Date of Award
Master of Science
Geological and Atmospheric Sciences
Franciszek J. Hasiuk
The Cenozoic has been characterized by global cooling. However, the timing and magnitudes of this transition remain clouded due to conflicting evidence. The Mg/Ca of foraminiferal calcite has been shown to be an accurate proxy for paleo-seawater temperature, which when combined with the 18O of foraminiferal calcite, can be used to decipher the timing of glaciations by calculating the 18O of paleo-seawater. For this to work over long time scales (greater than 106 years), secular variation in seawater Mg/Ca must be accurately accounted for. Currently, there is a paucity of calibrated models that describe how Mg/Ca of foraminifera respond to variations of seawater Mg/Ca, despite extensive calibration of multiple species for temperature. Benthic foraminifera in particular, are one of the best proxies of bulk ocean properties, because they inhabit deep-ocean water masses less affected by high-frequency variations in sea surface temperature and salinity. To this end, a colony system was built to provide a constant supply of benthic foraminifera for experimentation. This culture system was designed after a thorough review of academic literature and in consultation with local aquaculture, engineering, and biology experts. This system currently houses live species of foraminifera from several locations around the world, such as Long Island Sound, Qatar, and the United Arab Emirates. To investigate how foraminiferal Mg/Ca responds to varying seawater Mg/Ca and temperature, 600 specimens of the high-Mg calcite foraminifer Peneroplis planatus were placed in experimental microcosms of varied seawater Mg/Ca and temperature. Of these 600 foraminifera, 102 survived the duration of the experiment and were analyzed via electron microprobe. These geochemical data show a positive, power law correlation between seawater Mg/Ca and foraminiferal Mg/Ca measured in the third chamber of growth at 25°C. This analysis supports a similar study done on high-Mg calcite foraminifer Operculina ammonoides. Geochemical data from specimens grown at other temperatures (3°C and 12.5°C) were inconclusive. Further research is needed to characterize the response of foraminiferal calcite to changing water Mg/Ca at seawater temperatures other than 25°C. This is necessary because the behavior of this proxy must be verified at temperatures that are similar to oceanic bottom waters (and thus benthic foraminiferal habitats).
Jennings, Deserae, "Culturing benthic foraminifera to understand the effects of changing seawater chemistry and temperature on foraminiferal shell chemistry" (2015). Graduate Theses and Dissertations. 14555.