School Papers

Estimates great place to obtain observations of sea

Estimates of sea level change can
also be made based on the sedimentary strata deposited on the continents.  The continents are a great place to obtain
observations of sea level change because past sea levels have been
substantially higher than they are now, and also because continents experience
uplift in many places.  Uplift occurs
when land that was previously below sea level is moved vertically until it is
well above sea level, allowing scientists to estimate the magnitude of sea
level rise and fall in that area for a given time.  The fact that the continents are not
stationary, and move vertically in response to tectonic driving forces can also
be problematic when investigating sea level change.  Since the continents are always moving, all
indicators of sea level change found in continental strata are assumed to be
relative.  Although an enormous amount of
information about sea level change can be extracted from continental
sedimentary deposits, periods of non-deposition and the constant movement of
the Earth’s tectonic plates make obtaining a global signature from these
observations extremely problematic (Kominz, 2001).

            Aside
from long-term changes in sea level, there is sedimentary evidence of sea level
fluctuations that are substantially shorter than the 50-100 million-year
variations, but longer than ones caused by orbital variations (< 400,000 years).  These shorter variations often last between 500,000 to 3 million years, and tens of millions of years, and are often called second and third-order sea level changes.  The causes of these specific, shorter sea level variations are often argued about, but it is agreed on throughout the science community that it is nearly impossible to globally determine the age of events that occurred during such short intervals.  Scientists argue that these changes can be attributed to tectonics, changing ocean basin volumes, and continental uplift and subsidence, but it is agreed upon that data limitations are the main reason for the controversies over second and third-order sea level changes (Kominz, 2001).