Reconstructing common era relative sea-level changes on the Gulf Coast of Florida

• Main Author: Gerlach, Matthew
• Format: Text
• Language: English
• Published: DigitalCommons@URI 2016
• Subjects: Geology|Marine Geology; Ice Sheet; North Atlantic
• Online Access: https://digitalcommons.uri.edu/dissertations/AAI10142164

Previous research on relative sea-level (RSL) changes in the western North Atlantic identified variations in the timing and magnitude of sea-level oscillations during the past 2,600 years. Quantifying the disparities between these records is reliant upon a robust database of sea-level reconstructions with an appropriate spatial and temporal distribution that can potentially capture a range of ice sheet melt mass balance fingerprints and ocean dynamic processes. To address an absence of high-resolution Common Era sea-level data in the southeastern US, we reconstructed ~ 1.0 m of RSL change encompassing the past ~ 2,400 years from the Gulf Coast of Florida. Paleomarsh elevation was reconstructed using a regional foraminiferal transfer function trained on 66 modern samples. A composite chronology of radiocarbon dates and pollution and pollen markers of known age were used to build an age-depth model. The geologic reconstruction was combined with a regional set of tide gauge records to create a continuous RSL dataset from ~ 450 BCE to present day. Quantitative trends with formal uncertainties were estimated (95% credible interval) by applying the errors-in-variables integrated Gaussian process (EIV-IGP) model to the combined RSL dataset. RSL fell at a maximum rate of -1.01 mm/yr. (0.65 to -2.68, 95% credible interval) from ~ 450 BCE to 50 BCE. The trend is consistent with a recent reconstruction of global sea-level variability derived from geological sea-level records. RSL then stabilized and began to rise ~ 0.3 mm/yr. until a change point was identified at 1270 CE (1000 CE to 1430 CE, 95% credible interval) and RSL rose ~ 0.5 mm/yr. until the late 19 th century. RSL reconstructions from northern Florida and Louisiana show similar stability throughout the majority of the Common Era. This observation is in contrast to reconstructions north of Cape Hatteras on the U.S. Atlantic coast that demonstrate positive and negative deviations from the background trend from 0 CE to 1850 CE. Our new data provides further evidence for the absence of these deviations in the records south of Cape Hatteras. This result supports suggestions that an ocean volume change is unlikely to explain them and that changes in the position and/or strength of the Gulf Stream are most likely responsible. Change point analysis reported modern rates of sea-level rise began between 1830 to 1940 CE. This observation is consistent with an overlap in change point timings (1865 to 1873 CE) identified in RSL reconstructions from northern Florida, North Carolina, New Jersey and Connecticut. RSL accelerated continuously from this inflexion until present rates of 2.27 mm/yr. (2.81 to 1.73 mm/yr.; 95% credible interval) were reached in 2014 CE. The consistent timing of this acceleration is in marked contrast to the north-south variation in previous deviations from background sea-level rise during the Common Era, suggesting a global ocean-volume change is the dominant cause.