Exercise Facies Relationships and Sea-Level Change 107 Figure 7.7 shows the suba

Question

Exercise Facies Relationships and Sea-Level Change 107 Figure 7.7 shows the subaerial and submarine topography of southerm Florida today. Above cur- rent sea level (green area) the contour interval is 20 ft. Below current sea level (blue area) the contour inter- val is 10 ft down to a depth of 100 ft, after which the contours change to 100-ft intervals. Figure 7.8 shows theglobal sea-level history for the last 15,000 years with feet on the left and meters on the right. Note that sea level began to rise abruptly about 15 000 years ago, but that the rate of sea-level rise has tapered off b Facies and Sea-Level Change The Pleistocene Epoch began 2 million years ago and ended approximately 10,000 years ago. Climatic cooling during this time resulted in growth of huge ice sheets at both the North and South Poles. During glacial maxima, 30% of Earth's land surface was cov. ered with ice, whereas only 10% is covered today during the current interglacial period. The shifting of water from the ocean reservoir to icecaps during glacial maxima resulted in a eustatic sea level fall of nearly 100 m (300 ft). If the polar icecaps and pack ice were to melt, sea level would rise 70 ft. over the last 6,000 years. Given these data: 3. Calculate the average annual rate of sea-level rise from 15,000 to 10,000 years ago. Although the Pleistocene is called the Great lce Age, the climate was not cold everywhere, nor was it continually cold. Episodes of ice build-up were separated by interglacial episodes when ice would melt and sea level would rise. At least 18 Pleistocene glacial-interglacial cycles have been detected thus far. This means that sea level rose and fell dramati- cally at least 18 times during the last 2 million years. 4. Calculate the average rate of rise from 5,000 years ago to the present. 1. How did these oscillations of sea level effect the face of south Florida? 5. Using the graph below the map in figure 7.7, draw a topographic profile from A to A'. At this scale, the slope of the western Florida "ramp" is highly exaggerated. The actual slope is approxi- mately 1 degree. 2. How will continued melting affect Florida's future? 6. How far must you travel from the west coast of Florida to encounter water depths of 200 ft?

Explanation / Answer

1. The oscillations of sea level during Pleistocene produced high enough sea levels that caused submergence of South Florida coast.

2. If the polar ice melts completely, the sea level would rise by 70 ft. Considering the scenario of complete melting, the future of low-lying communities (staying at or close to sea level) of Florida is at risk as such a land surface will probably get under the sea level. If sea level projections are to be believed, a rise of up to 2m by the year 2100 will be equally threatening.

3. The average annual rate of sea level during 15,000 to 10,000 year period can be calculated as:

60 - 20 / 15000 - 10000 = 40m per 5000 years or 8cm per year

4. The average rate of sea level rise since 5000 years ago can be calculated as:

3.5 - 0 / 5000 - 0 = 0.7m per 1000 years or 0.7mm per year

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