Senior Theses 2004
Terill A. Hollweg (2004). Multi-proxy, multi-species approach
to determine climate change in Tampa Bay over the last 21,000
Faculty advisor: David Hastings
Over the last 21,000 years Tampa Bay went from a lake system to the present day marginal marine system, illustrating the transition from the last glacial period through the deglacial to the present day environment. Past climate changes, including this dynamic period, are vital to study to more fully understand present day climate change, influenced by both natural and anthropogenic forces.
Microfossils, both non-marine and brackish, collected down core from a Tampa Bay sediment core were analyzed for minor elements and oxygen and carbon isotopes to constrain past climate change in TampaBay. A multi-proxy and multi-species approach (non-marine ostracodes and a brackish foraminifera) provides evidence of salinity and temperature variations over time, reflecting regional and global climate change.
Major trends were observed in minor elements and oxygen isotopes in both ostracode species analyzed. From 14 to 12.5 ka BP (thousand years before present), there is a two-fold increase in Mg/Cashell, Sr/Cashell, and Sr/Cawater values. From 14 to 12.5 ka BP, Mg/Ca values increase from 5 to 10 mmol/mol and 4 to 7 mmol/mol in Limnocythere floridensis and Candona annae, respectively. During this same time period, the Sr:Ca ratio of the water increases from ~12 to ~21 mmol/mol. From 13.7 to 11.5 ka B P, there is a gradual decrease values by 2.2‰, decreasing from 1 to -1.2‰.
Using minor element and oxygen isotope ratios it was determined that from 14,300 to 13,800 years BP, which falls within the Bølling-Allerød period, the climate was colder and wetter. Furthermore, from ~13, 700 to 11,500 years BP, which falls within the Younger Dryas period, the climate was warmer and drier with high evaporation and a salinity increase. Our climate record is asynchronously coupled to the Greenland Ice Core record, which can be explained by the presence or absence of thermohaline circulation. This multi-proxy, multi-species approach has produced a climate record that shows both regional and global climate change during the most recent deglacial period.