Two units (Q4 and Q5) of the Key Largo Limestone
exposed in the abandoned quarry walls found in
Key Largo Hammocks State Botanical Site, northern
Key Largo. Hypothesized contact is exposed about
a meter below the ground surface (dashed line in
lower photograph). Also shown are U-series ages
of Montastraea annularis from both units.
We address the question of potential future rates and magnitudes of sea level rise by examining times of higher-than-modern sea level rise in the past: the mid-Pliocene warm period ~3 Ma; the marine isotope (MIS) stage 11 interglacial period, ~400 ka; the last interglacial period, MIS 5, particularly MIS 5.5 (~125 ka); and the last-glacial-to-Holocene sea level rise from ~21 ka to the present. We document the magnitudes of past sea-level high stands by field mapping, stratigraphic measurements, and precise elevation measurements using state-of-the-art GPS techniques. Geochronology is accomplished by AMS radiocarbon dating of mollusks (for Holocene-to-last-glacial deposits), thermal ionization mass spectrometric (TIMS) uranium-series dating of corals (for last MIS 5 to MIS 11 deposits) and precise TIMS Sr-isotope measurements of mollusks (for MIS 11 to mid-Pliocene deposits). We reconstruct marine paleotemperatures during sea-level high stands by detailed paleozoogeographic interpretations of fossil mollusk assemblages, a time-tested traditional method of paleoclimatic studies in marine settings.
Why is this research important?
One of the most pressing issues in studies of climate change is the possible rise of sea level due to loss of major ice sheets, which in turn may result from global warming. It is not known which polar ice sheets (Greenland, West Antarctic, East Antarctic) are most at risk for mass loss that could contribute to sea level rise. Furthermore, it is not known what the possible magnitude of sea level rise is under interglacial climate conditions, how rapidly sea level may rise, or how long high sea levels may be retained. All these questions have been posed as major uncertainties in the second-order draft of the IPCC 2012 report, Chapter 5, section 5.6. The goals of this project are to shed light on these questions by studying warm climate analogs of the geologic past.