Asynchronous Antarctic and Greenland ice-volume contributions to the last interglacial sea-level highstand

The last interglacial (LIG; ~130 to ~118 thousand years ago, ka) was the last time global sea level rose well above the present level. Greenland Ice Sheet (GrIS) contributions were insufficient to explain the highstand, so that substantial Antarctic Ice Sheet (AIS) reduction is implied. However, the nature and drivers of GrIS and AIS reductions remain enigmatic, even though they may be critical for understanding future sea-level rise. Here we complement existing records with new data, and reveal that the LIG contained an AIS-derived highstand from ~129.5 to ~125 ka, a lowstand centred on 125–124 ka, and joint AIS + GrIS contributions from ~123.5 to ~118 ka. Moreover, a dual substructure within the first highstand suggests temporal variability in the AIS contributions. Implied rates of sea-level rise are high (up to several meters per century; m c−1), and lend credibility to high rates inferred by ice modelling under certain ice-shelf instability parameterisations

THE FLORIDA KEYS PALEO-REEF TRACT: CONSTRAINING REEF EVOLUTION AND THE RELATIVE SEA-LEVEL HISTORY DURING THE LAST INTERGLACIAL

One means of placing empirical constraints on the projected rates and magnitude of future sea-level rise is to draw upon evidence of ice sheet dynamics and sea-level rise during past episodes of warming. During the Last Interglacial period, global mean temperature was similar to the present and the poles were a few degrees warmer, making it an interesting time period to examine in this context. Here, we revisit some of the Last Interglacial shallow marine fossil reef sequences exposed in the Florida Keys to better constrain the evolution of sea level during the sea level highstand as a means of shedding light on the potential for rapid, dynamic changes in polar ice sheet mass during this past warm period. Previous studies in this region have focused on assessing the peak sea level position and dating fossil corals, most of which appear to have experienced open-system behavior of U and Th isotopes during diagenesis. To further constrain the local history of sea-level, we are examining the carbonate sedimentology, diagenesis, and geochemistry of several drill cores in collected in the upper Keys. We have drilled several new cores at three localities (Key Largo, Lignumvitae Key, and Windley Key) and are using additional cores previously collected from Lignumviate and Windley Keys. We are developing detailed core logs of the six new cores, and are conducting a combination of X-ray diffraction, stable isotope, and thin section analyses to assess preservation and diagenetic features before conducting additional U-series dating of some of the fossil corals. Several of these cores exhibit abrupt transitions in preservation and/or facies, and contain well-developed exposure horizons. Future efforts will focus on ascertaining episodes of subaerial exposure and dating the timing of these transitions