Brachiopods within the fossil record have many uses to help inform us about past seawater evolution. As they were one of the earliest animals after the Cambrian explosion to develop a hard skeleton, they have a strong presence in the fossil record throughout geologic time and are the subject of one of the preferred methods used for deep time isotopes. As the calcite within the hard shell of a brachiopod precipitates out of the surrounding seawater, trace elements are recorded within the shell, indicative of information detailing the surrounding water. Most species of brachiopod shells are composed of a low-magnesium calcite, one of the most stable forms of skeletal carbonate; much less prone to diagenesis than other species. These shells are then
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The changes in the ratio between the two isotopes over geologic time can be a result of multiple factors. Ocean water mixing with water from rivers, lakes or surface runoff from ice melts causes changes in the isotopic ratio due to the differences in the isotopes that occur within the seawater compared to that from fresh sources (Cummins et al., 2014). The changes in the ratio throughout geologic time is also strongly related to the reduction and growth of continental glaciers, which are higher in δ16O (Korte et al., 2005).
These oxygen isotope values can be used to determine the past temperatures of the ocean through the use of the carbonate δ18O thermometer (Urey, 1947). This thermometer is based on how temperature influences the fractionation between the δ18O values of the carbonate within the shell and the δ18O of seawater (Cummins et al., 2014). This fractionation is largely dependent on temperature, giving a relatively accurate calculation on the seawater temperature when the calcite in the shell was precipitated.
Boron
The changes in the ratio between the two isotopes over geologic time can be a result of multiple factors. Ocean water mixing with water from rivers, lakes or surface runoff from ice melts causes changes in the isotopic ratio due to the differences in the isotopes that occur within the seawater compared to that from fresh sources (Cummins et al., 2014). The changes in the ratio throughout geologic time is also strongly related to the reduction and growth of continental glaciers, which are higher in δ16O (Korte et al., 2005).
These oxygen isotope values can be used to determine the past temperatures of the ocean through the use of the carbonate δ18O thermometer (Urey, 1947). This thermometer is based on how temperature influences the fractionation between the δ18O values of the carbonate within the shell and the δ18O of seawater (Cummins et al., 2014). This fractionation is largely dependent on temperature, giving a relatively accurate calculation on the seawater temperature when the calcite in the shell was precipitated.
Boron