996 and Muhs et al., 2003).
 
Table 1.  Late Wisconsin Ice Sheet Volumes
(values in 106 km3)
Ice Sheet/Glacier Minimum 
Reconstruction
Maximum 
Reconstruction
Laurentide 30.9 34.8
Cordilleran 0.26 1.90
Innuitian * 1.13
Greenland 2.92 5.59
Iceland 0.05 0.267
British Isles 0.801 0.801
Scandinavia 7.25 7.52
Barents-Kara 0.955 6.79
Putorana ** 0.581
East Antarctica 24.2 24.2
West Antarctica 13.5 13.5
Glaciers/Ice Caps 1.894 0.75**
Totals 82.73*** 97.079***
Numbers are based on Hughes, et al (1981).
* Franklin Ice Complex not included.
** Included in Glaciers/Ice Caps category.
*** Totals differ than Hughes' based on re-calculations.

Ice Volume to Sea Level Height Formula

Using a two part formula (shown below), ice volume can be converted into sea level equivalent (Aber, 2004).  Glacier ice density is 0.9 (Stickler, 2004).  The area of ocean in 1995 values is 362 million km2 (National Geographic Society, 1996).

Part one:  Convert Ice Volume into Water Equivalent Volume
        ice volume (km3) times ice density = water equivalent (km3)

Part two:  Convert Water Equivalent Volume into Sea Level Equivalent
        water equivalent (km3) divided by area of ocean (km2) = sea level height

Using the total values from Hughes, the minimum reconstruction sea level change is 126 meters.  Maximum reconstruction sea level change is 161 meters.  Again, these numbers do not take into account sea floor isostasy.

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Reconstruction and GIS Modeling

Using Arc View 8.3 and Arc/Info, both the minimum and maximum ice sheet extents were reconstructed to map the Florida coast.  As discussed above, it is unlikely that all ice sheets reached a maximum at the same time.  The last model shows an  estimated change in sea level, which takes into account for sea floor isostasy.
 
Figure 2.  This is a GIS model of the current Florida coast.
Figure 3.  This image is of the Florida coast for the minimum reconstruction value according to Hughes in the Last Great Ice Sheets.  This model is based on the total volume of ice during the ice sheets minimum extent and does not take into account for sea floor isostasy.
Figure 4.  Generated model of the Florida coast for the maximum reconstruction value according to Hughes in the Last Great Ice Sheets.  This model is based on the total volume of ice during each ice sheets maximum extent and does not take into account for sea floor isostasy.
Figure 5.  Generated model of the Florida coast.  This image shows the more acceptable sea level change of -120 meters.  This model takes into account for sea floor isostasy and may be the most realistic based on the accepted values for sea floor change.

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Conclusion

Using both methods for determining coast line positions, a rough estimate can be modeled.  There really is not muc difference between figures 3,4, and 5.  The coast line varies a little, but usally after the 90 m mark.  It is not cost effective to take cores along the entire coast of Florida to get an exact reading from the shallow water reefs.  Even if it were possible, erosion of the reefs could play a part in hampering the procedure.  Although it is impossible to determine the exact coast line of Florida during the Late Wisconsin Glaciation, GIS modeling can give us a rough estimate as to where the sea level was located.  Using the sea level values associated with Florida, other areas of tectonic stability, such as the British Isles, can also be modeled to determine paleo-coast lines.

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References

Aber, James S.  2004.  Glacier Ice Volume and Sea-level Equivalent.  URL retrieved  in October 2004.  URL:  http://academic.emporia.edu/aberjame/ice/labs/lab01.htm

Carroll, Wayne D.  2002.  The Late Pleistocene Epoch.  URL retrieved November 2004.  URL:  http://www.srs.fs.usda.gov/sustain/report/histry/histry-03.htm

Hughes, T.J., Denton, G.H., Andersen, B.G., Schilling, D.H., Fastook, J.L. and Lingle, C.S.  1981. The Last Great Ice Sheets: A Global View.  In Denton, G.H. and Hughes, T.J. (eds.), The Last Great Ice Sheets.  J. Wiley & Sons, New York. p. 274.

Muhs, D.R., Wehmiller, J.F., Simmons, K.R., and York, L.L. 2003. Quaternary sea-level history of the United States.  In Gillespie A.R. (ed), Atwater, B.F., and Porter, S.C., Quaternary Period in the United States: Developments in Quaternary Scence.  Elsevier Science.  p. 147-53.

National Geographic Society. 1996.  National Geographic Atlas of the World, Revised 6th edition. Washington, D.C.  National Geographic Society.  p.131.

National Geophysical Data Center.  2004.  NGDC Coastal Relief Model.  URL Retrieved October 2004.  URL:  http://www.ngdc.noaa.gov/mgg/coastal/coastal.html

Schweitzer, P.N., and Thompson R.S.  1996.  Global Gridded Pliocene and Late Quaternary Sea Level.  USGS.  URL retrieved November 2004.  URL:  http://geochange.er.usgs.gov/pub/sea_level/

Strickler, Mike.  2004.  Introduction to the hydrosphere and surface processes.  URL retrieved November 2004.  URL:  http://supercow.uoregon.edu/~mstrick/RogueComCollege/RCC_Lectures/IntroWater.html#Magic

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Created by Patrick Laird, November 20, 2004.  Corrections and comments, please send to: laird_patrick@stumail.emporia.edu