Using Clumped Isotopes and Radiocarbon to Characterize Rapid Climate Change During the Last Glacial Cycle

Abstract

We generated records of carbonate clumped isotopes and radiocarbon in deep-sea corals to investigate the role of the deep ocean during rapid climate change events. First we calibrated the carbonate clumped isotope thermometer in modern deep-sea corals. We examined 11 specimens of three species of deep-sea corals and one species of a surface coral spanning a total range in growth temperature of 2–25°C. We find that skeletal carbonate from deep-sea corals shows the same relationship of Δ47 to temperature as does inorganic calcite. We explore several reasons why the clumped isotope compositions of deep-sea coral skeletons exhibit no evidence of a vital effect despite having large conventional isotopic vital effects. We also used a new dating technique, called the reconnaissance dating method to investigate the ecological response of deep-sea coral communities in the North Atlantic and Southern Ocean to both glaciation and rapid climate change. We find that the deep-sea coral populations of D. dianthus in both the North Atlantic and the Southern Ocean expand at times of rapid climate change. The most important factors for controlling deep-sea coral distributions are likely climatically driven changes in productivity, [O2] and [CO32-]. We take 14 deep-sea corals that we had dated to the Younger Dryas (YD) and Heinrich 1 (H1), two rapid climate change events during the last deglaciation and make U-series dates and measure clumped isotopes in them. We find that temperatures during the YD and H1 are cooler than modern and that H1 exhibits warming with depth. We place our record in the context of atmospheric and marine benthic Δ14C, δ13C, and δ18O records during the deglaciation to understand the role of the deep North Atlantic during the deglaciation. We also investigated the role of climate change in the distribution of terrestrial megafauna. To help with this, we also developed a method for compound-specific radiocarbon dating of hydroxyproline extracted from bones in the La Brea Tar Pits. We find that the radiocarbon chronologies of megafauna from several locations around the world, including the La Brea Tar Pits, exhibit an increase in abundance of megafauna during Heinrich events.