Late quaternary sea-level highstands and deep-ocean circulation variability during the mid-pliocene : implications for future climate change

Abstract

In Chapter 3, I reconstruct millennial-scale variability in deep-ocean circulation during the last period in which global temperatures were substantially higher than present for an extended period of time and atmospheric CO₂ concentrations comparable to 21st century values. These records demonstrate that relatively rapid changes in ocean circulation lead corresponding changes in temperature and/or ice volume occurred during this time period, without the presence of major northern hemisphere ice sheets. This information helps constrain the ultimate driver of abrupt periodic climate cycles, while also emphasizing that they will likely continue to occur in the future

Reconstructing climate conditions during Earth’s recent history provides us with the best idea of what changes can be expected in the future. Such reconstructions also provide critical information helping to constrain models predicting the range of scenarios we can expect with continued anthropogenic carbon emissions. The contents of this work focus on past variations in sea level and relatively large and abrupt climate cycles during periods particularly relevant for understanding future impacts of climate change on the human species, and vice versa.

In Chapters 1 and 2, my colleagues and I identify eight major time periods in the past 0.5 million years when regional sea level was higher than today from Virginia to Florida in the southeastern U.S. Atlantic Coastal Plain. Furthermore, we disentangle the regional versus global sea-level signals, while identifying the most likely ice sources for each sea-level highstand event. This includes two time periods when global climate conditions were ~1-2℃ warmer than today. Sedimentary units deposited during these highstand events are studied to reconstruct sea-level variability for specific time periods. I reconstructed such variability within sediments deposited during the last interglacial period at two sites on either side of the Chesapeake Bay, in Virginia. This was accomplished by combining a variety of proxy records, each providing unique sea-level insights. Overall, results suggest that ice sheets are inherently unstable and we can expect a significant increase in sea level even if anthropogenic warming is limited to 1-2℃. Furthermore, large portions of the southeastern Atlantic Coastal Plain will remain threatened by higher than average rates of sea-level rise.